Hydropower, the cleanest of all renewable power sources, harnesses the force of moving water to generate electricity. It has long been used for a variety of industrial purposes, such as factories and sawmills, and is one of the oldest technologies for generating electricity.

"Hydro is an economical, emission free, and flexible source of renewable power. It is valuable and important for system operations, and for meeting the state's renewable goals," said Stu Hemphill, director of SCE's Renewable and Alternative Power department.

SCE continues to work toward meeting the goals of California's renewable portfolio standard. By 2010, the utility hopes to have contracts which, when fully operational, will represent 20% or more of our customers' energy needs.

Most electrical generation technologies convert one form of energy into another, and hydropower is no different. Hydropower converts the energy stored in water at a high elevation as it moves to a lower elevation to make electricity – this is known as “potential energy.”

Hydropower is also a form of solar energy, because the energy stored in water is provided by the sun’s heat, which evaporates and expands water, causing it to rise, eventually releasing it back to the earth as rain. When water rushes down a river, creek, or waterfall, the solar energy stored in the water is converted into other forms of energy such as motion and heat. To convert the water’s energy into electricity, the water is directed to a pipe called a “penstock” that leads to a turbine. The water pushes the blades of the turbine which turns a generator. A magnet within the generator turns and its magnetic field pushes the electrons in a coil of wire to produce electricity.

There are two basic ways to harness water to generate electricity. The first is to catch it and use it as it flows. This form is called diversion hydro. The second involves collecting and storing the water in a reservoir. This is called storage hydro.

BUT IT’S NOT PERFECT

The state of California has defined different types of hydroelectric power: Large hydro (produces more than 30 MW of electricity), small hydro (100 KW to 30 MW) and micro hydro (up to 100 KW). Under California laws, only small hydro and micro hydro are classified as “renewable” resources. Large hydro often requires a dam which results in what was originally dry land being covered with water to create the reservoir. The construction of new large hydro facilities is a very controversial topic because there are benefits and drawbacks when land is taken over by water.

DIVERSION HYDRO

If water is diverted from its natural path to pass through a hydro plant that has no ability to store it, the configuration is called “run of the river hydro” or “diversion hydro.” In this type of system, the energy in the flow of water must be continually converted or it will be lost as the water spills past the diversion.

SCE contracts with a number of special diversion hydro projects called “pressure reducing stations.” Water that is to be transported long distances is often pumped to high pressure to provide the push it needs. This is similar to electricity in SCE’s high-voltage wires that provide for long distance transport of electricity. When the water reaches its destination and the pressure is no longer needed, a pressure-reducing station can be used to recover the energy packed into the water. Often these facilities are hidden underground, under sidewalks, or in nondescript buildings right in our neighborhoods.

STORAGE HYDRO

In a storage hydro system, water accumulates in a reservoir or lake behind a dam. A demand for electricity prompts an operator to release water through the pipes and turbines. 

In this arrangement, the conversion of energy can be timed to best match the varying needs of the electrical system. The ability to store and release energy on demand, along with the ability to change the rate of generation rapidly, make storage hydro a valuable tool in meeting the varying demands of electricity customers. Rapid reaction helps maintain the balance between generation and consumption that is required at all times. This type of resource can help in the incorporation into the system of other, more intermittent, types of renewable energy resources, such as wind and solar. 

A special kind of storage hydro power called “pumped storage” provides a way to store electric energy for later use. In a pumped storage system the water can be pumped up hill using electricity that may not be needed at that moment. The water, stored in a reservoir at higher elevation, is packed with potential energy that can be recovered when needed, by flowing it back to the lower elevation through a hydro power plant.

THE HARDEST WORKING WATER IN THE WORLD 

SCE has operated its Big Creek Hydro system in the Southern Sierra mountains since 1911. Big Creek is one of the oldest generating facilities in the State, and was built to provide electricity for the Red Car system of trolleys in Los Angeles in the 1920s. The "hardest working water" phrase came about because the same water is used over and over and over again to generate electricity as it cascades down the mountain. It flows from one powerhouse to another, and eventually empties into the Central Valley to be used one more time for crop irrigation.

The entire system of 9 powerhouses, 23 generating units, six major lakes and a vast infrastructure has a capacity of more than 1000 megawatts (enough to meet the energy needs of about 1 million modern homes), enough to call it “the hardest working water in the world.” Big Creek includes large and small hydro facilities. SCE also operates a pumped storage hydro facility in the Big Creek complex called the Eastwood Power Station, which has a capacity of 200 megawatts, enough to power about 200,000 homes. The generator and pump are located deep underground, inside of a mountain.

In addition to Big Creek, SCE operates 12 plants in other areas with a capacity of 98 megawatts, of which 58 is considered small hydro. SCE also has contracts with 33 independent power producers for an additional 97 megawatts of hydropower.

Learn more about Big Creek, SCE's premier hydroelectric facility.