Clean Energy | Article

The Continued Rise of Energy Storage

Utilities tackle energy supply and demand through advanced batteries and other methods.

Written by: R.P. Siegel

In the energy storage industry, the quest for improved battery technology is an opportunity for engineers. While mobile electronics and electric vehicles typically garner most of the attention in this realm, a shift in power generation sources has created a substantial need for utility-scale batteries, as well.

The two main goals of energy storage are to supplement and fill in for the renewables when their generation falls below rated output, and to capture excess clean power when supply exceeds demand.

“There are three things we can do with excess clean energy: Sell it, store it or spill it,” says Stephen Rourke, vice president, system planning at ISO-New England (ISO-NE), the regional transmission organization responsible for the entire New England region.

When there is excess energy available to the system, storage devices can absorb that excess energy until they’re full. Since the 1970s, New England has had very large pumped hydro storage facilities that can store up to 1,800 megawatts of energy per hour until the storage ponds are full. Meanwhile, the Electric Reliability Council of Texas, Inc. (ERCOT) manages the variability of wind resources through sophisticated wind forecasting tools, ensuring that other resources are available as needed when wind output decreases.

“We have not yet reached the point where the flexibility provided by the rest of the generation fleet is being exceeded by the variability in the wind resources,” says Warren Lasher, senior director of system planning at ERCOT. However, he acknowledges that point will potentially come as more renewables are added to the mix.

There is value to batteries in the ancillary services market because they can react to grid disturbances much more quickly than a conventional generation resource.
Warrant Lasher Electric Reliability Council of Texas

The state of large-scale batteries

Batteries can switch between storing and producing energy nearly instantaneously. However, the current fleet of large-scale batteries is only able to produce power at full capacity for little more than two hours. New technologies such as flow batteries should provide improved storage depth. Some projects in New England’s proposal queue are already specifying 8-hour battery storage. A pilot installation in San Diego is using flow batteries to provide four hours of storage.

While mechanical engineers working on conventional batteries mostly focus on materials, packaging and thermal management, much larger flow batteries involve the additional elements of pumping and fluid flow. These fluid electrolytes are pumped from separate tanks and through the stack for a charge. As these flow batteries get bigger, the capacity increases as well.

In the near term, batteries will mostly be used for ancillary services such as frequency regulation, operating reserves for contingency and flexibility, and to restore power after an outage.

“There is value to batteries in the ancillary services market because they can react to grid disturbances much more quickly than a conventional generation resource,” Lasher says.

Rourke adds, “They can also provide arbitrage in the energy market, [buy low/sell high]… or participate in our ancillary services markets or capacity market.”

The flood of battery storage facilities that are already lining up to get connected to power grids across the United States will provide a more responsive, cleaner tool for managing both fluctuations in supply and demand that increasing renewables will bring. While supply will fluctuate with weather patterns and daily cycles, demand will be affected by homeowners that purchase their own rooftop solar (behind the meter) installations.

Another method to tackle energy supply and demand is using quick response, or just-in-time assets, that usually take the form of quick-start natural gas or coal plants that are standing by, and ready to be switched on to the grid at a moment’s notice. These are also sometimes called “non-spinning reserves.” Lasher says ERCOT’s roughly 60,000 MW of flexible dispatchable generation assets has allowed it to incorporate some 22,000 MW of wind power (the most in the U.S.) without much trouble.

Finally, regional utilities east of the Rockies, except Texas, are interconnected and exchange power with each other, generally with neighboring states.

As renewable energy sources grow in popularity, the need for smart energy storage solutions will only increase. Engineers will be at the forefront of these innovations.