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

[Bradley Bassett]

Jay,

I don't really remember, it was years ago that I had that setup, and did
not have any way to keep records except on paper which I did not do.

Brad

On Wed, Oct 25, 2023 at 6:07 PM Jay via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Hi Brad
>
> Out of curiosity, what is the actual difference between the two on those
> cloudy days.
>
> Thx
> Jay
>
>
>
> On Oct 25, 2023, at 5:04 PM, Bradley Bassett via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
> 
> 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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