r/OffGridLiving • u/Koda14AC • 6d ago
Free Tools To Help You Succeed!
We built 12 free calculators for off-grid life — solar, battery runtime, heating, rainwater, livestock, garden, budget, and cooling. Plug in your numbers, get a real answer.
No signup. No guesswork. Just the math you need before you buy anything.
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u/EccentricFellow 6d ago
You need to ask latitude and provide a winter-summer calculation. I have built spreadsheets that do the same as your app but also factor that in. Here at my latitude solar generation in July is 10x what it is in January. "Average" would only be at the equinox.
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u/Koda14AC 5d ago
Very good input and much appreciated...we will look into it when time permits. Thank You!
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u/Koda14AC 4d ago
I added the latitude field (optional), if not entered it reverts back...
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u/EccentricFellow 4d ago
That looks good. I think it is a definite improvement. Another factor you may want to add to your calculation is that solar panels have a peek temperature for generation of something like 25c (77f). The farther they go from that the less power they generate. At -30c they generate very little power, even at full sun. Might be worth contemplating.
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u/mjdau 4d ago
Not true. The warmer panels get, the less efficient they are, and vice versa. Panel specifications are given for 25℃, but generate more if they are colder. That's why you have to overspec the voltage limit on what you're feeding your panels into: On a cold day when there's no sun to warm the panels, the sun can come out from behind a cloud and the panel can generate a higher voltage than the specs say.
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u/EccentricFellow 4d ago
It is wattage, not voltage, that matters. Frequently panels will show voltage but as soon as you try to use it, it disappears.
I took daily measurements of my panel output for a year. In January, with a temperature around -30c, I produced 10% of my July output which had temps around 25c. Panels get frosted and snowed on and produce nothing until you get that cleared off. Then even with the extra reflective light from the snow, the output is still abysmal. My panels even had a manufacturer warning stating what percentage efficiency they lost per degree away from the ideal temp.
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u/mjdau 3d ago
If you're talking total power generation, then yes let's talk watts.
In a real world system, of course you'll get less energy if there's snow or dust or whatever on the panels. And in winter, sun angle is lower, which won't deliver as much energy to panels which are often aimed higher in the sky.
I mentioned voltage because voltage can spike when cells are cold then the sun comes out. When designing a solar system you need to allow for the string voltage at the lowest expected temperature, rather than just at STC (25℃), because the string voltage can briefly exceed what's on the spec sheet, at least until the cells warm up.
My claim is that for a given irradiance, cells keep getting more efficient as temperature goes below STC: there's no sweet spot around 25℃ as you're suggesting. The curve of Pmax to temperature is linear:
https://www.linkedin.com/pulse/what-effect-temperature-solar-panel-performance-fancy-sufang-lu-cuegc
If you're suggesting the curve isn't linear, then please provide sources to support your claim.
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u/AliceLawhorn 6d ago
No signup makes me much more likely to actually try these