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| Solar cell outdoor longevity? |
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| Styno:
Background: For a project I need to power some sensors without access to mains power at least two years without maintenance. The electronics (control, sensor readout, RF and sensor connectors) are housed in a tube and installed outdoors in various unspecified locations. Some of the sensors use quite a bit of power (e.g. inductive conductivity) so I don't want to rely on one or more primary battery cells. So I'm researching a solution whereby solar energy harvesting is used to charge a 18650 li-ion cell with a primary cell for backup during long heavily overcast periods in autumn/winter. The solar cell will be glued to the top of the tube. I found several ic's that are suitable for the energy harvesting, protection and power OR-ing (e.g. adp5090, bq25505, spv1050, s6ae102a, ltc3105) and some small solar cells/panels on Aliexpress. My question is about those solar panels, e.g. this one. It is no problem when the primary battery cell needs to be replaced every few years but I would like the solar cell to last (much) longer, preferably for the lifetime of the sensor (10+ years). Does anyone have experience with this kind of solar panel in outdoor usage? How long would these last realistically? I'm specifically worried about moisture creeping between the laminate. |
| Kleinstein:
The crystalline silicon cells itself usually last very long - more like many decades and it is more the glue to put it on a glass and seals / cables that are an issue. The round disks from the link don't look that good when it comes to the seals. If it fits, I would prefer a ready made panel/laminate with protective glass. They are available even for marine use, though the small size might be an issue. The other possible issue might be algae growing on the surface. So it would help to have a really smooth surface to start with. It may like cleaning every few years too. |
| splin:
There are at least 3 main enemies here - UV degradation of the transparent cover, sealing against water ingress and damage due to thermal expansion/contraction cycles including seal failure, delamination and mechanical breakage of cells or interconnections. The panels you linked use PET which are better than the cheapest epoxy panels but I doubt that you'd get any manufacturer to guarantee them for much more than two years (they may well last much longer in practice for many users of course). ETFE is better, but more expensive than PET; glass is the best. It's not easy to find independant studies on the lifetimes of the various materials but module manufacturers and distributers put out marketing statements which may provide some guidance. The numbers vary wildly though with some claiming 25 year lifetimes for ETFE and others say 5 years. Similarly for PET (2 to 5 years). The actual operating conditions are going to have a big impact - a panel facing north in a location with lots of cloud cover (eg. northern europe) is going to be exposed to very much lower UV than one facing the sun in sunny climes. The temperature and water exposure conditions are going to be very different as well and thus it is very difficult for a manufacturer to specify how long a panel will last. I think you will need to look for panels with ETFE or glass topcovers but that isn't sufficient to ensure a long lifetime. It's a difficult problem which will probably boil down to finding a manufacturer you trust - which is unlikely to be a cheap, random sellor on Aliexpress. Good luck and please let us know what you find. Here is one manufacturer's opinion: https://www.voltaicsystems.com/custom-solar-panels#faq_7 --- Quote ---What are the coating options? All solar cells are protected with some sort of coating material. For commercial solar panels, it is often glass. For smaller panels there are a number of different options. Urethane: Highly UV resistant, but heavier than ETFE. Our standard panels have a urethane coating and last up to 10 years in the sun with minimal power degradation. The urethane coating is poured or "potted" on the solar cells and leads to a highly waterproof panel. Each individual cell is completely encapsulated by the urethane. ETFE: Slightly less UV resistance than urethane, but lighter weight. ETFE and EVA are attached to the cells via a lamination process. With high quality materials (there is a difference in the production quality of ETFE and EVA), these panels have an expected life of 5 years outside. Epoxy or PET: Panels made with these coatings will be inexpensive, but we don't recommend this coating as it tends to have a relatively short lifetime. They are the least UV resistant of any of the options. Glass: Most UV resistant, but also the heaviest and can be challenging to mount in a streamlined manner. --- End quote --- More marketing 'information': https://qookka.com/en/blog/etfe-and-pet-two-key-materials-in-the-field-of-semi-flexible-panels-n3 Here is another report about a 3M topcover material: https://www.osti.gov/servlets/purl/1166732 Although not particularly relevant to your problem, it would be interesting to know peoples experience with garden solar lights which are usually either epoxy encapsulated crystalline cells or amorphous glass panels. The former tend to crack or go cloudy with time and the latter suffer water damage - but I bet some people will have panels that worked fine for 5+ years whilst others have had numerous failures after only a year or so. |
| CatalinaWOW:
I have quite a few of those garden lights when I lived in southern Arizona. The results are very mixed. You would expect cells that came in the same box to be of the same technology and probably even the same manufacturing lot. But I had one group that had one cell yellow and crack badly in well under a year. The rest of those soldiered on until they were retired after their second battery replacement (about four and a half years). All had similar exposure. These had some yellowing and very minor cracking but still provided ample power for the application. Other groups didn't show any real issues with the solar cell. In some cases for up to ten years. Sorry, but no real quantitative information. |
| boB:
I have seen several modules last 50 years or more... What usually happens or happened was that they turn a yellow or brownish color. Of course, their output degrades somewhat too. Old ARCO modules are some that we still see being used but discolored. One of the problems with some of today's modules by newer companies that haven't been making PV for a long time is that they can delaminate. Bypass diodes can also fail. Don't spray them with water, especially on their backs when they are hot. Good PV modules should last a very long time. |
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