A peaking project impounds and releases water when the energy is needed.
A storage project extensively impounds and stores water during high-flow periods to augment the water available during low-flow periods, allowing the flow releases and power production to be more constant.
Pumped storage projects differ from conventional hydroelectric projects in that they normally pump water from a lower reservoir to an upper reservoir when demand for electricity is low.
Water is stored in an upper reservoir for release to generate power during periods of peak demand. For example, in the summer water is released during the day for generating power to satisfy the high demand for electricity for air conditioning. At night, when demand decreases, the water is pumped back to the upper reservoir for use the next day.
Microhydropower Distributed Generation Projects
Smaller, single community projects are termed Microhydropower and produce 100 kilowatts (kW ) or less.
Microhydro plants can utilize low heads or high heads. The hydraulic head is the elevation difference the water falls in passing through the plant.
These are projects that can pass on RE towards small communities or single households.
Basic Microhydropower Formula
Approximate power available at any given site can be assessed using the formula:
head (feet) x flow (gpm) / 8 -- Watts
e.g., 100 feet x 30 gpm / 8 = 375 Watts
head (m) x flow (l/m) / 10 = Watts
e.g., 30 m x 120 I/m / 10 = 360 Watts
Most hydroelectric projects serve other purposes such as navigation, flood control, recreation, and irrigation, and flow augmentation.