# Gone Solar

Homework Helper
The panels are up. 7kW system will be 110% of our electrical needs. Grid intertie, no batteries, no pile of money up front: $109/month for the next 15 years. Plus dig the new deck I built last summer. --Chi "Happy Homeowner" Meson ## Answers and Replies Looks good. I have always wanted to put solar on our home. You mentioned no batteries. What about night time? Just curious, if you did not finance, what was the total cost? Astronuc Staff Emeritus Science Advisor I hope you monitor the electrical power output during the year to see how effective the system is, particularly during the winter, and particuarly with snow covering the panels, and only cloudy/rainy days. So without batteries, one uses the grid at night? Does the system supply the grid when generation exceeds utilization? Science Advisor Homework Helper Batteries are not only unnecessary, they are "negatively beneficial" if talking 'bout environmental concerns OR financial concerns. The price of small inverters has come way the **** down, so it is much better to tie the solar output directly to the grid through the electric meter. When the panels crank out the kilowatts (mine is optimized for summer sun), the meter runs backward, and I get credit for the electricity I provide to the grid. At night, and in cloudy weather, the grid supplies electricity to me. The thing is, rooftop panels will be at maximum production exactly when electric demand is highest: mid-day summer, when all the AC units in malls and businesses are cranking to achieve stupidly cold indoor climates. New incentives are working their way through state legislature where residents will be credited 3x the rate when they produce more than they use. I chose the best incentive/financing plan available now: it's a "lease" of the system, where I pay about 90% of my usual monthly electric bill over the next 15 years. If I produce more than I use, a credit is set aside and used to pay for any repairs required along the way. Next year, Connecticut will require that new systems get credited 55 cents per kWh when they produce, as opposed to 18 / kWh when they use. This will be an incentive to put the largest # of panels possible for an array. I can't get this deal until the lease runs out. Science Advisor Homework Helper I hope you monitor the electrical power output during the year to see how effective the system is, particularly during the winter, and particuarly with snow covering the panels, and only cloudy/rainy days. There's an App for that! I'll be able to check production from anywhere. If you see the space above the panels over the garage, I'm putting in 4 skylights. One of these will be used as an access portal if I need to scrape some snow off. They are 0% effective unless under direct sunlight, so even a light dusting of snow makes them useless But as I mentioned, my grid is optimized for summer. Due to the pitch of the roof, I'll only get just under 3000 kW from November through February in the best conditions. From March through October, it should be 7000kW-ish, peaking over 9000kW in June/July. turbo Gold Member Sweet setup, Chi! I'd love to do something like that, though are snow-loads are incredible in recent years, and I would fear for the physical viability of the panels. Damn, what a nice, big house! I love the deck and congratulations on the solar! Damn, what a nice, big house! I love the deck and congratulations on the solar! Yeah. That's a sweet house Chi! Where do you live out of curiosity? New England? EDIT: Just read your profile. I am waving from the next state over! Astronuc Staff Emeritus Science Advisor Speaking of the nice deck, is that TREX? I need to replace my front porch because the cheap wood that the contractor used has weathered and the handrails have warped. I replaced the wood on the small backdoor deck with TREX, and it turned our really nice. dlgoff Science Advisor Gold Member Sweet setup, Chi! I'd love to do something like that, though are snow-loads are incredible in recent years, and I would fear for the physical viability of the panels. I can just imagine the damage caused by roof-rakes and snow-blowers. Ivan Seeking Staff Emeritus Science Advisor Gold Member Most excellent, Chi. The fixed monthly cost makes this completely mangeable. It's looking like solar may be viable here in Oregon pretty soon. But it has stiff competition with the low-cost hydro power we have locally. It may be another generation or two [of the technology] before it's worth doing here. ....The thing is, rooftop panels will be at maximum production exactly when electric demand is highest: mid-day summer, .. Please don't shoot the messenger. http://www.reuk.co.uk/Effect-of-Temperature-on-Solar-Panels.htm Assuming the reflectivity of 5% of black panels and at say 30 degrees relative lattitude they absorb 0.95 * sine(45) * 1360 W/m2 = 911 W/m2 at noon. Stefan Boltzman transfers this to a temp of 356K or 83 degrees C, so the effectivity may drop 30% or something, due to the heat. I guess it would be a double whammy if the panels were liquid cooled, the heat of the water being stored under ground. Last edited: Ivan Seeking Staff Emeritus Science Advisor Gold Member Please don't shoot the messenger. http://www.reuk.co.uk/Effect-of-Temperature-on-Solar-Panels.htm Assuming the reflectivity of 5% of black panels and at say 30 degrees relative lattitude they absorb 0.95 * sine(45) * 1360 W/m2 = 911 W/m2 at noon. Stefan Boltzman transfers this to a temp of 356K or 83 degrees C, so the effectivity may drop 20% or something, due to the heat. I guess it would be a double whammy if the panels were liquid cooled, the heat of the water being stored under ground. You are assuming that 100% of the energy goes to heat. No the sad lessons learned by my brother in law. Ivan Seeking Staff Emeritus Science Advisor Gold Member No the sad lessons learned by my brother in law. No, you took the total incident energy and assumed that it all heats the panel. That is incorrect. The panel is producing power. Also, where did you get 1360 Watts. That seems too high even for the total incident power per sq meter. No I did not I merely looked at the graph in the link Experiment Results - How Does Temperature Affect Solar Panel Power Output Note that 83 degrees C is off the scale Also http://www.jsgregg.com/teaching/GEOG345/Assignments/Examples.pdf [Broken], so I was 10 W/m2 too low for the safe side. But we have indeed to substract the energy which is converted to electricity. 6-12% and for 12% the numbers would be 802 W/m2 remaining absorbed energy gives 345 K or 72C Last edited by a moderator: 256bits Gold Member But as I mentioned, my grid is optimized for summer. Due to the pitch of the roof, I'll only get just under 3000 kW from November through February in the best conditions. From March through October, it should be 7000kW-ish, peaking over 9000kW in June/July. Where did you get the kW figures from as they seem a little high for the area of solar panel, guessing about 100 square meters. Would not 9000 sq meter be needed for 9000 kW? It must be a local thing. My electric bill is$40 a month in the winter and $80 in the summer. Science Advisor Homework Helper It must be a local thing. My electric bill is$40 a month in the winter and $80 in the summer. Is your stove gas? Hot water? In my previous home, we had all propane and my electric bill was mostly the monthly connect fee. This house had electric everything, plus we developed a family of five constantly wearing clothes. 90% of the lights are cf, I installed the thermal panels 5 years ago, and still we consume a ridiculous 18 kWh per day. Science Advisor Homework Helper Where did you get the kW figures from as they seem a little high for the area of solar panel, guessing about 100 square meters. Would not 9000 sq meter be needed for 9000 kW? My error there (a little high indeed): Summer peak should be just over 8000W, not 9000 kW, ideally. And of course, I will be expecting ideal conditions. The Panels tested at 250W for 1000W/m2, so nominally I should get 7400 W. Around solstice, the sun will be near normal to the panels at noon, so I'll keep people posted as to what the actual output will be (watch it rain for 6 weeks next year!). Oh, and it's not even connected yet! the electrician took a vacation. Switch happens next week. Evo Mentor My error there (a little high indeed): Summer peak should be just over 8000W, not 9000 kW, ideally. And of course, I will be expecting ideal conditions. The Panels tested at 250W for 1000W/m2, so nominally I should get 7400 W. Around solstice, the sun will be near normal to the panels at noon, so I'll keep people posted as to what the actual output will be (watch it rain for 6 weeks next year!). Oh, and it's not even connected yet! the electrician took a vacation. Switch happens next week. Lovely house Chi. Hope this works out for you. Is your stove gas? Hot water? Yeah, I forgot about that. The total gas and electric bill runs closer to about$110 a month.

Homework Helper
Sweet setup, Chi! I'd love to do something like that, though are snow-loads are incredible in recent years, and I would fear for the physical viability of the panels.

For higher latitudes, a ground-mount system with tracking would be a better option. If not full tracking, then a seasonally adjustable tilt. During winter, a 60 degree tilt will keep the snow off, however you need a large treeless swath of land. Nothing's easy.

Drakkith
Staff Emeritus
I thought about going solar and hooking them up to the grid, however my electric company would charge upwards of 70+ dollars a month JUST to hook it up and the amount they would pay me per KWh would be terribly low.

AlephZero
Homework Helper
No, you took the total incident energy and assumed that it all heats the panel. That is incorrect. The panel is producing power.

Also, where did you get 1360 Watts. That seems too high even for the total incident power per sq meter.

There seem to be several things wrong here. 1360W/m^2 is the solar radiation at the top of the atmosphere, not what reaches ground level. The temperature calculations seem to be assuming only radative heat transfer, not convection to the atmosphere. But considering the conversion efficiency to electricity is low (certainly less than 20% and possibly less than 10%) ignoring that is probably not the biggest error in the thermal calculation.

Homework Helper
There seem to be several things wrong here. 1360W/m^2 is the solar radiation at the top of the atmosphere, not what reaches ground level. The temperature calculations seem to be assuming only radative heat transfer, not convection to the atmosphere. But considering the conversion efficiency to electricity is low (certainly less than 20% and possibly less than 10%) ignoring that is probably not the biggest error in the thermal calculation.
The panels are rated at 14.7% efficiency, but this is certain to diminish by 10% in the first two years; so realistically 13%. It is essentially only the visible portion of the spectrum that can produce electricity, while the majority of the spectrum (IR) is counterproductive for photoelectrons. For this reason, panels are designed to maximize thermal conductance through the aluminum frames and support. Our house is particularly good for this since it faces south and is situated at a high point in the neighborhood aptly named "Windy Hill." We have coastal winds which generally blow to the north during the summer, so it was speculated (though not even worked into the calculations) that our panel temperatures will generally be lower than the assumed temperatures.

The specs for the panels take five different thermal coefficients into account, their specific purposes are unknown to me, but there are three sets of professionals that gone over this system to determine that on my roof, where I live, with these panels, with our typical wind and temperature and rain, with the expected loss to heating the system should be producing over 7000 kWh per year. We use only 6500 kWh per year.

IF anyone wants to get geeky over the specs, find the link to the pdf here.
http://www.schueco.com/web/us/resid...odules/Schueco_MPE_modules_in_the_PS08_series

I've got the PS 08 245W

256bits
Gold Member
The panels are rated at 14.7% efficiency, but this is certain to diminish by 10% in the first two years; so realistically 13%.

Didn't know solar was up to that high an efficiency.
Continued research pays off.

Looks good.

OmCheeto
Gold Member
There seem to be several things wrong here.
...

I concur. This struck me as a test thread from day yesterday. Almost everything has been wrong.

Though it might just be a tryptophan induced dream state.

hmmm.... never mind...

I'm going back to sleep now..... :zzz:

Homework Helper
Didn't know solar was up to that high an efficiency.
Continued research pays off.

Looks good.

The highest efficiency so far is now over 20%. The breakthrough was something like silver nanoglobules added to the surface. Not exactly on the cheap shelf yet.

rhody
Gold Member
Nice set up Chi, as others have mentioned, what do you do to remove a thick layer of warm heavy wet snow ? Four hair dryers taped to the front end of a leaf blower ? Another issue, how sturdy are those panels to snow and ice ? The roof look moderately steep, I bet it would be dicey to try to navigate between them to free the ice and snow. I like your idea though, very cool, especially the part about getting credit or cash from the power companies.

Rhody...

Homework Helper
Nice set up Chi, as others have mentioned, what do you do to remove a thick layer of warm heavy wet snow ? Four hair dryers taped to the front end of a leaf blower ? Another issue, how sturdy are those panels to snow and ice ? The roof look moderately steep, I bet it would be dicey to try to navigate between them to free the ice and snow. I like your idea though, very cool, especially the part about getting credit or cash from the power companies.

Rhody...

Like my wood burning stove, you have to accept this sort of thing as a hobby. Some people spend more on their HO trains. I was going to put a venting skylight to provide an easy access to the roof, but the only ones that I could fit through are over $1000. Next option is a roof hatch that I can put on the north side of the roof, near the peak ($500).

Then, in order to not die, I was going to set up a walkway using roof jacks that would let me walk across the roof with my big broom to shove off the snow. Then I thought about it...

I would probably lose 7 to 10 days of sunlight due to snow-cover-on-sunny-days. That means, with intensity down around 300 W/m2 due to latitude and roof tilt, I'll be missing out on about 120 kWh, or nearly \$24 of electricity per year.

So I'm going to put in 4 skylights anyway (3 of which I already salvaged from a remodel; like new Velux FSF 106's!), and I might buy a 4th that opens, but I'm not crawling through it; from it I could hose-off the panels above the garage and get half the system working.

Ouabache
Homework Helper
Then, in order to not die, I was going to set up a walkway using roof jacks that would let me walk across the roof with my big broom to shove off the snow. Then I thought about it...

So I'm going to put in 4 skylights anyway (3 of which I already salvaged from a remodel; like new Velux FSF 106's!), and I might buy a 4th that opens, but I'm not crawling through it; from it I could hose-off the panels above the garage and get half the system working.

How about some running some roof de-icing cables across your panels and melt the snow off? We've used those to eliminate ice dams on our roof.

Homework Helper
How about some running some roof de-icing cables across your panels and melt the snow off? We've used those to eliminate ice dams on our roof.

It would take quite a few of those cables, and I would have to look into how much electricity they require, and whether it is a break-even endeavor.

rhody
Gold Member
This is one of those FYI eye opening moments, what is going on here ?
This means the shakeout among manufacturers will likely continue for some time. "The industry simply cannot support 300-plus cell and modular manufacturers, so the companies left will capitulate and exit the industry," said Zhengrong Shi, chief executive of Chinese solar-panel manufacturer Suntech Power Holdings Co., during a late-November call with investors. Suntech is cutting its operating expenses by at least 20% next year as it hopes to stem this year's 70% stock-price slide.

The glut of manufacturers stems from various sources over the last several years, including efforts by the U.S. government to encourage clean technology, venture capitalists pouring into the sector and institutional investors buying into IPO issues of solar companies amid an oil-price boom and a heightened sense of climate-change urgency. At the same time, European governments offered rich subsidies for solar installation, driving demand in the market.

"People were doing what they can to make a profit, without thinking ahead," said Pallavi Madakasira, an analyst with research firm Lux Research Inc.

Rhody...