Dr Mike Dennis at the Australian National University is developing a Solar air conditioning system for homes which runs from the same type of solar panels used for water heating. This would provide hot water and room heating in winter, as well as cooling in summer. This uses an "ejector jet pump" (aka "Steam jet cooling") based on a well know principle used in industry, but not for domestic air conditioning. The system is not entirely solar powered, but will need only about 150W of power, compared to a conventional 2,000W air conditioner. It occurs to me that a computer CPU gets hot enough to heat water, as noted in my spoof "co-generation web coffee appliance" proposal . Thus air-conditioning might be powered by the waste heat from computer data centres.