As the world population grows, so does our need for electricity. Our need for electricity varies dramatically throughout the day. Utility companies are seeing demands on the power grid at various times, which creates a need to store energy to handle maximum spikes. According to Smart Planet, counties such as China and UK have developed a method of using liquid nitrogen to store clean energy, which helps handle brief demands on the power grid. Energy storage reduces the need of keeping expensive gas-powered power plants idle, waiting for a potentially large spike.
According to Yulong Ding, a University of Leeds professor and lead researcher, storing excess energy saves money because there is no need to ramp up production of gas-fired plants, which may generate electricity that may not be used.
Researchers at the University of Leeds and the Chinese Academy of Sciences have found an environmentally friendly method to cope with additional energy demands, which also happens to be cheaper than the gas-fired generator. On an industrial estate in Slough in the UK, a small cluster of containers and a white liquid nitrogen tank sit in one corner of the site owned by Scottish and Southern. This 300-kilowatt plant helps supply electricity to the UK’s National Grid through the process of storing excess energy at times of low power demand by using it to cool air to around -190 Celsius.
Air is chilled through refrigerators powered by excess electricity, the resulting air, or cryogen, is then stored in a nitrogen tank at ambient pressure, or 1 bar. The cryogen is introduced to a pressure of 70 bars and warmed in a heat exchanger, which produces a high-pressure gas that drives a turbine to generate electricity. The emerging cold air is then captured and reused to make additional cryogen. The process is used only when electricity is needed to the power grid. The process of using liquid air to store clean energy and using ambient heat to warm it, recovers around 50 per cent of the electricity that is fed in, according to Highview Power Storage’s chief executive.
The process reduces greenhouse gas emissions, thanks to an efficient combustion process and the capture of carbon dioxide in solid form. Air is fed to the combustor to mix with the natural gas before it is burned. This creates an efficient combustion process that produces carbon dioxide in a solid form as dry ice.
The United Kingdom’s cryogen plant has an efficiency of around 70 per cent and its storage costs are around $1000 per kilowatt. A cryogenic plant requires fewer expensive materials than other electricity storage plants, such as a pumped-storage hydropower plant.
Highview Power Storage receives cryogen from an external source and uses it to store and produce electricity. The plant recently added an on-site liquefaction plant, which will start producing its own cryogen from late March. The researchers estimate a fast return on investment thanks to the fuel saved and with additional benefits from an effective environmentally-friendly carbon capture system.