Several banks of 100-kW ultracapacitors (right) in a 20-ft shipping container can store 1 MW and discharge it for as long as 60 sec. The capability allows for VAR support, regulation up and down, and renewable-energy firming for wind and solar-power smoothing.
Ultracapacitors are similar to batteries in that they can store energy but with a significant advantage in that they can charge and discharge quickly, in a matter of seconds. Another plus: ultracapacitors are excellent at cycling – some are rated for a million cycles. On the downside, they store less energy than batteries of similar sizes.
Engineers at Maxwell Technologies now provide them in a size to store 1 MW and discharge it in as little as 60 sec., a power capability that makes them well suited for improving the power-quality output of individual wind turbines or full wind farms. “As wind conditions vary, power output and resulting voltage levels can vary by 10% of the average output power,” says Maxwell spokesman Michael Eliseo. When voltage spikes occur, ultracapacitors can absorb the energy and release it at the right time to prevent dropouts, and in the process, smooth voltage to the grid. “Because most grid events span milliseconds to a minute, ultracapacitors provide the most cost-effective, maintenance-free solution for power quality problems,” says Eliseo.
As renewable-energy sources become more widespread, the percentage of grid power met by renewables increases making grid stability increasingly important. “With ultracapacitor energy storage, it is easy to design scalable systems with lifetimes over a million charge-discharge cycles and at 100% depth of discharge,” adds Eliseo
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