Exploring My Solar System

After I tweeted the installation of solar panels on my roof in late September, a couple of people asked me to blog the details. The panels sat up there inert for a month, waiting for the electric utility, PEPCO, to install a "net meter" at my house, one that can run backwards when we produce more power than we consume. (Ironically, old-fashioned analog meters run backwards just fine, but my digital one was programmed dumber.) A kind man from PEPCO installed the net meter on Wednesday, perhaps because I threatened the previous Friday to complain to the Public Service Commission, PEPCO's regulator. So yesterday the panels had their first full day of use. Live production graphs are here.In exploring my options, I came to appreciate that panel installations are roofing jobs. They touch the roof, which is a thing of delicacy and importance. One way to install the panels is to to drill lots of holes in the roof and bolt the panel support structures to the rafters. But then you've got dozens of holes in your roof. Sure, they'll coat the holes with black gunk, but will it last? Another option for "flat" roofs like mine (it's just slightly tilted, like most in my neighborhood), is to stretch wood or steel beams across to rest on the exterior walls. The beams then support framing for panels. Steel is more expensive and harder to hoist than treated wood, but lasts longer. At any rate, as you can see, the facade on my house sticks up on two sides, making this hard. So I ended up with a structure that just sits on the roof, held there by friction and the ballast of thin cinder blocks laid out under the panels. That's why the panels lie parallel with the 4 degree pitch of my roof (which is fortunately southerly) rather than sticking up at the optimal angle for my latitude, about 39 degrees. If they protruded, the remnants of a hurricane might sweep them away. There are no batteries. The system hooks to the grid, so any moment-to-moment surplus goes into my neighbors' houses and any deficit is filled by the utility.Astrum Solar put 30 Sanyo HIT 215 watt panels up there, for a total peak capacity of 6.45 kilowatts. They remind me of the black monoliths in 2001. If I get the equivalent of 1,000 hours of peak performance out of them (there are 4,380 daytime hours in a year), we will generate 6,450 kilowatt-hours (6.45 megawatt-hours) per annum, almost exactly what we consumed in the last 12 months. Upgrading our early-1980s air conditioner could give us a significant surplus.One nifty feature: microinverters. As a general matter, inverters convert the constant ("direct") current from the panels into the wavelike ("alternating") form naturally produced by spinning generators. (DC adapters for computers convert the other way.) Microinverters are inverters for poor people, financed with tiny loans. Ha ha. Traditional inverters are big boxes that require high input voltages, which can only be provided by a string of panels in series. If one panel in a string falls under a shadow, they all shut down. Microinverters are new. One is installed under each panel. If an individual panel is shaded, the others remain unaffected. This flexibility allows more panels to be placed suboptimally. Also, amazingly, each microinverter encodes a weak digital signal in the waveform it produces, through which it transmits information about its status. In my house now is a small box that connects to my Internet modem and to a power outlet, from which it extracts both energy and those 30 digital signals. Every few minutes, it uploads the production data to the manufacturer's web site where you and I can view it. This allows panel-level monitoring for failing components (automated with e-mail alerts) plus cool graphs.The installation cost $53,212.50. But the 2009 U.S. stimulus bill included a ten-year 30% tax credit provision for solar power. And the Washington, DC, city council enacted a comparable subsidy, funded by a tiny tax on electric bills. It pays $3/watt for the first 3,000 watts and $2/watt for the next 7,000. These lower my cost to $21,348.75.That is the I (investment). What is the R (return) on I? Most of my $1,000 annual electric bill will disappear. In addition, the city council has mandated that the utility generate a rising share of its power from renewable sources. Most interestingly for policy analysts, PEPCO will buy from me the right to count my panels towards its quota. In other words, the Renewable Portfolio Standard created a market---in a way that seems more politically palatable than carbon taxes and cap-and-trade. With my installer acting as the broker for my Solar Renewable Energy Credits, I will sell them at 65% of the penalty rate PEPCO pays for falling short of the standard, which is 65% of $500/megawatt-hour. That should work out to about $2,000/year, perhaps $1,400 after state and federal income taxes. (Thanks to financial engineering, I could have gotten 5 or 10 years of payments up front at a discount, to cover the installation cost.)So: I = $21,000 and R = ~$2,400, for an ROI of 2400/21000=11.4%. Not bad. I could have gotten a higher ROI with cheaper, somewhat lower-capacity panels.Clearly, I am receiving a lot of subsidies, which raises questions about whether my experience can scale. Can everyone do it? One rationale for the subsidies is that they reward early adopters for taking risks with new technologies (how much experience is there really with ballasted installations?), for inspiring others, and for pushing the solar panel makers and installers along their learning curves. Historically, as the industry has grown and built experience, costs have fallen. So there is hope that subsidies will become less necessary. On the other hand, the U.S. government maintains permanent, massive subsidies for home ownership, farming, and oil drilling. Given the political difficulty of taxing pollution, subsidies, however implicit, are likely to figure large in the response to climate change.Here in the Capitol Hill neighborhood, I am part of solar mini-boom. Everybody's doing it (sort of). It's exciting to be generating power from something as benign as sunlight, to watch how the silent, descending photons propel our computers and lights. It is exciting to visualize a world in which panels adorn houses as a matter of course. What is most striking is how my sense of normality has changed. Last year, solar power was a vague, long-term hope. Now it is here. Like when I got my first mobile phone in the late 1990s, I feel like I am riding the early wave of a technology adoption curve. I would be flip to say "you can do it too." But I hope you can.