It may be mature technology but hydro is still a promising solution to the UK’s energy-storage problem. Helen Knight reports
It can be hard to imagine after the travails of a typically blustery winter, but the wind does not always blow in the UK.
This means the country’s increasing number of wind turbines, which provided 11 per cent of our electricity supply in 2015, are not always spinning at times of peak demand. Conversely, the wind often blows at night, when demand is low.
This can make life very difficult for the National Grid, which has to ensure there is always sufficient electricity available to meet demand. Last year, for example, UK wind farms were paid £90m not to produce energy at times of low demand.

Although the supporters of renewables counter that the difficulties of incorporating them onto the grid have been exaggerated, since wind speeds tend to vary across the country at any given time, thereby helping to balance out supply, the problem is likely to grow as their use increases.
To tackle this problem, two government-funded reports, both published in March, argue that electricity storage will need to play a significant role in the UK’s future energy mix.
The reports, by the National Infrastructure Commission and the Carbon Trust, both argue that energy storage could ease constraints on the grid by allowing excess electricity produced by generators to be siphoned off and used later when demand is higher. This could save the UK electricity system between £2.4bn and £7bn a year by 2030, depending on the regulatory framework in place.
The most mature of all the available energy-storage technologies is pumped hydro, in which low-cost electricity is used to pump water uphill to a reservoir at night, and the water is then allowed to flow back downhill during the day, to drive a turbine.
In order to utilise all or at least a significant portion of the available renewable energy, we will need a storage technology with a large capacity, according to Prof Ånund Killingtveit, department of hydraulic and environmental engineering at the Norwegian University of Science and Technology.
“Storage is expensive, and [pumped hydro storage] is really the only technology that can supply large, grid-scale storage at a low cost,” he said.
What’s more, the technology can respond to demand in a matter of seconds, he said. “With an ability to respond almost instantaneously to changes in demand or supply, pumped storage is an essential component in the electricity network.”
As a result, there is growing interest in increasing the UK’s pumped hydro storage capacity. Scottish Power said recently that it could add 400MW of on-demand electricity to the UK market by building a new dam in front of the existing one at its Cruachan plant near Oban, if it can secure a guaranteed floor price for its use from the government.
Meanwhile, UK firm Quarry Battery is seeking planning approval to build a new 99.9MW pumped hydro energy storage facility at Glyn Rhonwy in Snowdonia in Wales.
The project would see two disused slate quarries converted into the upper and lower reservoirs of the pumped hydro plant, according to Dave Holmes, managing director of Quarry Battery.
The plant will be equipped with two reversible-speed Francis pump turbines, which will act as a pump in one direction, to push the water up the hill, and as a turbine in the other, to generate electricity.
But it will differ from the existing pumped hydro stations in the UK in its use of a variable-speed drive, said Holmes. This should allow the plant to operate much more flexibly.

Variable-speed drives enable turbines to operate at peak efficiency over a larger portion of their operating band. They also allow a plant to quickly vary the amount of power it consumes in pumping mode, meaning it can be used to regulate the frequency of the grid by drawing off more or less electricity as required.
“This fast response can allow for compensation of power fluctuations and damping of power oscillations, and thereby improve the stability and frequency control of the power system,” said Killingtveit.
While the technology itself is not new – variable-speed pump turbines were developed and used in Japan in the 1990s – the age of many of the world’s pumped storage plants means it has yet to be applied in the UK.
For example, the UK’s largest existing pumped hydro station, 30-year-old Dinorwig in Snowdonia, has six single-speed turbines that can generate up to 288MW, said Holmes. However, the turbines cannot generate any less than 133MW, as operating at this level causes them to stall.
“With our scheme we will have a variable-speed drive, which enables us to go anywhere we like, from -100 to +100MW,” he said. “This allows us to be much more flexible, to follow the load and to carry out frequency regulation more easily.”
This will be particularly important at the quarry storage facility, where the reservoirs are deeper than conventional pumped hydro sites, said Holmes. This means there is a considerable change in pressure between the start of the day, when the upper reservoir is full and the lower reservoir empty, and the end of the day when the reverse is true, he said.
To cope with this, Glyn Rhonwy will need a slightly over-sized turbine, with a wider operating range than conventional plants. The variable-speed drive will help to manage this, said Holmes.
In a conventional, single-speed pump turbine, the magnetic fields of the stator and the rotor are coupled, and always rotate at the same speed.
In a variable-speed machine, in contrast, the magnetic fields are decoupled, for example, by using
a frequency converter between the grid and the stator winding.
The technology is more expensive and complex than traditional single-speed pump turbines, which operators will therefore need to take into account when weighing up the benefits of upgrading existing pumped hydro storage plants, or building new ones, according to Killingtveit.
But with the growth in the use of renewables, the greater flexibility that is offered by variable speed technology could allow pumped storage facilities to provide a larger, and far more lucrative, range of services to the grid.
Used in this way, the technology could give this most mature form of energy-storage battery a whole new lease of life.
Pump storage is fantastic for dealing with surges in demand or sudden lulls in the wind supply, but what happens when there is a stable winter “high” sitting over the UK for more than a week?
Notice that the article ignores energy. It only talks about power, as do almost all the web pages about Dinorwig.
I managed to track down the energy stored at Dinorwig as 9.1 GWh. That’s enough to supply the UK for 15 minutes. There are other pump storage facilities in the UK. Altogether they could supply us for 45 minutes (on an average day, shorter in Winter).
Yes we need more pump storage. Where there is an existing Hydro plant it may be easy to convert it. Just add a bottom reservoir and pump the water back up the hill when there is a plentiful supply, but there will still be a shortfall in a long cold winter.
I am in favour of building more pump storage facilities, but could we have betting reporting and include figures for energy as well as power.
Good point about considering the energy, but surely the point of Hydro will only ever be too smooth out the demand and account for peaks, it is not realistic to think it could be used as a base load.
“It is not realistic to think it (PHS) could be used as a base load.” – No, but conventional hydro is. The two are combined wherever sensible. Spain is a good example, as water conservation is highly valued. Even so, they have over-capacity and use curtailment to balance their network. Wind farm operators get no payments. The UK ‘system’ is ‘run’ according to an insane economic dogma.
http://www.windpowermonthly.com/article/1209700/integration-success-leads-easy-curtailment
“Last year, UK wind farms were paid £90m not to produce energy at times of low demand.” Yes, but constructing PHS is not an answer to that problem. The Spanish after-generator storage is the wrong technology. Before-generator energy storage is the only truly viable solution and the wind industry must build it, because their current technology is not fit for purpose, off-shore.
The location of energy storage is critical. Install pressurised water accumulators, which charge and discharge simultaneously, before-generator, and the system virtually controls itself. If your energy harvest from (marine) renewables is surplus to demand it is stored. When generation exceeds energy harvest, storage makes up the deficit. After-generator energy storage is a waste of money.
I managed to track down the energy stored at Dinorwig as 9.1 GWh. That’s enough to supply the UK for 15 minutes. There are other pump storage facilities in the UK. Altogether they could supply us for 45 minutes (on an average day, shorter in Winter).
Ian, your point is well made;
sorry to be pedantic but Dinorwig = 11.3GWh & we have a total of 78.6 GWh of pumped storage,
See this good article & comments,
Excellent article on the only available large scale energy storage technology. Am amazed that Dinorwig is limited by turbine turn-down: this seems ridiculous to me!
As a note to any engineer visiting / passing through the west coast of Scotland, Cruachan is well worth a visit. Even my wife was impressed by it.
Energy Fluctuations and Storage is not a new problem.
The following quotation by William Stanley Jevons in 1865 introduces chapter 26 of the book “Sustainable Energy – without the hot air” by the late Professor Sir David MacKay who sadly died last week at the age of only 48.
“The wind, as a direct motive power, is wholly inapplicable to a system of machine labour, for during a calm season the whole business of the country would be thrown out of gear. Before the era of steam-engines, windmills were tried for draining mines; but though they were powerful machines, they were very irregular, so that in a long tract of calm weather the mines were drowned, and all the workmen thrown idle.”
David MacKay, chief scientific advisor to DECC for 5 years until 2015, suggests in his book page 195 that the most promising option for balancing fluctuating demand and fluctuating supply, in terms of scale, is switching on and off the power demand of electric vehicle charging.
“However, the turbines cannot generate any less than 133MW, as operating at this level causes them to stall.” Somewhere in the depths of my memory is a recollection that this will result in cavitation: and this can seriously weaken (and eventually destroy?) the blades/vanes of the turbine? Anyone know more?
I do recall a lecturer in 1961 (yes, I studied Engineering that long ago…with a slide-rule, log tables and a Tee square, drawing board with drawing-pins! paper and pencil!) descrbing a scheme ( Loch Tummell?) that required the river at Pitlochry to incorporate a ‘salmon-ladder’ so that the fish had somewhere to spawn! Indeed if I recall he seemed more interested in that than the energy efficiency the system was supposed to offer.
If Hydro Storage can be managed by variable speed machines, then can why not use existing reservoirs? Water is drawn off at a steady rate from most large reservoirs, Cow Green, Haweswater etc to serve our hunger for water. If they have large dams or any good head of water why not make use of it. The steady energy rate might only be 200- 500 kW per dam, however we do have a lot of reservoirs scattered around the country.
On a similar note how does the National Grid (Gas) reduce the gas pressure from 40 bar plus to the 24 millibars used for domestic gas? The process used to be via steam heated expansion venturis. Why not used expansion work turbines and generate electricity at peak times ie when gas is at its peak domestic use.
Excellent article on hydroelectrics. With the excess power available offpeak can any of the existing sites benefit from pumping water rather than using say river flow?. Suggest some of the sites could be cost effectively enlarged for greater water capacity thus extra power output. Need to make good use of the high rainfall in our country, maybe control excess water runoff from mountains and the resulting flooding downstream.
James & Peter’s comments are surely excellent examples of Engineers’ (hopefully) natural ability to find solutions (or at the least pose valuable questions) between differing areas of technology. “Engineers do for 10 pence what any fool can do for £1.00” [Nevil Shute Norway – Engineer turned author and v popular in 30,40,50s] used that quotation at the start of many of his books.]
We do have a ‘national Infrastructure ‘body/plan/ committee’. Perhaps it ought to have a couple of good recent graduates constantly monitoring the views and comments made in our illustrious organ? If not, why not!
“This can make life difficult for the National Grid, which has to ensure there is always sufficient electricity available to meet demand.” Life is never difficult for a private monopoly – it’s a breeze.
An annual profit of £2bn is seen as the minimum they ‘deserve’ to extract from the UK economy. NG spends a miserly 0.1% of revenue on R&D. They spend their ill-gotten cash on mergers and acquisitions. It’s what big corporations do. There’s no profit in serving the nation. When I joined the industry in ’72 customer service was king and salaries reflected the contributions of all staff. Frontline staff (like me) were paid a bonus on performance. Managers were paid to perform.
“Storage is expensive, and pumped hydro storage is at present the only technology that can supply large, grid-scale storage at a low cost.” That’s why we needed innovative engineering, yesterday. I told NG about before-generator energy storage seven years ago, but they don’t do R&D.
“utilise all of the available renewable energy” means you never build the installed over-capacity of orthodox wind-power. The capex saving is more than enough to build the BGES option, integrated into wave/wind and tidal harvest. BGES means that nameplate capacity = storage capacity. It sets new paradigms in marine renewables and energy storage design, which would make a world of difference to the cost of network operations, and our bills.
My experience of contributing radical new design proposals to the National Grid’s ‘Operating2020’ consultation revealed why they put no investment into UK innovation. The main reference in 2009 was a report by Pöyry Energy Consulting – ‘Impact of Intermittency’
From the Follow Up Report – 2010:-
Question 38: Are there further aspects of storage or other storage technologies we should consider when looking forward to 2020?
“One respondent argued strongly that storage could be integrated into intermittent generation installations thus eliminating a range of issues raised within the consultation document. Another respondent wrote that investment would be stimulated if National Grid identified a requirement for storage.” Exactly so; when you design for BGES, intermittency is ELIMINATED.
Both of those respondents were ignored. NG didn’t identify the requirement, as it’s not their job!!
So their incompetent conclusions were published in NG’s final report: ‘Operating the Electricity Transmission Networks in 2020 – Update June 2011’:-
2.46 There is considerable value in storage across the entire supply chain but perhaps insufficient for any discrete part. “National Grid believes that suitable (taxpayers?) funding streams for using innovative storage technologies should be established so that they are developed and supported in the intervening years in order that all stakeholders can consider how such technologies could be applied, making them viable in later years.”
2.47 Whilst NOT considered within this paper, National Grid believes that large scale hydro such as pumped storage could provide the necessary system level flexibility and make a significant contribution to the security of supply. However it is difficult to identify how the economic investment would work within the current market framework
The “market framework” was and is ‘designed’ by ideologues in a vain (both senses of the word) attempt to prove that their neoliberal economic theory can be made to ‘work’. It has failed. It will always fail. At best it just hikes prices to attract more investment.
NG is forbidden by UK privatisation law from owning or operating any generation asset, and under that law energy storage is defined as ‘generation’!!! Neoliberal economics will never work without a FREE market. Corrupt laws are needed so that rigged markets can deliver the necessary corporate welfare to attract investment. It all ramps up our bills.
Yours sincerely, NG pensioner No. PU1NT******68. aka Dave2020
I propose 2 solutions which can provide all the energy storage needs of the UK.
1. A site in the Scottish Highlands suitable for pumped storage hydro development, which can be super-sized for British or European needs.
2. An offshore variant of power-to-gas energy storage – Deep Sea Hydrogen Storage.
1.
World’s biggest-ever pumped-storage hydro-scheme, for Scotland?
https://scottishscientist.wordpress.com/2015/04/15/worlds-biggest-ever-pumped-storage-hydro-scheme-for-scotland/
“The maximum potential energy which could be stored by such a scheme is colossal – about 6800 Gigawatt-hours – or 283 Gigawatt-days – enough capacity to balance and back-up the intermittent renewable energy generators such as wind and solar power for the whole of Europe!”
2.
Off-Shore Electricity from Wind, Solar and Hydrogen Power
https://scottishscientist.wordpress.com/2015/04/23/off-shore-electricity-from-wind-solar-and-hydrogen-power/
“The diagram shows how hydrogen gas can be used to store energy from renewable-energy platforms floating at sea by sending any surplus wind and solar electrical power down a sub-sea cable to power underwater high-pressure electrolysis to make compressed hydrogen to store in underwater inflatable gas-bags.
It’s potentially very cheap because no super-strong pressure containment vessels are required – the ambient hydrostatic pressure which is proportional to depth serves to compress the hydrogen gas to containable densities.”
Scottish Scientist
Independent Scientific Adviser for Scotland
https://scottishscientist.wordpress.com/