"Developing cheap energy storage is a critical step in moving to renewables and away from fossil fuels as the primary source of electricity: it’s the only way such intermittent sources can supply power to the grid when the wind’s not blowing and the sun’s not shining.Duke Energy, the nation’s largest utility, is trying a novel strategy to tackle this challenge. At its Rankin substation, in North Carolina, it has installed a system of hybrid energy storage that combines a battery from Aquion Energy and ultracapacitors from Maxwell Technologies.The two technologies are complementary. The ultracapacitors, which are good for large, short-duration power surges, help supply power when the solar power on the grid fluctuates because of cloud cover. The Aquion batteries, which are better for storing energy over longer periods, can supply power later in the day, when the sun goes down and electricity demand rises. Combining the two using smart electronics enables the system to efficiently handle power demand over periods ranging from seconds to several hours. The system is the first of its kind at utility scale, says Thomas Golden, technology development manager for Duke."
from technologyreview.com ... full artcile can befound here.