System Stores Energy for the Grid – Using Gravel

Cabe Atwell

August 8, 2014

2 Min Read
System Stores Energy for the Grid – Using Gravel

British scientists from Isentropic have found a way to use gravel to store collected energy from renewable sources reliably and efficiently.

Gathering power from renewable resources such as solar and wind is on the rise, but has yet to be implemented as a primary source of power, due to inefficient grid-scale storage. Simply put, current methods of energy storage fail on a technical scale. Most storage methods rely on chemical (battery) solutions, such as molten salt or hydrogen-based battery backups to pump out power when it cannot be collected.


Isentropic's solution does away with conventional storage means and instead, adopts a thermodynamic approach known as Pumped-Heat Electricity Storage (PHES). The system uses two large-scale silos that are both filled with regular, ordinary gravel. The silos are connected to each other by a series of pipes filled with the inert gas argon, which is compressed using a heat-exchange pump until the temperature of the gas rises to around 500°C.

The superheated gas is then pumped through the first gravel-filled silo and imparts that heat to the stored rocks. The gas then expands and as a result, becomes cooler (-150°C) and is pumped into the second silo, where it cools the gravel. The resulting temperature difference between both silos is capable of generating electricity by reversing the process.

This means that the electrical energy collected by renewable resources can be used to kick-start the PHES process and thereby keep the grid flowing with juice even on cloudy, windless days. OK, so it isn't really leaps and bounds more efficient in its energy storing capabilities, since it has a "store/discharge" energy rate of 72%-80% of efficiency, but it's better than the 74% maximum for pumped hydro-based facilities.

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About the Author(s)

Cabe Atwell

Cabe is an electrical engineer, machinist, maker, cartoonist, and author with 25 years’ experience. When not designing/building, he creates a steady stream of projects and content in the media world at element14,, MAKE ─ among others. His most recent book is “Essential 555 IC: Design, Configure, and Create Clever Circuits.

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