The good folks at SIREN gave a stirring presentation last month about how now is the time to switch to solar electricity. Panel prices have fallen significantly due to the recession, electricity prices look poised to raise (at least here in Indiana where Duke Energy is spending several billion dollars to construct a coal gasification plant in Edwardsport and pass costs on to customers), and there’s a brisk market for renewable energy credits. We had already caught the fever a bit and the talk just convinced us it was time to get an actual site assessment and cost estimate.
We’re working with Alex Jarvis of Solar Systems of Indiana, a quirky guy who knows a heck of a lot about solar. He came out to discuss some different options and to do a site reading of a few potential spots using his handy dandy Solar Pathfinder. It’s a very simple little device that maps shade to determine if a particular spot has a good solar window. The image above is from the middle of our roof, which has a very good solar window of about 85% between the key sunshine hours of 9:00AM and 3:00PM – solar time. (See rant on Daylight Savings Time below.)
He also measured a few other spots in our yard so we could think about doing a pole-mounted solar panel. You could argue that the pole-mounted systems are a little on the ugly side but they are very practical in terms of maintenance – no climbing on the roof, no trying to patch the roof under the solar panels – and they are great for houses that have a shaded roof but sunny yard. We are leaning in that direction simply because our roof is 20 years old and will need to be replaced well before the solar panels. Alex actually has his panel (shown at right) configured so he can move it around during the day to maximize its exposure to direct sunlight and therefore maximize electrical generation. He is the first to admit that is way too hardcore for most people but he is a tinkerer and enjoys fiddling. Most people just retilt their panels twice a year at each solstice. At the spring solstice, the panel is tilted closer to horizontal since the sun is higher in the sky during the summer. At the fall solstice, the panel is tilted more vertical since the sun is low in the sky during the winter.
After that is the decision of what kind of solar panels and inverters to get, which I must confess is mostly Greek to me but Will is drooling a bit at the thought of enphase microinverters that broadcast all kinds of exciting data for him to analyze with a fine-toothed comb. We’re looking at getting six modules that are each rated somewhere around 240 watts, giving us a system that is around 1.44 kilowatts. Here in southern Indiana, we average about 4.7 hours of direct sunlight per day once you factor in cloudy days and the fact that our days are significantly longer in the summer but shorter in the winter. In a perfect world, our solar panels would produce 6.8 kw-hr per day (1.44 kw x 4.7 hours) or 2,470 kw-hr per year. However, there are some losses that we have to take into account with our lovely fudge factor friend, the derate factor. The derate factor has several components:
- Shade on our system. Our solar window is about 85% open, 15% shade.
- Losses from the inverter, connections, and wiring
- Losses from dirty solar panels (we’re going to assume we can keep ours clean – with a hose if needed)
- Losses from improper angling (again, we’re in good shape with a pole-mounted system that can be tilted at least twice a year)
In the end, we figure our derate factor is about 0.8 (meaning we lose about 20% of the ideal production level), which reduces our expected output to about 5.4 kw-hr per day or 1,970 kw-hr/year. That should still just about cover our needs and in our area it’s not worth overproducing since the electric company will just keep rolling over our credits until we move. If you’d like to try this game at home, check out the PV Watts calculator developed by the National Renewable Energy Lab. Soon we should have some prices to go along with our power estimates but for now we’re excited about the possibilities and also trying to brainstorm how we might landscape our yard to make the solar panels blend in a bit. Any and all suggestions are welcome!
Daylight Savings Time Rant: Indiana only recently adopted Daylight Savings Time while staying in the Eastern Time Zone, and I am not a fan. Today the sunrise was at 6:30AM and sunset at 9:15PM, which means our solar noon is really about 1:50PM and our key sunshine hours are 10:50 to 4:50. It also means that the fireflies don’t come out until 10:00 and it’s awfully hard to schedule fireworks, bonfires, or drive-in movies that children (or I) can stay awake for. I liked it better when we were in straight-up Eastern Standard Time and never had to worry about changing our clocks.