One of the most commonly quoted disadvantages of using wind power is the intermittency of the service that it can provide. Because the wind cannot be depended on to either be constant or to blow at all in some cases, there will be times when a wind farm will not be able to keep up with the demand for power. Power storage systems such as batteries provide a means of storing electricity that has been generated during times of strong and constant winds but early versions of commercial sized battery storage systems are very expensive.
There is now a need for energy production companies to meet government imposed energy storage targets. California has just announced such a decision and this means there will be an increasing need for cost effective energy storage methods.
Another method of storing energy for later use is with a compressed air energy storage system (CAES). Like a battery system a CAES can store energy for later use but it can do so at a much lower cost making it a more desirable option.
The use of this technology, which has been around for some time in one way or another, has been progressing so that it is becoming possible to set these storage systems up closer to the source of the energy production. It is an option that is worthy of further investigation and discussion.
What Is Compressed Air Energy Storage?
Compressed Air Energy Storage has been around for quite some time now in one form or another. It involves injecting compressed air into subterranean caverns up to a kilometre below the earth’s surface. It is stored there until peak electricity needs dictate that it should be released again.
A traditional CAES method of operating is for the released compressed air to be reheated in a process that involves natural gas. While this means that there is less dependence on fossil fuels in the creation of electricity it means that a renewable energy generation plant is no longer 100% renewable.
A more modern process, and one that is still in the process of being improved so that it operates at a highly efficient level, is an adiabatic process where the heat is retained and then used in the power generation process.
An operations management system can dictate that electricity production must be enhanced and this can trigger the release of the compressed air to drive a generator through a turbine that will produce electricity.
How Can Compressed Air Energy Storage Systems Benefit Wind Farms?
The use of a CAES can balance the intermittent nature of wind power by providing the operator with a means of releasing stored compressed air as required. This reduces greatly the commercial risk that is inherent in all wind power projects.
Using a CAES can lower the cost of a wind power-based renewable energy power system which will lower the prices for the consumer.
Limiting factors such as the lifespan of the components of a wind farm as well as other unexpected technical limitations can affect the production of a reliable source of electricity. The use of CAES can control the frequency of the energy flow and can be provided very quickly.
Problem areas in the world that has trouble with handling grid loads and overcoming constraints on transmission will benefit from the use of CAES. By integrating this storage system into what was once an intermittent source the creation of production of electricity is smoothed out. Peak loads that might overload the system will be smoothed so that there is a more consistent supply and demand level.
One of the big drawbacks of wind power electricity production is that the turbines are typically installed in weak grid areas, often times in coastal regions. Electricity feeds can be inhibited for periods at a time due to grid overloading. Installing a CAES near the location of the wind farm will help to overcome this drawback.
Efficiency of Compressed Air Energy Storage
In terms of the efficiency of a CAES compared to other forms of energy storage, it rates reasonably highly without really challenging other methods. The measured efficiency of the existing models gives a round trip efficiency of a little higher than 70%.
The best results can be attained by using Superconducting Magnetic Energy Storage (SMES) systems. It is possible to achieve 90-95% efficiency with these systems. Similarly, Supercapacitor energy storage systems can also achieve a 95% efficiency rating.
Where the modern CAES systems shine, such as the adiabatic design is they can produce completely emission-free electricity. This design can produce electricity without depending on any fuel consumption.
Cost of CAES
In order to run a 300 MW CAES it would be necessary to find 22 million cubic feet of storage space. This would provide the capability of producing eight hours of electricity. You can expect a CAES system to cost somewhere in the region of around $400 per kW.
With a round trip efficiency expectation of over 70% this represents an option that is better than many other energy storage options. You can also expect that the life span of a CAES to be up around 30 years which is equivalent to that of a Pumped Hydro system and much longer than other options such as batteries, flywheels and fuel cells.
The latest versions of CAES models can be built at an even lower cost because they are being built with some type of pressure vessel which can be stored above ground as opposed to an underground salt cavern.
Currently Operating CAES Projects
The following CAES power plants are currently in existence today.
|Location||Huntorf, Germany||McIntosh, USA|
|Storage method||2 salt caverns
150,000 cubic meters
600 – 800m deep
538,000 cubic meters
450 – 750m deep
|Output||290 MW over 2 hours||110 MW over 26 hours|
|Energy requirement for 1 kWh||0.8 kWh electricity1.6 kWh gas||0.69 kWh electricity1.17 kWh gas|
|Pressure Tolerance||50 – 70 bar||45 – 76 bar|