Liquid Air Energy Storage, or LAES, is a way to store extra renewable electricity by using it to make air extremely cold until it becomes a liquid. This matters because wind and solar power do not always match the times when people need electricity. A LAES plant can charge when electricity is abundant and discharge later when the grid needs power.
The main machine is a cryogenic system with compressors, heat exchangers, an insulated liquid air tank, pumps, and expansion turbines.
Key Facts
- Air becomes liquid near -196°C at atmospheric pressure.
- During charging, electrical energy runs compressors and refrigeration equipment to liquefy air.
- During storage, liquid air is kept in an insulated cryogenic tank to reduce heat leak.
- During discharge, liquid air is pumped, warmed, and expanded through a turbine to generate electricity.
- Approximate stored cold energy depends on mass and temperature change: Q = mcΔT.
- Electrical power is energy transfer per time: P = E/t.
Vocabulary
- Cryogenic
- Cryogenic refers to extremely low temperatures, usually below about -150°C.
- Liquefaction
- Liquefaction is the process of cooling and compressing a gas until it becomes a liquid.
- Expansion turbine
- An expansion turbine is a machine that extracts useful work from a high-pressure gas as it expands.
- Thermal insulation
- Thermal insulation is material or structure that slows heat transfer between a cold or hot system and its surroundings.
- Round-trip efficiency
- Round-trip efficiency is the fraction of input electrical energy that is returned as useful electrical energy after storage.
Common Mistakes to Avoid
- Thinking liquid air burns like a fuel is wrong because liquid air stores energy through temperature, pressure, and phase change rather than chemical combustion.
- Ignoring heat leaks is wrong because even a well-insulated cryogenic tank slowly absorbs heat from the surroundings, which can reduce stored energy over time.
- Assuming 100 percent energy recovery is wrong because compressors, heat exchangers, pumps, and turbines all have losses due to friction, heat transfer limits, and electrical resistance.
- Confusing power with energy is wrong because power is the rate of energy transfer, while stored energy is the total amount available over time.
Practice Questions
- 1 A LAES plant uses 200 MWh of electricity to liquefy air. If its round-trip efficiency is 55 percent, how many MWh of electricity can it deliver later?
- 2 A discharge turbine produces 40 MW for 3.5 hours. How much electrical energy does it generate in MWh?
- 3 Explain why a LAES system is useful for a grid with lots of wind power, even though it loses some energy during the storage cycle.