The Scottish Government has just given consent to utility Scottish and Southern Energy (SSE) to convert the Coire Glas into Britain’s biggest battery. Picture courtesy of Scottish hills.
I am instinctively in favour of pumped storage as a means of load balancing. The UK’s 4 existing pumped storage schemes were built to store surplus nuclear and coal base load power produced at night and to release this energy into the late afternoon peak in electricity demand. Coire Glas is different, designed to store surplus wind power produced when it is windy and to release that energy when it is not. It is a massive beast, but does it make any sense?
Information is from this non-technical summary from SSE.
- 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
This is the equivalent of a large combined cycle gas turbine with capacity to run for a little over 2 days before needing to be recharged.
A massive but puny beast
The idea is to pump water into the reservoir when it is windy. The UK wind carpet recently produced 6GW peak output and so let’s assume that 3 of those 6GW were used to pump water into Coire Glas and other such schemes, and 3GW got fed directly onto the grid. If we are to have a renewables based system that can run independently of fossil fuel back up then it needs the stamina to survive a 7 day lull in the wind. So what we need to know is the amount of storage for 3GW of supply to run continuously for 7 days. This also assumes that we had 7 days producing 6GW of wind beforehand to fill the reservoirs – and we are still light years away from achieving that!
3GW * 24 hours * 7 days = 504 GWh of storage
That is 17 times greater than Coire Glas and 3 GW is only about 5% of UK peak demand. Coire Glas, therefore, is simply window dressing in efforts to “Green” UK power supply with pylons, turbines and dams.
There are different ways to skin this cat. How much power could Coire Glas provide operating continuously for 7 days?
2 / 7 * 600 MW = 171 MW
Which is also puny compared with the scale and cost of this structure and when compared with UK peak demand that is of the order 50,000 MW.
A partial solution
It may no doubt be argued that Coire Glas is only meant to be part of the load balancing solution which is fair enough. But what this means is that we are getting wind turbines, lots and lots of them, pylons and dams and still need to keep virtually all of the legacy fossil fuel plant going to provide back up power when the wind isn’t blowing. We are heading for an effective doubling of our energy infrastructure – Green irony!
SSE have conducted an environmental impact assessment. One question I had was about the impact of pumping water from and release of water into Loch Lochy and subsequent impact upon the flow of the River Lochy. The Coire Glas will be run in conjunction with other hydro schemes in the area to ensure stable water levels in Loch Lochy.
No free lunch in the energy world
My 2050 pathway, that I hope to present to this forum soon, currently includes 90 GW of nuclear power plus 4 GW of pumped storage that I envisage being deployed along the Great Glen in sites similar to Coire Glas. This scheme goes some way towards providing that – a good hedge for SSE. Pumped hydro for Nuclear requires more muscle and less stamina and so I wonder if the Coire Glas scheme could be adapted to provide 2400 MW for 12 hours? Turbulent times perhaps for Loch Lochy. Delivering 2400 MW for 12 hours every day seems much more valuable than 171 MW for a week – though I wonder if the battery could be charged in time?