Pumped Storage Hydropower: Providing reliable storage for wind

The United States Department of Energy recently projected that in order to meet a national goal of obtaining 20% of our electricity from wind generation by 2030, utilities must integrate some 300 GW of wind generation onto the grid. To accommodate the variability of this new wind generation, an estimated 50 GW of new peaking generation, probably from natural gas, would be needed, according to the DOE. However, new generation is not the only way to address this need. In its December 2008 report to DOE, the Electricity Advisory Committee advocates using storage to provide some of this capacity, rather than new-generation sources. Pumped storage from hydropower offers a proven, reliable storage method.
 
What is pumped storage hydro?
Pumped storage is a type of hydroelectric power generation that stores energy in the form of water in an upper reservoir, pumped from a second reservoir at a lower elevation. Historically, it has been used to balance load on a system, allowing large, thermal-generating sources to operate at optimum conditions. Pumped storage is the largest capacity and most cost-effective form of grid-energy storage currently available.

Pumped storage systems also provide ancillary electrical grid services such as network frequency control and reserve generation. This is due to the ability of pumped storage plants, like other hydroelectric plants, to respond to load changes within seconds. Pumped storage is now being applied to firm the variability of other renewable power sources such as wind and solar generation. It can absorb excess generation (or negative load) at times of high output and low demand, and release that stored energy during peak demand periods, enabling wind power's growing penetration into the United States energy supply system.

The critical need for energy storage 
Increasing bulk energy storage capacity has not been a priority of utility planners or energy legislation in recent decades. Since many utilities de-regulated in the 1990s, the industry has had no mechanism or incentive for coordinated integration of new-generation storage and transmission. Yet, these three components of a reliable energy generation and transmission system require coordinated long-term planning.
 
Nevertheless, the demand for renewable generation continues to grow. Washington and Oregon are among 29 states that have enacted Renewable Portfolio Standards requiring that renewable sources represent a certain percentage of new generation brought online. Climate policy initiatives are also driving investment in renewable sources. This has created rapid growth in variable generation, such as wind and solar, but there has been no corresponding storage or transmission planning. As a result, in areas such as Texas, California, and the Pacific Northwest, there's excess energy from wind without corresponding demand at times when the electricity is available (typically occurring at night). Alternatively, there isn't enough peaking power supply to provide on-demand capacity when the wind and solar plants cannot generate.

Many advocates of increased renewable generation point to Denmark as the example for integrating large amounts of variable generation and, similarly, how it can be adopted by the US. The key point that's overlooked, however, is the Denmark transmission system doesn't provide its own system balancing services-the two systems (East and West) depend on interconnections with Germany and Norway, countries that are rich in pumped storage and conventional hydro, respectively. Moreover, research has shown a direct correlation between wind generation and power flow over the interconnections with hydro and pumped storage being the generation source to balance wind's variability (Mason 2005; Sharman 2005; White 2004; VTT 2007).

With the emergence of new renewable technologies and the ever-increasing investment in variable generation sources, the need for storage has never been greater.
 
Reaching the 20% goal
Pumped storage hydro projects are critical transmission system tools, currently providing crucial storage, generation, and ancillary services throughout the US. In response to the growing need for storage, and the exceptional synergy between pumped storage and variable renewable energy sources such as wind, the hydro industry is proposing to more than double the pumped storage capacity in the near future. The Federal Energy Regulatory Commission recently issued 23 preliminary permits for new pumped storage hydro projects, representing approximately 15 GW of new pumped storage capacity. Another 15 applications for preliminary permits were pending before FERC could provide an additional 16 GW of capacity.
 
With its current proposals the pumped storage sector of the hydropower industry is poised to fulfill an estimated 30% to 60% of the storage capacity needed to meet the national 20% wind initiative. This would reduce the need for additional fossil fuel derived peaking generation and avoid the greenhouse-gas emissions associated with those resources. Importantly, by directing investments in new energy infrastructure to storage facilities that would be used at or near capacity-while also providing many ancillary benefits-we would avoid investing in large fossil fuel generation sources that operate only a fraction of the time.
 

Rick Miller, P.E., is a senior VP and national client director of the Hydropower Division of HDR, as well as the past president of the National Hydropower Association.

HDR www.hdrinc.com

National Hydropower Association
http://hydro.org