At 8:14 AM 4/10/5, Robin van Spaandonk wrote: >In reply to Horace Heffner's message of Sat, 9 Apr 2005 06:36:37 >-0800: >Hi, >[snip] >>Storage of *both* the heat and cold generated by air liquifaction might be >>a sensible way to go. Liquid air is easy to store at high efficiency, and >>heat from compression can be stored in thermal wells or by using salt phase >>exchange, though a much lower melting point salt would have to be used to >>directly obtain the heat from the compression. I would expect thermal wells >>to be cheaper than salt tanks, and if drilled deep enough, they produce >>geothermal heat also. >[snip] >Are you suggesting thermal wells as an alternative to salt phase >exchange, or a combination of both?
I would think the choice of combinations would depend on local economics and geology. High temperature salt melting can clearly be achived by resistance heating. Lower temperature solt melting can be achived using post compressor gas temperatures. The use of thermal wells depends on local geology and regulations. The important point with regard to thermal energy storage I think is the notion of storing both heat and cold simultaneously so as to maximize the carnot efficiency when the energy is recovered by Sterling engine or turbine. For some reason you just don't see that concept in use. Typically the approach is storing cold in the form of liquid nitrogen or air, or otherwise storing heat in the form of thermal mass or phase change, and then later doing an exchange with the ambient environment to effect the recovery. Liquifaction produces both waste heat and cold products. Both should be stored to maximize later energy recovery. This can work well for a home sized energy storage system, but it should be workable for a large wind or solar system as well. Regards, Horace Heffner
