[RE-wrenches] Off Grid, Cloudy Days, Solar Tilt Question

[Bradley Bassett]

I used to have both an array at a 60° tilt and one at 14° tilt. In the
winter the high tilt array did better on sunny days, and on cloudy days the
shallow array did better. They were different modules and different sized
arrays, so without more analysis than I did, it would be hard to tell which
is better through the winter, but it looked like they were similar in
overall output. However, once March rolled around the steeper array started
to do much better (more sun), and by summer the shallow array did much
better. I'm at 47° N and I think if I had a choice of any tilt, but without
adjustability, I'd probably set it at latitude or therabouts. If you're
west of the mountains you're probably going to need another source of power
anyway. I say that, but judging from the modelling I did of the output of
my micro-inverter system it might just be possible to get through the
winter with an array 500% overisized. And that with only 2 or 3 days of
battery autonomy. This was surprising to me. Do keep in mind that an array
with snow on it has 0 output.

Brad Bassett

On Wed, Oct 25, 2023 at 3:47 PM Kirk Bailey via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Hi All!
>
>
> We don't do a lot of pure off-grid systems and I recently ran across
> something I wanted to run by folks with more experience in this area:
> Optimal array tilt for our very cloudy PNW winters!
>
> My understanding has always been that latitude plus 10-15 degrees was the
> best tilt to address our winter energy shortage. However a paper I recently
> read (1), makes a compelling case for a much shallower tilt in situations
> where the cloud cover is so heavy that "diffuse" solar radiation is all
> that makes it through. They indicate that under those conditions a
> horizontal array will produce significantly more energy than even a
> two-axis tracker!
>
> Given that the challenge in our off-grid setups always seems to be making
> it through the really cloudy stretches, and that there is usually enough
> energy the rest of the time, should we be installing off-grid arrays at a
> shallower angle?
>
> Anyone tried this?
>
>
> Kirk Bailey
>
> kirk at abundantsolar.com
>
> www.abundantsolar.com
>
>
> (1) Kelly, N.A., Gibson, T.L, 2011, Increasing the solar photovoltaic
> energy capture on sunny and cloudy days. Solar Energy 85, 111-125.
>
>
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