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

[integrityenergy101]

This is too funny.  I just stumbled upon this phenomenon last week and have tested it several times with my irradiance meter over the last week or so.  I'm seeing consistently higher irradiance/panel output with panels at a very shallow to horizontal angle than those set to latitude on cloudy days in VT.  And we have plenty of them this time of year!AmosSent from my Galaxy
-------- Original message --------From: Bradley Bassett via RE-wrenches <re-wrenches at lists.re-wrenches.org> Date: 10/25/23  7:03 PM  (GMT-05:00) To: RE-wrenches <re-wrenches at lists.re-wrenches.org> Cc: Bradley Bassett <bbassett2 at gmail.com> Subject: Re: [RE-wrenches] Off Grid, Cloudy Days, Solar Tilt Question 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 BassettOn 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
Baileykirk 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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