# Is now a good time to invest in solar?

by Artman
Tags: invest, solar, time
 P: 1,600 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.
 PF Patron P: 2,949 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
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P: 2,949
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.

 According to Harry Fleming, the CEO of Acro Energy Technologies in Oakdale, CA, these changes mean that the cost of a typical five-kilowatt rooftop solar system has dropped from $22,000 after state incentives are applied ($40,000 without them) to $16,000 in the last 18 months. Prices are expected to fall to$13,000 by the end of the year ($25,000 without incentives). "This is going to make solar a middle-class product," he says. 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.
P: 1,600
 Quote by 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
Thanks for working that out for me (math is not my strong suit).
P: 1,600
 Quote by OmCheeto (Does this mean over the following ~34 year lifespan of the system, Artman will make $241,026? Hmmm... Even without the SREC's that's$71,026. Wow. Seems the answer to the original question is: not only yes, but ......)
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.
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P: 1,321
 Quote by 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.
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?
P: 1,600
 Quote by 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?
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.
Mentor
P: 21,651
 Quote by 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....
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).
 1.Irradiance (sunlight intensity or power), in Watts per square meter falling on a flat surface. The measurement standard is 1 kW per sq. m. (1,000 Watts/m2) 2.Air Mass refers to “thickness” and clarity of the air through which the sunlight passes to reach the modules (sun angle affects this value). The standard is 1.5. 3.Cell temperature , which will differ from ambient air temperature. STC defines cell testing temperature as 25 degrees C.
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.
P: 1,600
 Quote by russ_watters ....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.
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.
 P: 1,600 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.
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P: 2,949
 Quote by 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.
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.
P: 1,600
 Quote by 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.
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.
 PF Patron P: 2,949 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.
Mentor
P: 21,651
 Quote by 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.
All motors have a "service factor" of 1.15 that means the true rating is actually 15% higher than nameplate - I suspect your inverter has such a saftey-factor built into its design.
P: 1,671
 Quote by russ_watters All motors have a "service factor" of 1.15 that means the true rating is actually 15% higher than nameplate - I suspect your inverter has such a saftey-factor built into its design.
There's no doubt a factor of safety, but often operating a device outside of its specified range wont damage it but it may shorten its lifespan.
 P: 1,600 Latest update, the Electric Company estimated our last bill so even after the solar array saved us 750 kwh we got a bill for $160.00. To be fair, there was still a foot of snow on the ground around here, so I didn't expect them to read the meter. My wife called and told them the reading I took on meter reader day and they are going to amend the bill and send out a new one. The Electric Company has been very reasonable through this whole process. I was anxious to see the difference in the bill after nearly a month of solar power generation. It was an odd month anyway because of snow, clouds, some time left from the old meter, and a few days on the new without solar assistance. Currently the system has generated over 900 kwh, should earn us our first SREC soon. Then we get to see how that works.  P: 3 good thread, suscribing.  P: 1,600 We had our first non-estimated bill this weekend.$47 and change for 281 kwh. $15 of that was distribution and connection fees. We are still ending up paying more than expected (the design was for an average bill of$11.00), but it has been unusually cloudy. The hope is that the summer months will help reduce the actual average bill to meet the design. System has been functioning well with several sunny days just after the last meter reading. We are still waiting for the SREC number to come through. It is tied to the rebate which is tied to the home energy audit, which has to be submitted to the state still (waiting for a computer program code of some sort). The whole energy audit part of the process came as a surprise to me. I hadn't realized at first that a home energy audit was required to get the rebate and the SREC number, but it is. More later as it happens.

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