Grid-tied solar

dave1949 · Jul 26, 2012

I have been thinking about using some solar electric for a couple of years. The time seemed right this summer.

The system is rated at 4.3 KW annually using the NREL PVWATTS calculator. The panels are made by Canadian Solar and the inverter is a Solectria Renewables PVI 4000 model.

The installation was completed yesterday afternoon and the electric utility is supposed to swap-out our not-so-smart meter for one that does net metering on Monday. I am looking forward to getting some generating history built up. So far, it says it has generated 7 KW, 2 KW yesterday afternoon and 5 KW today which was heavy overcast all day long.

The system was purchased from and installed by Revision Energy based in Portland and Liberty, Maine. A really great A-1 crew from start to finish.

The close-up pic of the panel mounting shows the clamp-on brackets used on standing seam metal roofs.

TheGoose · Jul 27, 2012

Looks great.

Costs? Estimated payback time?

dave1949 · Jul 27, 2012

The upfront cost is $19,774. That includes all parts and labor. Also includes purchase and complete install of a 58 gal. Rheem/Marathon electric water heater, and removing our old indirect boiler-heated tank. So, there was wiring and plumbing to mess with for that part of it.

The system qualifies for Maine's energy efficiency rebate maximum of $2000 and a 30% federal tax credit (which can be carried-over if you cannot use all of it in one tax year) that is worth $5,932. My net cost for everything is $11,842. I can probably sell the old water heater tank for $500-$600. It's a 60 gal SuperStor in great shape, 5 years old.

I estimate the payback period at around 17-18 years but won't really know until I have some actual history. Our electric rates here are $0.15 per KW and the old water heater accounted for at least 260 gal. of propane per year by my best guesstimate. We used right around 315 gal of propane a year for our range cooktop (elec. oven) and domestic hot water for two people.

Propane is pretty cheap now with the gas glut, but I expect it will climb depending on how many LNG gas compression plants get built.

The 72 degree mounting angle on the panels does hurt the output, but to buy or have fabricated special mounts to help the angle is more expensive than adding a few panels to the system. They were concerned too that if the panels stood off the roof too far, they could catch too much wind behind them for the roof to withstand.

I checked with the roofer that did our roofs, he thought with the weight distributed across there (the 18 panels are 45 lb each) it shouldn't be a problem. The roof is 24 GA. They put a clamp on every standing seam rather than every third as would be normal for a flatter install. The installers were standing on the rails like on ladder rungs and nothing seemed to be giving at all.

We looked at ground A-frame rack and pole mounts but decided in the end to go with the roof. Couldn't find a location I really liked on the ground, ironically the best spot would have had our power lines throwing a shadow on them which would have led to burying our service line for about 400 feet. We have to think about snow build-up here too. I don't think snow will stick on the panels at that angle very long once the sun hits them. It doesn't stick to that roof surface now.

Redneck in training · Jul 27, 2012

I am thinking about solar too. Can you say how much was the hardware and how much was the labor?

dave1949 · Jul 27, 2012

Hi Ladia, Sorry, no I never asked for a break down on that. I can tell you two guys worked 5 hours each the first day and four guys worked 6.5 hours each the second day. They put up staging due to the steepness of the roof, made it much easier to get the panels in place and fastened down. Anyways, something like 36 man-hours total. They have to charging at least $60/man-hour I would think. Plus they had 1.5 hours each way in travel time to get here and back.

The panels are mono-crystaline 240 watts from Canadian Solar. The Inverter is the PVI 4000 model from Solectria Renewables. The standing seam clamps are made from aluminum and the panel rails are extruded aluminum. The overall length of the panel array is about 59 feet. Two extruded rails run parallel that entire distance. I guess you could price those things or similar out on-line and get a good idea.

It's a really clean setup, tie the panels together in two strings, 9 panels per string. Connect those to the inverter. Connect the inverter to any service panel using a 240v double slot breaker. They put everything from the junction box on the roof (mounted behind the first panel) to the inverter in heavy metal conduit and the same from the inverter to the service panel. I was impressed with their attention to detail.

TheGoose · Jul 28, 2012

Sounds good. Good luck, I like reading threads like these. Keep us posted on your system ups/downs.

dave1949 · Jul 28, 2012

TheGoose said:
Sounds good. Good luck, I like reading threads like these. Keep us posted on your system ups/downs.

Thanks. So far, the inverter says the system has generated 30.6 KW in 40 operating hours. I plan on recording the accumulated output on the same day each month for a year or so until I see what's what. My electric bill will have some info too regarding credits and debits to the net usage.

In a net-metering system, you never want to generate more power than you use since most state utility regs don't require the utility to pay you for any excess. Basically, the excess credits generated in summer's long days get used up during winter's short days. My utility banks any credits for up to 1 year, then they delete the oldest credits in a FIFO method. The credits will be worth different amounts as/if rates change.

For those thinking about solar hot water or electric, geothermal heat pumps or small wind turbines, the 30% federal tax credits for consumer energy are scheduled out to the end of 2016: Federal Tax Credits for Energy Efficiency : ENERGY STAR. It applies to existing and new construction principal residences only, not to second homes or rentals.

dave1949 · Aug 7, 2012

Generation update.

After 13 days of operation, the inverter says the system has generated 182.5 kwh in 179 operating (daylight) hours. It got a real boost today with the crystal clear skies all day, it made 19.9 kwh. The highest output I have seen so far just over 2900 watts (dc) for one sample period. I may see higher sample time outputs with the lower winter sun angle which favor my steep mounting angle, but of course the total output for a day will be lower.

The net meters installed 9 days ago show 76 kwh in from the power company and 92 kwh out to the power co.

This link shows the calculated/modeled system output for my location: http://rredc.nrel.gov/solar/calculators/PVWATTS/version2/pvwattsv2.cgi

For the month of August, modeling says it should generate 383 kwh, or an average of 12.35 kwh per day. It has averaged about 14 kwh over the past 13 days. I have been curious as to how accurate the the model is and so far, it looks reasonable.

grsthegreat · Aug 7, 2012

im all for alternate energy, but i just dont understand how these systems pay for themselves. So far your figures for 13 days average aprox 14KW/day.

i pay $0.5/kwh for electricity, so this system would save me 14 x .05 = about $0.70/day x 365 = about $255/yr

19,000 / 255 = 75 years needed to pay fopr itself. are there some govt %%% incentives that are coming to offset this 19 grand?

MapleLeafFarmer · Aug 7, 2012

grsthegreat said:
im all for alternate energy, but i just dont understand how these systems pay for themselves. So far your figures for 13 days average aprox 14KW/day.

i pay $0.5/kwh for electricity, so this system would save me 14 x .05 = about $0.70/day x 365 = about $255/yr

19,000 / 255 = 75 years needed to pay fopr itself. are there some govt %%% incentives that are coming to offset this 19 grand?

my thoughts as well.
we pay 7 cents /kwh so $0.07 * 14 = $0.98 / day.