Backup capacity in Czechia is not the preserve of renewables alone

No electricity source operates continuously; each has periods when it supplies no electricity to the grid. Renewable sources depend on the weather, nuclear power plants on refuelling and planned inspections as well as unplanned outages, while coal-fired power plants here operate around half the time. Their output is regulated according to demand, also taking emissions allowances into account. Gas-fired power plants account for about 5-8 % of generation in Czechia and are used mainly to cover peaks in demand.

To prevent the grid frequency from falling and avoid a blackout, backup sources must be brought online very quickly, especially rotating equipment. In Czechia, this function is provided by the rotating mass of turbines in thermal or hydroelectric power plants, while in countries with a higher share of renewable electricity, the grid is stabilised by synchronous condensers or flywheel energy storage. Batteries and pumped-storage hydropower plants are next in line, followed by fast-starting gas-fired power plants.