For the financial analysis we assumed the money would be committed to paying for power one way or the other, there isn't really an option for putting it aside in the mutual fund so the 'invest' option was off the table. With the use of a current measuring system[1] we also have time of day usage numbers which is an option that helps people who aren't home during the day. In our case there is always someone in the house so the tiered rate metering was the only rate schedule we needed to consider[2].
With this information we can calculate the total money would would have spent just paying for power from PG&E and making no change, to the money we spent on the system install ($20,000) and the subsequent money we paid to PG&E for power and for their meter reading service. A bit more than 11 years after the install the total money spent over the period was less for the solar option. Our current annual electricity spend is about $420 (that is $120 for their meter reading + about $300 in additional KWh of energy above what we generate) vs roughly $3000/year or average $250 a month. Effectively $2600 a year is not being spent. If I were a min-maxer then I'd be putting that money into a mutual fund and it would start compounding and well, then the difference would start to look ridiculous.
[1] "The Energy Detective" -- http://www.theenergydetective.com/
[2] While it is true we could have changed further things about our lifestyle to fit into other rate schedules that avenue wasn't pursued.
Plugging the figures into: https://smartasset.com/personal-loans/personal-loan-calculat... and adjusting the interest rate slider you get a monthly payment of $217 when the interest rate is 11.75%. That's a pretty good rate of return for your investment. Not ridiculous, but solid.
The point I was trying to make is that a dollar spent 11 years ago isn't the same as a dollar spent today.
As for costs, maintenance included replacing a failed inverter, that was $3500, and a panel, that was $450. The way in which electricity has also changed, when we started it was just kilowatts in vs kilowatts out annual true-up, they dumped that and switched to time of day, but changed their mind when the economics didn't work out for them, and now they are on the tiered system. They also blew up the town of San Bruno and convinced the PUC that they should be allowed to raise rates to cover their costs, so the price of electricity has gone up. Net result is that we didn't save as much per month when we started, incurred maintenance costs above the original $20K, and PG&E has changed the rules several times on how the accounting works. Fortunately all of that complexity can be factored out just by computing the bills vs what we paid.
For my house in Nov of 2014 the tiers were Tier 1: 15 cents/kwh Tier 2: 18 cents/kwh Tier 3: 26 cents/kwh Tier 4: 32 cents/kwh
And the baseline allowance is 10KWh a day (our house typically uses 24 - 28KWh per day.
Put those numbers in to your power bill and tell me what the number comes out to.
