[steven2012]

http://www.gosolarcalifornia.org/tools/clean_power_estimator...

Using this calculator, pick a zip code in the Peninsula, I put in a 4000 watt system, estimate my bill to be $200/month, assume 2.5% increase in electricity prices per year, and assume I pay in cash. This gives me a 15 year payback period. At $100/month, it's a 24 year payback period.

[ChuckMcM]

Not that anyone would do it this way, but that calculator got me thinking. Often I have heard home affordability expressed as dollars per month vs dollars financed. So for example this worked example of a $200,000 mortgage [1] has a $1553.45 monthly payment, so for each $1 per month you got $124.24 of house. Does that make sense?

If so, now consider that your $200/month electricity bill is the equivalent of $124.24 x $200 or $24,847 worth of "house".

Our actual bills were $250 - $300/month pre-panels and effectively about $15/month post panels. In terms of money returned by 7 years we had paid less in electricity than we had paid for the panels. But that discounts what $20,000 would have been worth if we had invested it (that is the 'do nothing' alternative since you aren't really considering putting that money under a mattress :-) And of course we also made our house more efficient which we would have gotten that pay back either way.

The only downside to our system has been trying to explain to people why it doesn't provide power when the power is off.

[1] http://hfa3741.hubpages.com/hub/How-Much-Does-a-200-000-Hous...

[fancyketchup]

I don't have a PV system, but I know people who do, so take this with a grain of salt: The default assumptions in that calculator are probably a little wrong.

First I think most people are paying closer to $5 per Watt, and I know someone who just refinanced his house in Long Beach at 3.5%, fixed. For comparison, the calculator assumes $10 per watt, and 8%. If you use halve the installed cost, there is obviously a big effect on the payback period (down to 6.5 years with tax incentives).