Sun hours

[J.P.M.]

Any recommendations for when it DOESNT naturally slide off? My installer said the same thing, not to worry about it and that gravity will take care of this as my roof is well pitched. Reality is that half of my array cleaned itself, the other is completely covered in snow and has a huge snow/ice dam at the bottom that will prevent anything from sliding off. Both halves of my total array are identical and face the same direction with same roof pitch. Unclear why one side is fine, the other is a disaster.

Looking for ideas how to fix this mess. It's a colonial house so the roof is high up and I can't get a ladder up there this time of year with all the snow. Hesitant to use a roof rake for fear of damaging the panels.

To be clear, I never wrote, and do not mean to suggest not being aware of possible dangers.

Might be that wind patterns are slightly different and there is some drift buildup on the covered array that doesn't manifest itself under prevailing wind patterns. Might be that the clear portions of the array run warmer than the other portions and melt snow quicker, and run warm enough to refreeze the melt and disallow ice damming. Might be a different response to variable freeze/thaw cycles. When it comes to weather, you can pretty much bet that whatever happens will be the result of several things and may or may not happen the same way every time.

[bcroe]

Any recommendations for when it DOESNT naturally slide off? My installer said the same thing, not to worry about it and that gravity will take care of this as my roof is well pitched. Reality is that half of my array cleaned itself, the other is completely covered in snow and has a huge snow/ice dam at the bottom that will prevent anything from sliding off. Both halves of my total array are identical and face the same direction with same roof pitch. Unclear why one side is fine, the other is a disaster.

Looking for ideas how to fix this mess. It's a colonial house so the roof is high up and I can't get a ladder up there this time of year with all the snow. Hesitant to use a roof rake for fear of damaging the panels.

Do you have pictures? The installer leaves experience to show all that can go wrong. My feeling is that with limited
options, a roof mount system is pretty much SOL in snow. If panels are 2 high, the snow will have to slide twice as
far to clear; unless there is a big gap between upper & lower panels. Even a ground mount can have problems with
snow build up at the bottom. Here a 2' gap between panels and the ground is marginal; 3' would not build up to
obstructing sun so fast. Guess that could be done on a roof; haven't seen it yet.

Assuming the snow has a place to go, there will be motorized vibrators attempting to shake it off on the next round.
Bruce Roe

[Burningislove]

Do you have pictures? The installer leaves experience to show all that can go wrong. My feeling is that with limited
options, a roof mount system is pretty much SOL in snow.

Yes, see attached. Also started a new thread to not (further) distract this one that has more details on the system, roof, house, etc.

https://www.solarpaneltalk.com/forum/solar/the-pros-and-cons-of-solar-energy/304077-ice-dam-forming-but-only-on-half-the-array-help-needed

[Mike90250]

Turn up the heat in the other part of the house (the part with the insulated ceiling) ?

Are the 2 arrays on 2 inverters ? Maybe 1 inverter shut down and is not working ?

[Burningislove]

Turn up the heat in the other part of the house (the part with the insulated ceiling) ?

Are the 2 arrays on 2 inverters ? Maybe 1 inverter shut down and is not working ?

Both sides have very good, modern insulation in the attic floors (ceiling of the livable house). So cranking up the heat wouldnt do much as it wouldnt reach the attic. The house is already quite warm due to the wood stove that heats the whole house, including keeping the hobby room above the garage at a comfy 60 degrees in the winter.

The two arrays are fed into a common inverter (Solar Edge), but are run separately and then joined in the inverter box. It's been producing some power, but of course not that much given it's winter and one half of the array is covered with snow.

I took the advice and used a snow rake to carefully remove the snow dam from the edge of the roof up to about a foot away from the lowest panels. It seemed to work well as there was just an avalanche and the covered array is now about 50% clear and the rest should fall off in today's warm, overcast weather and tomorrow sunny, colder weather.

[DanKegel]

Victory!

[SunEagle]

Victory!

For now. I would hate for Burningislove to have to wait until Spring to get any future snow off the panels.

[Mike90250]

When the panels are clear, are you getting full power from the array ? Got to be some reason half the panels didn't clear.

[DanS26]

When the panels are clear, are you getting full power from the array ? Got to be some reason half the panels didn't clear.

Just looking again at the pic....it appears to me that there is a slight offset between building sections...maybe 6 to 12 inches. This offset may be enough to create a wind eddy that built up a drift on the covered panels. A deeper snow mass could cause the slower melt. Just guessing though.

[bcroe]

The electric bill came Wed. The sun came out seriously for the first time in
Feb and gave me 101 KWH. That kept my 15 KW inverters pegged out for
6.73 sun hours. Today I didn't see the sun for the clouds, but got 65 KWH
anyway.

Cloudy Jan averaged only 38.1 KWH per day or 1200 for the month, but
still a lot better than 1000 a year ago. This might be weather, but reduced
shading probably helps esp when the sun is low. 18 Jan at 80 KWH
showed what is possible when the sun comes out. I think the 2 dozen trees
that disappeared here in 2015 have something to do with getting power out
earlier and later in the day. Half were killed by the severe drought (severe
by IL standards, not CA) a few years back. The others were trying to take
over the south fence line, so now they are gone. There are 7 more trees
back there that will not survive 2016, if I do.

Net metering reserve 1 Feb 16 was 9713 KWH, vs 3200 KWH 1 Feb 2015,
3 times a year ago. Some credit goes to the heat pump in earlier months,
but I think my generation is just up. I made it into positive reserve before
bottoming out a year ago, but this year looks like a big surplus at the true
up this April first.

Jan had some serious cold and I used 127.4 KWH a day, that's 88.7 KWH
out of my summer reserves after 38.1 KWH I generated.

14 Feb it snowed all day; 13 KWH. 15 Feb was solid overcast, with 3" on
the south facing panels it was running at 1/6 capacity. Those near vertical,
snow free east and west facing panels really work. I cleared the snow and
it doubled.

I am not done improving the array. If this surplus is repeatable, I will make
arrangements for some to go to my shop building. Generally I have kept it
around freezing with propane, and blasted it up to 60 F to do car repairs.
Maybe a mini split (capable of operating down to zero F) can take over
maintaining a minimum temp. Bruce Roe

[bcroe]

1 April 2016 anniversary date for my net metering has passed, and after 3 weeks the POCO got
around to mailing me a statement. The 2 questions were:

Can I make it through April without buying any KWH, starting with no reserve, and;

How did the KWH reserve for 2015-2016 play out.

April started cold and cloudy, but then it got warm and sunny. At 100 KWH a day average
generation and the outside temp now 81 deg F, its obvious I'll finish the month in the black.

A year ago, after a pretty cold winter, remaining reserve at anniversary true up was about
700 KWH or 2.5% of generation for the year. Pretty close, but in the black.

This year was warmer, and with the heat pump, more generation went into reserve instead
of being immediately consumed. Generation for very cloudy 2015/16 was less at 26,800 KWH,
down 3.1% from 27,670 KWH in 2014/15. Perhaps some will say that is due mostly to panel
aging, but I don't think so. Any time the panels are unshaded the inverters are clipping as
before; aging could effect cloudy generation, but its reduced to begin with.

Anyway, the graph shows that reduced consumption left a huge anniversary date surplus of
8348 KWH. The POCO gets to keep it for free, but I didn't pay anything extra for it. What
I read, is better energy management is needed. The amount generated and the amount
consumed for heating can't be controlled. But water heating and heat in the shop building
could be shifted over to electric as reserve is available. If some mini splits get set up, the
consumption could be even more efficient. I would need to better keep track of day to day
reserve, waiting a month for a POCO statement won't do.

BUT, its been years since I bought a KWH, and a minimum amount of propane is purchased
annually at the rock bottom July price. Bruce Roe

[DanKegel]

Does sound like shifting some load to electric is in your future. I'm in a similar situation, throwing away power until I get an A/C or something. At least I got a Leaf, that soaks up a bit.

[bcroe]

I'm wondering how much of the energy hitting a panel turns into pure heat for different conditions? For open circuit, short
circuit, and delivering into an MPPT load. Seems to me, for MPPT about 20% of the incident sun leaves, but for the
other conditions, all of the sunlight is converted to heat. Another way to suggest this, is a panel heats the least when
delivering the maximum power? Bruce Roe

[J.P.M.]

I'm wondering how much of the energy hitting a panel turns into pure heat for different conditions? For open circuit, short
circuit, and delivering into an MPPT load. Seems to me, for MPPT about 20% of the incident sun leaves, but for the
other conditions, all of the sunlight is converted to heat. Another way to suggest this, is a panel heats the least when
delivering the maximum power? Bruce Roe

As a 1st approx., all the irradiance hitting a panel that is projected into the plane of the array is either reflected or absorbed with the absorbed portion then either turned into electricity or rejected as excess heat to the environment via conduction through the frame, convective loss to the ambient air or radiation loss to the surroundings. All the energy is accounted for via an energy balance on the cell, panel or array. The amounts/%ages will vary as the panel and environment warrant to maintain an energy balance.

[sensij]

More specifically, yes, in the Isc or Voc operating condition, zero electrical power is produced, so any light that is not reflected is absorbed and becomes heat. However, neither of those are real world operating states for a functional array. Under normal conditions, for the reasons J.P.M. described, panel temperature is positively correlated to power output.