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.
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