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Posted on May 25, 2011

How PG&E’s Hydroelectric Staff Balances the Power of the Sierra Snowpack

By James Park

In the high Sierra Mountains outside Fresno, PG&E’s Paul Linderman watched as a powerful rush of cold water came spilling over a small dam outside the Balch 1 Powerhouse and flowed rapidly down river, feeding the Kings River Powerhouse, filling the Pine Flat Reservoir and irrigating much of the vast Central Valley farmland.


The power of the water is evident at the Black Rock Reservoir along the Kings River

The water came from the abundant mountain snowpack, a result of this winter’s unusually heavy storms.

That’s good news for a region no stranger to droughts. But for PG&E’s widespread hydroelectric system, it means managing a delicate balance of water storage and power generation to ensure customers get the clean electricity they need throughout the hot summer months and into the fall.

“Our customers depend on PG&E to safely and reliably provide the energy they need this summer. The four powerhouses on the lower Kings River can generate up to 335 megawatts,” said Linderman, a technical supervisor in PG&E’s hydroelectric operations department. “The above-average snowpack should let us to continue to deliver the power to customers later into the year.”

Hydro operations play an important role in delivering that clean power, as approximately 50 percent of PG&E’s electricity comes from a combination of renewable and greenhouse gas-free resources including the hydroelectric system in years rainfall is normal.

Maintaining a delicate balance

Achieving this balance is no easy task: The continuous rising and falling of the Kings River water level in conjunction with the warming days must be carefully observed in order for hydro operators to properly monitor water spill.


Inside the Haas Powerhouse, where moving water generates electricity.

As of May 24, California’s Department of Water Resources said the average snow depth statewide was still 107 percent of the April 1 average. That made it 249 percent above normal for that date.

With the cooler-than-average spring prolonging the snowpack, predicting how fast the snow will melt and how much water will be released can be difficult. The weather can change daily and even by the hour. For example, crews at the Helms Pumped Storage Power Plant upriver from Balch 1 recently got short notice that eight inches of snow was forecast for the area — an unusual amount for mid-May.

In order to generate hydropower later in the year, PG&E must maintain the right volume of water in its system of more than 100 reservoirs while trying to control the overflow coming down from the Sierra. Throughout the hydro system, almost all of the reservoirs are spilling water, flowing past powerhouses that are already roaring at full capacity. Hydro operators, hydrologists and technicians have their work cut out for them this season as they work to keep reservoirs full while spilling water to accommodate melting snow throughout the summer.

Helms at the helm of integrated system

The Helms plant has the unique ability to alleviate over-generation by using extra energy to pump water up from its lower reservoir (Wishon) to its upper site (Courtright). It plays a crucial role as powerhouses downriver run at full power with the overflow.


Water spills over the dam at the Balch Afterbay.

Helms’ generating capacity, second only to the Diablo Canyon Power Plant in the PG&E system, will be a vital source of power for customers turning on air conditioners during peak summer months.

“Helms has the ability to go from dead stop to 1,212 megawatts in only eight minutes,” said Keith Heimbach, a PG&E senior manager in power generation. “These unique operating characteristics are what make it a critical part of maintaining electric system reliability, not just in California, but along the entire West Coast of the U.S.”

As temperatures rise this summer, the important work being done by the men and women in hydro will continue to play a critical role in providing our customers with the energy they need at competitive rates.


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