Investigating Home Solar Power

We recently got an electric car which is used an 85 mile round trip daily commute. We’re estimating that this adds 400 kwh (about $80) to our monthly electric bill. This is much better than the estimated $275 per month (425 miles per week / 26 miles per gallon times $4.25 per gallon times four weeks) in gas that it would have cost with our old car. So, right off the bat, we’re saving $195 / month in direct commuting costs. Additionally, the car is only $100 / month more expensive, so we’re coming out ahead $95 / month.

We’d always been sort of interested in solar power for our home, but thought that it wasn’t feasible. Luckily, there are a few things which may change that.

  1. SRECs – credits for installation of renewable energy sources. You can read about them in MA, here.
  2. PPAs – a Power Purchase Agreement where a company installs solar panels on your home and you pay for the electricity at an agreed upon rate.
  3. Federal tax credit of 30% on the cost of a solar system.
  4. The company that we are leasing our car from has announced a deal with a solar provider, RealGoods.

A solar installation for a typical home would typically cost at least $25000. This page seems to be a pretty good and accurate solar system calculator.

I’ve been talking to SunRun, SolarCity, and RealGoods about solar installation.

Some facts about our situation:

  • Including charging the car, we’ll use about 11,000 kwh a year.
  • Our home is pretty well sited for solar, with a south-facing fairly unobstructed roof.
  • The roof could fit an approximately 4,000 kw solar panel system.
  • Unlike the other two companies, RealGoods’ PPA $0.1299/kwh is flat for the 20 year duration. That rate likely depends on system size and other factors, so you may not get the same rate.

With the PPA offered by RealGoods, we’d save roughly $75 in the first year and $434 in the last year. I’m conservatively estimating that my electric utility rates will increase 2.5% per year. If they increase 5% per year, the savings in the last year would be $992 for the year. The savings increase each year due to rising electric rates. Total savings at a 2.5% nstar rate increase would be $4,808 after 20 years and at a 5.0% nstar rate increase would be $8,832.

I’ll write another post about the purchase option.