EET

A more intelligent way of dealing with peak power demands

Here's a novel idea. Instead of installing a lot of renewable energy sources to handle peak power loads, instead store the excess energy produced by power plants handling the base load. Then draw down from this storage when energy use is at a peak.

That's the basic premise of researchers at the University of Leeds and the Chinese Academy of Sciences. They suggest using their scheme to replace the natural gas-powered plants that normally go online during peak loads. They say the technique could halve the fuel needed to handle such peaks.

The idea comes about because of the way energy companies typically top up a 'base' supply of energy with electricity from gas-fired generators that are notoriously inefficient, expensive to run and sit idle for long periods.

University of Leeds Professor of Engineering, Yulong Ding, and colleagues are proposing a system that would store excess energy made by a plant supplying the 'base' demand and use this to supply the demand peaks as and when they happen.

The key idea is to use excess electricity to run a unit producing liquid nitrogen and oxygen - or 'cryogen'. 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.

Meanwhile, the oxygen would go to the combustor and mix with the natural gas before it is burned. Burning natural gas in pure oxygen, rather than air, makes the combustion process more efficient and produces less NOx. Instead, this 'oxy-fuel' combustion method produces a concentrated stream of carbon dioxide that can be removed easily in solid form as dry ice.

Leeds researchers say this scheme could cut the amount of fuel needed to cater for peak demand by as much as 50%. Greenhouse gas emissions would be lower too, thanks to the greatly reduced nitrogen oxide emissions and the capture of carbon dioxide gas in solid form for storage.

"On paper, the efficiency savings are considerable. We now need to test the system in practice," Professor Ding said.

Details of the system recently appeared in the International Journal of Energy Research. http://onlinelibrary.wiley.com/doi/10.1002/er.1753/abstract

More info from the University of Leeds: http://www.leeds.ac.uk/news/article/874/energy_storage_system_deals_with_sudden_draws_on_the_grid

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