Drought Impact on Hydropower Frequently Asked Questions

What is the energy-water nexus in California?
Water and energy are interdependent. If you reduce water use, you can reduce energy use. Energy is used to pump water, transport it and treat it so that it meets drinking water standards. Energy is also used to treat wastewater and recycle and bank water for future use. The more efficiently we use water, the less of it we have to transport, treat and recycle, which reduces both energy and water demand and costs.

How much of California's energy supply is provided by hydroelectric power?
On average, anywhere from 14 to 19 percent of California's energy in recent years has been provided by hydroelectric facilities including power plants located in California and imports. In-state hydropower plants have provided 10 to 15 percent of energy supplies consumed in California.

How has this percentage changed over time?
California is much less dependent on hydropower today than 50 years ago when hydroelectricity accounted for more than half of California's electricity supply. One reason that we are less dependent on hydroelectricity is the significant progress that California has made bringing renewable energy online. Last year alone, 3,300 megawatts of renewable energy capacity became commercially operational.

How much hydroelectric power can be generated in California?
Hydropower dams in California have the capacity to generate 14,000 MW. On average, 25,000 gigawatt-hours (GWh) are generated. In a dry year, about 15,000 GWh of energy are produced (roughly the same as solar) and in a wet year, about 40,000 GWh can be generated.

How will the drought impact the state's supply of hydropower?
This year's small snowpack means there will be less hydroelectricity generated by in-state facilities. These power plants will operate during fewer hours this year, especially during spring when water is being conserved and in the fall when water supplies may be severely limited.

Electric utilities can use stored water to optimize electric generation during hot summer days. Some facilities, though, have very little reservoir storage and little flexibility to schedule electricity production at specific times. In the mountains, power plants are often located far from the water supply. Water must be diverted from lakes and rivers into canals, flumes, and tunnels. It flows to a forebay, and then down a high-pressure penstock to a powerhouse often located in a river canyon. The instantaneous capacity to generate power, measured in megawatts (MW), depends on gross head – the elevation difference between the forebay and the powerhouse. At these facilities, the rated ability to generate power (in MW) is not diminished by drought, as long as water supply to the forebay is reliable.

At lower elevation, multi-purpose reservoirs such as Folsom Lake, the power plant is often located immediately below the reservoir's dam. At these facilities, when reservoir elevation drops, the facility's ability to generate electricity is reduced.

How does California make up shortfalls in its supply of in-state hydropower?
California facilities using natural gas and renewable fuels are expected to generate significantly more energy in 2014 than in past years to fill reductions of in-state hydroelectricity generation. In addition, California normally imports hydropower from the Pacific Northwest and from Hoover Dam in the Pacific Southwest. Indeed, additional energy imports from Pacific Northwest are often available, a condition that is expected in 2014. Conditions for hydroelectric generation in the Pacific Southwest appear stable through 2015, and the Pacific Northwest is projecting surpluses of hydropower through 2018.

Is California at risk of missing its 2020 greenhouse gas emissions reductions targets if more natural gas is needed to replace hydropower?
No. The electricity sector is capped under AB 32, which calls for reducing greenhouse gas emissions to 1990 levels by 2020. If more natural gas is needed to replace hydropower in the coming years due to the drought and it results in increased emissions, utilities must still reduce emissions or procure compliance instruments (allowances, limited offsets) for those emissions in order to comply with the law.

Is one region of the state—or are certain utilities—more reliant on hydropower than others?
Yes, there are different levels of dependence. Northern California utilities have more in-state hydroelectric facilities than Southern California utilities. For example, Pacific Gas & Electric (PG&E) and the Sacramento Municipal Utility District (SMUD) rely on hydropower to a greater extent than San Diego Gas & Electric (SDG&E) or Southern California Edison (SCE). Some municipalities have a significant dependence on hydropower as well and receive their supplies through the federal hydropower system.

Should ratepayers expect to see higher electricity bills if more expensive types of energy are used to make up for less-expensive hydropower?
Hydropower is one of the least expensive types of energy. While capital intensive to build facilities, they are generally less expensive to operate than fossil fuel resources. Whether rate increases occur (and their magnitude) could depend on how well a utility has prepared, hedged, or diversified their power procurement portfolio for these extreme drought conditions. The effects of the drought and additional power replacement expenditures will not be known immediately. For the major investor-owned utilities, power purchase costs and rates are primarily based on forecasts; for their customers, potential drought-related rate impacts will not be passed on this summer, but may be later. Retail rates for major investor-owned utilities, nonetheless, may increase this year due to other factors (for example, already scheduled rate increases).

Is the drought likely to impact reliability and lead to more outages?
We do not anticipate seeing drought-related outages as a result of reduced hydropower. Climate change is leading to higher temperatures—we have seen an increase of 2 degrees over the last 125 years—and it could get much hotter. Climate change and droughts lead to dry conditions that increase the risk of fires. Of the top 20 recorded major fires in California's history, 11 have occurred in the last decade. In January 2014, the state was already seeing an increase in wildfires that threaten lives and the environment. Wildfires can make our state's electric grid more susceptible to outages because fires can take out substations and transmission lines. This interruption to transmission is more of a concern than outages resulting from a reduced supply of hydropower.