The sun doesn’t always shine, the wind doesn’t always blow and the water doesn’t always flow when people want it to. Thus, the problem for renewable energy — if the sun, wind and water become America’s main sources of power, how will the grid function when those sources aren’t generating?
That is, perhaps, the largest reason why the country is focusing so much on energy storage at the moment. There are other reasons: Energy storage can help grid-managing entities flatten out the peaks and troughs in demand, and regulate voltage and frequency, helping it avoid upgrading or building expensive new infrastructure. Energy storage can help keep critical services like police, shelter and medical care working in the event of an emergency. It can help avoid blackouts, and bring the grid online faster when a blackout does happen.
But storage can be expensive, on the order of millions of dollars when it’s built at utility scale. Industry observers have noted that research efforts and increasing production capacity are helping the prices of batteries come down, but they are still relatively scarce compared with the size of the country’s generation capacity.
There are also many different ways of storing energy. Tesla Motors, BMW and other automakers are betting on chemical storage in batteries, and that’s the technology many homeowners with rooftop solar panels are beginning to look to in order to get the most out of their small-scale photovoltaic installations.
But utilities are beginning to look toward the idea of large-scale batteries as well. In California, regulators are requiring the state’s largest utilities to procure certain amounts of energy storage, and Pacific Gas & Electric has begun signing contracts for batteries. In Minster, Ohio, a municipal utility used a battery array to make the financing for a village-scale solar installation work in its favor. Data from the U.S. Energy Information shows that utility-scale battery projects are coming online every month.
And then there’s the looming presence of the electric vehicle. Though the cars are still relatively scarce — HybridCars.com reports that battery electric vehicles have made up less than 1 percent of car sales in the U.S. so far this year — they hold the potential to provide storage to the grid because of the size of their batteries. The California Independent System Operator recently received federal approval for a program that would allow entities to aggregate electric vehicle owners together into groups and tap into those batteries to store and pull out energy when needed.
But a more established technology is pumped hydro-storage — it’s so established, in fact, that the U.S. Energy Information Administration divides storage capacity into “hydro” and “non-hydro” pools. The concept is mechanical: Using electricity, water is pumped into an elevated reservoir, where it sits until whoever is managing the water is called upon to generate electricity. Then that entity releases the water, allowing it to flow downhill over turbines that generate power. The Energy Storage Association reports that the process can achieve 80 percent efficiency, meaning the downhill trip produces about 80 percent of the amount of energy it took to pump the water uphill in the first place.
A similar concept, set to make its debut in Nevada in 2017, is called rail storage. The idea simply substitutes water for trains — trains that can be filled with heavy objects, then rolled uphill. When the managing entity needs to generate power, it lets the trains roll back downhill, using motors to create electricity.