The Batteries Behind The Power Lines

The battery under the hood of your car doesn’t look anything like the battery in your cell phone. They’re different on the inside as well, because they’re designed to perform specialized tasks.

Specialized batteries also play a part in running the nation’s grid of electric transmission and distribution lines. Researchers are looking for ways to improve these devices to keep the power flowing smoothly to you when you need it.

The long lines of poles and wires marching up and down the hills of Kentucky bring electricity to farms, homes, and businesses. That might look like all there is to the system. But controlling how the electricity flows through those lines involves split-second communications and other kinds of equipment that you don’t see.

In south-central Kentucky, Warren Rural Electric Co-op’s 5,571 miles of distribution lines run though eight counties. In key locations, communications towers provide vital links for voice and data from the central office in Bowling Green.

Reliable batteries for reliable electricity
Tom Martin, vice president of technical services at Warren, says, “At every communication point where we have microwave radio links, we also have storage batteries in place. Usually lead-acid, these batteries are similar to a normal car battery but up to four times larger. These batteries provide backup power when the primary distribution power is lost, and enable our communications network to continue to function until service is restored in the power lines. These batteries can provide energy for between four and six hours.”

Engineers describe these kinds of batteries as a “mature technology,” meaning they’re manufactured using materials and design features that are well-understood and have a proven track record. Martin says, “These batteries are built tough for use in a harsh environment, and they typically can last for 15 to 20 years.”

Another typical use of batteries within the grid involves substations that help control the flow of electricity. Warren Rural Electric Co-op has 36 substations within its service territory. If energy isn’t flowing through the distribution lines to a particular substation due to a problem somewhere in the system, there still has to be a separate source of energy to operate switches and other devices in the substation until the normal power is restored. For that backup power, each substation includes a rack of batteries, with the lead-acid style being the most common choice. Up to 24 batteries are connected to each other in a series and mounted in sturdy racks.

Over the years, this kind of instant backup power has become more important as the grid is modernized to include more electronic controls instead of old-fashioned flip-the-switch style circuit breakers and other devices. Martin notes that the batteries in substations are used more often than the ones in the communications towers, and typically have a shorter useful life, often just eight to 10 years.

No dimming, please
The electricity for Kentucky’s 24 distribution co-ops comes from three generation and transmission businesses:

• The Tennessee Valley Authority generates the electricity for five co-ops (including Warren)

• Big Rivers Electric co-op generates electricity for three co-ops

• And East Kentucky Power Cooperative generates electricity for 16 co-ops in 87 counties.

East Kentucky Power uses lead-acid batteries for communications networks and to control devices during power outages, just like distribution co-ops do. But generating electricity and transmitting it to the distribution co-ops presents special challenges that require a different kind of energy storage system.

The power running through the transmission lines must stay at a constant voltage. If that voltage goes up too high, it can damage equipment; if it drops too low, customers will notice things like lights dimming. When it dips toward unacceptable levels, the East Kentucky co-op needs a way to add more voltage quickly to keep the power flowing smoothly.

The best energy storage device for this situation is a capacitor.

Although often compared to a battery, a capacitor is quite different. A capacitor doesn’t use reactions among chemicals to store and release energy. Instead, a typical capacitor used in the electric utility grid uses two thin plates, usually made of a metal that will conduct electricity, separated by a material that does not conduct electricity. It’s all wound up tightly inside an insulated outer jacket, rather like a roll of paper towels inside a tube. Arranged on racks called “banks” that are about the size of a bread truck, these groups of capacitors are a vital part of each of East Kentucky’s many substations.

Darrin Adams, manager of transmission planning in the Power Supply Business Unit at East Kentucky, says, “The majority of our capacitor banks are not ‘on’ very often. Generally, they come on in the summer when the load is very high, or in situations when some other part of the system is not working, such as during a planned outage or during a weather event.”

Adams says, “We are adding between one and five new capacitor banks to our system every year because there is an increased demand for electricity. The banks are about the same technology as we’ve had over the years, but the devices that are used to switch the capacitors off and on within the banks are new and different today. They provide a much better interface for controlling the flow of power.”

Kentucky researchers
At UK’s Center for Applied Energy Research in Lexington, Steve Lipka and his team are working on improvements that will make capacitors even more useful. Capacitors have many advantages compared to batteries. Capacitors can charge and discharge much more rapidly than batteries. Capacitors don’t change chemically or structurally during the charging and discharging process, and they have a long life cycle. But batteries have one big advantage—a higher energy density. That means you can pack a lot of energy into the space available inside a battery.

Lipka says, “What we’re trying to do in our work here is take capacitors to another level, to make devices that have an improved energy density approaching that of battery systems. To accomplish this, we’re trying to develop better materials that can store greater amounts of electric charge.”

Lipka and his team are working with carbon materials that have been specially treated to extend the surface area with lots of micro pores. Just glancing at the piece of carbon it would look like it has a flat surface, but looking at it through a microscope would reveal lots of little nooks and crannies, like an English muffin. Lipka says, “This is very important because that extra surface area means there are more places to store the electrical charge.”

Lipka and his team also want to make capacitors with higher operating voltages. This new kind of capacitor would be about the size of a dishwasher or as large as a refrigerator. They could be hooked together to suit each situation. Work on this aspect of energy storage is in the very early stages of pure research. Completing the research will take about three years, with deployment in field tests at least five years away.

BIG BATTERY IN ALASKA

Golden Valley Electric Association, an Alaska co-op, is testing a $30 million energy storage system featuring a huge bank of special nickel-cadmium batteries, capable of storing and releasing 27 megawatts of power instantly into the grid for 15 minutes—that’s enough electricity for more than 13,000 homes. The battery energy storage system consists of 13,760 battery cells. Golden Valley co-op hopes the system will improve reliability. For more information, including a slideshow explaining this innovative technology, visit www.gvea.com/about/bess/bessslideshow.

Next month: Gov. Beshear’s energy plan