Scotland is to get a new pumped storage hydro scheme, not in the Highlands but in the Scottish Borders. With a capacity of 400 MW and an estimated 1.7 GWh of storage this plant can make a meaningful 4 hour contribution to peak generation every day. But wooly arguments made about smoothing intermittent renewables makes it unclear if this commendable strategy is the intended use.
The Glenmuckloch pumped storage hydro scheme is to be owned and operated by Buccleuch, a company that owns and operates Estates in southern Scotland, in partnership with 2020 Renewables. The scheme is located on the site of a recently abandoned open cast coal mine, that will form the lower reservoir, and one of the objectives is to rehabilitate the land. The upper reservoir will be located on a high ridge above the mine. The high ridge will also host a new wind farm and the scheme therefore has much in common with the Gorona del Viento scheme on El Hierro that has been subject to exhaustive analysis by Roger Andrews and the Energy Matters readership.
This excellent presentation provides an overview and a handful of pictures from the presentation is the best way to describe the scheme:
Figure 1 The now disused Glenmuckloch open cast coal pit. In Scottish, glen=valley, muck=dirt and loch=lake. And since I cannot find a proper place that is actually called Glenmuckloch, I will speculate that this dirty pond is it. The lower reservoir will be located in this void. The upper reservoir on the grass covered ridge above, just in front of the barely visible trees.
Figure 2 What the site looks like on Google Earth. The pit is located close to the town of Kirkconnel. Note the grassy ridge to the N, backed by a forest, that will host the upper reservoir and a wind farm.
Figure 3 Map showing similar view to the GE image (Figure 2) and the locations of upper and lower reservoirs.
Figure 4 Detail of the site layout with locations of wind turbines around the upper reservoir.
Figure 5 Schematic of how the scheme will work. Left shows water draining from the upper to the lower reservoir, generating electricity. Right shows water being pumped up the hill into the upper reservoir, drawing electricity from the grid. As a rule of thumb schemes like this are about 90% efficient. That means it will generate just 90% of the power it consumes. So how does this work financially?
The vital statistics I found in the excellent presentation are as follows:
- Generation capacity 400 MW
- Volume of water 3.3 million m^3
- Cost £150 million
But the most vital statistic of all, the storage capacity, is absent from all the documentation I can find, and an omission like this always makes me a little suspicious. So I have had to get the back of my envelope out once again.
Using Google Earth, I estimate the upper reservoir is at 430 m and the lower at 230 m giving a fall of 200 m.
The Engineering Tool Box says this:
- Thus lifting 10m^3 of water by 10 m produces a store of 0.27 kWh.
- ….lifting 10m^3 of water 200 m produces a store of 5.4 kWh
- ….lifting 3.3 million m^3 of water 200 m produces a store of 1.78 GWh
I have been concerned about getting this sum right and so I have compared with the Cruachan pumped storage scheme that has the following statistics:
- Volume = 1o million m^3
- Head = 396 m
- Storage = 10 GWh
(3.3/10)*(200/396)*10 GWh = 1.7 GWh for Glenmuckloch. Thus I’m happy that the storage capacity of Glenmuckloch is of the order 1.8 GWh. What does this mean?
The vital statistic here is that operating at 400 MW, the reservoir can produce power for 4.5 hours. This is a very useful unit of energy to have that can be produced into the 6 pm ± 2 hours demand peak every day thus saving on 400 MW of fossil fuel peaking plants. So what’s not to like?
My Main Gripe
My main gripe with this scheme is the business premise upon which it is based. Buccleuch say this in their nice presentation:
- Will help in securing electricity supplies by balancing electricity demand with intermittency of some types of generation;
- Increases the availability of renewable electricity at times of peak demand, thereby supporting the security of renewable energy supply, increasing the diversity of energy supplies and reducing carbon emissions;
And the Scottish Government had this to say:
“The Scottish Government believes there is a huge opportunity around pumped storage hydro. This tried and tested technology can support peak demand and effectively store greater levels of electricity at times when renewable energy output is high but demand is low.”
These statements are worded very carefully in an effort to be true but are in fact deceptive half truths trying to be all things to all people. It is true that pumped storage hydro is a very useful energy technology that can be used to support peak demand and this scheme is ideally scaled for this purpose. But it is only useful in this context if it is available to support peak demand every day. And it is there that the fantasy about storing surplus renewable electricity turns this half truth into a non-truth. Figure 6 is a reminder of what the real world of wind looks like
Figure 6 UK wind production in September and October 2015 from BM reports as reported by Gridwatch. Only large HV connected wind farms are captured by these data.
Over 2 months, Figure 6 shows 9 episodes where it was windy (>3 GW wind at UK level) followed by lulls where it was not. The elegant plan to store the high wind peaks for use when the wind drops (as illustrated with high wind peak “2”) turns out to be a Green fantasy for at least two reasons. The first is that to make the investment in pumped storage economically feasible, it normally has to be used every day, unless another new “market mechanism”, otherwise known as a subsidy, is introduced to make it viable to store this energy for weeks on end. In this two month period, there are really only 9 opportunities, if that, to store surplus wind and dump the stored energy into the troughs. And so, instead of the daily opportunity to make money, this is reduced to once every 9/61 = 0.15 days owing to the stochastic nature of wind.
The second reason is the scale of the surplus peaks and deficit troughs. The > 3 GW surplus of “peak 2” I guestimate to be about 50 GWh and the following trough of similar magnitude. Therefore we need around 28 Glenmucklochs to properly address this intermittency issue that in this example is scaled at only two days duration. In the real world, the wind blows nowhere in Europe for several days on end.
I described the currently shelved Coire Glas pumped storage scheme as a massive but puny beast. Let’s revisit the vital statistics:
- Generating capacity = 600 MW
- Storage capacity = 30 GWh
- Generating duration at capacity = 50 hours
- Cost £800 million
- 5 years to build
- 150 workforce during construction
- 12 permanent jobs
We see that Coire Glas is 30 GWh / 1.8 GWh = 17 time bigger than Glenmuckloch for £800 million / £150 million = 5 times the price. But the operator of Coire Glas that is the FOOTSIE listed Scottish and Southern Energy has not gone ahead with the scheme because the financials are not right. RIGHT!
So what makes Glenmuckloch different to Coire Glas? There we need to look into the traditional model for pumped storage hydro in the UK, France and elsewhere. In the UK and Scotland, power is cheap at night when our nuclear power stations relentlessly churn out electricity at a time when it is not really needed. The operators of pumped storage buy this cheap power, store it and sell it into the high price daily peak demand period of 6 pm ± 2 hours, every day. Coire Glas is too big for this role but Glenmuckloch is not.
And so I want to throw down the gauntlet to Baccleuch. If Glenmuckloch is genuinely going to store surplus renewable energy for use at times of scarcity let us see the numbers and provide assurances that this is not yet another Green scam aimed at fleecing the consumer. If, on the other hand, Glenmuckloch is a commendable scheme designed to store nighttime surplus for use in the daytime peak then say so, and in doing so, enlighten Scotland’s deluded politicians.