California's Drought Could Mean Power Shortages This Summer

California's record-setting drought stands to do major harm to the state's ability to generate hydroelectric power, with a possible drop in output from just the state's ten largest hydro power plants potentially exceeding the loss of generating capacity from the shuttered San Onofre Nuclear Power Plant.

According to realtime data provided by the California Department of Water Resources (DWR), 10 of the state's 12 largest reservoirs are well below historic average water levels, with half of those reservoirs holding 55 percent or less of the average amount of water that managers generally expect in January.

Those reservoirs feed water through hydroelectric plants with a total generating capacity just above 2,500 megawatts. The longer the drought continues, the less likely it is the state will be able to count on that generating capacity, which could mean a loss of power greater than that from the closure of San Onofre.

Large hydro can do significant environmental harm to wildlife and habitats, but it's at least theoretically renewable. It's also "dispatchable": it's relatively easy to ramp up production of hydroelectric power during periods of peak demand by cranking a turbine's penstocks open, and then dialing back power production by letting less water through the power plant when demand slackens.

But low reservoir water levels make it more difficult to meet the diverse demands for water ranging from irrigation to keeping fish alive, and that can often tie the hands of those who manage the amount of water fed through hydroelectric turbines.

According to the DWR, as of Thursday January 16 only Castaic and Pyramid lakes were at higher than 77 percent of their historic average water levels. Those two reservoirs, filled by the California Aqueduct with water imported from the drought-stricken northern half of the state, feed water through the Los Angeles Department of Water and Power's 1,331- megawatt Castaic Power Plant, a pumped storage generating plant.

Why those two reservoirs are above 88 percent of capacity filled with water from the drought-ravaged Sacramento River is worth an entire post on its own. It's certainly not due to a statewide priority on pumped storage: the San Luis Reservoir near Los Baños, another pumped storage reservoir which powers the 424-megawatt Gianelli power plant, is currently at 41 percent of its historic average capacity.

Pumped storage is important in meeting peak demand, but it represents a net loss of primary energy produced, because the state has to generate more energy to pump that water uphill than it regains by letting it flow back down through turbines. The other nine reservoirs -- Millerton Lake, Don Pedro, Trinity Lake, New Melones, Lake Shasta, Lake Oroville, Folsom Lake, Exchequer, and Pine Flat -- provide water to primary generating facilities, andeach of them is at 55 percent of average capacity or below as of Thursday.

Those nine reservoirs directly account for at least 2,514 megawatts of primary generating power, which the state may not be able to count on unless winters storms raise water levels between now and the state's usual dry season. That's a prospect that seems increasingly unlikely as January wears on.

We say "at least" 2,514 megawatts of generating capacity because each of the reservoirs listed by DWR is just part of a whole-state watershed network. Releases from dams upstream have an obvious impact on the productivity of hydro plants farther downstream: restrict releases from the upper facility and there's less water for the lower one to use. And the same drought that's making all but LADWP's two pumped reservoirs far drier than usual is affecting the state's smaller streams and reservoirs.

California has hundreds of hydroelectric plants that use the water in the state's rivers and streams to generate primary power -- 343, in fact, in a list the state provides of generators larger than 100 kilowatts in capacity. All told, and excluding facilities that are entirely devoted to things like pumped storage or recovering waste energy as water pressure is restricted in pipelines, California's large and small hydro generating capacity totals upward of 10,500 megawatts.

And all of that generating capacity depends on water that we may not have this year. Not all of that power makes its way into the grid at once: in a typical non-drought year, hydro supplies about 15 percent of the state's total energy consumption. But if production figures for the last couple of days are any indication, that's going to be a lot lower this year. In the 48-hour period from 12:01 a.m. Tuesday January 14 to 11:59 Wednesday evening, California's grid received 45,913 megawatt-hours of hydroelectric power. That's less than half the 100,113 megawatt-hours produced in the same 48-hour period a year ago, and significantly less than a third the 148,511 megawatt-hours for those two days in 2011.

In other words, we may not have the hydroelectric power in 2014 that eased us through our first two summers after San Onofre closed down. That hydro power helped make sure we didn't have too many Flex Alert days in 2012 and 2013, but unless we get some rain this winter, and a lot of it, we may well face some serious power shortages as we climb into the triple-digit days of summer.