Should I get solar PV, or a renewable energy supplier?

[peelypeel]

I can't find an answer to this question from the angle that i'm asking it.

My goal is zero carbon energy usage (Or, as low as can be while I still use gas). My goal isn't a £0 electricity bill.

I'm considering solar PV + storage to help achieve this goal, but I will obviously still need a (renewable) electricity supplier. But then I thought, if my goal is renewable electricity, why even bother getting the PV panels?

The "point" of getting solar PV is to reduce your energy bill, and then in 10-15-20 years they pay themselves off, and then you are net positive. But, does this assume I will always have the same energy bill? Technology moves on. It's possible that in 15 years renewable energy is cheaper to buy (TBH I pray to all of Science that it's true, for the Climates sake)  than it is now, in which case my savings would be less and less, and the panels would technically take longer and longer to pay themselves off. At which point, their efficiency will be so "low" (in comparison to the efficiency of new panels/other sources will be 20 years from now), that they should just be scrapped (As we can also assume that my energy consumption will only increase).

In short, I trust all of the grid sized renewable and storage to be more efficient than my fix-in-time PV installation, so why would I even do it, I should just pay them and be renewable today with no £8000 outlay, and no modifications to my house, and nothing to maintain.