Snow Tolerant PV Mounting

[Mike90250]

Wanted to add some pics from my place this last week (currently northern california is getting hammered by storms, rain, snow, 160 mph winds in the sierra mountains)
and yesterday in the brief patches of sun that came out, my 3kw array was putting out over 3600 watts !! yummy, the batteries love that



20190205_081100.png


After some sun - the melt started and began to slide off. Days have been like this, sun, snow, sun, rain, dark, snow, ice....

20190210_111052.png

That's 10 F in the IR thermometer on the gravel at my back porch. A little snow, some clear night skies and it gets cold
and you can expect your PV panels in winter, to get cold like this too, way below ambient air temps (about 25F)

20190205_074959.png

[bcroe]

yesterday in the brief patches of sun that came out, my 3kw array was putting out
over 3600 watts !! yummy, the batteries love that

How the heck can you do that, mirrors?

Roller coaster weather here since the last of Jan. Snow, ice, sun, clouds, but never very warm. The the
high winter angle panels have consistently needed far less attention (sometimes none) to be cleared.
The last cycle I tried leaving snow on a low summer angle string to see what would happen (or maybe
just got tired of pushing snow). Temps running between 0 F and freezing. A couple days later we still
had not had enough sun to get the snow off, so I finished it. Bruce Roe

[Mike90250]

How the heck can you do that, mirrors?

nope, just ice cold weather, clouds clear, and ice cold panels kick out the volts.

here's a screen shot, depending on the particular day and conditions, the output can vary wildly
(apparently my controller is nearly 6 years old, Tristar MPPT 60 ) 3kw PV array

3622watts.jpg

[sdold]

That's crazy weather, Mike. We went through there to Fort Bragg on the 5th, and were advised to carry chains! They said it "snowed" at 500 feet in Gualala.

[Mike90250]

And they had snow in Ft Bragg a few days ago too! Redding was shut down for 10" a couple days ago Holler at me next time you head through, we get a cuppa or something

[sdold]

Will do, sometime after snow season ends up there. At least you're not getting our flooding.

[Mike90250]

Well here is a sad story in 1 photo. I can't fix this, but who expected 5' of snow ( not my array )

snow crushed panels PV solar.jpg

[SunEagle]

Well here is a sad story in 1 photo. I can't fix this, but who expected 5' of snow ( not my array )

snow crushed panels PV solar.jpg

Holly crap. Where was that picture taken?

[ButchDeal]

Well here is a sad story in 1 photo. I can't fix this, but who expected 5' of snow ( not my array )

snow crushed panels PV solar.jpg

Well looks like a DIY mounting system and not a pre-engineered system.

[bcroe]

Well looks like a DIY mounting system and not a pre-engineered system.

Yes, the panels are not broken, the frame collapsed. I think the reverse would
happen here, if at all. Bruce Roe

[J.P.M.]

Yes, the panels are not broken, the frame collapsed. I think the reverse would
happen here, if at all. Bruce Roe

I wonder if anyone knows or has investigated the cause of failure. One factor (snowload, avalanche, wind, other), or combination of loadings such as snow and cyclic loading from winds ?

[inetdog]

'''
How the heck can you do that, mirrors?
...
...

Exactly, for some folks. If the panel angle to horizontal is high enough, at some times of day the additional light falling on the panels from diffuse reflection off snow cover can increase the insolation of the panels. Add that to the temperature and clear air effects and you are cooking.

[Mike90250]

The collapsing array was in Nevada County, California, about 4'000 feet and 5' of accumulated snow. These were wet storms, that is heavy snow, not powder. Theres been a lot of damage at low elevations from this last weeks of February 2019 storms

[J.P.M.]

Exactly, for some folks. If the panel angle to horizontal is high enough, at some times of day the additional light falling on the panels from diffuse reflection off snow cover can increase the insolation of the panels. Add that to the temperature and clear air effects and you are cooking.

For those interested, some things I learned, some of it anecdotal in nature:

Either albedo (reflection from the surroundings) or intentional reflection from mirrors or specular reflectors attached to the sides/bottom of a flat pate solar device can increase irradiance on that device by substantial or at least measurable amounts. In the case of fresh snow, I've measured total POA irradiance on an experimental air cooled solar thermal collector I built back in Buffalo in the mid '70's as high as > ~ 1100 W/m^2 By my notes from one measurement from back then (from 02/18/1976 coincidentally) the unenhanced Direct Normal Irradiance (DNI) was 820 W/m^2. The calc/est. of the diffuse was 120 W/m^2 for an est. total of direct plus diffuse POA irradiance of 940 W/m^. So, the est. enhancement to the POA due to albedo which was mostly due to fresh snow was ~ (1,100-940)/940 ~ = 17 %. I've never been able to get close to the 30+ % enhancements some claim for snow, but My data is somewhat sparse in that respect.

As for booster mirrors for the collector, I could attach side or bottom booster mirrors to that same collector which measured ~ 2 X 4 feet, and the mirrors could be adjusted for angle with respect to the plane of the collector. The whole assembly was small enough so that it could be oriented at any azimuth and tilt (I had it on a hand truck). Anyway, One day in the summer (08/08/1977) I was running a stagnation test with inlet and outlet blocked to estimate overall collector loss coeff. That was the year I returned to school in the fall.

The collector was made of wood except for the nuts, bolts, glazing (1 or 2 lites) and the absorber, both of which I could change out to investigate the effect of different absorber types and materials and the effect of 1 vs. 2 glazings on thermal performance, and the blower.

Anyway, as an example of my ignorance at the time, I had both side booster mirrors and the double glazing in place and as I recall (but did not record) the air outlet was ~ 370 F. when I started seeing smoke from the collector outlet. In my engineering ignorance and lack of common sense, I didn't know that with all my experimentation, I'd managed to dry out the collector internals and in so doing had lowered the kindling temp. of the wood, and I (or rather the sun) started a fire. No damage, except to my ego and the collector which was mostly a loss. But I learned a valuable lesson about engineering, safety, and what ignorance can do.

Anyway, the reason I recount the whole episode is as an example of how irradiance can be enhanced by side mirrors. In such cases, such schemes won't work well for PV arrays for many reasons, the biggest one being it's hard to get the usually necessary uniform irradiation on a solar PV panel with a side or bottom or top mirror throughout the day without making the mirror very large ( ~~ 2X the size of the panel or so) and so making it unwieldy for lots of reasons (wind being the biggest) not to mention unsightly and quite costly. Even smaller mirrors present problems with strength for wind. Also, unless the reflector is really flat, it'll have local irregularities that can produce hot spots that can damage a PV cell or panel. So, aluminum foil on plywood is out.lThere are some compromises such as something called Compound Parabolic Concentrators ("CPC's) or modified CPC's that use 2 or more mirrors/side that approximate some of the CPC characteristics. Details can be found on the net.

As usual. take what you want, scrap the rest.

[bcroe]

I'd managed to dry out the collector internals and in so doing had lowered
the kindling temp. of the wood, and I (or rather the sun) started a fire.

Veeeery Inteeeeresting! Smoke seems to be a universal part of learning processes. Bruce Roe