Carnot batteries

Electricity stored as heat and cold, then turned back into electricity.

Storage · Thermal · No. 85

• Storage
• Duration: Hours to days

Store electricity as hot salt and freezing liquid in two tanks, then run an engine between them to get it back.

Chart: Illustration: Carnot batteries

Where it comes from

Chart: Map of where it comes from

A heat pump moves heat from a cold tank to a hot one, using only steel, salt, sand or rock and standard turbines, with no critical minerals.

Three things to know

1. Power and energy are sized apart, so a 100-hour plant cost falls to about USD 38/kWh against USD 245 at 10 hours (modelled).
2. Retiring coal plants are a natural home, already holding turbine halls and grid links; Chile has eight such units due to retire.
3. No grid-scale Carnot battery is yet operating, and a rock-store version returned only about 25% of its electricity.

The journey

1. 1 Spare powerDrives a heat pump
2. 2 Hot storeMolten nitrate salt up to about 557 C
3. 3 Cold storeMethanol chilled to about -41 C
4. 4 Heat engineRuns across the temperature gap
5. 5 GridSpinning generators supply power and inertia

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