Wind and solar energy holds a lot of promise when it comes to replace the conventional energy sources such as fossil fuels and coal. However, there is one problem: How do you store solar and wind energy for times where wind doesn’t blow or sun doesn’t shine? Using compressed air energy storage is a possible solution.
A good example to illustrate this is the use of solar panels in warm areas of the world where you want air conditioning during the night. The solar panels can only generate electricity during the day when the sun is up, but by using compressed air storage, we could save the surplus of this electricity and spend it during the night.
The same principles also go for wind energy. Wind is a highly fluctuating and unpredictable energy source. On top of this, wind is strongest during the night, when the energy demand is low.
How Does Compressed Air Energy Storage Work?
The surplus energy is pumped and compressed into storage tanks on smaller scale, but on utility scale stored in underground caverns. The amount of energy that is stored in compressed air is directly related to the air’s density. The storage tank or cavern that holds this air has to be robust enough to handle the high density and pressure. Carbon fiber is usually the material used in storage tanks on smaller scale, while salt caverns store compressed air much as we would with natural gas on utility scale.
By the law of conservation of energy, wind or solar energy (or other energy sources for that matter) has now ended up as potential energy in compressed air. It is important to realize that we lose energy during these processes. This does not mean that some of the energy disappears, but rather is transferred into lower quality energy states, not usable for electricity generation.
How do we get electrical energy from compressed air? We simply use convert the high pressure into electricity with a gas turbine.
Compressed Air Energy Storage Efficiency
Determining efficiency for CAES systems can be hard. If we compress and decompress at a rate that is not appropriate for the specific cavern, efficiency takes a huge hit. In general, CAES is not very efficient to store energy, which is driving costs up. On the other hand, storing the surplus of energy is better than not using this energy at all.
The reason why CAES typically only has an efficiency of about 50% is because we have to reheat the compressed air to be able to generate electricity with a gas turbine.
CAES is currently not very applicable for small-scale residential situations, but rather on larger-scale, closer to where the energy is being harnessed. However, CAES can be used on smaller scales by air cars and air-driven locomotives.
There are currently only two CAES facilities operating on utility scale in the world, one in Alabama and the other one in Huntorf, Germany. We can expect to see more of these facilities in the future when renewable energy sources are taking up more of the grid.
RWE Power and General Electric (GE) (along with their partners) are currently developing ADELE, an adiabatic compressed air energy storage project with better efficiency.
People are starting to realize the potential in compressed air energy storage and its role in future energy systems, and this is pushing the technology forward.