 Thermoelectric (Peltier) heat pumps are generally only around 10-15% as efficient as the ideal refrigerator (Carnot cycle), compared with 40–60% achieved by conventional compression cycle systems (reverse Rankine systems using compression/expansion); however, this area of technology is currently the subject of active research in materials science.This is popular for thermoelectric coolers, where the low efficiency is not much of a problem, while being lightweight, cheap, and endurant are valuable qualities.It also has a "long lifetime" as there are no moving parts, and it does not use potentially hazardous refrigerants.