Your response was a bit disingenuous though, you must admit. You can't say your panels generate uninterrupted, because we know that's not true. Solar has its own suite of issues, such as the duck curve at high levels of penetration.
Apologies, I did not mean to mislead, that's why I included the solar in my post.
I don't think I said the solar panels supplied the electricity to my home, but it is easy to read it that way.
I guess what I meant was, my system has produced electricity to me uninterrupted for a very low cost.
The system includes the PG&E grid use.
My break even point is probably 7 years. 7 years (or more) was the original calculation but that was using 3 years past usage at then current prices. I use far more now, due to COVID (multiple computers and a tv on much of the day), air conditioning (I rarely used it in the past), charging an EV, etc.
PG&E prices go up every year. In the past decade, PG&E rates have gone up 31% — faster than inflation.
PG&E rates increased this past March and they proposed a 10% across the board increase to cover wildfires and other issues.
The panels are guaranteed for 20 years as I recall. I know I live in a solar bubble area. Around here, a solar project is a no brainer.
The solar project in an investment with an expected return. Otherwise, very few would people would buy solar.
What calculation do you want for the solar project cost? Over 7 years? 20 years? Usable life?
The panels were about $12K after Federal Tax Credit. I did not qualify for CA benefit. I also got 30% off the new roof that was installed at the same time, an additional savings of $3,700 over the $12,400 full price.
Over 20 years that's $50 per month. Less if you include the roof money.
Usable life cost? You can estimate that far better than I.
By the way, in finance, you do not amortize tangible assets, you depreciate them.
Straight line depreciation would be $50 per month. But what might be more accurate would be the 20 year cost, which is easily -$40,000, netted with savings.
Very conservatively, if I save $120 per month for 10 years, that's $14,400.
Conservatively, if I save $150 per month for 10 years, that's $18,000.
Compared to the $12,000 sunk cost, the panels are free. No, less than free.
There are many ways to look at the solar project cost. I appraoched the solar project as an investment in risk management.
Perhaps you have a solar panel project cost calculation that is appropriate. All good.