I am yet to see systemic renewable power source that is available to country like Germany (or Poland where we also have discussion about going nuclear).

All renewables available to us are considered supplementary (they generate power when conditions are favorable, eg. wind blows, sun is shining). But this means they can’t be used to maintain power grid.

Ofc you can try hydro or geothermal, but those depend on your river network, underground warm waters availability, as well as population density around country. Those work for country like Norway but in practice German increasingly relies on French nuclear power as systemic source to maintain their grid, and Poland (sadly) sticks to coal and gas.