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I do not believe your claim. Your numbers cannot be correct especially for a 15 year old system.

Here is a system quote given to me two years ago. The system was a 4.3 KW system. However, the typical peak output was less than 4.0 KW. The cost was $30,000. The system could save me about $1,000 per year in electricity costs. However, this savings is based on the utility being forced to offset my excess solar panel generation. The utility would not buy my excess power. Most of the power generated was during periods that I did not use much power. Without the utility offset, the electricity cost savings would be less than $500 per year. Thus, the unsubsidize payback is more than 50 years.

To entice me to buy the system, the utility was forced to invest $15,000 (it earns a healthy rate of return on this investment). I would also receive a federal tax credit about $6,600. I was told that the inverter would last 10 to 20 years. The solar panels decline about 1 percent per year.

There was a interesting economic analysis of the California initiative for 1 million rooftop panels. The estimated cost was $20 billion. This investment would provide little baseload and peak power. Thus, this investment would still need comparable backup capacity. During the winter, the system output would decline sharply.

Contrary to your assertion about peak power, residential solar does not match peak power needs very well. During the peak power demand hours (4 to 6PM), rooftop solar output declines sharply.