This just in!!! We now have a year’s worth of data from our inverter and our utility bills and I’ve done some comparisons.  First the good news:  Our west-facing 3.15 kW system generated 3226 kWh of electricity from March 1, 2008 – February 28, 2009.  Now, for the shockingly good news.  This is only 90 kWh (about $10) less than what PV Watts (http://www.nrel.gov/rredc/pvwatts/version1.html) projected we would generate.  But all in all, I am pleasantly surprised that our generation matches up so closely to the PV Watts estimates. 

This should be VERY good news for anyone considering a PV system.  It’s an expensive proposition, so accurate estimates are important when determining your potential return on that investment.  So, I think my results show that – at least in the case of the sun’s energy – past performance is a good indicator of future returns!      

The next bit of good news I have to relate concerns our electric bills.  In the 12 month period before we installed the PV system we used 10,701 kWh.  In our first full 12 months of using the system we drew only 7,491 kWh from BGE.  The difference (3210 kWh) corresponds very closely with the amount we generated (3226) over the last year.  This means that net metering is working out for us - when our meter spins backward we are getting properly credited for the excess electricity we generate. 

I would love to hear from other households on this issue.  Got data?