How does compressed air energy storage function

Compressed Air Energy Storage (CAES) is a system used to store energy by compressing air during low-demand periods, typically using surplus electricity from renewable sources like wind and solar. The compressed air is then stored in large underground caverns or tanks until needed. Here’s how CAES functions:

Basic Functionality

Compression (Charging Phase):
- During off-peak hours, excess energy (e.g., from wind turbines) is used to power an air compressor.
- Ambient air is compressed and stored in underground facilities like salt caverns, aquifers, or steel tanks at high pressures (up to 100 times atmospheric pressure).
Storage:
- The compressed air remains stored until energy demand increases.
Expansion (Discharging Phase):
- When energy is needed, the compressed air is released from storage.
- The air is often mixed with a combustible fuel (like natural gas) and heated to maintain efficiency.
- The mixture then expands through a turbine, generating electricity as it drives the turbine connected to a generator.

Types of CAES Systems

CAES systems can be categorized based on how they manage heat during compression and expansion:

Diabatic Systems: These are the most common type, where excess heat from compression is not stored but dissipated. The air must be reheated (often using natural gas) before expansion, leading to lower efficiency (around 40-50%).
Adiabatic Systems: These systems aim to store the heat generated during compression for use during expansion, potentially achieving higher efficiencies (up to 70%) by reducing reliance on external fuels.
Isothermal Systems: These are ideal systems where compression and expansion occur at constant temperature. In practice, they are difficult to achieve on a large scale due to heat transfer limitations.