No, it's vice versa, you put $30k more on your mortgage and pay it out over 30 years with lowest interest rate. So theoretically it should come at no cost to you since your additional mortgage payment will be countered by smaller electricity bill. But of course that depends on your electricity usage, pricing and how much money is required for maintaining the system.

But in the end, there is no net benefit to you. So why would you do it?

Support green energy, being more independent in case of grid electricity blackouts. That's the point of Tesla's roof tiles (at least how it's supposed to be), if you get same looking house and around the same net price, why don't do it?

> being more independent in case of grid electricity blackouts

That's generally not the case in California, as we're net-metering here. Very few people install storage and transfer switches to handle blackouts.