This article appeared in the August 2011 issue of Power Engineering magazine.
Challenges for renewable energy, including hydropower, were highlighted last May when the Bonneville Power Administration (BPA), which supplies one-third of the energy consumed in the Northwestern U.S., faced an energy supply-and-demand dilemma. BPA was forced to decide how to deal with excess energy generated from the highest snowpack runoff since 1999, coinciding with high wind energy output and decreased regional electricity demand. This resulted in an oversupply of energy causing power prices in BPA's system to go negative for the second consecutive year. BPA's decision, outlined in its Environmental Redispatch Policy, was to temporarily limit output from non-hydropower sources—including coal, natural gas and wind—until supply could more adequately meet demand. Some in the energy community disagreed with the decision given that it limited output of some energy sources in what appeared to be in favor of hydropower.
With no way to store or utilize the energy, BPA had to make tough decisions based on numerous environmental and economic factors. The National Hydropower Association (NHA) joined the discussion to help clarify the debate, emphasizing the need for a missing piece of the energy puzzle: energy storage. In its "guideposts" for the dispute, NHA outlined long-term solutions including how hydropower, wind and other resources can best work in tandem. These recommendations included increasing energy storage, both from existing conventional hydropower projects and new pumped storage hydropower facilities, and continuing to provide incentives that encourage the development of complementary technologies to help mitigate this issue and facilitate additional growth of renewable energy projects in the region.
Pumped storage hydropower is one of the few proven and economically viable technologies capable of providing ultra-fast, responsive grid-scale power delivered reliably and on demand when it is needed most; an important component to integrate high levels of variable generation worldwide. Pumped storage provides the balance, stability and capacity needed for dispatch coordination of the energy grid, proving value in its ability to complement other renewables with variable sources, like wind and solar. The energy industry should consider ways to tap into the potential of pumped storage to help strengthen their state's renewable portfolio and the nation's energy independence and security.
Pumped storage is a fairly straight forward technology. It requires two bodies of water which are relatively close in proximity, with one at a higher elevation than the other. When energy is needed at peak hours, water from the upper reservoir is directed through a powerhouse to the lower reservoir. When energy costs and demand are at their lowest (or in oversupply), water from the lower reservoir is pumped back and stored in the upper reservoir, acting like a large battery. From a power utility's perspective, pumped storage essentially converts inexpensive off-peak power into a higher value asset for times of high demand. Efficiency of conversion in each direction is typically greater than 90 percent including electrical, mechanical and hydraulic losses. From a transmission or system perspective, pumped storage brings flexibility and response times that no other grid-scale plant can match. Documented response times from no load to full power of less than 10 seconds with ramp rates up to 50 MW/second can be delivered. A pumped storage project can serve as load or generator and even act as a large flywheel or synchronous condenser.
In the U.S., pumped storage currently has a capacity of more than 22,000 MW, including one of the largest pumped storage projects in the world, the 2,772 MW Bath County project in Virginia. Even with this generation, the U.S. is slow to realize the potential of this technology. Despite its capabilities and successful track record, no new pumped storage project in the U.S. currently has an active Federal Energy Regulatory Commission (FERC) license to construct the project, primarily due to long-term uncertainty of the project revenue streams and a licensing process that is much longer and more cumbersome than other renewables. Fortunately, the U.S. Department of Energy demonstrated a commitment to pumped storage earlier this year, committing more than $10 million of technical and financial assistance to accelerate the development of pumped storage projects already in the pipeline, prioritizing projects best able to integrate wind and/or solar. This is an encouraging sign that energy leaders are beginning to understand the importance of energy storage for the future of the nation's energy grid.
With the U.S. preparing to come off a 20-year lag in new construction of pumped storage projects, an aging fleet ready for rehabilitation and upgrades to improve efficiencies and more than 20 pumped storage projects currently in the FERC licensing process, it is an opportune time to engage the entire power industry and make the necessary investments to turn the power of pumped storage into a more concrete reality. The end result will be a more reliable energy grid that complements existing generation sources, while meeting the energy needs of today and, more importantly, for tomorrow and beyond.