Hydroelectric Power in California

Shasta Lake and Dam, USBR photo

Hydroelectric power is a major source of California's electricity. In 2014, hydroelectric power plants produced approximately 14,000 megawatts (MW) of electricity, or 6 percent of the total in-state electricity generation, down from 12 percent in 2013. The amount of hydroelectricity produced varies each year, and is largely dependent on rainfall. Unfortunately, California is in its fourth year of a severe drought.

Hydro facilities are broken down into two categories:

  • Facilities larger than 30 MW of generation capacity are called "large" hydro.
  • Facilities smaller than 30 MW of generation capacity are considered "small" hydro and are part of the Renewables Portfolio Standard.

California has 287 hydrogeneration plants, which are mostly located in the eastern mountain ranges and have a total dependable capacity of about 21,000 MW. The state also imports approximately 4 percent of its hydro-generated electricity from the Pacific Northwest.

The larger hydro plants on dams in California (such as Shasta [pictured], Folsom and Oroville) are operated by the U.S. Bureau of Reclamation and the state's Department of Water Resources. Smaller hydro plants are operated by utilities, mainly Southern California Edison, Pacific Gas and Electric Company and the Sacramento Municipal Utility District.

Three types of conventional hydroelectric facilities are dams (pondage), run-of-river and pumped storage. Dams raise the water level of a stream or river to an elevation necessary to create a sufficient elevation difference. Dams can be constructed of earth, concrete, steel or a combination of such materials. Dams may create secondary benefits such as flood control, recreation opportunities and water storage. Run-of-river, or water diversion, facilities typically divert water from a natural channel to a course with a turbine, and then usually return the water to the channel downstream of the turbine.

Such conventional methods offer the potential for low-cost electricity, but their output is dependent on the time of year as well as annual precipitation. By contrast, pumped storage methods are typically used to provide power during peak demand periods on very short notice and are not dependent solely on runoff.

In a pumped storage facility, water is pumped during off-peak demand periods from a reservoir at a lower elevation for storage in a reservoir at a higher elevation. Electricity is then generated during peak demand periods by releasing the pumped water from the higher reservoir and allowing it to flow downhill through the hydraulic turbine(s) connected to generators. During the off-peak pumping cycle, the pumped storage facility is a consumer of electricity. In fact, the amount of electricity required to pump the water uphill is greater than the amount of electricity that is generated when the water is released during peak demand periods. Pumped storage facilities, however, can be economical because they consume low-cost off-peak electricity and generate high-value on-peak electricity.

Pumped storage methods include both typical on-stream conventional and modular off-stream technologies. The major differences between modular pumped storage (MPS) and conventional pumped storage is that MPS systems are much smaller, use closed water systems that are artificially created instead of natural waterways or watersheds, and sites are selected with predetermined elevation differences so that modular pre-engineered equipment can be used. With the exception of evaporative losses, reservoirs are charged only once, either with groundwater or even municipal wastewater.

Permitting Issues

Some of the issues associated with conventional hydroelectric power generation and typical on-stream pumped hydroelectric storage facilities include:

  • Water resources impacts (hydroelectric facilities may change stream flows, reservoir surface area, the amount of groundwater recharge, and water temperature, turbidity [the amount of sediment in the water] and oxygen content)
  • Biological impacts such as the possible displacement of terrestrial habitat with a new lake environment, alteration of fish migration patterns, and other impacts on aquatic life due to changes in water quality and quantity
  • Possible damage to, or inundation of, archaeological, cultural or historic sites (primarily if a reservoir is created)
  • Changes in visual quality
  • Possible loss of scenic or wilderness resources
  • Increase in potential for landslides and erosion
  • Recreational resources may be gained

Because modular pumped storage systems are not dependent on natural waterways and watersheds, they can be sited in areas that avoid many of the issues described above. In fact, desirable sites are not near rivers, lakes, streams and other sensitive environmental areas in order to avoid the regulatory complexity and time associated with conventional pumped hydroelectric storage facilities.