Pumped Storage and Electricity from Wind Farms

Dave Windle

The recent announcement of the proposed pumped storage scheme at Dores, above the eastern side of Loch Ness (www.redjohnpsh.co.uk), made me start to think of what could be coming our way.

© ILI Group Red John Pumped Storage scheme, Dores

We already have the SSE scheme planned for Coire Glas, to the west of Loch Lochy on the Caledonian Canal, and now being upgraded to higher capacity, although not for increased storage. http://sse.com/whatwedo/ourprojectsandassets/renewables/CoireGlas/.

Pumped storage schemes are needed because wind energy is intermittent, and some form of storage helps to balance the days when the wind isn’t blowing with the days when it is. At the end of 2017, there were installed wind capacities of 7.4 GW onshore and 0.2 GW offshore in Scotland, generating 46% of electricity consumption from wind energy. (For comparison, the capacity of Longannet, before it was closed, was 2.4 GW). There is a further 3.7 GW of onshore capacity and 4 GW of offshore capacity consented, and 2.1 GW of onshore capacity in the planning stage. We can expect wind generation in Scotland to more than double in the coming years. https://www.scottishrenewables.com/sectors/renewables-in-numbers.

If all this capacity was built, the difference between electricity produced on very calm and very windy days would be like switching 7 Longannet power stations on and off. Managing this scale of variation is a major challenge and energy storage is needed to help smooth out the peaks and troughs.

The economics driving storage of any form are very simple. Wind farms cost very little to run and so the operator will run them even when they are getting a low price for the electricity. This causes the spot price of electricity to fall to a low value when the wind is blowing, and, correspondingly, when the wind isn't blowing the price will rise to a point where it is cheaper to start up a gas-fired generating station (with its associated CO2 emissions). Spot prices can already vary by a factor of at least 6, and this ratio is likely to increase as wind generation makes up an increasing proportion of the total. Profits can be made by buying cheap electricity, storing it by pumping a lot of water up a steep hill, and, when the price is high, allowing the water to flow back down the hill to generate electricity. This is explained in a lot more detail in a report commissioned by the industry lobby organisation. http://www.scottishrenewables.com/publications/benefits-pumped-storage-hydro-uk. We can expect to see a lot more pumped storage schemes.

The difference in height between the upper and lower reservoirs is a key factor in determining the capacity of the scheme, strongly favouring mountainous terrain. Another, albeit lesser, factor is nearness to nearby wind farms (to minimise transmission losses). Such schemes are likely to be developed in Scotland and, to a lesser extent, North Wales.

However, it is not just a case of power generator profit. We, as the consumers, should want to see increased storage. Switching gas-fired generation on and off is expensive and will lead to higher electricity bills. Pumped storage is also expensive, involving high capital costs and consuming say 25% of the energy stored. As in many things, we need a balance, not providing storage for 100% of the potential variation but finding the minimum additional cost for managing the intermittency of renewables.

Unfortunately, pumped storage schemes need to be very large to store an appreciable amount of energy. A look at Cruachan from the mountain ridge followed by a trip into the underground generating chamber leaves no doubt as to the scale of endeavour. However, all this work exists just to satisfy the national desire to make a cup of tea when the adverts come on. This means that some very large schemes would be needed to balance between the "high" and "low" wind days, particularly when a sustained period of high pressure such as happened in May/June earlier this year is taken into consideration. Coire Glas is three times bigger than Cruachan. We are likely to see proposals for even bigger schemes.

Leaving aside the landscape destruction, building the Glendoe conventional hydropower scheme above Loch Ness was a painful experience for all involved following the tunnel collapse. (https://en.wikipedia.org/wiki/Glendoe_Hydro_Scheme) So, companies are likely to be cautious about committing to very large schemes, but we should expect to see a steady stream of applications over the coming years. The costs are likely to reduce as we gain experience in building them. Might we see a return of the Balmacaan scheme to the west of Loch Ness or of the Loch Sloy scheme?

However, pumped storage is far from a complete answer. To build sufficient capacity to cover us for an extended period of high-pressure weather is not feasible. Despite the hype, other storage technologies, such as the giant battery supplied to South Australia by Elon Musk, are a long way behind. It stores 1.3% of the energy stored at Cruachan! We need to build more connectors with other countries, to make use of both their existing hydropower and their wind generation (it's rare for the wind not to be blowing somewhere in Europe). The growth of solar photo-voltaic, another intermittent source but with different highs and lows, will help to ease the overall storage problem. Demand reduction is an important step on the way to reducing our overall energy use but won’t help dealing with intermittent renewable energy sources. We need to start learning how to manage demand using smart meters and variable pricing. More connectors and steps to manage demand will reduce pressure to build more dams in our mountains.

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