A technology called 'regenesys' converts electrical energy to chemical energy and is potentially capable of storing massive amounts of electricity. Energy is stored in two concentrated aqueous electrolyte solutions, sodium bromide and sodium polysulphide. On charging the bromide ions are oxidized to bromine while sulphur in the polysulphide anions is converted to sulphide ions. On discharging, the sulphide ions act as the reducing agent and the tribro-mide ion as the oxidizing agent. The system can be switched from fully charging to discharging in about 20 milliseconds. The city of Toronto is investigating the feasibility of using the advance RGN flow battery as back-up for its grid during periods of peak demand to prevent outages and 'brown-outs' on such occasions. An appropriate 600 MWh urban scale storage system would need 30 million litres of electrolyte stored in 6 m high tanks covering the area of a football pitch. It is still considered more cost-effective than providing the extra generating capacity to meet the same demand.
In the opinion of the Royal Commission on Environmental Pollution, hydrogen and regenerative fuel cells will be in widespread operation by the middle of the century. If global warming and security of energy supply issues simultaneously become critical then viable large scale storage technologies will arrive much sooner.
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The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.