RATE OF GROWTH IN ENERGY STORAGE
CONNECTED TO THE U.S. POWER GRID
BETWEEN 2017 AND 2018
Large andin Charge_To build a truly green electrical grid, you need
more than just solar farms and wind turbines.
You also need some very, very big batteries.
RENEW
SOMETIMES THE SUN JUST SHINES TOO
brightly on California. The state is such a
glutton for solar energy—a million solar-
paneled rooftops, hundreds of enormous
solar stations—that it routinely harvests more
megawatts than people can use or the grid
can handle. During a couple of cloudless
weeks in March 2017, California actually
had to pay Arizona to siphon off the sur-
plus. More often, though, the solution is to
reduce the gush of solar to a trickle, a pro-
cess called curtailment. And at night, when
the sun isn’t shining? The state must make up
the difference by burning fossil fuels. Right
now, California gets about a third of its elec-
tricity from renewables. To banish all car-
bon emissions from the system by 2045, as
a recent law requires, it will have to find a
cleaner way of bringing balance to the grid.
A few years ago, San Diego Gas & Elec-
tric, the state’s third-largest private utility,
teamed up with Sumitomo Electric, a Japa-
nese manufacturing giant, to test a possible
solution. In the dusty hills just east of San
Diego, they have installed a pair of so-called
vanadium flow batteries, capable of stor-
ing enough energy to power 1,000 homes
for four hours. Erase your mental image of
the compact lithium-ion battery that’s rid-
ing in your back pocket or the trunk of your
Prius. These vanadium batteries are big.
Each one consists of five shipping contain-
ers’ worth of equipment, eight 10,000-gallon
BYEva Holland ILLUSTRATION BY Jan Siemen tanks of electrolyte solution (the stuff that