Today my colleagues Phil Forest and Jonny Lange, the ace PV crew at South Mountain, put the finishing touches on a 4.76 kW solar electric system here at House 5. With the help of Sean Welch, my go-to electrician for all the work here, they had it fired up shortly after lunch and by the end of the day the system had produced its first 11 kWh.
My first solar electric system was 1.06 kW, installed in 1999 when NH first mandated net metering. We've come a long way in system and component quality and reliability and efficiency, and costs have dropped dramatically over that time. And of course, the cost of electricity has risen significantly. My new system is almost 5 times as large as the one I had back in NH.
The system consists of twenty Sunpower 238 Watt panels and a Sunpower 5000 Watt inverter that is manufactured by SMA. The premium aspects of Sunpower products (they offer the highest efficiency panels, for example, and an excellent warranty) are a good fit for South Mountain. We have been seeing annual kWH outputs per watt of panel that exceed the modeling we do. Of course, this could be variations in weather as easily as product quality!
The system is grid-intertied, which means that it only runs when the grid is up (unfortunately it's not an emergency power system). When energy is being produced it is first used here in House 5 to satisfy our energy needs. Any excess is exported to the utility grid and turns the electrical meter backwards. A concept called net metering, which was legislated into being in the late 1990s, allows this direct back-feeding of the grid and allows the exported power to be traded one for one for imported power. In the bad old days, the utility would charge retail for power in and pay wholesale for power delivered to the grid.
It's quite likely that our excess energy won't ever hit the grid, because there are fifteen other houses here plus the Common House, so my guess is that the excess will be used here in Coho. My electric utility, NSTAR, generously swapped my meter for a commercial demand meter. This is a bit of special treatment (thanks!) that will allow me to know more than the net energy in or out each month. This meter shows separately the net, plus the energy supplied by the grid and the energy received by the grid from the PVs. Say that in a month we use 350 kWh and the PVs generate 400 kWh. A normal meter will read 50 kWh lower at the end of the month that it did at the beginning. Because the inverter has a record of the energy generated, a PV system owner can still determine how much energy they used during that month. My new meter takes this a step further and will tell me how much of the energy generated was used on site and how much was exported.
It feels like it's been a long road to get this system in place. In a Coho monthly meeting a few months ago where we discussed solar access and the cutting of trees, one of my neighbors read an impassioned statement that included assertions that solar was not economically feasible and no one besides me wanted solar anyway. I was pretty shocked, not because of the statement (in the interests of diversity we have a token Tea Party supporter and this was his shot across the bow of the ship of liberal fools), but because no one spoke up to counter a passel of distortions. House 5 had significant shading from trees on my neighbor's land to the south, and even though we'd just bought the house, I was ready to put it back up for sale if those trees were staying. When the cohousing was being planned, there were design guidelines put in place, one of which was to provide at least 300 sf of unobstructed south facing roof on each house for future solar collection. Unfortunately, they decided trees could always be cut later, so they actually did an oustanding job of preserving trees quite close to the houses. People here in Coho don't seem to crave natural light inside their homes nearly as much as Jill and I do, so the houses are generally in a very wooded setting, and very shaded. PVs are wired together in strings of several panels, so when one is shaded the output of all the panels in that string is degraded (see the comment about microinverters for a technical approach that can minimize this issue.)
I was quite fortunate that my southerly neighbor came around and was very gracious about allowing some tree cutting. In the end, I didn't ask for 100% solar access, and only took the largest and closest tree. She picked lovely dogwood to replace the big white oak we cut, and I did get some firewood for my pains :-)
The system we installed, completely unshaded, would make perhaps 5,700 kWh/year in a typical year (the eight houses SMC designed and built at Eliakim's Way have 5.04 kW arrays and averaged over 6,700 kWh this past year.) I'm expecting at least 5,000 kWh - we'll see!
This is an excellent time to install solar electricity in MA. The MA Clean Energy Center is still offering a rebate on PVs, which is declining every year as the costs drop. There is the 30% Federal tax credit and a $1,000 MA state tax credit. (Info on all this stuff, and more is at DSIRE) These all buy the system cost down from a cost of perhaps $7/Watt to slightly over $4/Watt. In MA, there's a sales tax exemption if this is a primary home, too. On MV, if a system makes 1.25 kWH/Watt of rated output annually, that is worth about $0.23. So the simple payback is eighteen years. But electricity has inflated far above the general rate of inflation, and the actual payback will be significantly quicker. The average person can't get a guaranteed return on their investment anywhere near as good as solar electricity, and offset energy usage is income that isn't taxed.
The current financial frosting on the cake, however, are what are called Solar Renewable Energy Credits, or SRECs. The state requires utilities to get a percentage of their power mix from renewables, and some of that specifically from solar, and they can buy SRECs to satisfy that requirement from solar power producers such as moi. In practice, most SRECs are bought from individual producers by aggregators who sell larger blocks at auction. The goal is 400 MW of solar generating capacity in MA. One megawatt-hour (MWh) is one SREC. The auction prices have been as high as $550/MWh, and the floor price is $285/MWh. If our system makes 5 MWH/year, we could be receiving an additional $1,500 - $2,500 per year! Even if that program falls flat on its face, though, it's a great feeling watching that meter spin and rack up the solar energy.