The Anonymous Widower

Drax’s Plans For Cruachan

Cruachan Power Station is a pumped-storage hydroelectric power station in Argyll and Bute, Scotland.

  • It can generate 440 MW of power.
  • It has a storage capacity of 7.1 GWh.
  • The power station is owned by Drax.

This Google Map shows the area around the power station.

Note.

  1. Cruachan Reservoir is the upper reservoir for the power station.
  2. The River Awe is the lower reservoir.
  3. The turbines for the power station are in a hollowed-out Ben Cruachan.
  4. There is a visitor centre, which is two-hundred metres from the Falls of Cruachan station, that can be seen on the map, by the river.

More information on visiting can be found at the Visit Cruachan web site.

This second map shows the Southern part of the  Cruachan Reservoir to a larger scale.

Note the strength of the dam.

The Operation Of Cruachan Power Station

Wikipedia says this about the operation of Cruachan power station.

The station is capable of generating 440 megawatts (590,000 hp) of electricity from four turbines, two of 100 megawatts (130,000 hp) and two of 120 megawatts (160,000 hp) capacity, after two units were upgraded in 2005. It can go from standby to full production in two minutes, or thirty seconds if compressed air is used to start the turbines spinning. When the top reservoir is full, Cruachan can operate for 22 hours before the supply of water is exhausted. At full power, the turbines can pump at 167 cubic metres (5,900 cu ft) per second and generate at 200 cubic metres (7,100 cu ft) per second.

What I find surprising, is that they only upgraded two turbines to 120 MW. I would suspect that there was some other factor that stopped all turbines from being upgraded.

So I would be very surprised if Drax upgraded the power of the existing station.

The Wikipedia extract claims that the Cruachan power station can provide power for 22 hours, if the reservoir, which has a capacity of 7.1 GWh is full. A simple calculation gives an average output in 323 MW. Does that indicate an efficiency of 73.4 %, by dividing 323 by 440.

But no pumped storage system of the 1950s is 100 % efficient. The Ffestiniog Power Station, which opened two years before Cruachan has an efficiency of 73 %. , which appears to be in line with the figures for Cruachan.

Cruachan Power Station And Nuclear Power

Wikipedia says this about Cruachan power station and Hunterston A nuclear power station.

Construction began in 1959 to coincide with the Hunterston A nuclear power station in Ayrshire. Cruachan uses cheap off-peak electricity generated at night to pump water to the higher reservoir, which can then be released during the day to provide power as necessary.

Note.

  1. Hunterston A power station closed in 1990.
  2. Hunterston B power station closed a few days ago.
  3. Scotland now only has one nuclear station at Torness.

It looks like the method of operation will have to change.

Cruachan Power Station And Wind Power

The obvious replacement source of energy at night to replace the nuclear power is wind power.

As I write this the UK is generating 8.5 GW of power from wind turbines.

Surely, enough can be diverted to Cruachan to fill the Cruachan Reservoir.

Cruachan 2

Drax’s plans for Cruachan are based around the building of a second underground power station, which is not surprisingly called Cruachan 2. This page on the Drax web site describes Cruachan 2.

  • It will be a 600 MW power station.
  • It will be to the East of the current power station.
  • More than a million tonnes of rock would be excavated to build the power station.

The existing upper reservoir, which can hold 2.4 billion gallons of water, has the capacity to serve both power stations.

I think it is reasonable to assume the following about Cruachan 2.

  • Design of the turbines will have improved in the sixty years since the Francis turbines for the original power station were ordered and designed.
  • The turbines will now be precisely computer-controlled to optimise the operation of the power station.
  • The turbines will have a faster response, than even that of Cruachan 1, which will help to match output to demand.

But most importantly, I suspect that the efficiency will be higher due to improved turbine design.

I can do a simple calculation, where I will assume the following figures for the two power stations.

  • Cruachan 1 – 440 MW – Efficiency – 73 % – Full Power – 323 MW
  • Cruachan 2 – 600 MW – Efficiency – 80 % – Full Power – 480 MW

It looks to me that 1040 MW can be used to store water in the reservoir and at this rate it would take 6.8 hours to fill the reservoir. With just Cruachan 1 in operation, filling the reservoir would take sixteen hours.

It looks like with moderate winds generating sensible amounts of electricity, it should be possible to fill the reservoir overnight using both Cruachan 1 and Cruachan 2.

When running flat-out, the combined station can generate 803 MW. At that rate it will generate the power for just under nine hours.

The Wikipedia entry for Francis turbines says this.

Francis turbines are the most common water turbine in use today, and can achieve over 95% efficiency.

Applying 95 % Efficiency to Cruachan 2 would give the following.

  • An output of 570 MW for Cruachan 2.
  • A total output of 1010 MW for the combined station.
  • This would mean the combined station could deliver 1.01 GW for just over seven hours.

Modern control technology would probably be used to ensure that the output of the combined Cruachan station filled in the gaps between demand and supply.

Could The Size Of Cruachan Reservoir Be Increased?

This would increase the amount of energy stored.

I suspect that it probably can’t be increased, as any increases would have been done by now.

Conclusion

It looks like very good engineering to me.

  • There is a good chance, that on most nights, the reservoir will be filled using wind energy
  • The maximum output of the Cruachan power station has been more than tripled from 323 to 1010 MW.
  • There has been no increase in the size of the Cruachan reservoir.

Scotland will now have a GW-sized hydro-electric power station.

 

 

January 11, 2022 - Posted by | Energy, Energy Storage | , , , , ,

1 Comment »

  1. It’s rather difficult to address some of the points

    Comment by fammorris | January 11, 2022 | Reply


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