Methods and means for storing energy

DETAILED DESCRIPTION Electricity supply organisations prefer to operate generating stations at constant high output to make the best use of both plant and fuel.
But consumer demand normally falls at night, so some short-term storage systems have been built to absorb energy at night and release it when demand is high during the day.
For example, a reversible plant comprising motor/dynamo plus water pump/turbine can absorb electrical power by pumping water to a higher reservoir overnight, and generate hydroelectric power from the raised water next day.
Very large volumes of water are needed for such systems and, for social and geological reasons, suitable sites are rare.
An essential requirement of any practicable storage system is that a high proportion of the energy absorbed should be recoverable.
In this invention of improved means of energy storage, energy is absorbed by refrigerating and liquefying air, and liquid nitrogen and liquid oxygen, the main atmospheric constituents, are stored at temperatures considerably below atmospheric.
The cold stored liquid gases are subsequently used, in conjunction with a source of heat at a higher temperature such as the atmosphere, to drive a heat engine and thus make energy available when required.
A cold liquid gas such as nitrogen or oxygen will not yield mechanical energy if quite isolated, but can do so in combination with a source of heat at a higher temperature.
One such source is the atmosphere, in which a virtually infinite amount of ambient temperature heat is available at no cost.
Two basically different methods may be employed.
(A) The cold liquid may be boiled, for example by blowing air over pipes containing it, thus producing cold gas which can be further warmed and pressurised by atmospheric heat and used to drive an open cycle engine such as a turbine, hence making mechanical energy available.
(B) Instead of passing atmospheric heat directly to the boiling liquid as in (A), the liquid may be cirulated around the "cold end" of a closed cycle "heat engine" with separate working fluid (such as a Stirling engine using trapped helium as working fluid), the engine "hot end" being held close to the atmospheric temperature by blowing air over it