>Conventional air conditioners employ refrigerants such as chlorofluorocarbons to absorb heat from the room to be cooled. That heat is then expelled outside, requiring electrically powered pumps and compressors.

One idea to conserve energy is to replace coolant fluids and gases—which are often super-powered greenhouse gases capable of trapping more than 1,000 times more heat than CO2—with solid materials, such as bismuth telluride.

A new device from Sheetak, developed in part with ARPA-E funding, uses electricity to change a thermoelectric solid to absorb heat, and could lead to cheaper air conditioners or refrigerators.

Such refrigerators, which lack moving parts and are therefore less likely to break down, can be lifesavers in remote, rural areas for keeping medicines cool or food fresh.<