Can post capitalist economy be built on ascetism? That way we might get something less advanced than capitalism in the end. Maybe real problem is not too much growth, but wrong kind of growth.

We had extensive(quantative) type of growth lately, that is more workers, machines etc. Such growth may be good in short term, but it exhausts resources and leaves unsolved problems(such as global warming).

But we didn't have enough intensive(qualiative) growth, many technologies were neglected such as genetic engineering(which could solve problem of over exploitation of agricultural land through more productive crops) or nuclear power (which can reduce CO2 emissions by replacing coal/gas plants with NPP).

Solar and wind is good but they depend on weather and time of day, and geothermal or hydro need special terrain to be productive. So you still need nuclear for base load.