A Carnot battery works by converting electricity into heat during its charging phase, storing that heat, and then converting it back into electricity during discharge. The process involves the following steps:
- Charging (Electricity to Heat Conversion): Excess electricity, often generated by renewable sources like solar panels or wind turbines, is used to power a heat pump or an electrical heater. This device converts the electrical energy into thermal energy (heat). This heat is then stored in a thermal energy storage medium such as molten salt tanks, which can retain high temperatures efficiently over time.
- Storage: The thermal energy is stored in materials that can hold heat for extended periods with minimal loss. Common storage media include molten salts, rocks, or other substances with high heat capacity.
- Discharging (Heat to Electricity Conversion): When electricity is needed, the stored heat is extracted and converted back into electrical energy through a thermodynamic power cycle, typically involving a turbine driven by heat expansion. This process relies on the principles of Carnot efficiency, which governs the maximum theoretical efficiency of converting heat to work (electricity). The roundtrip efficiency of Carnot batteries can approach 100% if both the heat pump and power cycle are reversible, though practical systems achieve less.
- Additional Uses: Waste heat generated during the discharge process can be further utilized for heating purposes, such as district heating, enhancing overall system efficiency.
In summary, a Carnot battery converts electricity into heat using a heat pump or electrical heater, stores this thermal energy in a medium like molten salt, and later converts the stored heat back into electricity through a heat engine cycle when needed. This approach enables large-scale, potentially low-cost energy storage suitable for balancing renewable energy supply and demand fluctuations.
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