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All pumped up: making the case for hydro storage

Networks going green means utility scale electricity storage is in demand. As John Pullen reports, pumped storage hydro has a role – and the Highlands can provide an ideal location.

As we move to more intermittent and variable sources of generation, there is no doubt that energy storage will be an essential requirement of the modern electricity grid. 

The recently commissioned 50MW Statera Energy battery installation at Pelham, near Bishop’s Stortford in Hertfordshire, can store up to 50MWh of electricity in its seven 40ft containers, encompassing 150,000 lithium ion batteries. It is the largest single installation in the UK, yet it can supply back to the grid only for a maximum of one hour at full power. 

But there’s more than one way to stockpile power. Pumped-storage hydro (PSH) is a type of energy storage used by National Grid for load balancing. Surplus power is used to pump water to an upper reservoir. It is later released through turbines to produce electric power in periods of high electrical demand. 

A long-established mainstay of UK energy storage are the four pumped hydro storage schemes operating in Scotland and Wales. When constructed, the main purpose of these plants was to hold surplus overnight power from large nuclear and coal power stations for peak morning and evening demand. Despite the huge 2.8GW generating capacity and 24GWh storage ability of these schemes, no PSH schemes have been built in the UK in almost 40 years. 

Although on one level these are the most efficient form of energy storage, with no degradation in performance even over the expected 50year life, it is hard to justify the huge capital cost of these infrastructure-scale projects. 

The demands on the network are changing at a pace faster than new developments can be approved, let alone constructed. 

The energy group SSE has reworked its consented 600MW Coire Glas PSH scheme above the Great Glen to see if a much larger 1,500MW project can make financial sense against a shifting landscape of revenue opportunities. 

Demand for clean power can only rise with the expected rapid adoption of electric vehicles, domestic heat pumps and other technologies associated with modern living,

As reported in issue 16 of Energy Matters, National Grid uses the capacity market to incentivise flexible, fast-responding generation during peak times. Similarly, as noted in issue 15, National Grid is also procuring an ever increasing quantity of system services, such as enhanced frequency response to ensure the grid operates within strict parameters. 

Agile generators with flexible systems such as PSH can maximise these payments in addition to merely absorbing cheap electricity and re-selling it later at peak times, so called energy arbitrage. While combining or “stacking” these different revenue streams offers electricity suppliers additional income, the short duration and plummeting value of the available contracts make any new projects difficult to finance. 

Difficult, but not impossible. Intelligent Land Investments, part of ILI Group, is developing the 400MW Red John PSH scheme on the outskirts of Inverness. Close to several wind farms, with good grid infrastructure and suitable topography, this will pump water from Loch Ness to a manmade reservoir 200 metres above. 

The developers have clearly calculated that a consented PSH scheme has a rich financial future.