In 2021, the Grohnde nuclear power plant in Lower Saxony on the Weser River was shut down. Now, immediately next to it, the Emmerthal energy cluster is growing with three very large battery storage systems, ground-mounted photovoltaic systems, and a new substation for several 380-kilovolt high-voltage lines.
Hot sand stores a huge amount of heat, and the bigger the storage, the less heat it loses. With modern insulation, even the cheap options, it lasts months. Circulate water or some other fluid through pipes embedded in the sand, and you can introduce or extract the heat.