Researchers in the EU-sponsored RICAS 2020 research project have in mind all parts of the world wheredisused sealed caverns they could be used as storage sites.
Wind and the sun, two unpredictable resources, are increasingly important as sources of energy in Europe. This means that we are faced with a growing need for energy storage facilities, because If energy cannot be used immediately when it is generated, it must be stored until needed.
The least expensive method is to use the hydroelectric energy deposits such as 'batteries': that is, generating electricity using stored water when energy is scarce and subsequently pumping the water back when surplus renewable energy is available. However, this is a practical solution only in mountainous regions, such as Norway and some other countries.
What if less fortunate countries and regions could use air instead of water as a way to store energy? RICAS 2020 intends to respond to this demand.
The general principle, which has already been adopted in some places around the world, is essentially a question ofuse surplus electrical energy to compress air, which is then stored in an underground cavern. When power is required, air is released through a gas turbine that generates electricity.
Existing plants of this type are often used to meet peak demand as a complement to classic power plants, providing the correct amount of electricity needed at different times during the day.
The physics that regulates the storage of energy in the form of compressed air is the result of a law of nature, familiar to users of a bicycle pump:the air compression process heats it. Bicycle pumps compress air in order to increase tire pressure, and by doing so, it causes the pump to heat up.
“The more heat of compression the air has retained when it is released, the more work it can do as it passes through the gas turbine. And we think that we will be able to conserve more of that heat than current storage technology can, and thus increase the net efficiency of the storage facilities ", says in a statement Giovanni Perillo, project director of the contribution to RICAS 2020 of SINTEF, partner Norwegian project.
The two largest compressed air stores in the world are located in Germany and the United States. They are underground chambers created in salt formations. But these plants lose a large proportion of the potential energy of compressed air,because they do not incorporate a system to store the heat produced during the air compression stage.
RICAS 2020 participants have a recipe for reducing these losses in future underground storage caverns. In the center of the recipe is an extra station that they have incorporated into their solution. On its way to the underground cavern, the hot compressed air passes through a separate cavern filled with crushed rock.
The hot air then heats the rock, which retains a large proportion of the heat. The cold air is stored in the main cavern and, when the air subsequently returns through the crushed rock on its way to be used to generate electricity, the airflow is reheated by the stones. Finally the hot airit then expands through the electricity generating turbine.
The SINTEF project manager explains that it is estimated that this technology could increase the efficiency of the system by up to 70-80%. The figures for most existing storage sites are no better than 45 to 55 percent,meaning that the energy produced is only half of what was initially used to compress the air in the cavern.
“The project is based on the belief that our solution will offer better energy storage than batteries can provide, thanks to its longer life and lower capital cost per kWh of energy stored.We also hope that it can be used practically regardless of the type of geological formation available. Perillo says.
The Energy Newspaper