Hydroelectric Power in California

[Shasta Lake and Dam, USBR photo]

Hydroelectric power is a major source of California's electricity. In 2013, hydroelectric power plants produced 24,075 gigawatt-hours of electricity, or 12.11 percent of the total. Hydro facilities are broken down into two categories larger than 30 megawatts capacity are called "large" hydro. Smaller than 30 MW capacity is considered "small" hydro and are totalled into the renewable energy portfolio standards. The amount of hydroelectricity produced varies each year. It is largely dependent on rainfall.

California has nearly 259 hydro plants, which are mostly located in the eastern mountain ranges and have a total dependable capacity of about 13,753 MW of capacity. The state also imports hydro-generated electricity from the Pacific Northwest.

The larger hydro plants on dams in California (such as Shasta [pictured on the right in this U.S. Bureau of Reclamation photo], Folsom, Oroville, etc.) 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 Sacramento Municipal Utility District.

Two types of conventional hydroelectric facilities are dams and run-of-river. Dams raise the water level of a stream or river to an elevation necessary to create a sufficient elevation difference (water pressure, or head). 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 its natural channel to run it through a turbine, and then usually return the water to the channel downstream of the turbine.

Such conventional methods offer the potential for low-cost baseload 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, are economical because they consume low-cost off-peak electricity but 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 land-slides 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.

Original Source: Energy Aware Planning Guide II: Energy Facilities.