In my place (NZ) finance is only available for 3 years, power is cheap and install is expensive. No subsidies either. I’m looking at anywhere from 15-25 year payback (assuming same power prices and interest rates I pay for house (7.5% atm)).

I’m still keen to at least DIY a shed, but even then it’s like 5 years to pay back.

To compare with my parents place in LT (or even Australia) - power is 3x more, install 2x less and subsidies are available. You are basically looking at 6x quicker payback.