R&D Status

Energy Compression’s pending patents cover a range of system designs that go all the way from “pure” energy storage to hybrid designs that are “efficient” only because they harvest low-grade heat from external sources

Implementing the temperature-swing cycle involves moving the following three kinds of heat around (listed here in order of increasing quantities of heat):

• The heat of compression of the air, which must be returned to the air before or during expansion if the mechanical energy is to be efficiently recovered
• The heat of adsorption of the air, which must be returned to the nano-porous material again as the air is desorbed from it
• The sensible heat in the porous material, which must be removed from it in order to lower its temperature and returned to it again to raise it

Pure energy storage would require all this heat to be stored and recovered, which is possible in principle but would be expensive in practice. Fortunately, even though a lot more heat must be moved around in AE-CAES than in conventional CAES, it is all “low-grade” heat (meaning it is at temperatures not far removed from common ambient temperatures). Such low-grade heat is often available very cheaply, either by utilizing waste heat from industrial processes or by means of simple (non-concentrating) solar thermal panels.

Diagram illustrating the flows of compressed air and heat at the beginning of each “leg” of the storage cycle to be used with Zeolite-based AE-CAES. The box at bottom depicts the discharged state, wherein the adsorbent is hot and holds very little air (green) but considerable heat (red). To charge the system, the adsorbent is allowed to cool spontaneously, causing it to take up the compressed air being fed to it from a compressor (not shown). Once the adsorbent is near room temperature (left), active refrigeration is used to further cool it to deep-freeze temperatures while it takes up more air. The fully-charged system (top) is discharged by allowing it to heat up spontaneously. The cold that was stored in the adsorbent can then be used for refrigeration or A/C, while the compressed air that comes off performs useful work or is converted back into electricity. Finally the remainder of the air is driven off by active heating, closing the cycle.