Run-of-river hydro schemes use the water available in the watercourse at any given time, so will not be able to run at full power continuously and will turn off when flow rates are low.
Storage hydro schemes collect water in reservoirs, which can then be released to drive the turbines as required. Water collected during wet periods, which would otherwise be lost, can be saved and used during dry periods, or when electricity prices are higher.
Pumped storage schemes will run a pump to refill their reservoirs when the power price is low, so they can generate when prices are high. Large pumped storage schemes help to provide grid stability, and can be used to store excess energy from wind farms.