Is There A Successful Energy Storage Technology on the Horizon?

Ask the Scientist - October 2014

H. Bryant of Dandridge, TN, asks "It would be a lot easier to transition to renewable energy if we had better storage technology. Is there any energy storage technology on the horizon that is likely to succeed?" and is answered by Senior Energy Analyst Laura Wisland.

At any given time of the day, our nation’s electricity grid operators have to match supply with demand. Since some renewable energy resources, such as wind and solar power, only produce electricity when the wind is blowing or the sun is shining, the ability to store excess power and use it later is a huge benefit.

There are many types of storage technologies. Some of these technologies have been used for decades to help integrate power from coal and nuclear plants into the grid, and to compensate for variability and uncertainty more generally. Unlike coal or nuclear plants, most of these storage technologies can respond within seconds to meet demand, and operators can easily adjust their energy output. They can also be useful in remote locations such as rural and island communities, where long-distance transmission lines are expensive and difficult to build. Here is a quick overview of what’s currently available.

  • Pumped hydroelectric is the largest and oldest form of storage. Water is stored in a high elevation reservoir and released to generate electricity when needed. When more storage is required, the system pumps water “upstream” to be released later. This type of storage can store large amounts of potential energy, but it is limited by the amount of available land and water for new reservoirs.
  • Concentrating solar power plants can store solar heat in water, molten salts, or other fluids, and use it to generate electricity for hours after sunset. Several of these plants are currently operating in Arizona and Nevada, and another is slated for California.
  • Power plants, such as wind farms, can use excess electricity to compress air and store it in underground caverns. When needed, the compressed air is heated and used to generate electricity in a natural gas combustion turbine. One such facility is operating in Alabama, and developers have proposed similar projects in California and Texas.
  • Rechargeable batteries, such as those in mobile phones and laptop computers, can be used on a much larger scale to supply electricity to the grid. For example, grid operators on the Hawaiian islands of Kauai and Lanai use batteries to smooth out the output variability from solar power plants, which generate a large portion of the two islands’ electricity. Batteries also can be combined with rooftop photovoltaic (PV) installations to enable households to capture excess solar power and generate electricity from it after the sun sets. Likewise, plug-in electric vehicle batteries outfitted with special equipment can supply electricity to the grid when the vehicles are idle. Unfortunately frequent charging cycles can wear out rechargeable batteries faster, but newer designs may address this shortcoming.
  • Excess electricity also can produce hydrogen gas from water molecules. The hydrogen is then stored for later use in a fuel cell, engine, or gas turbine. The National Renewable Energy Laboratory also has investigated the possibility of producing hydrogen from wind power and storing it so it can be used to generate electricity when demand is high and the wind is not blowing. But this technology is still in a demonstration phase; no commercial-scale hydrogen storage systems currently exist.

It’s difficult, if not impossible, to predict which of these technologies will become the predominant storage type. But keep in mind that there are several viable strategies besides storage to make the grid more flexible and enable it to handle more renewable energy. They include upgrading grid infrastructure, better weather forecasting to more accurately predict when renewable resources will generate power, finding ways to lower usage during peak demand times, and allowing regional grid operators to share resources. With thoughtful planning and policies, there is no doubt that the country will be able to transition to a clean energy system. We have the technology. What we need is the political will.

 

Laura Wisland

As a senior energy analyst at the Union of Concerned Scientists, Laura Wisland focuses on developing state policies that will effectively increase the amount of renewable energy used in California.  Ms. Wisland has a master's degree from UC Berkeley’s Goldman School of Public Policy, and a bachelor's degree from the University of North Carolina at Chapel Hill honors program in public policy.

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