Supposing the electricity grid needs longer-duration energy storage to regenerate power of up to 40GW, as the Renewable Energy Association suggested in March 2021.
- Glasa Morie Glass, in Easter Ross – which I have scoped as suitable for an energy storage capacity of up to 170 GWh.
- Coire Glas / Loch Lochy, in Lochaber – where the SSE plan a scheme with capacities of 1.5 GW power / 30 GWh energy storage but the site is good for many times that power and energy storage by building a bigger size of dam etc. as necessary.
The graph’s x-axis is what power capacity in GW each scheme should be built to generate and the y-axis is the design duration time y in hours of regeneration at full power.
The power capacity equation for Glasa Morie Glass 170GWh is –
Power = 170/y GW
– where y is the duration in hours.
The power equations for Coire Glas / Loch Lochy are –
Power = T – 170/y GW
– where T is the total power in GW of both Glasa Morie Glas plus Coire Glas / Loch Lochy and y is the regeneration duration in hours.
The required energy storage capacity of Coire Glas / Loch Lochy is –
Energy = ( T × y ) – 170 GWh
So to use the graph, you pick a duration time in hours and note where the horizontal for that y value crosses
- the red line for Glasa Morie Glass 170 GWh, and
- the lines for Coire Glas / Loch Lochy – orange for T = 10 GW, purple for T = 20 GW, green for T = 30 GW and blue for T = 40 GW
and from the crossing points read vertically the power for either scheme from the x-axis.
Example – 5 hours
For example, suppose the required regeneration duration from energy storage is at least 5 hours at the full Total power T.
Glasa Morie Glass
Then the power capacity required from Glasa Moire Glass could be up to 170/5 = 34 GW.
Coire Glas / Loch Lochy
Then the power and energy storage capacity required to be built at Coire Glas depends on the total regeneration power capacity T required for the grid’s needs.
– 0GW for T = 10 GW (in this case Glasa Morie Glass 10GW / 50 GWh is all we need to build and we can leave the Coire Glas site undeveloped)
– 0 GW for T = 20 GW (in this case Glasa Morie Glass 20GW / 100 GWh is all we need)
– 0 GW for T = 30 GW (in this case Glasa Morie Glass 30GW / 150 GWh is all we need)
– 6 GW / 30 GWh for T = 40 GW
Example – 10 hours
For the next example, suppose the required regeneration duration from energy storage is at least 10 hours at the full Total power T.
Glasa Morie Glass
Then the power capacity required from Glasa Moire Glass could be up to 170/10 = 17 GW.
Coire Glas / Loch Lochy
Then the power and energy storage capacity required to be built at Coire Glas depends on the total regeneration power capacity T required for the grid’s needs.
– 0GW for T = 10 GW (in this case Glasa Morie Glass 10GW / 100 GWh is all we need)
– 3 GW / 30 GWh for T = 20 GW
– 13 GW / 130 GWh for T = 30 GW
– 23 GW / 230 GWh for T = 40 GW
Example – 15 hours
For the next example, suppose the required regeneration duration from energy storage is at least 15 hours at the full Total power T.
Glasa Morie Glass
Then the power capacity required from Glasa Moire Glass could be up to 170/15 = 11.333 GW.
Coire Glas / Loch Lochy
Then the power and energy storage capacity required to be built at Coire Glas depends on the total regeneration power capacity T required for the grid’s needs.
– 0GW for T = 10 GW (in this case Glasa Morie Glass 10GW / 150 GWh is all we need)
– 8.666 GW / 130 GWh for T = 20 GW
– 18.666 GW / 280 GWh for T = 30 GW (practical at Coire Glas)
– 28.666 GW / 430 GWh for T = 40 GW (possible at Coire Glas)
Example – 20 hours
For the next example, suppose the required regeneration duration from energy storage is at least 20 hours at the full Total power T.
Glasa Morie Glass
Then the power capacity required from Glasa Moire Glass could be up to 170/20 = 8.5 GW.
Coire Glas / Loch Lochy
Then the power and energy storage capacity required to be built at Coire Glas depends on the total regeneration power capacity T required for the grid’s needs.
– 1.5 GW / 30 GWh for T = 10 GW (this is what the SSE plan for Coire Glas)
– 11.5 GW / 230 GWh for T = 20 GW (practical at Coire Glas)
– 21.5 GW / 430 GWh for T = 30 GW (possible at Coire Glas)
– 31.5 GW / 630 GWh for T = 40 GW (exceeding what’s possible at Coire Glas alone)
Example – 13 GW
For the next example, suppose the required Total power was to be 13 GW.
Firstly, suppose the required regeneration duration from energy storage is 13 hours or less. In these cases, Glasa Morie Glass is all we need.
The rows of the following table represent alternative regeneration durations and how the 1 pumped hydro scheme would scale to suit.
| 1 Pumped Hydro Scheme. Glasa Morie Glass Power = 13 GW |
|
|---|---|
| Generation Duration (Hours) |
Total Energy Storage (GWh) |
| 4 h | 52 GWh |
| 5 h | 65 GWh |
| 6 h | 78 GWh |
| 7 h | 91 GWh |
| 8 h | 104 GWh |
| 9 h | 117 GWh |
| 10 h | 130 GWh |
| 11 h | 143 GWh |
| 12 h | 156 GWh |
| 13 h | 169 GWh |
Secondly, suppose the required regeneration duration from energy storage is longer than 13 hours. In these cases, both Glasa Morie Glass and Coire Glas are needed.
The rows of the following table represent alternative regeneration durations and how the 2 pumped hydro schemes would scale to suit.
| 2 Pumped Hydro Schemes. Total Power 13 GW | |||
|---|---|---|---|
| Glasa Morie Glass 170GWh (GW) |
Generation Duration (Hours) |
Coire Glas Power, Energy |
Total Energy Storage (GWh) |
| 13 GW | 13.07 h | 0 GW, O GWh | 170 GWh |
| 11 GW | 15.45 h | 2 GW, 31 GWh | 201 GWh |
| 10 GW | 17 h | 3 GW, 51 GWh | 221 GWh |
| 9 GW | 18.88 h | 4 GW, 76 GWh | 246 GWh |
| 8 GW | 21.25 h | 5 GW, 106 GWh | 276 GWh |
| 7 GW | 24.28 h | 6 GW, 146 GWh | 316 GWh |
| 6.5 GW | 26.15 h | 6.5 GW, 170 GWh | 340 GWh |
| 6 GW | 28.33 h | 7 GW, 198 GWh | 368 GWh |
| 5 GW | 34 h | 8 GW, 272 GWh | 442 GWh |
The next graph plots together both the 1 and the 2 pumped storage hydro schemes cases for a power of 13 GW.
Scaling 1 or 2 Pumped Storage Hydro Schemes for 13 GW from 4 to 34 hours
Scottish Scientist 
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