It's about 25 cents/KWHr-- this month.
The economic case also depends on how cheaply you can get the parts, how much labor you can do on your own, and state/federal tax subsidies. It might be less burdensome than you think, especially if you factor in 3-4% annual inflation over two decades.
In the current issue of Time, it is said that electricity cost in Hawaii is (or going to be) 29c/KWh, because all power comes from expensive oil rather than coal as on mainland.
I just took a look at our bill. Normally, my wife takes care of all bills and expenses, so I did not know. We signed up for the demand rate. The only lifestyle change we make is to not run washer/drier/pool pump during peak hours, and to put a timer on the water heater.
Last month, ignoring the fix charges, we used 727 KWh during on-peak, and 2927 KWh during off-peak. The cost is 19.5c on-peak, and 5.8c off-peak.
727 * 0.195 = $142
2927 * 0.058 = $170
Average = $312/3654 = 8.5c / KWh
If we use the straight rate option, then it would have cost 10.5c / KWh. So, the demand rate saves me money.
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A couple of years ago, I looked at just component costs (panels+inverter) and no labor costs, as I was going to do it all myself. At the straight rate of 10c/KWh, and just a rough estimate of how much power production to expect, I figure a return of just 5 to 6% a year on the principal. So, without rebate or subsidy, I am about breaking even with investing money elsewhere (bonds perhaps).
With maintenance cost, I would be in the red with solar panels.
That was before I signed up for the demand rate. That would have nearly doubled the return. But then, solar panels have gone up in price since I looked, I am sure.
Here is another complication. During the summer, solar panels complement the A/C usage very well during the day, when the peak period is set. But the peak period during the winter is different.
In short, I am sure yours works, i.e. saves you money. But, a residential solar system in AZ is something a tinkerer would love to have, but may not be able to make an economic case of.