Is now a good time to invest in solar?

ramonegumpert

will solar panel reflection cause glare problems for pilots? just curious. thanks.

dr dodge

I have often wondered that. I live basicly right under final approach for Bush. They fly over all day and night, pretty high up. With my luck, they'd create a new law limiting panels right after I dropped the $$$


dr

russ_watters

I haven't looked too closely at a solar panel, but I'd think they'd be coated to reduce glare. After all - if they are reflecting light, it isn't being absorbed and converted to electricity!

Artman

The surface is low iron "solar" glass material over the bluish-black PV cells. Not much glare.

mheslep, mine are Schott Poly 220 panels.

Schott Solar Poly 220

Artman

Just saw my monitor show me 8.811 kw output after the inverter. That's over 100% of the panel nominal capacity of 8.8 kw. Not too shabby.

I wonder if studies have been done on the effects of snow reflectance on solar panel output? The ground is covered with snow, the panels are in cool ambient air and under very clear sunny skies. I really think the snow must help.

mheslep

Clear day solar insolation on a perpendicular ground surface is ~1000W/m^2 x cos(zenith angle).

For NJ at Noon in Feb,
cos(zenith) = sin(φ)*sin(δ)+cos(φ)cos(δ) = 0.61,
where δ=solar declination (Feb) ~ -10 deg, φ=latitude = ~40.3 deg.
Note for June 21 with δ=+23.5, cos(zenith) = 0.96 at Noon.

So received peak power in Feb for a panel facing South at latitude should be ~610W/m^2.

Given 40 panels at 1.67 M^2, total received power by the surface of the array is 41.1
kW. If measured power today was 8811 Watts, then the conversion efficiency of the panels, assuming 94% efficiency for the inverter, is
eff = 8811W / (1.67M^2 * 40 panels * 610W / M^2 * 0.94) = 20.3 %. That's extremely high for a polycrystalline panel.

In June output power after the inverter should hit 12.2kW

mheslep

From Monday's MIT TR:


U.S. Solar Market to Double in the Next Year

Government incentives and lower solar prices are starting to pay off.
Scaling their 5kW typical system to Artman's 8.8kW system gives
with (without state incentives)
$39k ($70k without) - more than 18 months ago [in the ballpark with post #41]
$29k ($51k without) - last 18 months,
$23k ($44k without) - end of 2010.

a 40% price drop, giving $2.6 per Watt-peak for a theoretical 2011 residential system.

Artman

Thanks for working that out for me (math is not my strong suit).

Artman

I was told as part of the sales pitch (so take it for what that's worth) that solar electric generation systems purchased with the current level of incentives will payback $3 for every $1 spent over about 25 years given escalation rates of electricity and expected rise and eventual fall of SREC values. Of course this is just speculation, much of it hinges on the weather. So far it has been the snowiest winter on record where I am. This means lots of cloudy days. Fortunately we have had a few sun on snow days to go with them and the output goes way up then.

OmCheeto

I'm very interested in your system voltage vs. temperature. I learned yesterday that most solar panel manufacturer's under-rate their panels, knowing that they have a certain degradation over time. (I'm still trying to figure out how to gracefully retract my "100%" claim from the other day)

I have to admit that I've learned more about solar panels in the last two weeks than I have in the last 4 year. It's easy to ignore the scientific facts when these little buggers appear to be the ultimate "Energizer Bunnys".

But mheslep and I both posted graphs that indicate that ratings on the panels start at 25'C and voltage output degrades as temperatures go up. So my questions are: Do the graphs continue linearly in the opposite direction? Does a panel operating at 0'C give a 6 to 7 % increase in power output? Was it the solar reflection from the snow, or the temperature that are giving you increased power output? Or was it both?

Artman

I understand both low temperatures and reflectance can add to performance. I was told that my ground mount system will perform better than a roof mounted system (everything else being equal) because it will be better arranged for air movement to transfer heat away from the panels, since the backs are wide open on a metal rack angled 40 deg up to 12' in the air at the high end from 3' above the ground in the front. Where roof mounted panels lying flat on racks against the angle of the roof tend to gain heat from attic spaces and trap heat between the panels and the roof, driving down performance.

russ_watters

That's not quite right. Manufacturers rate their panels according to a set 3rd party standard. Like any other device, mechanical or electrical, performance will vary based on test conditions, so *someone* has to decide on a standard set of conditions unless the industry is to be a free-for-all. The rating point is then based on a set of conditions near the top of what is likely to be seen, but there is no such thing as perfect conditions, so there is no real set maximum.

Here's an article about the Standard Test Conditions for rating panels (on which, Artman's panel's 220W nominal rating is based). http://www.altestore.com/howto/Elect...s-PV-Modu/a87/

Because of #2, #1 seems to me that it should be the irradiance at the top of the atmosphere. The real value varies from 1.321-1.412 kW/sq m, so I would think if you mounted one of these on the top of Mt Everest, it would put out a good 285W. I'm not really sure of what #2 means in terms of real-world conditions, though.

#3 is significantly cooler than what you'll actually get in summer, so that one works against you.

....speaking of which, does anyone make a combo solar water heater and power panel? I'd think that you could collect nearly as much heat as with a regular solar water heater while also significantly improving the electrical output of the panel.

Artman

Not sure about water, but a company called Solarwall makes a combination PV panel and air preheater duct. Air is ducted behind the panels to cool them while simultaneously preheating fresh air for roof mounted Air handling units.

Solarwall PV and roof mounted solar air heating.

Artman

At 11:45 yesterday, sunny, clear, with snow on the ground temps in the upper 30's deg F, the system monitor showed 9.34 kw output after the inverter. Around 106% of the panels' kw rating. The inverter is only rated for 10 kw. Anyone know what happens should the panels go over that? It's beginning to look like a possibility.

mheslep

The panels will go well over that - to 12kW come a clear day in June/July. I doubt you'll have any problems with the panels themselves, but the inverter concerns me if it is indeed rated 10kW. It must have a breaker or fuse, e.g. UL safety, but it's likely have a shorter life if its run at full or over capacity all the time. Doesn't make sense that an experienced installation company would have given you an inverter underrated for the job.

Artman

I looked up my inverter and checked the ratings. The maximum output is 9995 watts. The maximum input current is 46.7 amps nominal input amps is 27.6 amps. I think my system is wired for 480 volts DC. 12,000 watts/480v = 25. Should be fine. I'm breathing better again.

mheslep

Hold on, I didn't account for the temperature coefficient before. The SCHOTT data sheet gives a -0.47% / deg C coeff, 20deg C as the rating point. Assuming your Noon temperatures lately have been 5 deg C outside, the panels would run 15*0.47%=7% better than rated. In the Summer, assuming 30 deg C on the roof, the panels would run 10*0.47=4.7% worse, an 11% decline due to temperature from now. So the peak June solstice power for the Artman array declines to ~10.7kW at 30 degC, better when the odd clear cold front comes through.