2.0 Hydropower production
Overview of hydropower production
Dams produce hydropower by releasing water through the penstocks and using the power of that falling water to turn a turbine (see Figure 2.0a).
Figure 2.0a. Folsom powerhouse components
The amount of power generated depends primarily on the discharge through the turbines and the hydraulic head, or height between the reservoir surface and turbines:
P = ηρ gQH
where, P is power (MW), η is turbine efficiency, ρ is water density (lbs/ft3, kg/m3) Q is discharge (ft3/s, m3/s), g is gravity (32 ft/s2, 9.81 m/s2), H is hydraulic head (ft, m). Using the English units for ρ, g, Q, and H, and including a conversion factor for P to MW, yields the simplified equation:
P = (η QH) / (1.181 * 10^4)
We will use this equation and English units in the following activities.
Types of powerplants (base vs. peak)
Hydropower plants can generally be classified as either base-load plants or peaking plants, with some plants serving both purposes. Base loading plants output a steady flow of power to meet electrical demands that exists throughout the day and throughout the year. Alternatively, peaking plants output energy that fluctuates on a daily and/or seasonal basis to meet prime hour power demands (typically during weekdays). Hydropower plants posses the capability to quickly reach full power in response to increasing electrical demands, making them ideal for meeting peak demands. Put more simply, hydropower is easier to turn on and off than other power supplies, such as coal or natural gas. Under reliable water supply conditions, hydropower may also contribute to meeting base power demands. The graph below show shows example discharge regimes for producing peaking and baseload power.
Figure 2.0b. Example discharge regime from a peaking and baseload hydropower dam