Is It a Lake, or a Battery? A New Kind of Hydropower Is Spreading Fast.

For a century, hydroelectric power has been synonymous with gigantic dams — feats of engineering that provide renewable energy but displace communities and destroy ecosystems.

New research released Tuesday by Global Energy Monitor reveals a transformation underway in hydroelectric projects — using the same gravitational qualities of water, but typically without building large, traditional dams like the Hoover in the American West or Three Gorges in China. Instead, a technology called pumped storage is rapidly expanding.

These systems involve two reservoirs: one on top of a hill and another at the bottom. When electricity generated from nearby power plants exceeds demand, it’s used to pump water uphill, essentially filling the upper reservoir as a battery. Later, when electricity demand spikes, water is released to the lower reservoir through a turbine, generating power.

Pumped storage isn’t a new idea. But it is undergoing a renaissance in countries where wind and solar power are also growing, helping allay concerns about weather-related dips in renewable energy output.

“Our data show that pumped storage is set to grow much faster than conventional dams,” said Joe Bernardi, who runs Global Energy Monitor’s hydropower tracker. “This trend is most pronounced in China, which accounts for over 80 percent of planned projects worldwide.”

Some of the largest systems produce enough energy to power two million average American homes for an hour.

Diagram of a pumped storage facility. When electricity is cheap, water is pumped to an upper lagoon that acts as a battery. When demand is higher, water flows downhill, generating power through giant turbines.

City of Hohhot

The upper lagoon is

basically the “battery.” When

electricity is cheap, it’s used

to pump water uphill, storing

it to generate power later.

UPPER

RESERVOIR

When electricity demand

exceeds supply, water is

released to race downhill,

spinning giant turbines.

GENERATORS

+ TURBINES

LOWER

RESERVOIR

Hohhot

Gobi Desert

has many solar

and wind projects.

City of Hohhot

The upper lagoon is

basically the “battery.” When

electricity is cheap, it’s used

to pump water uphill, storing

it to generate power later.

UPPER

RESERVOIR

When electricity demand

exceeds supply, water is

released to race downhill,

spinning giant turbines.

GENERATORS

+ TURBINES

LOWER

RESERVOIR

Hohhot

Gobi Desert

has many solar

and wind projects.

City of Hohhot

The upper lagoon is

basically the “battery.” When

electricity is cheap, it’s used

to pump water uphill, storing

it to generate power later.

UPPER

RESERVOIR

GENERATORS

+ TURBINES

When electricity demand

exceeds supply, water is

released to race downhill,

spinning giant turbines.

LOWER

RESERVOIR

Hohhot

Gobi Desert

has many solar

and wind projects.

City of Hohhot

The upper lagoon is

basically the “battery.”

When electricity is cheap,

it’s used to pump water

uphill, storing it to

generate power later.

UPPER

RESERVOIR

GENERATORS

+ TURBINES

When electricity demand

exceeds supply, water is

released to race downhill,

spinning giant turbines.

LOWER

RESERVOIR

Hohhot

Gobi Desert

has many solar

and wind projects.

City of Hohhot

The upper lagoon is basically

the “battery.” When electricity

is cheap, it’s used to pump

water uphill, storing it to

generate power later.

UPPER

RESERVOIR

GENERATORS

+ TURBINES

LOWER

RESERVOIR

When electricity demand

exceeds supply, water is

released to race downhill,

spinning giant turbines.

Hohhot

Gobi Desert

has many solar

and wind projects.

City of Hohhot

The upper lagoon is basically

the “battery.” When electricity

is cheap, it’s used to pump

water uphill, storing it to

generate power later.

UPPER

RESERVOIR

GENERATORS

+ TURBINES

LOWER

RESERVOIR

When electricity demand

exceeds supply, water is

released to race downhill,

spinning giant turbines.

Hohhot

Gobi Desert

has many solar

and wind projects.

City of Hohhot

The upper lagoon is basically

the “battery.” When electricity

is cheap, it’s used to pump

water uphill, storing it to

generate power later.

UPPER

RESERVOIR

GENERATORS

+ TURBINES

LOWER

RESERVOIR

When electricity demand

exceeds supply, water is

released to race downhill,

spinning giant turbines.

Hohhot

Gobi Desert

has many solar

and wind projects.

City of Hohhot

The upper lagoon is

basically the “battery.” When

electricity is cheap, it’s used

to pump water uphill, storing

it to generate power later.

UPPER

RESERVOIR

When electricity demand

exceeds supply, water is

released to race downhill,

spinning giant turbines.

GENERATORS

+ TURBINES

LOWER

RESERVOIR

Hohhot

Gobi Desert

has many solar

and wind projects.

City of Hohhot

The upper lagoon is

basically the “battery.” When

electricity is cheap, it’s used

to pump water uphill, storing

it to generate power later.

UPPER

RESERVOIR

When electricity demand

exceeds supply, water is

released to race downhill,

spinning giant turbines.

GENERATORS

+ TURBINES

LOWER

RESERVOIR

Hohhot

Gobi Desert

has many solar

and wind projects.

In recent years, China has accounted for about half of global growth in renewable energy. According to official documents, China will roll out more wind and solar capacity each year between now and 2030 than Germany currently has in total.

As renewables contribute more and more to China’s grid, the country is seeking ways to ensure that fluctuations in wind and solar output don’t leave the grid in the lurch. Some of that insurance comes from continued growth in fossil fuels, especially coal, which China has in abundance.

China’s pumped storage strategy won’t directly equate to a reduction in coal use. China has stopped financing coal projects abroad, but at home last year it approved the building of more coal plants than ever before. And it is already by far the world’s biggest user of coal, a particularly dirty fuel.

But even as China doubles down on coal, it is reducing the overall proportion of power it derives from it. China now leads the world in wind, solar and hydroelectric power capacity.

“For China, pumped storage is the winning horse to provide a flexible backup for wind and solar. It is cheaper than the other battery options and can store more energy,” said Liu Hongqiao, an independent energy consultant focused on renewables in China.

Pumped storage has also been critical in making the business case for renewable energy in China, Ms. Liu said, because the national grid is not prepared to take on 100 percent of the wind and solar energy in the pipeline. Some of it will have to be stored, if it isn’t to be wasted, she said.

“Coal in China isn’t going anywhere anytime soon,” said Cosimo Ries, an analyst at the research firm Trivium China. “But over the coming decades it will gradually become a flexible power source, and a lesser one compared to pumped hydro.”

Global Energy Monitor data shows another kind of hydroelectric technology becoming prevalent, particularly in mountainous places like Nepal. So-called run-of-river facilities are located, as the name suggests, on rivers, but don’t create giant reservoirs behind them.

Without the reservoir, power generation is dependent on seasonal water flows but is less environmentally damaging and less prone to catastrophic failures in tectonically active zones like the Himalayas. Hundreds of run-of-river facilities have been built or are in the pipeline across the world, though they tend to produce smaller amounts of power.

Environmental disruption isn’t the only reason conventional dams are becoming less prevalent. They are also bad at saving water because their reservoirs provide large surface areas for evaporation. And when installed on rivers that cross international borders, they can often lead to water disputes. Many rivers simply have too many dams already.

Hydroelectric reservoirs can also release considerable methane, a potent greenhouse gas, from microbes that thrive in these environments and as vegetation decomposes in flooded areas. According to Dr. Bridget Deemer, an ecologist with the U.S. Geological Survey, reservoirs could be the source of 3 to 7 percent of methane emissions caused by humans.