Research from Imperial College London has concluded that suspending weights in disused mine shafts could be a cheaper way of storing energy for frequency response than using batteries.

Projects on the drawing board propose connecting weights of up to 2,000 tonnes to winches.

When there is a surplus of energy in the grid – on windy or sunny days – then the winches will pull the weights to the top of the shafts.

When the power is needed, the weights can then be released quickly to generate a burst of electricity from the winches – which will then act as generators – or they can be released slowly to give a longer flow.

Levelised cost of storage calculations

Academics calculated that gravity-fed storage providing frequency response would cost $141 per kW, compared to $154 for a lithium-ion battery, $187 for lead-acid batteries and $312 for flywheel.

Their calculations assume each storage device performs 700 cycles per year of 15 minutes each, at a power output of 4MW, to help manage the real-time grid balance between demand and generation.

The analysis was based on the levelised cost of storage (LCOS), which took into account the projects’ capital expenditure, operating costs, discount rate and degradation costs over 25 years.

> Find out more about Imperial College's energy storage work