Energy consumption varies according to the season, the day of the week, and the time of day. Periods of low demand (summer, weekends, nights) alternate with periods of high demand (winter, working days). Energy production therefore has to be constantly adjusted to demand.

Continuous energy

When demand is constant, the base load of the network is supplied by nuclear power stations and run-of-river power stations. These produce energy continuously, and always at the same capacity.

Peak energy

Peak energy must cover peaks in demand by rapidly injecting a large number of additional kWh into the network. This is the role of storage hydroelectric power stations. By storing water in reservoirs, they are able to deliver energy on demand. They operate in winter in particular, on working days, when human activity is at its most intense, or when the temperature goes below a certain threshold. The value of peak energy is noticeably higher than that of continuous energy.

Super-peak energy

This involves making available, within an extremely short period, a number of kWh which is even higher than that required for peak energy, to cope with a further increase in demand. The value of super-peak energy is even higher than that of peak energy.