# Carnot batteries

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

Source page: https://www.materialinsights.org/energy/e_carnot/

Storage · Thermal · No. 85

- Storage
- Duration: Hours to days
 Storage · Thermal · Foundation · Energy

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 power**Drives a heat pump
2. 2 **Hot store**Molten nitrate salt up to about 557 C
3. 3 **Cold store**Methanol chilled to about -41 C
4. 4 **Heat engine**Runs across the temperature gap
5. 5 **Grid**Spinning generators supply power and inertia
 Covered in [Storing energy: from fuel stocks to batteriesEnergy](https://www.materialinsights.org/learn/energy/storing-energy/)

##### Go deeper pick a tab to open it in full

## Other sections

- [Overview](https://www.materialinsights.org/energy/e_carnot/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_carnot/correlation/index.md)
- [Science and technology](https://www.materialinsights.org/energy/e_carnot/sg-sci/index.md)
- [Engineering and performance](https://www.materialinsights.org/energy/e_carnot/sg-eng/index.md)
- [Economics](https://www.materialinsights.org/energy/e_carnot/sg-econ/index.md)
- [Impact and additionality](https://www.materialinsights.org/energy/e_carnot/sg-impact/index.md)
- [What to track](https://www.materialinsights.org/energy/e_carnot/tracking/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_carnot/links/index.md)