The design of large low aspect ratio energy storage solenoids for electric utility use

The preliminary conceptual design of a low aspect ratio solenoid (large diameter and small height) for diurnal energy storageuse is presented. The main advantage of this design is that the total radial force is only 5 ~ 10% that of previous designs resulting in small conduction heat leak through the insulating struts. The external pressure is less than 2 atmospheres which allows surface trench construction in surface rock; the pressures for previous underground bedrock designs were 20 to 100 atmospheres. A new use for diurnals to rage is presented in which larger SMES storage units replace intermediate load generation. In the example given an allowance of $60-100 per kwh could be credited t o SMES. This new higher value comes from replacing cycl ing coal or large oil burning intermediate generation. SMES can be used for intermediate load because its storage efficiency is 95%; all other storage systems, only 50 to 80% efficient, could not meet the intermediate use requirenent.