Critical to enabling a wholesale shift to variable sources of renewable power like solar and wind will be Utility-Scale Energy Storage which, alongside grid flexibility, places #77 on Drawdown’s list of climate solutions.
“When solar and wind power supplied a small fraction of the total electricity in the grid, their variability was not a major problem,” Drawdown notes, since “traditional fossil fuel-powered plants could adjust for any shortfalls without undue stress.” But as variable renewables “begin to account for 30 to 40% of total power,” the capacity to store electricity becomes imperative—both to avoid shortfalls that are currently accommodated by hugely polluting and expensive “peaker” plants, and to deal with power surpluses that would otherwise need to be discarded to avoid overloading the grid.
One well-established option for utilities looking to store large quantities of electricity is a pumped storage system, which involves “pumping water from lower reservoirs into higher ones, ideally 1,500 feet higher,” then releasing it as needed through power-generating turbines. “There are more than 200 pumped storage systems in the world at present,” notes Drawdown, “accounting for 97% of the global storage capacity.”
Where there is no water, “gravity can still be enlisted”—as in Nevada, where “mining railcarsfreighted with 230 tons of rock and cement are sent up to a rail yard 3,000 feet in height,” Drawdown explains. “Equipped with two-megawatt generators that act as an engine on the way up,” the railcars thumb a lift with gravity on the way down, while their “regenerative braking system converts rolling resistance to electrical power.”
Notably, both pump storage and the railcar option respond incredibly quickly to shifts in electricity demand, with ramp-up times to full power measured in seconds, compared to minutes or hours for fossil plants.
Newer but already proven storage technologies include a molten salt mixture used in concentrated solar power plants that “remains hot for five to 10 hours, and returns as much as 93% of the energy absorbed,” Drawdown notes.
And storage batteries will play an ever-more prominent role in grid-scale storage. “By 2021, Los Angeles plans to take its natural gas peaker plant offline, replacing it with 18,000 batteries that will be charged by wind power at night and solar in the morning.”