As debate continues to rage over the UK’s energy mix, a collaborative project between engineers in Britain and researchers from China could provide the basis of a technology that could manage peaks in electricity demand in the future.
The researchers, from Leeds University and the Chinese Academy of Sciences, are excited about the possibilities of an energy storage system that employs liquid nitrogen and oxygen, or “cryogen”, to generate electricity. They announced last month that it could match highs and lows in electricity demand in an environmentally-friendly manner, cutting down burning of gas in power generation.
The project has been funded by the Engineering and Physical Sciences Research Council and the Chinese academy, and the researchers are now looking for investors to take it to the next stage. This would involve the development of a large pilot plant that could be retrofitted to an existing gas-fired power station, or included in new build. An estimated 29GW of gas-fired power plant is now under construction or in the planning process as another “dash for gas” looms.
The system has been developed in response to the fact that the amount of electricity drawn from the national grid varies greatly at different times of day. It usually peaks in the early evening for a couple of hours as people arrive home from school and work. Short-lived spikes are also common after major televised sporting events, or during commercial breaks. Spikes also occur in the morning hours.
But matching the highs and lows in demand with a steady supply is a major challenge, according to the researchers. Energy companies typically top-up a “base” supply of energy with electricity from power plants that are just switched on to cope with the peaks. The researchers, however, argue that the gas-fired generators often used to feed these peaks are inefficient and expensive to run, sitting idle for long periods of time.
The engineers have now developed a new system that, in theory, could manage short-lived draws on the electricity grid and halve consumption of fuel. Crucially, the system would store excess energy made by a plant supplying the base demand and use this to supply the peaks in demand as and when they happen.
The basic principle is to use excess electricity to run a unit producing liquid nitrogen and oxygen. At times of peak demand, the nitrogen would be boiled using heat from the environment and waste heat from the power plant. The hot nitrogen gas would then be used to drive a turbine or engine, generating “top-up” electricity.
Yulong Ding, professor of engineering at Leeds University, who led the research, says the system could obviate the need to ramp up the output of gas-fired power stations to meet peaks in demand because it would store excess energy for later. The oxygen produced by the system would be fed to the combustor to mix with the natural gas in the power station before it is burned. Burning natural gas in pure oxygen, rather than air, makes the combustion process more efficient and produces less nitrogen oxide, the researchers say. Instead, this “oxy-fuel” combustion method produces a concentrated stream of carbon dioxide that can be removed easily in solid form, such as dry ice.
Using such an integrated system, the amount of fuel needed to cater for peak demand could be cut by as much as 50%, says Ding. Greenhouse gas emissions would be lower, too, thanks to reduced nitrogen oxide emissions and the capture of carbon dioxide gas in solid form for storage. “This is a much better way of dealing with these peaks in demand for electricity,” he adds.
Ding and his team are now looking for investors to take the project to its next phase. The idea has been in development since 2005 and it is thought a working plant could be developed in the next five to eight years.
Full details of the system will be published shortly in the International Journal of Energy Research.