That's an inherent problem of non-fossil electricity production. Electrical energy is expensive to store (some hydro plants e.g. in Austria do that). For both

That's an inherent problem of non-fossil electricity production. Electrical energy is expensive to store (some hydro plants e.g. in Austria do that). For both nuclear and renewable, the marginal costs for producing an extra MWh, once the plant is built, are close to zero. Because on a market of any commodity, the marginal costs determine the market price, this means that once there is more electricity produced than there is current demand, the price goes to zero. This is actually the realization of the old promise from the fifties that with nuclear energy, energy would be so 'cheap' that it would not be worth the effort to install an electrical meter. The flip side of the coin is that energy production with this cost structure, marginal costs at zero, need some degree of subsidies to be economically interesting for the operators. Renewable energy in Germany is funded by a very visible green energy tax. Nuclear power in turn is expensive to build and was mostly funded by research funds and hidden subsidies. Such as that the final storage of spent nuclear fuel is paid by the state. Extremely expensive but it does not appear in the books of companies.