Will Gravel Batteries Improve the Energy Efficiency of Solar Panels and Wind Turbines?

Jul 16, 2010· 1 MIN READ
Salvatore Cardoni holds a political science degree from the George Washington University. He's written about all things environment since 2007.
What to do when the wind won't blow? (Photo: Christian Charisius/Reuters)

Two clean energy technologies long thought to be silver bullets in the heart of climate change—solar and wind power—have an inherit flaw: intermittency.

What to do when the sun goes down and the wind stops blowing?

Install a giant battery that can store the energy using gravel, says Isentropic, a British energy company behind the new idea.

"If you bolt [the giant battery] to a wind farm, you could store the intermittent and relatively erratic energy and give it back in a reliable and controlled manner," said Jonathan Howes, Isentropic’s founder, to the Guardian.

The step-by-step process behind the technology isn't so complicated:

1) Two silos filled with rock, such as gravel, would be installed on the solar or wind farm.

2) A gas is fed into one of the silos, heating the gravel to around 932 degrees Fahrenheit.

3) After leaving the first silo, the gas is fed into the second silo. This gas-swapping process acts like a refrigerator, forcing the gravel inside the second chamber to drop to -256 Fahrenheit.

4) The energy—which originated from the solar panel or wind turbine—is then stored as a temperature difference between the two silos.

5) To release the energy, the cycle is reversed. As the energy passes from hot to cold, it powers a generator that makes electricity.


Don't worry—all the lay person really needs to grasp about this process is the economics.

According to the Guardian, Isentropic “claims a round-trip energy efficiency of up to 80 percent and, because gravel is cheap, the cost of a system per kilowatt-hour of storage would be between $10 and $55.”

Isentropic says that its gravel battery idea is a far cheaper method than the alternative: pumped hydro—where leftover electricity is used to force water up a hill. The water is impeded by a dam until the energy is needed, when it is released down the hill, turning turbines and thereby generating electricity.