Over the last decade solar energy has gone from the hobby of oddball engineers and rich eccentrics to a viable way of generating energy for millions of people. Unfortunately, I live in Bolivia, a country where almost nobody uses solar electricity and it is difficult and expensive to import solar panels. Out of curiosity, I wondered whether I could get solar energy by building my own solar panels. I spent a couple weeks investigating how to make my own solar panels online and I would like to share what I found with anyone else who is thinking of building do-it-yourself (DIY) panels.
The idea of being able to generate my own carbon-free energy is very enticing. I live in a country where solar energy only comprises 0.25% of the national grid’s electrical capacity and bad public policy is currently deepening the country’s dependence on fossil fuels. Perhaps my desire to build a solar panel are born out of my sense of frustration at the powerless I feel to change the dirty development and environmentally-destructive policies being promulgated by the Bolivian government. I feel like I have to do something, however small it may be, to resist the relentless march toward the destruction of the planet and humanity’s role in that destruction. In this context, the idea of being able to build my own solar panels and participate in the democratization of energy is very empowering.
When I checked on ebay and Amazon, I was pleasantly surprised on how little solar cells now cost for DIY enthusiasts. A standard six by six inch monocrystalline cell which used to cost $7 – $8 a decade ago, now only costs $2.0 – $3.5 and their output over the same time period has increased from 3-4 to 4-5 watts. Just as exciting has been the development of polycrystalline cells. Their efficiency has improved dramatically so they output almost as much as monocrystalline cells and they can be obtained for a price of $1.50–$2.50 per cell. There are even broken and cracked cells on ebay which can be obtained for less than $1 per cell.
Given how cheap solar cells have become, I expected to be able to build my own solar panels for very little, but once I started adding up the costs of the materials, I found that there is no economic justification for DIY solar panels. It will cost me almost as much to build my own panels as buy them and they probably won’t last as long because there is a good chance that I won’t seal them correctly to prevent moisture from entering the panels and degrading the cells and solder connections. I also probably won’t use as good of materials, such as low-iron anti-reflective tempered glass, a water-proof aluminum case that tightly seals, UV resistant and waterproof wires, an IP67 rated junction box with UV resistance, the right kind of diodes, and waterproof MC4 connectors.
Plus, buying these materials on ebay, I don’t know what I’m getting. I might get good solar cells, but I’m likely to get the factory rejects. If I only buy from reputable sellers who sell new grade A cells, then I will end up paying significantly more. I have no idea whether the tabbing and bus wire, flux pens, wiring, junction boxes and MC4 connectors sold by ebay sellers is of good quality. A Kester brand rosen flux pen costs twice as much as a generic Chinese one and I have no idea whether it makes any difference. Tests by the NREL (p. 19) shows that some brands of EVA film yellow far faster than other brands, which means more blocked sunlight, but I have no idea what kind of EVA film I am buying on ebay. A solar panel manufacturer who is willing to offer a 10 year equipment warranty and a 25 year performance warranty knows exactly who makes its materials and has tested those materials to make sure that they will last. Plus, a solar panel manufacturer can get far better prices by buying in bulk. The price for tempered glass, EVA film and Tedlar-polyester-Tedlar (TPT) is very expensive when buying in small quantities.
I might be able to save money if I can find used tempered glass and aluminum frames and buy B grade cells, but I have no idea how long my DIY panels will last. James Biggar, an ingenious carpenter on Youtube who built his own heated vacuum table to do solar panel encapsulation with EVA and Tedlar, calculates that he saves 30% by building his own panels. However, it took him a lot of experimentation to get the process right and he has a whole shed of expensive tools and was able to find a cheap lot of temperated glass. The more I read about DIY panels online, the clearer it becomes that building them will be a fun project and provide a great way to learn about solar energy, but they are a risky endeavor if thinking about them as a 25 year investment. There is also a lot of waste involved, since it is a good idea to first build a couple small panels in order to perfect the construction technique, before deciding whether to build something bigger, but those smaller panels won’t have much practical use unless strung together in series to equal one larger panel.
DIY panels made a bit more sense in the past when panel manufacturers were able to mark up their panels by a significant margin over their bill of materials, but the solar panel industry is so competitive today that panels are now being sold at tiny margins. As the solar panel manufacturers perfect their materials and do more testing over time, the warranties are getting longer. The standard is now a 10 or 12 year equipment warranty and a production warranty guaranteeing 90% of their initial output after 10 years and 80% after 25 years. These warranties are growing even longer at the high end of the market. SolarWorld now offers a 20 year equipment warranty and Panasonic, SunPower and SunEdison offer a 25 year equipment warranty. Almost all the major solar manufactures followed SolarWorld’s example and now offer a 30 year performance warranty on their double glass panels. It is hard for the DIYer to obtain the specialized materials and practice the quality control of the panel manufacturers in order to match their longevity. As the price of solar cells falls, the price of the glass, frame and encapsulant become larger factors and the commercial panel makers can get those materials for much cheaper and at better quality than the DIYer.
For example, the super white, low iron tempered glass with an anti-reflective coating used by panel manufacturers costs between $4.9 and $7.5 per square meter when ordering in large lots from China, but the DIYer will pay $40-$50 per square meter for generic tempered glass which isn’t as good. Standard glass has a solar transmission rate of 83.7%, meaning that 16.3% of sunlight won’t reach the photovoltaic cells below the glass. In contrast, the patterned glass commonly used in solar panels prevents much of the reflection of light, so it has a solar transmission rate of 91.4%. The addition of an anti-reflective coating raises that rate to over 94% and can reach as high as 96.2% for the best glass such as ArtSolar. Using that kind of specialty glass, good commercial panels will get roughly 10% or more light than the DIY panel.
Despite these reservations, I have decided to build my own solar panel, not only because I find it inherently interesting and self-empowering, but also because I live in a country where obtaining a solar panel or two is still quite expensive. Common manufactured goods that are imported from China only cost 10% to 20% more in Bolivia than they do in the US and less than in Europe. However, specialty goods that have limited demand often end up costing twice as much in Bolivia. When I checked the prices being charged for solar panels in Bolivia, they cost double what they would cost from a seller like Renvu in the US. More importantly, any knowledge I gain by building my own panels can be shared in our local climate activism group and an alternative living house, so that others may benefit by learning from my success or failure in this venture.
Before I took the plunge and tried to build a panel myself, I decided to write down everything I have learned, not only for myself, but also for others. Hopefully this information will help other DIYers get started.
Which solar cells to buy?
Solar cells form 60% of the total costs of materials in commercial panels, but they will be roughly a third of the total cost for a DIY panel. I first thought that I would go for the cheapest solar cells available, but I soon realized that would be a mistake.
There are some great deals on ebay for broken and cracked solar cells. MLSolar sells 250 grams/70 watts of broken cells for $15+shipping and 4kW of broken 3×6 cells for $670. Almost all broken cells are 3×6 or smaller, presumably because large 6×6 cells which are broken on one side are then cut in half to get one whole 3×6 piece to resell and a broken one as scrap.
There are many DIY videos online (1, 2, 3) of people building solar panels out of broken cells, so it seems like a great way to get solar energy on the cheap. The trick is that all the pieces in the panel need to be roughly the same size. The amperage of the panel will be limited to the smallest cell, so if you have a 59 cells that are 3×6 and one which is 1×1 in size, then you will only get the amperage of that 1×1 cell. You will spend a lot of time testing for bad cells and you will waste space on your panel because the cells aren’t uniform in size, but you can build something for very cheap.
Using broken cells is not a bad idea if you want to have fun and experiment, but panels using broken cells don’t make much sense if you are planning to encapsulate your cells and put them inside an expensive frame with glass. The high cost of these other materials means that you want to generate as much electricity as possible in as little space as possible so that you can use less encapsulant, glass and framing. If it takes a 30% larger panel to generate the same amount of energy with broken cells as whole cells, then you end up paying more for your panel even if you can get broken cells at half of the price of whole cells.
If you don’t want the hassle of dealing with broken and cracked cells, which require a lot more work and testing, but still want to play around with solar cells, then you should look for cheap amorphous or polycrystalline cells, which can be found for $1.5 – $2 per 6×6 cell on ebay.
The question is whether you want your fun little DIY project to still be working 5 years from now. Solar cells and the wiring will oxidize over time and slowly degrade in performance if they are not covered with an encapsulant which keeps out the moisture and the oxygen. If the solar panel is left outside where it is exposed to UV radiation, wind, rain and constant changes in the temperature, then microcracks will develop, bus bars will break, solder joints will grow brittle and crack and the panels will not produce as much energy over time. If you leave your cells and wiring exposed and keep your panel outside, then not only is it a fire risk, but you will have to periodically retest your panel and resolder broken connections in your panel. Even if you place your cells inside a glass case, such as a double paned window frame, you can expect the cells and wiring to oxidize if you don’t use encapsulant.
Cheap cells are great if you just want to occasionally pull your homemade panel out of the garage to charge up a battery or an electronic toy, but they don’t make any sense if you plan to leave your panel outside all the time or if you want your panel to last more than a couple years. Once you start to calculate the cost of properly protecting your cells, it simply doesn’t make economic sense to buy 3×6 cells that are less than 2.0 watts or 6×6 cells that are less than 4.0 watts. If you are buying new frames, glass and encapsulant, then you want to get higher efficiency cells to reduce the size of your panel and minimize the other costs of your panel.
You always have to buy a few extra cells when building a solar panel, because you will inevitably break a few when trying to solder the delicate cells together. Most DIYers buy 40 cells when building a 36 cell panel or 80 cells when building a 60 or 72 cell panel. When thinking of building a 36 cell, 18 volt panel capable of charging a 12 volt battery, I considered the following cells:
The SunPower Maxeon cells are literally the best cells in the world, measured at a 24.2% conversion efficiency rate in 2010 and the cells produced in SunPower’s fab 4 in the Phillipines now average 25% efficiency. Maxeon cells have a copper base covering the entire bottom of the cell, so there are no fragile bus bars on the top of the cell that can crack and break. Even if hit or holes are punched through them, they are designed to keep producing power. They are semiflexible and joined with busbar dogbone connectors that can withstand a great deal of abuse. The Fraunhofer Institute in 2013 found that SunPower modules are the most durable of any brand they tested and they suffered the least performance degradation under PID (potential induced degradation), damp heat and UV, thermal cycling, dynamic pressure loads and static pressure loads. Based on field testing and modeling, SunPower’s predicts that the power output of its modules under standard test conditions (STC) will only degrade 0.17% (± 0.12%) per year. The SunPower warranty not only guarantees against equipment failure for 25 years, but it also guarantees that the modules’ performance (i.e., watts produced under STC) will only fall 5% in the first 5 years and 0.4% per year afterwards, so they will have at least 87% of their initial performance after 25 years. SunPower modules also have excellent power output in the shade and at high temperatures, although its temperature coefficient of –0.29%/°C is not as good as than Panasonic’s HIT (Heterojunction with Intrinsic Thin layer) modules which rate at -0.258%/°C, because they contain an extra layer of amorphous cells that handle heat better than monocrystalline cells.
LG and Panasonic manufacture high efficiency cells which are significantly cheaper than SunPower, but their cells aren’t available for DIYers to buy on ebay, so the SunPower Maxeon cells are basically the only choice available for building a high efficiency panel that will generate a lot of energy in a small space. Maxeon cells are semiflexible, so they can be placed in a plastic laminate sheet or mounted on a curved surface. I would also choose them if needing to create a panel that has to withstand very damp conditions, large temperature swings, high winds, hail and strikes by blown objects. However, they are generally too expensive for me to consider.
If I want to build a high-efficiency panel, I would instead buy the 4.8 watt cells from Vikocell, which offer almost as many watts per square inch as the Maxeon cells, but at a low price of $0.47 per watt from Amazon or $0.42/W on ebay. I was unable to find detailed specs for Vikocell, so I don’t know how the cells will function in the heat and the shade or how they will degrade over time, but they are a known brand and they seem to be a good compromise between performance and price.
If I’m on a limited budget and can’t afford Vikocell, then I am left with the tough choice between buying polycrystalline cells rated at 4.5 watts or monocrystalline cells rated at 4.2 watts for the same price. Unfortunately, I can’t find good technical specs on any of these cells and if I want that information, then I will have to pay for cells which cost significantly more, so it is hard to make an informed decision.
There are a number of advantages to monocrystalline cells compared to polycrystalline cells. Monocrystalline cells generally perform better in the shade and in the heat than polycrystalline. Solar manufacturers measure the difference of how well a cell performs in the heat with the temperature coefficient, which is the percentage that the output is reduced for every degree above 25ºC (77ºF). It is hard to find this information for individual cells, but many panel manufacturers do list their temperature coefficient for wattage, voltage and amperage. Monocrystalline cells typically have a temperature coefficient for wattage between -0.40% and -0.42% per ºC, whereas polycrystalline cells are typically around -0.45% / ºC. This may be a concern in a place like Arizona or the MiddleEast, where roof temperatures regularly reach 45ºC or higher. However, heat doesn’t seem that significant considering that a 0.05% higher temperature coefficient only means that polycrystalline cells will produce 1% less power than monocrystalline cells at 45ºC. Heat and shading are even less important factors for me since I live high up in the mountains in La Paz, Bolivia where I get very direct sun with few clouds. I don’t need to worry about high heat reducing the energy output, since the average daily low in Bolivia is 1ºC / 34ºF and the average daily high is 13ºC / 56ºF.
A larger concern is the fact that polycrystalline degrades faster over time than monocrystalline. According to a metastudy by Jordan and Kurtz (2012), the efficiency of the median monocrystalline module fabricated after 2000 will degrade 0.36% per year, whereas the polycrystalline module will degrade 0.64% per year. Many of the studies examined by Jordan and Kurtz are old and polycrystalline cells have improved quite a bit in the last decade, so there may not be such a large gap anymore. However, if we assume those degradation rates are still true, then the 4.5 watt polycrystalline cells will be producing 3.8 watts in 25 years time, which is the same wattage as the 4.2 watt monocrystalline cells. Given the fact that I probably won’t seal my panels as well as commercial panels to prevent oxidation, the faster degradation of polycrystalline might be a significant worry. I don’t have to worry about damp heat living in the cool, dry Andean highlands, which would hasten oxidation, but I do have to worry about high levels of UV radiation and regular cycling between freezing and daytime heat, which will stress the cells and the wiring over time.
The monocrystalline cells are rounded around the edges since they are sliced from silicone ingots that are formed in round cylinders, then their edges are cut off to square them. This means that mono cells waste a little more space on the panel than poly cells. Those rounded edges provide larger spaces where encapsulant will pool, which might be a small factor to consider if using expensive silicone to seal the cells.
I wonder whether the monocrystalline cells will be able to generate more power during the early morning and at dusk when the sunlight is less direct, but since I am experimenting and on a limited budget, I plan on buying the 4.48 watt YSD polycrystalline cells to build my first panel. I would prefer to use the Vikocells, but their sellers don’t ship to Bolivia. I couldn’t find out any information about Huizhou YSD Technology Co., other than the fact that they sell on Aliexpress and ebay and they dissolved their UK branch in 2016, so I consider their risk to be the same as buying no-brand mono cells from heartofthesun-fo on ebay. If the first panel I build works, then I will get friends traveling abroad to bring me Vikocells to use in subsequent panels, since they have the lowest cost per watt once all the other costs of the panel are included.
I don’t want to spend a lot of time testing each cell, so I am not considering using cracked or broken cells. When shopping online, I avoided anything rated as C grade cells, since they don’t have the same electrical properties as the A grade cells. Often they have problems like broken bus bars or non-functioning sections of the cells, which would lower the amperage of the cell. I did consider buying B grade cells to save a few bucks, which are cells which have visual blemishes but the same electrical properties as A grade cells, but I couldn’t find many that were substantially cheaper than the A grade, except for the Maxeon cells. It doesn’t look too hard to attach the tabbing wire to each cell, so I won’t buy pretabbed cells, but it does look like a good option for people who want to save time.
Once I calculated the cost of the cells, tabbing wire, bus wire, encapsulant, frame, glass, diode, wires and silicone caulk to build my own panel, I was surprised to discover that using monocrystalline cells with 19.6% efficiency actually has the lowest cost per watt. I am not the only one discovering that higher efficiency cells can be cheaper. As the price of solar cells has dropped and become a smaller proportion of the total costs, the solar industry is also starting to realize that using higher efficiency cells is actually cheaper in terms of dollars per watt. In the past, cheaper polycrystalline solar panels cost significantly less in terms of dollars per watt than high efficiency monocrystalline, but that difference has reduced considerably in recent years and once the racking, cabling and inverters are included, it is no longer the case that cheaper polycrystalline always costs less per watt. LONGI Solar now calculates that the hardware costs of using monocrystalline PERC in a US residential installation are $0.48 per watt, compared to $0.51 per watt for polycrystalline. Similarly, the company calculates that monocrystalline PERC is 2 cents and 4 cents cheaper per watt for the hardware costs in utility and commercial installations, respectively.
It has long been the case that it was cheaper per watt for residential solar companies such as SolarCity (now Tesla) and Vivint to use panels with high efficiency cells, because they lowered the cost of their labor and racking and increased the wattage compared to their fixed soft costs per installation such as marketing and permitting. However, DIYers don’t pay for marketing and their time spend in installation and permitting is free, plus they often makes their own racking and cabling, so cheap polycrystalline or broken cells were the best route for getting the lowest dollars per watt when solar cells were expensive. Now the prices have fallen so much that panels using high efficiency monocrystalline are actually cheaper per watt than polycrystalline, even for the DIYer. Only if able to reduce the other costs of the panel by obtaining used window frames or building panels with standard glass or Plexiglass does it make sense today to use the cheapest polycrystalline or broken cells.
What size of cells to buy?
Solar cells are generally fabricated in 5×5 inch and 6×6 inch squares and have 0.5 volts per cell. The 6×6 cells generally cost less per watt, so they are recommended if trying to save money. The problem for the DIYer is that you are often constrained by the size of your glass and frames. It is very difficult to find tempered glass in the large sizes required for a traditional 60 or 72 cell panel. You might be able to find a large piece of tempered glass for a glass door, but most DIYers build panels that are one meter squared (39 inches squared) or smaller, since they can’t find anything larger. Even if you can find a seller of large panes of tempered glass, shipping panes larger than 1 meter squared is very expensive.
The trick is to get enough volts out of a small panel in order for it to be useful. To charge a 12, 24 or 48 battery, the voltage of the panels needs to be 50% greater, so 18, 36 or 72 volts, respectively. That means building a single panel with 36, 72 or 144 cells, respectively, or stringing several smaller panels together in series that reach that total number of cells.
36 6×6 cells can be crammed on a square meter of glass, which will charge an 12 volt battery. However, if needing a higher voltage, then that can be achieved by simply using 6×6 cells which have been cut into smaller pieces. The voltage remains the same, no matter whether the 6×6 cell has been cut into 1, 2, 3 or 4 pieces. To generate 36 volts to charge a 24 volt battery, then 72 3×6 cells can be placed on a panel that is one square meter in size. To generate 72 volts to charge a 48 volt battery, then 144 3×3 cells can be placed on the same size panel.
The other way to generate 36 volts is to string two 36 cell panels wired together in series or four 18 cell panels in series. Likewise, a 48 volt battery can be charged by two 72 cell panels in series, four 36 cell panels in series or eight 18 cell panels in series.
Just remember when connecting panels in series that the voltage is additive, but the current will be the same for all the panels. If one panel has a lower current, then it will draw down the current of the rest of the panels in the series. For example, if connecting a 4V, 8A, 32W panel in series with a 6V, 6A, 36W panel, then you might expect that the total output to be 68 watts by adding up the watts of each panel. However, the output is 10 volts x 6 amps which equals 60 watts. This means that it is a good idea to use solar cells with the same rated current in all the panels in a series, so that the lower current in one panel won’t draw down the current in the rest.
If needing higher voltage, you can cut the cells into pieces with a Dremel diamond blade saw or even a simple glass scorer, but it is easier to simply buy pre-cut cells off ebay. You can also salvage your broken cells by cutting them into smaller pieces. Just remember that all the cells wired in series should be the same size in order to not loose amperage. Don’t wire a panel with 3×6 cells in series with a panel which has 6×6 cells, because the amperage will be limited to the 3×6 cells. A cracked cell generally isn’t a problem in a solar panel, as long as the bus bars aren’t broken, but a broken cell should be replaced since it limits the amperage of all the other cells in the series.
The drawback of working with smaller cell sizes is that you have to do more soldering to achieve the same amount of energy. Some DIYers, however, prefer to work with smaller cells because they are easier to handle and less likely to break while soldering them.
If planning on building a grid tie system that feeds AC power into the electrical grid, most AC pure sine wave power inverters require between 22 and 60 DC volts coming from the solar panels. The 18 volts from a 36 cell panel will not be enough, so two of these panels will need to be wired in series. There is the chance that the wires between the panels might get broken and the inverter won’t get enough voltage. It is probably better to use 72 3×6 or 2×6 cells so that the panel produces 36 volts, rather than wiring two 18 volt panels in series. It is possible to buy low voltage grid tie inverters that accept between 10.5 and 28 DC volts, but I couldn’t find any of these low voltage inverters which are water-proof or guaranteed longer than one year. It is probably best to avoid using them if possible.
What glass to buy?
It would be ideal to use the same kind of low iron textured tempered glass with an anti-reflective coating used by commercial panel makers, but good luck finding it. The best bet is to use any clear tempered glass which you can find at a reasonable price. The size of that glass will end up determining the number and size of cells per panel, as explained in the previous section.
Unfortunately most of the tempered glass that I can find in Bolivia is not low iron, so it has iron particles suspended in it which block sunlight and it has a reflective flat surface which reflects even more sunlight. In fact, most tempered glass that I can find has a blue or green tint to it to block the overly strong sun in the Andes and it is made for table tops, doors, showers and glass fronts in stores, so it is ¼ to ½ inches thick. This kind of glass will block far more sunlight than the clear 3.2 or 4 mm panes used in commercial solar panels. Based on what I have read about potential induced degradation (PID), I also imagine that this glass would have a higher risk of causing PID since it has more metal ions in it which can migrate in the glass. It is recommended to attach solar panels to a ground wire to reduce the risk of PID, but Bolivia generally doesn’t use grounding in its wiring, so I would have to wire up my own ground wire if I want it.
Short of ordering a load of specialty solar glass from China, it seems to be impossible to get my hands on any decent tempered glass in Bolivia for solar panels. The only supplier of solar glass in the US that I could find is americansupplysolar.com which sells 1 meter square panes for $45. The kicker is it would cost me $162.90 to ship it to Bolivia. Even in the US, the cheapest shipping is $34.75 for 3 day UPS. If I were going to make 50 solar panels, I might consider ordering 100 m2 of tempered solar glass from China, but if I needed that much solar energy, I wouldn’t waste my time making my own panels in the first place.
Right now I’m considering using using standard glass that is called “double strength” because it is 3 mm (3/32 in) or 4 mm (1/8 in) thick and building small panels with 12 6×6 cells, so that I can use glass panes that are only 20 x 26.5 inches, which should be better at withstanding hale and less of a loss if one gets broken.
The other option is to use Plexiglass, which has a light transmission rate of 92%, which is significantly better than 83.7% for standard glass. Plexiglass, however, is not recommended because plastic expands and contracts more than glass when the temperature changes, which can crack the solar cells. The other problem is that Plexiglass may warp over time and it absorbs heat which could reduce the output of the panels in hot regions. I figure that if I put a thick layer of silicone rubber between the Plexiglass and the solar cells, they probably won’t break, but the repeated stress of expanding and contracting over time might cause microcracks in the cells that will reduce their output over time. It seems the safer course to risk using small standard glass panes than to use Plexiglass. I might experiment with both to see which works best, but it will probably take years to detect any microcracking caused by the expansion of Plexiglass on solar cells.
What frames to use?
The next question is what type of frame to use. There are a number of videos on Youtube showing people making their own solar panel frames out of wood. These frames look pretty, but I am skeptical of anything made of wood holding up over time when exposed to the elements on top of a roof. Having to reapply paint or waterproofing to the frames every couple years years seems like a task that I will never get around to doing, so it is best to use a material which can’t rot.
The cheapest option is to use PVC plastic frames, which are more waterproof than wood, but PVC can also grow brittle and “rot” over time, especially if I buy PVC frames which aren’t UV resistant. In Bolivia, there are windows and glass shops where I can get custom frames made, but very little is labeled so I have no idea if I’m buying UV-resistant PVC or not.
Besides, PVC is problematic for the environment and human health. Mercury is used in the production of PVC and trace amounts remain in the plastic. Cadmium and lead are commonly used as stabilizers and added to the inks in PVC. The heating of chlorine during manufacturing releases dioxins and furans which cause cancer and those same carcinogens will be released if the solar panel ever catches fire. I would also like to avoid using wires with PVC insulation, since it contains phthalates, which are an endocrine disruptor causing birth defects and developmental problems in children, but most wiring in Bolivia contains it.
The best option is to use an aluminum frame, since aluminum is strong and light and won’t rust or rot, so the frame will last the life of the solar panel which could be as long as 40 years if I make it right. ARCO solar panels are still producing energy after 37 years and SolarCity examined 11,029 solar arrays to predict that the panels it installs will be producing 82.5% of their original power after 35 years. The drawback of using an aluminum frame is that it can conduct current, which increases the risk of PID (potential induced degradation).
In addition, producing aluminum requires significantly more energy and emits more greenhouse gases than either wood or PVC. Converting bauxite into aluminum consumes large amounts of energy and releases large amounts of greenhouse gases, especially if the aluminum is produced in China, India or Australia where the energy comes from burning coal. Nuss and Eckelmann (2014) estimate that 194 megajoules of energy are consumed and 12.2 kg of CO2-eq are emitted to produce a kg of virgin aluminum. If my panels don’t end up generating much carbon-free energy, then I will have needlessly wasted resources, so it is best to plan to make something that works, rather than just making it to have fun.
I can buy frames and cut them down to size to fit my glass, but there will be a lot of wasted frame with my non-standard sized pane. Keeping with the do-it-yourself spirit, it seems better to buy some pieces of angle aluminum and make my own frames. They will be heavier than standard frames, but they will also probably be stronger. As long as I separate the glass from the aluminum with a good layer of silicone caulk, they should work fine. The important thing is to make sure that all the wiring in the solar panel is insulated from the aluminum frames. A number of YouTubers, such as Robert Smith and Pippi Peterson, have posted videos how to make frames for solar panels from aluminum angles and it doesn’t appear that difficult.
What encapsulant to use?
Encapsulating the cells and wiring so that they are sealed from water and oxygen is the critical step where DIY solar panels are most likely to fail. Cells which aren’t encapsulated will rapidly degrade, even within a year, so there is little point in building a solar panel if it won’t be properly encapsulated. The solar cells and wiring can be encapsulated with silicone rubber or with EVA inside a water-proof shell of glass and plastic. Both methods are expensive and have their drawbacks, but there is no alternative if wanting the solar panel to last for a long time.
There are videos on Youtube of people who wire together solar cells and use silicone caulk to stick them to the glass inside a sealed double paned frame. This method works well enough for a while, but these home-made panels are unlikely to last longer than 10 years. Moisture which oxides cells and corrodes wires tends to build up inside double paned windows if they don’t have air holes, but providing those air holes will let in oxygen that will also oxide the cells over time. People living in a dry climate might be able to completely seal the frame without air holes, but that still won’t protect the cells as well as proper encapsulation.
Most commercial panels encapsulate the cells by the sandwiching together the following materials under a heated vacuum:
- 3.2 or 4mm tempered glass
- EVA (ethylene vinyl acetate) film
- Solar cells connected with tabbing wire and bus wire
- EVA (ethylene vinyl acetate) film
- A composite backsheet made of TPT (Tedlar-polyester-Tedlar), TPE (Tedlar-PET-EVA), KPK (Kynar-PET-Kynar), KPE (Kynar-PET-EVA) or PPE (PET-PET-EVA)
The cells are cocooned between two layers of EVA (ethylene vinyl acetate) which is an elastomeric polymer that is rubber-like in softness and flexibility. It is the same material used in hot glue sticks. Inside the EVA, the photovoltaic cells and the wiring is insulated and can thermally expand and contract which is important for panels which will be exposed to large temperature swings. If a more rigid glue or caulk is used, the cells may crack and the wiring may break.
The backsheet of the panel is typically composed of Tedlar, which is DuPont’s trademarked name for polyvinyl fluoride (PVF). It is impermeable to water vapor, burns very slowly, and has excellent resistance to UV radiation, weathering, staining and most chemicals, plus it is light, which makes it a very good material for sealing the back of a solar panel. In order to save money, many panel manufacturers are now using TPE, which only has a single layer of Tedlar, rather than the two layers found in TPT. TPE has a middle layer of polyethylene teraphthalate (PET) plastic which is also a little cheaper than the polyester found in TPT.
According to DuPont, Tedlar has been used in over half of the 900 million solar panels made in the last 40 years, but the high cost of Tedlar and DuPont’s trouble supplying the booming solar industry has caused many generic producers of PVF and alternatives to PVF to appear. In 2013 Arkema introduced an alternative to Tedlar made of polyvinylidene fluoride (PVDF) which goes by the brand name Kynar. Like Tedlar, Kynar is sold in double sided KPK (Kynar-PET-Kynar) and single sided KPE (Kynar-PET-EVA).
Recently, new composites have appeared named TPF (Tedlar-PET-fluorine coating) and KPF (Kynar-PET-fluorine coating) which cost the same as TPE and KPE and should have similar performance. Be careful when applying these composites since the inner fluorine coating can be easily scratched. There is a cheaper alternative known as FPF (fluorine coating-PET-fluorine coating), which uses the same coating on both sides. FPF probably won’t hold up as well as backsheets containing PVF or PVDF.
Over the last decade a number of manufacturers have started offering backsheets that don’t contain fluoropolymers, which are bad for the environment. In 2008, Coveme introduced the composite PPE (PET-PET-EVA), and a number of manufacturers including Dunmore Corp., Flexcon and Micel now offer PPE backsheets. The outer layer of PET is water and UV resistant and the inner layer is water resistant. In 2014, the Austrian company Isovoltaic introduced PAP (polyamide-PET-polyamide) and TPA (Tedlar-PET-polyamide). Polyamide is better known by its brand name Nylon. Recently, the Italian company Filmcutter introduced a new monolayer PET backsheet that it developed with the Japanese company Toray. They claim that the monolayer PET will hold up better than composite PET and will cost just $2.75 per square meter.
The question is whether it is worth paying more for TPT or KPK, or whether a cheaper alternative will serve just as well. A 2013 study by Daiken found that the double-sided composites TPT and KPK have similar properties under a 7000 hour stress test, but the single-sided composites TPE and KPE have less tensile strength, so there may be some justification for using the more expensive double-sided composites. The same study found that PPE failed in most of its tests. The non-fluorinated backsheets have evolved quite a bit in recent years, but it is still probably safer to stick with a PVF or PVDF backsheet if wanting a panel that will last for 25 years.
In recent years, solar panel manufactures have also started offering higher-grade panels whose backsheet is a thin pane of tempered glass, which is even better than TPT at sealing the panels against the H20 and 02 that cause the delamination of the EVA, oxidation of the cells and corrosion of the wiring. Here are its layers:
- 3.2 or 4mm tempered glass
- EVA film
- Solar cells connected with tabbing wire and bus wire
- EVA film
- 2mm tempered glass
Many DIYers also sandwich their solar cells between two panes of glass. It is more expensive, and can trap more heat around the cells which lowers their performance, but it is a good way to keep out water and oxygen and it will hold up better over time. The problem is that it is very difficult to remove all the air between the two panes of glass, so DIY panels that use two panes almost always have air gaps in them, that can cause more refraction of light. If the air gaps touch the cells or their wiring, then these components are not as well protected against oxidation over time.
How to laminate panels with EVA
Panel manufacturers place their panels in a vacuum chamber to suck out the air that could form air bubbles inside the panels and heat them for 5 to 6 minutes at between 140 and 145ºC, which is hot enough to turn the EVA film into a clear hot glue that joins together the components, but not too hot to damage the solar cells. Then, they are pressed under heat and vacuum for another 15 minutes to push out any air bubbles and to form the chemical cross linkages in the EVA.
A DIYer can make a panel by using a hot air gun to heat up the EVA, but it is tricky to do it well and it generally takes a some experimentation to perfect the technique. It also takes a bit of patience, because the air gun has to be directed back and forth over the cells until the EVA turns clear and semi-liquidy, but without letting any one area get too hot that it will damage the cells or blow a hole in the EVA film. If a hole does develop, an EVA patch can be cut and placed over the hole to melt in with the rest of the EVA film.
It is recommended to heat the EVA in a well ventilated area to avoid breathing too much of the gases released by the EVA. When heated to over 400ºF, EVA produces gases which can irritate the skin, eyes and respiratory system. Tests have found that EVA is toxic to worms. Tests also found that vinyl acetate, which is a component of EVA, induces nasal cancer in rats. The evidence from workers exposed for years to vinyl acetate in chemical plants is inconclusive, but some believe it to be a possible carcinogen for humans. OSHA recommends that workers not be exposed to more than 10 parts-per-million of vinyl acetate in the air during an 8 hour work day.
Some DIYers tape down the edge of the EVA film and then hook up a shop vac or vacumn cleaner to suck out the air while heating up the EVA with an air gun. Using a vacuum is recommended not only because it reduces the amount of EVA gases you will breathe, but also because it will help suck out the air which helps prevent the formation of air bubbles in the EVA. Air bubbles will increase the amount of refraction and block a little more light. The problem is that using a heat gun only allows one side of the panel to be throughly heated, so the EVA on the other side of the cells probably won’t be heated very well, especially if using large 6×6 cells. I wonder if this problem could be solved by using a table with a hole cut in the middle of it, so you could use the heat gun on both sides of the panel; or more simply suspending your glass panel on top of sawhorses and 2x4s, so you can reach underneath the glass pane with the heat gun.
Some DIYers place the solar cells face down on the glass and place one sheet of EVA film, on top, so they don’t have to worry about heating both sides. Because there is no EVA layer between the glass and the photovoltaic material, the panel appears cleaner with no suspended air bubbles. However, this means that there there will be some space between the cells and the glass, which will cause some refraction and block more sunlight than a layer of EVA. Using EVA on both sides of the cells is recommended not only because it causes less refraction of light, but also because it is better for sealing and thermal expansion.
Other DIYers place the solar cells face up on the glass and a single EVA sheet over it, which means that the front side of the cells are sealed, which is the more important side, but then a second pane of glass needs to be placed on top, which adds to the costs of the panel. If the second pane of glass is immediately placed on top when the EVA is still warm, then there will be less air inside the panel to cause refraction, but it is hard to get out all the air bubbles. Most DIYers just wait for EVA to dry and allow there to be some air space between the EVA covered cells and the top pane of glass, which looks nicer, but causes more refraction and thus more blocked sunlight.
The more ingenious DIYers deal with the problem of heating both sides by building an enclosed heated table to bake the entire panel and connect a vacuum to suck out the gas. Some of these home-made heated vacuum tables work well and others produce mediocre panels with lots of air bubbles, but the ones that work well are quite expensive to build. Because these home made ovens do not press the panel layers together, they have to use higher heat and bake longer than the commercial solar panel laminators.
Buying EVA film in small quantities is expensive. It can be found on ebay for $9 for a square meter, but the price drops to just $40 for 10 m2, so you save a lot by buying more. I wouldn’t recommend buying the cheapest EVA, because you don’t know what you are getting. EVA will yellow over time, which blocks more sunlight. Tests by the NREL (p. 19) show that some brands of EVA will yellow three times faster than others, so it is worth paying a little more for better quality EVA, which lists its resistance to UV aging and its light transmission rate. AmericanSolarSupply sells a 10 m2 roll for $50 + $18.34 shipping and better quality EVA can cost $20 to $30 more for the same amount. Before buying, check to see whether the manufacturer is listed in ENF Solar’s directory of EVA manufacturers, which is no guarantee of quality, but it does indicate that it is not a fly-by-night company. Most sellers don’t say who is the original manufacturer of their EVA, but if it is a company like Eco-worthy or AmericanSolarSupply that has a reputation to maintain and specializes in selling to DIY solar enthusiasts, then it is probably acceptable quality.
The backsheet which protects the solar panel from the elements costs a lot if it contains Tedlar PVF from DuPont or Kynar PVDF from Arkema. There are many generic manufactures claiming to be producing Tedlar or Kynar backsheets although they don’t have the legal right to use the Tedlar or Kynar brand name. I have no idea whether there is any significant difference in the quality between the name brands and the generics, but the fact there are so many reputable producers of PVF and PVDF suggest to me that it isn’t worth paying for brand name backsheets.
AmericanSolarSupply sells a square meter of TPE for $9.50 + $7.52 shipping, but it also sells 10 m2 of EVA and 5 m2 of TPE together for $80 + 18.23 shipping, which is a much better deal if building several panels. It is possible find TPT for much cheaper. htzzrhone on ebay sells 6 x 0.68 meters of TPT for $35.50 with free shipping from China, but doesn’t list the original manufacturer.
The standard price for TPT when buying in large lots in China is between $6.87 and $8.25 per square meter, so if a manufacturer is selling for less, it probably isn’t quality material. If wishing to only buy from reputable manufacturers, then look for one of the large producers of backsheet material, which include DuPont (USA), 3M (USA), AGFA-Gevaert (Belgium), Alrack (Netherlands), Aluminium Féron (Germany), Anhui Green Cosmotec Photoelectronics (China) and Anhui JDPV New Material Technology (China). Also check to see whether they are listed in the ENF Solar directory of backsheet producers, which indicates that they are not a fly-by-night company.
Is silicone a better encapsulant?
The other way to encapsulate solar cells is to seal them with a silicone elastomer, which is a higher quality encapsulant. Silicone does not yellow over time like EVA and it is waterproof, so it doesn’t require the use of a waterproof backsheet to protect it, although many add a plastic backsheet just in case. Exposure to water and heat forms acetic acid in EVA, which corrodes the metal and electrical connections in cells and can cause delamination of the panels. Tests by Dow Corning, a silicone manufacturer, found that EVA encapsulated modules lost over 5% of their maximum power output after 3000 hours of exposure to damp heat and over 80% after 7000 hours. In contrast, silicone encapsulated modules only lost 3 to 4% of their maximum power output after 10,000 hours of damp heat. There is some empirical evidence that silicone encapsulated cells last longer. A 200 kW solar array that was fabricated in 1982 with Dow Corning’s silicone encapsulant only lost 5% of its power rated performance after 15 years of use in Maryland and 10 years of storage.
Silicone also has a higher solar transmission rate than EVA. Tests by Dow Corning found that silicone encapsulant absorbs less than 0.2% of light, whereas EVA encapsulant absorbs between 1.4% and 1.6% of light. UV light degrades EVA, so additives are included in EVA to block wavelengths between 280 and 400 nanometers, whereas UV radiation passes through silicone without harming it. Because silicone doesn’t block UV light, photovoltaic cells encapsulated with silicone receive 3.1% more light those encapsulated with EVA, which means more energy generation.
Silicon is better at handling temperature extremes than EVA, which is why silicone is used to encapsulate solar cells on satellites. Silicone is rated to function correctly between -45 and 200ºC. In contrast, EVA looses its flexibility at low temperatures and it expands more than silicone under heat. Tests by Momentive Performance Materials, a silicone manufacturer, found that EVA expands twice as much as silicon at 30ºC, which puts more mechanical stress on the components in a cell panel which have lower thermal expansion rates than the encapsulant. Silicone ages better and retains its elastic properties better than EVA, so it is less likely to mechanically stress and crack the delicate wiring and solder joints in solar panels. Likewise, tests by the Fraunhofer Institute and Dow Corning found that when solar modules were placed under dynamic and static pressure, solar cells in EVA cracked at -30ºC and 25ºC, whereas the solar cells encapsulated in silicone didn’t crack.
The degradation of EVA over time is a known problem and the solar panel industry has spent decades improving EVA and backsheets to make them better at holding up under UV radiation, damp heat and mechanical stress. These tests by silicone manufacturers should be taken with a grain of salt, since they have a financial motive for trying to prove that their product is better than EVA. They probably didn’t use the best EVA and TPT available for conducting in their tests, but the DIYer probably isn’t going to be using the best EVA and TPT either. The large commercial panel makers have subjected their panels to a whole series of tests specified by the IEC 61215 standard, so they have discovered what materials will hold up and they have perfected their lamination techniques so their encapsulation will last for at least 25 years. The DIYer, however, is less likely to know which are the better materials and be able to find them for a reasonable price, plus use the right technique of lamination to replicate their quality, so these tests might be more relevant for the DIYer.
Although silicone elastomer is a better encapsulant, none of the large commercial panel makers use it because it is too expensive. Not only does it cost more to manufacture silicone than EVA and plastic backsheets, but the price of silicone is also high because there are few manufacturers and low volumes of production. Unlike EVA and TPT, the price for silicon doesn’t decrease very much when buying in bulk, so panel manufacturers can’t get it very cheaply.
The other drawback for the DIYer is that it takes more time to encapsulate a solar panel using silicone than EVA.. It takes 2 to 7 days for silicone to cure at room temperature, but that time can be reduced when the silicone is heated. Sylgard 184 takes 10 minutes to cure at 150°C and PV-6100 only takes 1 minute to cure at 100°C. In contrast, it takes 20 minutes to laminate a panel with EVA at 140-145 °C, so silicone is potentially faster and consumes less energy in the panel factory. Panel manufacturers could save energy by curing silicone at room temperatures, but it takes a lot of warehouse space and can be highly variable depending on the weather. Manufacturers need predictable time tables, so they cure silicone under heat in a vacuum.
For the DIYer, however, the fact that silicone can be cured at room temperature is an advantage, because it means that it doesn’t require buying any special heating equipment and the 2 to 7 days that it takes for the silicone to cure doesn’t cost anything but one’s patience.
Where to get silicone encapsulant
Dow Corning is the principal maker of silicone for solar cell encapsulation. It offers Sylgard 184 which is faster setting and Sylgard 182 which is slower setting. Sylgard is has been widely tested and is often recommended, but it is too expensive for most people making their own solar panels. It costs more to encapsulate cells with Sylgard than the cells are often worth. A pound of Sylgard base with another tenth of a pound of catalyst typically costs $80 with shipping. That is only enough encapsulant to cover 36 6×6 cells or 72 3×6 cells. Encapsulating a full-sized 60 or 72 cell panel would cost $160. Amazon recently offered a sale on Sylgard for the low price of $49.26, which none of the other sellers could match. Perhaps it was a special promotion by Dow to get more people to try using Sylgard 184 in their 3D printers, but Amazon’s stock rapidly sold out, so Sylgard is now only available for $80 again. Even buying Sylgard by the gallon doesn’t get the price below $45 per pound, which is still too expensive for the DIYer on a tight budget.
Aside from Dow Corning which charges an arm and a leg for its silicone, there are only a couple other companies that sell their silicone encapsulant in small enough quantities so that they can be used by DIY solar panel builders. Quantum Silicon, Inc. in Virginia makes QSil 216 for cell encapsulation, which is is slower setting than Sylgard 184, but faster setting than Sylgard 182. Fortunately, it is much cheaper. Quantum Silicon packages it in containers of 16 fluid onces (1.58 lbs) which sell for $26 per lb on Amazon, or a third of the price of Sylgard 184. Unfortunately, that quantity is too much for a half-sized panel of 24 or 36 6×6 cells and too little for a full-sized panel of 60 or 72 6×6 cells. AmericanSolarSupply, however, bought QSil 216 in bulk and resells it in containers of 1.1 lbs, which is the right amount for most DIY panels. If needing large quantities, Chemical Concepts sells QSil 216 in bulk, but it is probably better to contact the company directly.
A little company in Poland, Silikony Polskie, produces POLASTOSIL M-2000, which is a transparent silicone that can be used for encapsulating solar panels. POLASTOSIL M-2000 is sold for roughly the same price as QSil 216 and can be bought in containers of 1, 5, 30 and 60 kgs. You can email the company at email@example.com to buy directly from Silikony Polskie, which Europeans report doing when they can’t get QSil 216 from the US. An ebay seller, electro_silicone, now sells POLASTOSIL M-2000 online and will ship world-wide.
The last option for the DIYer is Cell Guard which is offered by MLSolar on ebay. MLSolar probably found one of the many Chinese manufacturers who produce transparent silicone rubber for electronics and bought it in bulk to resell to solar DIYers. MLSolar doesn’t provide a data sheet for Cell Guard, but claims that is the exact same compound as Sylgard 184. If true, then it be worth buying, but QSil 216 is substantially cheaper and comes from a reputable company so it hardly seems worth the risk.
There is one more option for the DIYer who is willing to take a risk and doesn’t mind loosing a few bucks. There are half a dozen Chinese manufacturers on Alibaba who claim to produce encapsulant for solar panels. Most produce silicone for potting electronics and sex toys and it looks like they decided to also try to selling their silicone for encapsulating solar cells. It is unlikely that the performance of this silicone has been rigorously tested in solar panels like Sylgard 184, but they might work. Some of their prices are quite cheap. If you are serious about building a number of panels with silicon encapsulation, it might be worth experimenting with the silicone from Chinese manufacturers, because even QSil 216 bought in bulk is going to be quite expensive if building a lot of panels.
For example, here are three Chinese manufacturers who are willing to sell in small quantities so it wouldn’t cost too much to experiment with their silicone:
- Shanghai Jorle Fine Chemical Co., $2-$4 / kg, minimum order 10 kg
- APS SC-2205, $15-$20 / kg, minimum order 2 kg
- Shenzhen Jir Ri Feng Tai Co. (JRFT), $5.80 / kg, minimum order 2 kg
If you do try out a Chinese manufacturer’s silicone, please post the results of your experiment on a forum such as the “DIY solar panel” section of SolarPanelTalk. The more people who post about their experiences, the less others will have to start from scratch. One of the problems is that nobody knows which silicones are better, because people don’t take the time to share what they have learned. Sharing your failures online can save other people a lot of time and grief, so they know what to avoid.
Although silicone encapsulation may be expensive, it is generally the best option for the casual DIYer. Lamination with EVA is much trickier to master and requires a more complicated setup to do it right, whereas pouring and curing silicone is a simple process and doesn’t require as many tools. Plus, it is far easier to get the air bubbles out of silicone than EVA. You’re more likely to get silicone encapsulation right the first time, and thus more likely to be pleased with your work. Since silicone is a superior encapsulant that lasts longer and protects the cells and wiring better from oxidation and thermal and mechanical stresses, you’re also more likely to end up with decent panels that will serve you for many years.
It is also worth keeping in mind that silicone encapsulation probably won’t cost that much more than using EVA and a TPT backsheet, if you use QSil 216 or POLASTOSIL M-2000, instead of Sylgard 184. EVA and TPT is cheaper than silicone if buying them in rolls of 10 meters or more, but if you are just making one or two panels, silicone costs the same as EVA and TPT, because buying small pieces of EVA and TPT is expensive. Of course, these equations change if you plan on building a dozen panels, but it still might be worth calling Quantum Silicon or Silikony Polskie to see how much it would cost to order a large quantity of silicone encapsulant.
For example, let’s say that you plan on building twelve 36 cell panels that produce 160 watts each or 1920 watts in total. You are going to need 1 gallon of QSil 216, plus three 16 oz. bottles, which together will cost $339.31. In comparison, buying 30 m2 of EVA and 15 m2 of TPE from AmericanSolarSupply will cost $240 + $30 shipping. Maybe if you call up AmericanSolarSupply, you can convince them to sell you 25 m2 of EVA and 12 m2 of TPE for the price of $200 + $30 shipping, but you also might be able to get your QSil 216 a little cheaper by ordering directly from the manufacturer.
This difference of $70 to $110 extra for silicone compared to EVA and TPE is substantial, but remember that you are going to be paying that much just for the cells in one panel. If you mess up just one panel learning how to laminate with EVA, then you have already made up the difference. The probability that your panels will last longer and will loose less of their original output over time also makes up the difference. If you have to buy a heat gun or a shop vac to laminate the EVA, then you have also made up the difference. If you decide to build your own heated vacuum chamber to laminate EVA panels, then you certainly won’t have saved any money.
Given its superior qualities, it is surprising that silicone encapsulation is not widely used by the solar industry. My searches on the internet did not turn up a single commercial solar panel for sale with silicone encapsulant. Presumably, there must be some companies in the world making special order panels with silicone encapsulants for applications such as satellites and Arctic expeditions, but they aren’t being offered for sale to the general public. Despite its superiority as an encapsulant, none of the high-end panel manufacturer like SunPower, Panasonic, LG, Kyocera or SolarWorld offer silicone encapsulation even in their most expensive models. Even models like the Jurawatt Desert Technology Panels designed for weather extremes or Kyocera panels designed for salt water conditions don’t offer it.
Dow Corning conducted a marketing campaign to sell silicone encapsulation to the solar industry a decade ago. It produced a silicone encapsulant named PV-6100 that could be cured in 2 minutes at 150°C and conducted tests proving that PV-6100 was superior to EVA. The base of PV-6100 is mixed with its catalyst at a ratio of 1 to 1. It used to be possible to buy PV-6100 on ebay in 2010 and 2011 for about $40 per kg, which is cheaper than any of the silicone encapsulants available today on ebay. Several DIYers reported that PV-6100 worked well and noted that its viscosity is similar to 30 weight motor oil, so it flowed more easily under the cells when encapsulating than Sylgard 184, which has a consistency more like honey. Dow Corning claimed in 2009 that using PV-6100 would not only improve module efficiency, but also reduce the costs because was “less capital and labor intensive than incumbent EVA lamination.” A number of other chemical companies followed suit, advertising that they produce silicone for solar cell encapsulation, such as Smooth-on Solaris, Momentive Performance Materials SilTRUST E110, Wacker ELASTOSIL Solar 2202 A/B and Intertronics Opti-tec 7020.
None of these products appear to have garnered much commercial success. They simply cannot compete with the low cost of EVA. For the commercial panel makers, the superior performance of silicone as an encapsulant is not enough to justify its extra cost compared to EVA. It is possible to special order these silicone encapsulants in large quantities from Dow Corning, Smooth-on, Performance Materials, Wacker and Intertronics, but the DIYer can’t buy them in small quantities. Dow Corning no longer makes PV-6100 or its successor PV-6150. Instead, Dow Corning now offers PV-6212 to panel makers. This encapsulant is capable of curing in 1 minute at 100°C, so it should be able to reduce the energy costs and increase the throughput of the solar panel factories compared to EVA. Despite Dow’s advertising that it produces a solution for the solar industy, the company hasn’t managed to convince any of the large panel makers.
This lack of mass production means that DIYers can’t find silicone encapsulant at a cheap price, but it also means that they can potentially make solar panels with a superior encapsulant which transmits more light and protects the cells and wiring better than the commercial panels. Of course, this advantage probably won’t equal all the advantages of the commercial panel makers, but it does offer one benefit to building your own panel.
How to set the silicone in the panel
It is recommended to wait for a day that is cool and dry to set the silicone in the panel. The lower the temperature, the longer it takes for the silicone to congeal, which gives you more time to work any air bubbles out of the silicone. Cool air is also not capable of holding as much moisture as warm air. Keeping moisture out of the panel is important for its long-term longevity. It is also recommended to wait for a cool, dry day, because the air pressure will be lower. The lower the air pressure, the easier it is for air bubbles to be worked out of the silicone, because of the larger difference between the pressure in the liquid silicone and the atmosphere. For these reasons, people who live in hot or humid climates, often wait till the winter to start building their solar panels. The other option is to set the silicon inside an air conditioned room.
If you have already soldered together your solar cells and attached them to bus wires, but want to wait for a better day to set the silicone, then it is recommended to place the entire panel inside a bag and seal it, so that H20 and oxygen can’t get inside to start oxidizing the cells and wiring. Try to press as much air as possible out of the bag before closing it. If you have a shop vac or vacuum cleaner, attach it and suck out the air, before closing the bag. When closing the open end of the bag, use both twisty ties and rubber bands in several places. Folding the closed end several times also helps to keep air out.
Try to find a clean place to set the silicon. It is better to work inside to keep flying dust and debris out of the silicone. Before placing the cells face down on the glass, first clean the inside face of the glass with isopropyl alcohol (IPA), because you will never get another chance once you pour in the silicone. It is also recommended to clean the front of your solar cells with isopropyl alcohol to remove any excess flux and fingerprints that you may have left on the cells when soldering. Distilled water can be used for cleaning some types of fluxes.
If you haven’t yet placed the glass in its frame, there will be nothing to prevent the liquid silicon from running over the edge. To prevent this, take clear silicone caulk and create a bead around the entire perimeter of the solar cells on top of the glass. This is also recommended if you have excess space between the solar cells and the frame, since it will reduce the amount of silicone that is needed. 1.1 lbs of silicone is just barely enough silicon for 36 6×6 or 72 3×6 cells if the cells are tightly spaced together, so place the silicone bead close to the edge of the cells to waste as little silicone as possible. The silicon caulk will also hold down the bus wires around the edges of the panel and put some drops of caulk between the rows of cells to make sure that everything stays in place when the panel is shaken during encapsulation.
Silicone caulk bead around the edges of cells to hold in the silicone encapsulant and hold down bus wires. Screenshot from mark0177’s Youtube video.
Silicone elastomer comes with the base in a separate bottle from the catalyst which is a curing agent. The standard proportion is 10 parts base for 1 part catalyst in most silicones. Adding more catalyst will cause the silicon to cure faster and harder but it is best to stick to the recommended proportions. This is easy if you bought in small quantities, because the silicone already come in the correct proportions in the two separate bottles. POLASTOSIL M-2000 is different from the other silicones, because it has a proportion of 5 to 8 parts catalyst to 100 parts base. If using a 1 kg container of POLASTOSIL base, then only pour in 2/3rds of the catalyst bottle that comes with it.
Slowly pour first the silicone base into a large, clean container. Try to avoid splashing as you pour, since that will increases the amount of air bubbles in the silicon. Then, slowly pour in the catalyst and gently stir it into the base. Don’t mix vigorously, since that can also mix air bubbles into the silicone. If using Sylgard, the base comes in a big enough container to also hold the catalyst, so pour it directly into the base’s container and then mix it.
Once the silicone is mixed, then pour it along the cracks between the cells. Mark at AffordableSolarFrames.com recommends leaving one of the edges of the cells open, so that as the silicon seeps between the cells and the glass, the air under the cells can escape. The panel should be shaken to help spread the silicon under each cell, so that it is encapsulated on both sides. Shaking also helps to work out the air bubbles from the silicon.
Mark recommends using a table with a hole cut in the middle because it makes it easier to look up under it to see how the silicon is spreading and whether air bubbles are forming. Another option is to placing the pane of glass on boards and saw horses to be able to see under the glass, but it is probably a good idea to place the glass inside a frame if using this method to better protect it. If inside a frame, two people can lift up the frame to peak underneath as well.
Pour silicone encapsulant along cracks between cells leaving one side open so that air can escape. markp0177’s Youtube video.
After the silicon has spread out between the glass and the front of the cells, then take a brush to spread out the silicon so it covers the backs of the cells, the tabbing wire and all the spaces between the cells.
Don’t hurry when spreading out the silicone. QSil 216 takes 4 hours to set (congeal) and Sylgard 184 takes two hours to set at 25ºC (77ºF). It will take a substantially longer on colder days and a shorter amount of time on warmer days. People report that it can take days for the silicone to gel during the winter. If it is a hot day, then the silicone will gel much faster which can be a problem because it doesn’t give much time to work the silicone under the cells and get out all the air bubbles, especially if using Sylgard 184 which is faster setting.
Although you may not see any air bubbles, they will continue to form in the silicone encapsulant, especially between the front face of the cells and the glass. Some DIYers attach a vibrator to the panel’s frame to shake out the bubbles. A cement vibrator can be used, but see if you can rent one, since they are relatively expensive to buy. Since cement vibrators are strong, it might be better to tie the vibrator to a block of wood which is attached to the panel’s frame or to the leg of the table which is holding up the panel. A less expensive option is to get the type of electric sander which moves the sandpaper back and forth (not the rotary type). Remove the sandpaper and clean any dust off the sander. Then, tie it to panel’s frame and turn it on to vibrate the panel.
An additional way to help work the air bubbles out of the silicone is to place the panel inside a vacuum chamber. The difference in the relative pressure between the liquid silicone and the vacuum will help suck the air bubbles out, especially if accompanied by shaking or vibrating the panel.
The easiest way to create a vacuum around the panel is to have the glass already placed inside its frame when spreading out the silicone. Then, place some tag board or any flat board with some holes in it over the back of the frame. Place the entire panel inside a plastic bag. Attach a shop vac or the tube of a vacuum cleaner so it will be able to suck the air out of the bag. Tape the open end of the bag around the vacuum’s tube to make an air-tight seal and turn on the vacuum. The board placed over the back of the frame should keep the plastic bag which is sucked down by the vacuum from touching the silicone. Then, shake or vibrate the panel enclosed in the bag to help release the air bubbles in the silicone.
If unable to obtain a vibrator or use a vacuum, there is another method of avoiding air bubbles. A group in Nicaragua discovered that they could avoid air bubbles by first painting silicone over the fronts of the cells where air bubbles are prone to form and letting them dry. Then, they picked up the silicone covered cells and placed them face down on the glass and poured the silicon over the back of the cells. As the silicon congealed they pressed down on the back of the cells to force out any air bubbles. Because the cells were covered with a cushion of dried silicone, they didn’t break when being pressed.
The concern that I have about this method is that the silicone layer between the glass and the cells will end up being thicker which blocks more sunlight and it might create a boundary between the dried silicon and the new silicon that causes a bit more refraction, but these factors would only reduce the incoming light by a tiny faction and are probably not worth worrying about. The bigger problem is being able to move the solar cells that are soldered together. The silicon would probably have to be painted on string of cells that are not yet attached with bus wires. Otherwise, they would be too hard to move without breaking the connections. This means that each string of tabbed cells would have to be tested separately under the light to make sure that there are no bad cells. After painting on the silicone, then the strings could be placed on the glass and joined together with bus wire.
The ideal way to make sure that both sides of the cells are encapsulated and reduce the gas bubbles would be to first paint a thin layer of silicone over the glass. Then, lay the cells face down into the silicone and shake them a bit to get rid of any gas bubbles. Then, pour the rest of the silicon over the backs of the cells. Nobody does it this way probably because it is too difficult to pick up and move the cells once they are soldered together and there is too much risk of breaking the delicate cells when pressing them into the silicone. It would take many hands to be able to place the cells into the silicone. The panel manufacturers have an array of suction cups that attach to the solar cells to pick them up and move them as as a group once they have been soldered together, but DIYers don’t have those kinds of nifty tools on hand.
It is difficult to know whether gas bubbles are forming between the cells and the glass because you can’t see the front side of the glass when the silicone is setting. There is different technique of applying the silicone that allows you to see the front side of the glass. First, lay down a sheet of plastic and place the cells front-side-up on top of the plastic. Then, pour a dollop of silicon on each cell and spread the silicone out with a brush so the front faces of all the cells are covered. All the extra silicone is then poured in a line down the middle of the panel. A pane of glass is then placed on top of the cells. The plastic is taped up around the edge of the glass on the top and bottom of the pane, but not taped on the two sides. Then a piece of paper is laid down the center of the pane of glass to protect it and flat weights are slowly placed on top of the pane of glass to gradually increase the pressure on top of the bulge of silicone in the middle of the panel. As these weights press down, they will force the silicon out toward the edges and push out any air bubbles. The final result is a very clean panel with no air bubbles between the glass and the cells.
Using weights placed on glass to press out the silicone and force out air bubbles. Grzegorz Mucha on Youtube
The drawback that I foresee with this method is that it doesn’t allow you to do any last minute soldering of bus wires when the cells are resting on the plastic sheet, which is possible when they are resting on top of glass. However, the soldering of the bus wires can be done on top of a thin piece of plywood that is slid under the tabs and then removed once the bus wire is soldered to the tabs. A bigger problem with this method is that it doesn’t cover the backs of the solar cells with silicon encapsulant. If the plastic backsheet is waterproof, then they will be protected, but that means buying a PVF or PVDF composite for the backsheet which will add to the cost of the panel. The other drawback to this method is that it looks like it requires more silicone because the silicone has to fill in completely the spaces between the cells to force out the air bubbles. In the video of this technique, the cells used in the panel in the Youtube video are SunPower Maxeons, which are flatter cells and hard to break, but thicker cells would need more silicon to fill in the gaps between the cells. Also, other types of cells are more prone to cracking and breaking than Maxeons when pressing down on top of them with weights. If a cell has a big ball of solder on its back, it might crack under the pressure. The flexible Maxeon cells with their dogbone connectors that only connect the edges won’t have these sorts of problems.
The silicone will take a number of days to cure at room temperature. The data sheets say that Sylgard 184 takes 2 days to cure and QSil takes 4 days, but people have reported it taking much longer, especially in cold weather. The curing can be sped up by bringing the panel into a warm room or by setting it out in the sun.
What inverter to buy?
The DC (direct current) produced by the battery can be run into a DC charge controller which will regulate the voltage so that it can safely charge up a battery or some other DC device. Most charge controllers have USB ports on them, so that electronic devices such as cell phones can be plugged in and charged.
Most electrical devices, however, run on AC (alternating current), not DC. A power inverter is needed to convert from DC to AC power. If not connecting to an electric grid coming from the power company, then that inverter can produce a modified sine wave. Some AC devices don’t function as well with electricity in the form of a modified sine wave, but most will work with it. However, electricity flowing into the grid must match the sine waves produced by rotating generators from the power company. To produce that kind of electricity a pure sine wave grid tie inverter is needed.
Most residential solar arrays use a string inverter from a company such as SMA, Fronius, SolarEdge or ABB that costs between $1000 and $3000 and are guaranteed from 10 to 12 years. The problem is that the typical DIYer is only building a few panels and doesn’t need a large inverter which is outside their budget.
There are a whole slew of cheap grid tie inverters available on Amazon and ebay with prices ranging from $60 to $200. The DIYer will be tempted to buy one, but most of them should be avoided. First of all, most of them don’t have the UL mark, meaning that they haven’t been tested for safety by United Laboratories. No electrical company in the US will allow you to generate electricity for their grid with an inverter which isn’t UL certified. If they detect that you are generating grid electricity using a non-UL certified device, then they can fine you. If buying an inverter online from an Asian manufacturer who claims to be UL certified, it is probably a good idea to look up the device in the UL database to verify the claim.
Some of the cheap grid tie inverters that you can buy online do bear the CE mark, but that mark is self-certified, meaning that the manufacture simply declares that it means the EU health, safety and environmental requirements that ensure consumer and workplace safety. All products marketed in the EU which are covered by the “New Approach” directives must bear the CE mark, but the manufacturers can place that mark on their products after preparing a declaration of conformity that they comply with the directives for their product. In other words, the CE mark means that the manufacturer probably read the standard enough to figure out how to say that its products conform to it, but it is no real guarantee that they actually do comply with the standard.
Many DIYer’s, however, are building solar panels to charge up a battery to provide electricity for an off-grid cabin or RV, so they don’t care whether the power company approves or not. In my case, the Bolivian power company doesn’t even allow the public to generate solar electricity that is connected to the grid, but they are also probably never going to know or will simply ignore it.
Nonetheless, it is still a good idea to avoid most of the cheap grid tie inverters being sold online. Almost all of them use fans for their cooling, which are likely to break within a couple years. The comments in Amazon about these inverters are filled with complaints that the inverter died within a couple months after purchase. People also comment that the cooling fans are running constantly even at low loads, which indicates that the unit is poorly designed and doesn’t have good passive cooling.
PowerElectronicsBlog posted an interesting video examining a generic Chinese 500W grid tie inverter, which currently costs $83 for a similar model on ebay. During the video, the commentator points out several features in the inverter that wouldn’t pass UL safety standards and explains why a number of the components reflect poor design choices. He predicts that the inverter will only work for a couple years before dying and concludes: “It has some attention to detail here and there, but the details that matter for very long-term use are missing; and this is just exemplary of this non-mature market where people try to get the lowest possible purchase price rather than the lowest possible total cost of ownership.” These comments are striking compared to PowerElectronicsBlog’s other video about a high-quality 360W Enecsys solar microinverter. The commentator points out over and over the quality of the components and emphasizes why the Enecsys was designed to last.
The Enecsys microinverter doesn’t contain any moving parts and it is has a 94% conversion efficiency, so little of the incoming DC current will be converted to heat that needs to be dissipated. It only has to be able to dissipate up to 24 watts of heat, nonetheless, many of the components have thermal pads to conduct the heat to the outer case and it uses quality components that are designed to take thermal stress. In contrast, the generic Chinese inverter is only 84% efficient and can receive up to 550 watts, so it should be able to dissipate up to 88 watts of heat. Most of its components don’t have good thermal conduits to conduct heat to the outer case and its components are not designed to take much thermal stress. The cooling fan allows the designer to get away with using cheaper components and avoid adding passive cooling to the inverter which would be more costly. If the cooling fan dies which is highly likely given that it isn’t a high-quality fan, the unit will be toast.
Examining those two inverters, it becomes clear why it is a bad idea to buy a low-quality inverter which needs a cooling fan. Not only is a moving part much more likely to fail over time, but the fan allows the designer to take a lot of shortcuts to save on the costs. The components don’t have to be as thermally tolerant and robust, because the designer assumes that the fan will cool them down and they don’t have to have good passive thermal conduits to dissipate heat to the outer case or cooling fins.
Microinverters are particularly hardy compared to standard inverters, because they are designed to function outside in temperature extremes and they need to be waterproof. According to its manual, the Enecsys inverter can operate at temperatures between -40 and 85 ºC and up to 100% humidity. Its enclosure is rated at IP66, meaning that no dust can enter and it will keep out high-pressure water jets from a 12.5mm nozzle in any direction. The entire circuit board of the Enecsys inverter is coated with a thick sealant, so even if water condenses on the inside, the unit won’t short-circuit.
The DIYer who is only building a couple panels might be tempted to buy a generic Chinese 1000 watt inverter for $150, but that would be a mistake over the long term, because the inverter will have to be replaced every couple years. If the home-made panels last 12 years and the inverter lasts an average of 3 years, then the inverter will have to be replaced 4 times, which means spending $600 over the lifetime of the panels.
The best course of action for a DIYer who can’t afford paying for an expensive string inverter is to look for quality microinverters. They typically cost between $100 and $165 each and accept a maximum of between 200 and 360 DC watts, so only 1 large panel or a couple small panels in series should be connected to them. They might cost more initially than a cheap Chinese inverter, but they will save money over the long term. They typically carry a guarantee between 10 and 25 years. The best ones are designed to last as long as their accompanying panel, because solar installers don’t want to get up on the roof to replace them. In contrast, string inverters are designed to last roughly half the life of a solar panel, but it doesn’t involve nearly as much labor to replace one central inverter as a dozen or more microinverters on a roof.
Good quality microinverters have a California Energy Commission (CAC) efficiency between 94% and 97%, which is a weighted efficiency based on the percent of time an inverter will spend at different power levels in sunny southern California. Check the CAC’s database to see the efficiency of each model at different power levels. European models may list their Euro efficiency, which is a weighted average based on the weather in Italy, so a larger percentage of time is spent at lower power levels than in southern California. 21% of the CAC efficiency rating and 32% of the Euro efficiency rating is based on power levels of 30% or less.
Inverters typically have their best efficiency at 75% of their rated maximum power, but a good inverter will also maintain high efficiency at 10% and 100% of their maximum power as well. For example, the Enphase M250-60 (240V) microinverter has 95.0% efficiency at 10%, 96.0% at 20%, 96.6% at 75% and 96.4% at 100%, so its CAC efficiency rating is listed as 96.4%. The voltage and current output by a solar panel changes through out the course of the day. A good inverter has maximum power point tracking (MPPT) so that it selects the optimal voltage to generate the maximum amount of power as conditions change through out the day.
In contrast, generic Chinese inverters may claim 95% max efficiency, but in practice they often only get 70% – 80% efficiency because they have very poor efficiency when operating at lower power levels and they have poor maximum power point tracking. The fact that they list their max efficiency, but not their CAC efficiency is a good indication that they perform poorly at low power levels. A high-quality microinverter will often yield 10% to 15% more AC power than a generic Chinese inverter.
Not only are microinverters recommended because of their high efficiency in converting DC to AC electricity, but they also are generally more reliable and longer lasting than a standard string inverter. The California company Enphase pioneered the widespread use of microinverters for solar arrays, and it now controls 80% of the market for microinverters in the US. Many of the leading inverter companies, such as SMA and ABB, now produce microinverters to compete with Enphase. Enphase claimed in 2009 that its M190 microinverter which has a 15 year warranty would have a mean time before failure of 311 years, and it hired the engineering firm Relex to validate it with testing. Emphase designed an Accelerated Lifecycle Testing (ALT) to simulate a lifetime of use in 110 days. As part of the testing the microinverters are subjected to temperature extremes of -45ºC and 85ºC and have to operate during hard freezes and 85% humidity. Part of what allows Enphase microinverters to survive these tests is the fact that the insides of the inverters are potted with a thermal compound, which not only protects the internal components from oxidation, similar to the encapsulation of solar cells, but also draws away the heat so the components suffer less thermal stress. Enphase was the first company to offer a 25 year warranty on residential solar inverters when it introduced the M215 in 2011. The Australian solar installer, Solaray, reported in 2016 that only 1 out of 3000 Enphase micro-inverters have failed in the first 2 to 3 weeks after installation, which is typically the time with the highest probability of failure in electrical equipment.
The prices for Enphase microinverters are quite reasonable, especially considering the fact that they have the highest efficiency ratings in the industry and their long warranties. Enphase offers the M215 (215W), M250-60 (250W), IQ6-60 (240W) and IQ6+ (290W) for 60 cell panels and the M250-72 (250W) and IQ6+ (290W) for 72 cell panels. The CEC efficiency is industry-leading at 96.5% for the M215 and M250 and 97.0% for the IQ6 and IQ6+. The solar equipment seller Renvu, which generally has some of the best prices in the US, currently sells the M215 for $98, the M250 for $110, the IQ6 for $117 and the IQ6+ for $130. Some of the retired models are even cheaper on ebay. For example, MLSolar is currently selling the M190 for $44.
Unfortunately, Enphase and most of the other companies that make quality microinverters generally aren’t interested in selling to DIYers who make their own solar panels and try to avoid buying the rest of their kit. Enphase only sells microinverters which are designed to be paired with one large 60 or 72 cell panel, so they don’t accept a wide range of voltages. The microinverter manufacturers don’t look kindly on DIYers who often make smaller panels in non-standard sizes and often try to hook several panels to one microinverter, which the Enphase warranty forbids.
Enphase’s business plan is to sell a large number of microinverters at low margins, but then make a healthy profit on their Engage cables and connectors and their Envoy communications gateway. This gateway uses the Power Line Communications protocol to collect information about all the inverters in the network. It forwards this information every 5 minutes via a standard ethernet cable to a router connected to the internet, so that it can be directed to the Enphase servers. Customers can login to the Enphase web site to see graphs of their energy production and receive periodic emails telling them how much energy they are producing. The web site allows the energy output of each microinverter to be monitored, which is useful to locate a malfunctioning inverter or its panel and to check the effect of shading and the orientation of the panel. The Envoy-S Standard and the IQ Envoy Metered communications gateways currently cost $404 and $522, respectively, at Renvu and $20 to $40 more from other vendors.
Most DIYers conclude that there is little reason to pay for an expensive Envoy communications gateway. They can use a multimeter to check the current and voltage and pass the output of the microinverters through a simple power meter to check how much energy is being generated. If they need to keep track of energy generation over time, they buy a device such as the Owl Intuition-PV Cloud Based Energy Monitor or Eco Eye Smart PV Energy Monitor, which costs a third of the price as the Enphase Envoy. If they already have the TED Pro Energy Monitor, they buy an additional MTU/CT set for the solar array. If they are open source enthusiasts, they buy the emonPi Solar PV or build it themselves.
Enphase wants all its customers to buy its Envoy communications gateway, and its literature and training videos explicitly say that its microinverters must be connected to the Envoy. However, many people have reported using the Enphase microinverters without the Envoy gateway and Enphase engineers have admitted that the microinverters will produce electricity for the grid without receiving a signal from the Envoy gateway. It is unknown whether the newer IQ6 models will work without a gateway, but the older M-series models certainly will.
The problem is that the Enphase microinverters are configured for a particular country and the Envoy gateway is needed to reconfigure them for a different country. For example, the ones sold in the US are configured to produce 240 volts at 60 hertz, but in Bolivia I need to use 230 volts at 50 hertz, so I would need to buy the expensive Envoy gateway to reconfigure it. The other option is to order the M250 from Amazon.uk.com which is preconfigured for Europe where 230V at 50Hz is the standard.
Many DIYers prefer microinverters from APSystems, because the company does not insist that its microinverters be used with its Energy Communication Unit (ECU) for monitoring and the ECU supports both Power Line Communication (PLC) or wireless ZigBee, which provides more flexibility in the placement of the ECU. APS makes multiple module microinverters, which are designed to be paired with 2, 3 or 4 panels that contain 60 or 72 cells. The dual module microinverters from APS cost more, but end up being roughly 30% cheaper than Enphase, because half the inverters are required for the same number of solar panels. The dual module YC500A which is supports ZigBee wireless and daisy chaining costs around $200 and the YC500i which is connected to a central trunk cable and doesn’t support ZigBee costs around $170. The 3 and 4 module YC1000 is generally only used in commercial installations because it produces three phase 208 volt current, which isn’t suitable for most residences. The YC500 has a CAC efficiency of 95.0%, which is a 1.5% less than the Enphase M250. APS microinverters aren’t as tested and probably aren’t as hardy as Enphase’s equipment. They come with a standard 10 year warranty, which can be extended to 25 years for $25 more. APS is a great option for people who have multiple large panels, but too pricey for the DIYer who is only planning to build a small panel or two. Also APS hasn’t been around as long, so used APS microinverters can’t be found on ebay.
Used SMA and Enecsys microinverters, however, can be found on ebay for a song, probably due to the problems at both companies. The SMA Sunny Boy SB240-US-99-10 sells for $40 on ebay, but SMA says that it has to be connected to the SMA Multigate, which will cost $250 more. Unlike the Enphase M-series, I have been unable to find any reports of people successfully using the SB240 without its Multigate, so it is probably best avoided by the DIYer. It is doubtful how much longer SMA will continue making microinverters. The company was never very committed to microinverters and did not properly promote the SB240, so its sales have been very poor.
Enecsys entered bankruptcy in 2015 and unlikely to ever come out of it. People who bought Enecsys microinverters are out of luck if the units fail under warranty. They also can no longer get energy monitoring through the Enecsys web site, but EnecsysOutput offers a data monitoring service for an annual fee of 23.99 euros per year. An even cheaper option is to install the open source software EnecsysServer, which can forward the inverter data to PVOutput.org where data monitoring is free. The Enecsys SMI-240-60 microinverter for the US (240v, 60Hz) costs $80 at Amazon and $170 with a gateway and cable. The SMI-263-72 can be found for $74+$39 in shipping on ebay.
Generation 1 of the Enecsys microinverters are factory configured and will work without an Enecsys communications gateway. Generation 2 of the microinverters, however, need to be initialized by a second generation Enecsys communications gateway according to the owners manual (and I haven’t found any reports saying otherwise on the internet). Ebay sellers say that they are already initialized and configured, so it shouldn’t be necessary to buy the gateway. At any rate, the Enecsys GW-EU-RES-G20 communication gateway can be picked up for $50+$7 shipping on ebay, which a DIYer will want to buy if planning on using EnecsysOutput or EnecsysServer for monitoring.
Even if buying a generic Chinese inverter, it is better to buy a microinverter than a normal inverter. The requirement that microinverters be waterproof in order to be installed outside eliminates the cooling fan, which in turn forces the manufacturer to use more robust components and better passive heat management than the standard cheap inverter. An indication of their better equality is the fact that Eco-worthy sells most of its Chinese inverters with only a 1 year warranty, but its waterproof microinverters carry a 5 year warranty. As tempting as it may be to buy a 600W Chinese inverter on ebay for $70, it is better to buy a 300W Chinese microinverter that costs twice as much, because it will likely last 3 times as long. Sometimes the Chinese microinverters can be found at a great price on ebay. For example, Eco-worthy sells a 300W waterproof microinverter for $149, but the same microinverter can be found on ebay for $66 plus $10 shipping or for $129/$135 from another seller. Of course, the ebay microinverter doesn’t come with a 5 year warranty and it might be a factory reject that didn’t pass quality control, but it is probably a better risk than spending money on a Chinese inverter with a cooling fan.
Another issue for DIYers is the fact that microinverters are only designed for 60 cell panels operating at roughly 30 volts or 72 cell panels operating at roughly 36 volts and many microinverters are sold as either 60 cell or 72 cell models. In contrast, DIYers often build 24, 36, 40 or 48 cell panels that produce a lower voltage, and the only inverters available for low voltage panels are generic Chinese inverters such as this Eco-worthy model or this one on ebay that accept between 10.5 and 28 DC volts.
A microinverter connected to several small panels in series to total 30 or 36 volts is probably going to be more reliable and efficient than connecting those same panels in parallel to a low voltage Chinese inverter. If the inverter will only be turned on occassionally, such as in an RV or a weekend cabin, then a generic Chinese inverter is probably good enough; however, if planning to run the inverter day in and out for years on end, then a microinverter is a far better investment, even if it is just a generic Chinese one.
The environmental costs of solar panels
The fabrication of solar cells is a very energy intensive process and the production of glass and aluminum also consumes large quantities of energy. This energy consumed in the fabrication of solar panels needs to be counterbalanced by years of carbon-free energy production by solar panels. DIY solar panels that only last a couple years offer little environmental benefit. If you are producing a DIY solar panel as a hobby or an experiment, but don’t plan to use it for years of energy generation, then try to keep it small, so that you minimize the environmental impact of your hobby. Proper encapsulation of the cells and wiring, strong glass, a long-lasting frame, and waterproof wiring with UV resistance are important because they help ensure that the solar panel will have a long lifespan and generate more energy than was consumed in the fabrication.
The largest environmental impact lies in producing the silicon in solar panels. We often think of silicon as coming from common sand, but the raw material that is used to make silicon comes from mined quartzite which is mostly silicon dioxide (SiO2) and has fewer impurities than common sand. The quartzite is crushed and mixed with coke or another carbon-based reduction agent. Graphite electrodes are inserted to heat the quartzite to 2000ºC, so its oxygen will be released to bind with the carbon to form carbon dioxide (CO2). The resulting metallurgical silicon (MG-Si) is 98% – 99% pure silicon. Between 10 and 15 kWh of energy is consumed to produce a kilogram of metallurgical silicon.
In order to use silicon in solar panels, the impurities such as iron, aluminum and calcium need to be removed, so that it is 99.9999% pure silicon. A metallurgical process can be used to purify the silicon, but most metallurgical silicon is purified into solar grade silicon (SoG-Si) by using a modified Siemens process, which is a chemical process that is simpler and easier to implement, but it consumes more energy.
First, the metallurgical silicon is ground into a powder and mixed with hydrogen chloride gas (HCl) in a fluidized bed reactor. When heated at 300ºC, the Si and HCl combine to form gaseous chlorinated silicon compounds. 85% of the mixture becomes trichlorosilane (SiHCl3 or TCS) and the other 15% becomes tetrachlorosilane (SiCl4 or STC). Distillation is used to separate the TCS from the byproduct STC, which can be recycled to make more silicon or be used to make fumed silica.
Then, the TCS is fed into a Siemens bell-jar reactor where it is mixed with hydrogen (H2) gas. the bell jar contains high-purity silicon rods which are 2 meters long and 0.5 cm thick. When these rods are electrically heated to 1100°C, the silicon in the TCS will be attracted to the rods, and the HCl3 will combine with the H2 to form hydrogen chloride (HCl). The silicon rods are removed after chemical vapor deposition of the silicon grows them to a thickness of 12.5 cm. The inner walls of the bell jar have to be cooled to prevent the deposition of silicon on the walls. This combination of heating and cooling is very energy intensive and consumes roughly 200 kWh per kg of solar grade silicon (SoG-Si). Only 20-25% of the silicon in the TCS is deposited on the rods, so the majority of the silicon has to be reused or recycled. The TCS and STC gases are corrosive and toxic and they are explosive when exposed to water and hydrochloric acid.
The solar grade silicon can be used to produce polycrystalline, monocrystalline or amorphous solar cells, but the energy requirements are very different depending on the type of cell. Amorphous solar cells require the least resources and energy to fabricate. 1 micrometer of silicon is vapor deposited on a sheet of stainless steel or plastic at temperatures as low as 75ºC. However, the 6-8% efficiency of amorphous silicon makes it only suitable in applications such as pocket calculators or electronic toys that consume little energy or as substrate in multijunction cells. In 2016, 54% of global solar production was polycrystalline silicon, 41% was monocrystalline silicon, 3% was cadium telluride (CdTe), 1% was copper indium gallium selenide (CIGS) and only 0.1% was amorphous silicon.
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At this point, I don’t have an real experience building solar panels, so these observations are simply what I have gathered by reading online and using my own reasoning, but nothing beats real-life experience. Hopefully after I have built a few panels, I will be able to offer some better advice for DIYers and comment on what problems I encountered.