Storage useful, rarely essential for wind power

Matthew Wald’s article "Wind Drives Growing Use of Batteries" in yesterday’s New York Times could give many readers the impression that energy storage is an essential tool for integrating wind power onto the power grid.

In reality, large amounts of wind energy have already been reliably and cost-effectively integrated onto the utility system without the addition of any new energy storage resources.

Moreover, numerous studies as well as European wind integration experience have demonstrated that the U.S. could increase its use of wind energy by more than 10-fold without energy storage being needed.

How is this possible? The secret lies in using the sources of flexibility that are already present on the electric grid. Every day, grid operators constantly accommodate variability in electricity demand and supply by increasing and decreasing the output of flexible generators – power plants like hydroelectric dams or natural gas plants that can rapidly change their level of generation.

Thus, the water kept behind a dam or the natural gas held in a pipeline may be thought of as a form of energy storage, with operators using this energy when it is needed and "storing" it when it is not. Grid operators also move power from regions with momentary excesses of electricity to other regions that have a need for electricity at that moment. Grid operators use these same flexible resources to accommodate any additional variability introduced by wind energy.

A tremendous amount of flexibility is already built into the power system. Demand for electricity can vary by a factor of three or more depending on the time of day and year, which nationwide translates into hundreds of gigawatts of flexibility that are already built into the power system.

Because these power plants and other sources of flexibility have already been built, it is almost always much cheaper to use this flexibility than to build new sources of flexibility like energy storage facilities.

Even if these sources of flexibility are eventually saturated, a number of additional low-cost sources of flexibility can be deployed, such as building additional transmission, encouraging additional demand response resources, reforming grid operating procedures, or making the generating fleet more flexible. While continuing advances in energy storage technology can make it more economically competitive as a provider of grid flexibility, it is important to remember that resources like wind energy can already be cost-effectively and reliably integrated with the electric grid without energy storage.

Small island power systems like Hawaii’s are a highly unique case, since geography prevents them from sending excess electricity to neighboring regions, there is often limited access to sources of power system flexibility, the power grid is often very weak, and the price of electricity is often high.

Under these very unusual circumstances, projects like the one discussed in Mr. Wald’s article can make economic sense. However, it would be erroneous to extrapolate from these very unique cases to assume that storage is essential for integrating wind turbines, a conclusion that is strongly contradicted by the success of countries like Spain, Germany, Denmark, Portugal, and Ireland reliably and cost-effectively obtaining 10% or more of their electricity from wind farm without adding any storage resources. On several occasions, the main grid operator in Texas has obtained 20% of its electricity from wind energy, also without the use of energy storage.

The National Renewable Energy Laboratory (NREL) has reached similar conclusions about energy storage.

Quote : At present levels of wind penetration on the electrical grid, storage has not been a priority consideration. But eventually, as a system resource and not exclusively due to wind or other renewable resource capacity additions, the nation’s electrical grid will benefit from energy storage technologies. Essentially, the power system already has storage in the form of hydroelectric reservoirs, gas pipelines, gas storage facilities, and coal piles that can provide energy when needed. Read more about how power is balanced on the electricity grid. Today, storing electricity is more expensive than using dispatchable generation. In the future, through advances in technologies such as batteries and compressed air, energy storage may become more cost-attractive.

NREL has also developed an excellent conceptual diagram, which can be found at the top of this blog post, illustrating the wide variety of low-cost flexibility tools grid operators have at their disposal.

The diagram diagram shows that grid operators already have a number of tools for reliably and cost-effectively accommodating variability on the power system, including incremental variability introduced by wind energy. Europe and many parts of the U.S. have already successfully used these tools to integrate large amounts of wind energy.

By Chris Madison,