Report: Gravity-based energy storage could prove cheaper than batteries

Storing energy by suspending weights in disused mine shafts could be cheaper than batteries for balancing the grid, new research has found.

According to a report by analysts at Imperial College London and seen by BusinessGreen, gravity-fed energy storage systems can provide frequency response at a cost cheaper than most other storage solutions.

Gravity-fed systems use a heavy weight – up to 2,000 tonnes – suspended in a deep shaft by cables attached to winches. When there is excess electricity, for example on a windy day, the weight is winched to the top of the shaft ready to generate power.

This weight can then be released when required – in less than a second – and the winches become generators, producing either a large burst of electricity quickly, or releasing it more slowly depending on what is needed.

The Imperial analysis is based on a levelised cost of storage (LCOS), a calculation which takes into account all relevant performance factors including a project’s capex, operating costs, discount rate and degradation costs over a 25-year period.

 According to the paper, gravity-fed storage providing frequency response costs $141 per kW, compared to $154 for a lithium-ion battery, $187 for lead acid batteries and $312 for flywheel.

The numbers assume the storage performs 700 cycles per year of 15 minutes each, at a power output of 4MW, to help manage the real time grid balance between system demand and total generation.

Charlie Blair, the managing director of Gravitricity – a UK start-up which earlier this year won £650,000 of government backing to test its gravity-fed technology – said the research demonstrates the cost competitiveness of gravity-based systems.

“This independent report clearly shows that Gravitricity can be a very strong competitor in the frequency response market, where its low specific power cost and high cyclability sets it apart from other technologies,” he said. “Lithium batteries are just beginning to be a major provider of frequency response services around the world and we expect early Gravitricity projects to take an increasing proportion of this market.”

Despite its high upfront cost, the paper argued that unlike battery-based storage systems, gravity-fed solutions have a long lifespan of more than 50 years and aren’t subject to degradation. This means they could cycle several times a day – allowing them to ‘stack revenues’ from different sources.

SOURCE: Business Green