Intermittent renewables do not always generate energy when we want. This results in a huge need for storage, demand side response (DSR) and interconnectors to turn intermittent generation into dispatchable on-demand output. All are required, but a cost-effective grid needs each one to do their most appropriate roles.
Interconnectors
By 2040 most of Europe’s energy transition plans will rely on imports during “times of system stress”. But these are largely concurrent for neighbouring grids, for example after sunset on a windless winter evening. Interconnectors also have no inertia, so cannot support many aspects of grid stability. Each grid needs to have sufficient dispatchable power, and the interconnectors’ roles are to limit the cost of electricity.
Demand side response
DSR displaces short-duration demand mostly on distribution grids, limited in scale and duration (other than vehicle-to-grid, V2G) to 5-10 per cent of demand. V2G will add no more than around 25 per cent of their nameplate capacity. DSR units cannot be used multiple times in any period, so they must be subdivided to do so.
Batteries
Batteries are optimally up to 20MW, for 20-60 minutes, though some have greater capacity. Doubling their scale or duration increases capital cost by 70-80 per cent. They have outstanding responsiveness, but no inertia. Day one efficiency is 42-62 per cent grid-to-grid, the reduction from claimed 85-92 per cent efficiencies being principally cooling and AC/DC/AC power conversion. As cells deteriorate in five to 10 years, their cooling requirement roughly triples, reducing their average lifetime efficency further still.
Large-scale, long-duration storage
This is mostly pumped hydroelectric storage (PHES) and compressed air energy storage (CAES), suited to large scales and multi-hour to multi-day durations. Generation is inertial, providing grid stability. Their levelised costs of storage are much lower than batteries; PHES has few potential growth locations, mainly remote from both supply and demand. Traditional CAES burns lots of gas; similarly-priced adiabatic CAES burns none.
Storelectric’s CAES
Storelectric is developing innovative forms of CAES using existing technologies for 40MW to multi-GW installations, with durations of less than four hours, zero or low emissions, 68-70 per cent grid-to-grid efficiency and levelised costs cheaper than gas-fired power stations. The €/MW price is a third of pumped hydro and 1/75th per MWh. Levelised cost is already what batteries aspire to be by 2035 and their €/MWh is vastly cheaper. Most countries could store up to a fortnight’s worth of energy.
Storelectric is seeking funds to build a 40MW, 200MWh first-of-a-kind plant with more than 62 per cent efficiency (grid-to-grid) in three years; a 500MW plant will take longer. Storelectric’s second technology, CCGT CAES, is retrofittable to a suitably located gas-fired power station. It is cheaper, can almost halve emissions, and add storage-related revenue streams, re-lifing stranded assets.
Mark Howitt is founding director and CTO of Storelectric.
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