So California has a capacity factor of about 17.5% as far as I can find, and a residential cost per kwh of 17c roughly. Considering that, a 10.5KW system saves you $2.65k per year, that is if you use that much energy, if not you sell some at a slightly lower feed in tariff than the 17c retail rate.

That's pretty sweet. It kind of boggles my mind why this stuff isn't more popular...

For example, imagine instead of using the $25k to cover your entire electricity budget (let's assume it's $2.5k a year) for decades to come, you earmarked it to be invested in a different project, with the returns going towards paying the utility bill.

Had you invested the same $25k and got a typical long-term average stock return of 7%, you'd net $1.75k every year, assuming your utility bill was say $2500 and it was 100% covered by your $25k, 10.5KW system, you'd be short $750 on the first year compared to having put that money into a solar installation.

Which would mean it'd have to be made up, so you reduce the $25k stock investment by $750, added to the $1.75k stock return, to pay for your annual bill, and go into year two. Same story for year two, only now instead of making 7% on $25k, you make it on $24.25k, and so your return drops from $1.75k to $1.7k. As the years go on, your $25k cash becomes smaller and smaller, and by year 17 it has evaporated entirely, and you start the bear the full cost of paying $2.5k a year to your utility, without any equity or investment or $25k cash left.

Instead, the solar installation of $25k probably still has $10k of equity locked up in the value of your home, and is still generating about 85-90% of your annual bill two decades in.

Not to mention electricity prices have gone up every decade (not necessarily in real terms, but in nominal terms still), meaning your 10 KW system will save more and more in nominal terms, while the $25k investment isn't inflation adjusted. (it it was, the 7% return would probably drop to about 5%, making it even worse off). -- edit: the 7% return is already inflation adjusted actually, sorry.

And none of this even mentions the taxes that cut into your stock returns, again making it a worse off venture, while it appears saving money on your utilities with self-production is largely untaxed (?), just like making a sandwich at home or doing your own laundry isn't taxed.

I know you ended up leasing but I don't know the terms of your lease, but simply running some numbers for a buy scenario looks really appealing.

Of course it is very contextual. In cities where the kwh rate is just 9c instead of 17c, and where the credits, rebates and tariffs aren't very appealing, and where the capacity factor due to fewer sunshine hours is a third lower (e.g. in the UK it's closer to 10%, as opposed to 17% in places like California or Hawaii), it's a totally, totally different story. But it feels like in California it's a giant no-brainer. I mean I know solar is rapidly growing as an industry but we're also hearing of bankruptcies, of Solar City having lost hundreds of millions this year and last year, of solar still being a moral rather than a financial decision etc. And I can't seem to square it with the numbers I'm seeing which look really appealing.

Let me know if you'd like to share some of the terms, numbers, expenses etc for your lease by the way, would be curious to hear some real life cases!