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Old 11-18-2021, 07:00 PM   #1
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Solar panel efficiency

I'm going to put about 400W of panels on our trailer and I've been trying to decide which panels to use. I can buy Renogy 100w panels for about $100 ea.on Amazon. Solarland high efficiency panels are about $225 ea at Northern Arizona Wind and Solar. I can't find efficiency ratings for the Solarland panels, the Renogy is 21%. Could the Solarland be worth double the price? I've bought panels from Northern before (Kyocera) and they are a reputable company but that's a big price difference.
Thanks.
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Old 11-18-2021, 09:38 PM   #2
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21% is pretty good and I bet the Solarland panels aren’t much better, so go with the Renogys.

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Old 11-18-2021, 09:41 PM   #3
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Not in my opinion.
The easiest way to compare efficiency would be to divide the power output by the panel area. The answer is in watts per square inch. For example I looked up a renogy 100W panel that is 42.4 x 20 so you get 100/(20x42.4) = .118 W/in^2.
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Old 11-18-2021, 10:17 PM   #4
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I think efficiency refers to the actual real life watts the panels produce vs what they are supposed to put out. I watched one Youtube where several panels were tested and some actually produced more than they were rated for (109 watts from a 100 watt panel (Rich poly)) and some were only around 50% of their rating.
I'm not sure where you can get those efficiency rates from, they don't seem to provide that data from the manufacturer.
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Old 11-18-2021, 10:37 PM   #5
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It is watt per area. So if you want the latest in solar it will have a smaller foot print.
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Old 11-19-2021, 12:30 AM   #6
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It is watt per area. So if you want the latest in solar it will have a smaller foot print.
X2! Efficiency isn't much of a basis for selecting a panel. Simply stated, a higher efficiency panel will be smaller. End of story. Almost. More efficient panels tend to be newer technology and might have other benefits such as less annual degradation from age. Or better production at lower sun angles. However, these are not very significant advantages if they exist at all.

If you have a problem getting the Watts you need from limited roof area, higher efficiency panels will be a bit smaller and may fit where less efficient panels may not.

In my case I had about 170 inches to work with down each side of my fifth wheel. I wanted six 200W panels in that space. Some 60 inch long panels were available but would allow only two panels on each side. I found some new panels from Rich Solar that are about 56" long and allowed three panels in that available space.
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Old 11-19-2021, 01:10 AM   #7
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If budget is a concern, consider buying used panels. You can likely find 5-10yr old panels for VERY inexpensive online (craigslist or facebook marketplace local to where you are). I found 250w residential panels for $35 each and put 2 on top of two of my RVs (500w system on each RV). They work great! Solar panels have no moving parts and should last a VERY long time. Theoretically, then can lose SOME performance over the years, but will you notice? In my case, I was only planning on putting up 250w in the first place. When I found these panels for so cheap, I just put up two (500w) as overkill and I'll never worry about my batteries (...note: I am not a serious boondocker but can go almost endless provided I have sunshine, and if there is no sunshine I've always got a generator if needed, or the engine alternator). You can also ask yourself....how long are you planning on keeping that RV? 20 years? Or will it likely be gone in 5-10 years and maybe you've upgraded (or stopped RVing).


Just a thought. Buying new is always fun too...just more expensive.


Happy Camping!
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Old 11-19-2021, 12:36 PM   #8
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Thanks for all the replies. I can understand that efficiency would relate to the watts per square inch, makes sense. What I find confusing is in real world testing not all 100W panels actually produce 100 watts, and some exceed their rating. In a perfect world all panels would produce the same wattage in identical conditions but that doesn't seem to be true. I, of course, would like to buy the panels that actually produce the most wattage, all things being equal (price, etc).
The Rich Solar panels (both poly and mono) seem to regularly produce some of the highest wattages of those that are tested on Youtube and have good reviews so I'll probably purchase those.
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Old 11-19-2021, 02:55 PM   #9
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X2 on Rich Solar. I have two 170W panels on the roof and now rarely take the portable panel with us anymore... even in the PNW.
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Old 11-19-2021, 03:01 PM   #10
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...... I can understand that efficiency would relate to the watts per square inch, makes sense. What I find confusing is in real world testing not all 100W panels actually produce 100 watts, and some exceed their rating. .......
The performance of solar depends more on location than design of the panels.

The term 'efficiency' refers to the amount of energy produced divided by the amount imputed. It is a function of the equipment.

Capacity factor is the amount of power produced divided by the amount of power that could be produced if rated power was produces 24/7/365.

This a function of the location of the equipment.

For example, one utility scale solar project in Arizona had a CF = 19% (20% was ideal). The same manufacturer got CF =12% in New Jersey. Data was for the first year of operation.

I know of a utility solar PV in Washington State that has a negative CF. Takes more electricity to deliver the power than the panels produce.

I spent 20% of this year dry camping in north western Washington State. Let me estimate the CF if I had solar. About 2.5%

The OP stated that he does not boondock very much. I would suggest that solar would be wasted.

Part of the PNW is mild and rainy. Perfect for camping in an MH. Inlet it hot and dry with with cool nights. Every sunrise and sunset is beautiful. Perfect for camping in the shade.

I am currently in the Mojave desert because it has it has beautiful granddaughters. If I spent winters dry camping in the desert SW, amybe they would be useful.
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Old 11-19-2021, 06:37 PM   #11
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Plenty of good information above. One additional thing, your ability to match sun angle makes a difference in output. The angle of incidence of the sun on the panel affects the power produced. If you can adjust angle with the seasons it makes a difference. About 30%, because the earths axis is tilted 23 degrees to orbital plane so the sun will appear to change elevation by 46 degrees between summer and winter. The amount of energy impinged on the panel is related to the cosine of the angle (cosine 46 = .69). You could further improve your solar performance if you could track the sun through out the day. I have looked at some youtube videos of people doing that. My SA panel is portable with an adjustable angle so I always get a near optimal angle for the season. My house has fixed panels and if you ook at the power output over the day it makes a perfect cosine wave if it is sunny all day. A panel mounted flat is going to get terrible performance in the PNW in the winter. Portland has a latitude of 45 degrees in the dead of winter the angle would close to 80 degrees at noon (cosine 80 is .17). Fixed SA panels are typically angled for winter exposure to compensate for the shorter days.
There are different solar cell technologies, the underlying fabrication, that make a difference in the efficiency (and price). I think if the underlying technology is the same, the differences in efficiency is pretty small. Some different technologies are silicon, high efficiency silicon, gallium Arsenide, and amorphous silicon. There are probably more that I am missing. blah blah blah.
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Old 11-20-2021, 10:17 AM   #12
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We live near the Canadian border in WA, 48.58 degrees north latitude so at this time of year the sun is low on the southern horizon. Most of our winter travels will be well south of here (AZ), so the solar should be a big benefit. We've had solar on our boat for many years and with only 270 watts total we never worry about our state of charge and we're never hooked up to shore power.
If we go with 400+ watts of panels I think our weak link will be our battery bank (2- 240 AH 6V). Not sure I want to put 4 6V batteries on the trailer tongue though.
Thanks for all the help
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Old 11-20-2021, 12:12 PM   #13
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We live near the Canadian border in WA, 48.58 degrees north latitude so at this time of year the sun is low on the southern horizon. Most of our winter travels will be well south of here (AZ), so the solar should be a big benefit. We've had solar on our boat for many years and with only 270 watts total we never worry about our state of charge and we're never hooked up to shore power.
If we go with 400+ watts of panels I think our weak link will be our battery bank (2- 240 AH 6V). Not sure I want to put 4 6V batteries on the trailer tongue though.
Thanks for all the help
I would agree , 4 flooded or AGM would be heavy and really not as much power compared to lithium iron. I have been looking at the battleborn GC3 , when they make a heated verision that maybe my jump in point. The size lets me get 2 side by side and not have to move my brake pump off the floor for my disk brakes.
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Old 11-20-2021, 04:25 PM   #14
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P... Portland has a latitude of 45 degrees in the dead of winter the angle would close to 80 degrees at noon (cosine 80 is .17)...
I knew I messed up that math... 45 degrees latitude plus 23 degrees inclination is 68 degrees total. Solar is still going to perform poorly (.37)
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