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russ_watters
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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!
The surface is low iron "solar" glass material over the bluish-black PV cells. Not much glare.russ_watters said: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!
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.
mheslep said:Clear day solar insolation on a perpendicular ground surface is http://edmall.gsfc.nasa.gov/inv99Project.Site/Pages/science-briefs/ed-stickler/ed-irradiance.html" .
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
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 said:(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 ...)
Artman said: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 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.OmCheeto said: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?
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.OmCheeto said: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...
http://www.altestore.com/howto/Electrical-Characteristics-of-Solar-Panels-PV-Modu/a87/1.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.
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.russ_watters said:...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.
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 said: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.
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 said: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.
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.Artman said: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.
russ_watters said: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.
Artman said:The meter-reader came yesterday and found the reading over 300 kwh below the previous month (good sunny month). He said "System failure." I asked him what that meant, he said it kicks out any results too far below the expected average reading. It should be interesting to see the bill. I'll post the outcome.
By this time of year the utility/panels should be paying you substantially for your excess kWh produced, I would think? No summer air conditioning running yet, and we are <60 days away from summer solstice. I would think May might be your biggest pay off month, unless you don't use air conditioning in the summer.Artman said:On a month with a negative meter reading we got a bill for +- $2 (not sure of the exact amount, it's home, I'm not, my wife told me the total). There are a couple of charges that are based on days tied to the grid rather than kwh used. Those amounted to the +- $2 charge. I can stand that.
Because of the SREC program, I can only sell back a small portion of the excess at this time (about 5% I think). We had about 300 kWh under the last meter reading. We can carry it to the next month, but we won't get back any money for it.mheslep said:By this time of year the utility/panels should be paying you substantially for your excess kWh produced, I would think? No summer air conditioning running yet, and we are <60 days away from summer solstice. I would think May might be your biggest pay off month, unless you don't use air conditioning in the summer.
So you are supplying free power to the grid?Artman said:Because of the SREC program, I can only sell back a small portion of the excess at this time (about 5% I think). We had about 300 kWh under the last meter reading. We can carry it to the next month, but we won't get back any money for it.
mheslep said:So you are supplying free power to the grid?
Thanks dr. It's doing really good. The main problem right now is that the state still hasn't issued us our SREC code and instructions yet. It is in the works. However, I still think grid tied was the way to go. Our overproduction last month was around 300 kWh.dr dodge said:thanks, we all appreciate that...lol
this (IMHO) is why a separate off grid system is all I would invest in. Somehow the power company still wins
Glad your system is working good, and your thread is a great source of info for all
dr
Are the SREC's value seasonal dependent? i.e. Can you sell them back on peak times. I would guess not.Artman said:From what I understand, all of the SREC's produced prior to the registration number being issued are still credited to my account and can be sold.
mheslep said:Artman - what kind of daily kWh are numbers are you producing now that we are into June?
dlgoff said:Are the SREC's value seasonal dependent? i.e. Can you sell them back on peak times. I would guess not.
Y 04:13 PM
I'll run the numbers again and let you know. I think with a decent SREC rate, it should be around 5-7 years, worst case about 10 years.OmCheeto said:So, please. Given the SRE's, the cut in your electric bill, and the original cost, what is your current payback time for your investment?
And give us the answer. Was this the right time to invest in solar?
My honest answer is "no." I wish I had done it sooner (when rebates were higher).OmCheeto said:Was this the right time to invest in solar?
Artman said:I'll run the numbers again and let you know. I think with a decent SREC rate, it should be around 5-7 years, worst case about 10 years.
My original question wasn't really so much about the payback as it was the technology. I wanted to know if anyone here knew of any breakthrough technology that would make the old panels obsolete and very much more expensive. If the world was on the cusp of a breakthrough that would drive solar array prices way down or solar efficiency so good that fewer panels could do the same job. If the cost comes too far down, the market will become flooded and SREC prices will drop. Then payback would become an issue. Payback from electricity savings +rebate and tax credit, but with no SRECs is about 20 years.
My honest answer is "no." I wish I had done it sooner (when rebates were higher).
I attended an energy symposium where I had to answer questions about residential solar. there were several others there who had solar arrays as well and, from what they have said, all of them are very pleased with their investments. I'll post more about this later, some issues to be aware of came up out of that day.