Cells smooth power path

Power stations could be designed and run more efficiently thanks to energy storage technology developed by National Power. The company is on the look-out for a partner to help it develop the technology, named Regenesys.

Electricity is a commodity product, but it can't be stored. It has to be generated as it's needed, so power stations have to be designed to produce the peak power needed only for a few hours each day - mid-afternoon to late evening. The rest of the time, the power station operates below its maximum output and efficiency. Regenesys will allow power station operators to generate more power during the night-time troughs and less during the peaks. This would allow engineers to design power stations which operate at their peak capacity all or most of the time.

Regenesys is based on regenerative fuel cells. These are chemical batteries whose electrolytes flow through the cells past inert electrodes. The cells can operate in two directions: if a current is applied through the electrodes, the electrolyte charges up; in reverse, the charged electrolyte flows back through the power and regenerates the electricity.

The stumbling-block with this technology has always been the materials used for the electrolytes and electrodes. The National Power researchers settled on sodium bromide and sodium polysulphate, which are fairly cheap, soluble, available at high purity and hazard-free. The electrodes include a cation-selective membrane to ensure that the reversible redox reaction at the heart of the cell can proceed. External tanks store the electrolyte between charge and discharge cycles. An array of cells could store up to 500MW of power - a 120MW unit is currently under construction at Didcot power station.

Apart from helping with power station efficiency, Regenesys could be used to store the power from wind farms or solar cell arrays.