Dispatchable power plants are those that can change how much power they provide to the energy grid quickly. They can be switched on and off, or ramped up and down to meet power demand.
Depending on how much energy is needed during the day, power plants have to adjust how much energy they put out.
Gas turbines are the most flexible, though modern coal plants also ramp up and down well. Older coal plants prefer to be switched on and left running near full capacity, as do nuclear plants. Like gas turbines, generators running on biomass are generally quickly dispatchable, but they are the only type of new renewable source that can be considered dispatchable in Germany.
Wind and solar are considered “intermittent,” meaning that they do not produce power all the time, though power production can be reliably predicted at least a day ahead. Most importantly, wind turbines and photovoltaics cannot be “dispatched,” i.e.switched on and off. Aside from hydropower, the only other renewable sources of electricity that are dispatchable are geothermal and concentrating solar power, which Germany does not have in large quantities.