We Store Energy in Compressed Air

We aim to produce the world’s cleanest and most economical energy storage systems. Compressing air creates heat energy. Until now, this was wasted, drastically reducing efficiency.

Our innovation: an elegant method of capturing this heat energy and regenerating useful energy from it. We inject a fine, dense mist of water spray which rapidly absorbs the heat energy of compression and provides it during expansion.

Our Approach

1. The mechanical energy used for compression generates heat that is captured by the water spray.
2. Compressed air is stored in a tank.
3. The heat captured by the water is stored for later use.
4. During Expansion, the stored heat is sprayed into the air and converted back into mechanical energy.

Our System is Fully Reversible

To store energy, an electric motor drives an air compressor. To deliver energy, we reverse the process–the air compressor becomes an expander, and the electric motor becomes a generator.

Heat from compression is stored or routed to nearby buildings, providing heating. During expansion, heat is extracted from storage, or buildings providing air conditioning. This dramatically increases building energy efficiency.

Storage: The system draws electricity from the grid and converts it into compressed air and heat.
Delivery: Compressed air and heat are turned back into electricity using the same system.

Experimental Results

We have shown that we can achieve very high thermodynamic efficiencies without sacrificing performance. We have achieved these high thermodynamic efficiencies at higher RPMs than many thought possible. This is crucial to achieving low cost: the higher the RPM, the higher the power of the same machine, and the lower the cost per kW.

90% Thermal efficiency, roundtrip
<10°C Final temperature difference
1200 RPM, 100 kW scale; 500+ hrs reliable operation Reciprocating piston compressor/expander

Storage

Air can be stored in simple, low cost air storage tanks, packed in a convenient shipping container form factor using industry standard pipes and matching ASME and ISO safety standards. For truly massive installations, air can be stored in underground caverns which is the standard for large scale natural gas storage.

Model of Air Storage Tanks

Flexible and Modular Energy Storage System

The compressor/expander – which provides power, and the air tanks – which provide storage, are distinct modules that can be scaled independently. This allows our storage system to be tailored to customer applications.

Power Unit
  • 250 kW modules
  • 20+ year lifetime
Storage Unit
  • 750 kWh modules
  • Shipping container form factor
  • ASME certified