Solar Panels: What We Got
I had been eyeing our offending trees for some time and was looking for an excuse to take them down. The solar panel was definitely going to be the excuse, but our neighbor's trees were another matter. It was pointed out that the neighbor's trees were the bigger offenders, and they would cut the afternoon sun rather significantly. Not thinking it that big of a deal, I told him that wouldn't affect my decision, but then John informed me that the rebate is contingent upon a system that doesn't have too much shade.
To get the rebate at the time that I got it (the rules have since changed slightly), the solar panel system needs to produce 75% or more of the theoretical amount for a system oriented south at the best angle and with no shading. John's guess that a system on our roof would be close to failing the test, but he'd have to take the measurements and get back to me, and sure enough, the initial design failed.
After speaking with the neighbors, they agreed to let me take one of the shading trees down, but not the worst one (it is a nice tree, I have to admit) provided I paid for the removal. Putting the federal tax credit towards that, getting the array still made sense. So, we cut the tree down along with some in my yard. John came back out and said he could get an array to pass, but it would have to be smaller in size than originally intended to get the system to pass the efficiency requirement. Done! The picture below shows the front roof in the late afternoon in early November, the shadow of the neighbor's tree is clearly present.
The original plan of covering the front and some of the back roof to max out the rebate was thereby reduced to about a third of the original desired size. Of course I could still put more up, but it would mean foregoing the rebate, and without the rebate, the economics aren't as clear cut. In the meantime, I keep eyeing that neighbor's tree. If we had thought about it before we did the renovation, I'm guessing we would have tried to put a roof up in the back that wouldn't have had the shading issues and built our expansion around a good solar roof, but that is definitely hindsight.
We ended up with a 2.58 kilowatt peak array consisting of 12 of the 215 watt Sunpower panels (www.sunpowercorp.com), and a 2 kilowatt inverter (www.pvpowered.com) that converts the DC power from the panels into AC power that is on the electric grid.
The installation was done by Sunlight Solar by early May, 2006, and it went off pretty much without a hitch. All I did was write 3 checks, namely an initial deposit, a midpoint payment, and a final one upon state inspection. They took care of the rebate, and it all went exceedingly well. Since then, the panel has worked as advertised, producing the power at the rate that they estimated it would.
In the summer, the 2.5KW array should cover 30% of the power needs (based upon the usage we had prior to our renovation), but it only gives 10-15% of our historical power usage in the winter. The smallness of these numbers speaks to the difficulty of replacing all fossil fuel plants with solar panels--it just isn't so easy. A need exists to become more efficient with the generated power to make it work autonomously, or a serious reduction in living standards would be required. One area of work in the future is to deal with this issue. A combination of more panels and better use may do it, but we'll have to see.
I'll post more on the performance of the solar panels and how much it is relative to our electricity use. Part of the problem is that we are still having work done on the house, so we haven't reached our normal usage patterns yet. This doesn't affect the amount generated, but it speaks to the expected coverage of our needs from solar alone.
An interesting question to ask is how much did our array help in reducing our dependence on oil, and specifically foreign oil. The answer is a surprisingly small. That is the subject of the next post.