The strategy of using renewable energy when the weather is optimal and fossil fuels when it is not is one that Germany promoted to the point of getting EU to define natural gas as "green". To a degree it does work to make a country that heavily used fossil fuels to reduce consumption, which Germany itself has shown.

If it is cheaper is less clear case. Having all those peaker plants at standby is expensive and require a lot of subsidizes, and there need to be transmission both from the peaker plants and wind farms, which is also paid mostly through subsidies. German subsidies to both fossil fueled power plants and renewable energy producers has only increased by time. The owners of peaker plants can also recover most of losses from periods of optimal weather, not only by subsidies, but also by increasing prices during non-optimal weather as there is very little competition during periods of high demand and low supply.

Not everyone agree with this strategy. EU has no plan on phasing out fossil fuels from the energy grid, despite having a clear plan on phasing out fossil fuels from the transport sector. With the war in Ukraine and war in Iran, the strategy of peaker plants are also looking to be poor in terms of economic and national security.

EU need to issue a full phase out of all fossil fuels in the energy grid by banning any construction of new power plants that burn fossil fuels by 2030 and a final decommission date by 2040. The solution to non-optimal weather has to be done through some other way. The discussion of renewables vs nuclear will then be mostly irrelevant.