Wind and wave energy devices produce their output in the form of shaft work, with a power output which varies over a wide range as the input energy intensity changes. For many processes (desalination, thermochemical processes, steam raising, space heating) energy is required in the form of heat. The conversion of shaft work directly to heat is thermodynamically very inefficient. This efficiency may be greatly improved by using the shaft work to drive a heat pump which abstracts thermal energy from the environment (the sea or airstream) and upgrades it to the requisite temperature level. In this regard, wind and wave energy are ideal sources, since the thermal energy contained in the airstream or sea exceeds by several orders of magnitude the mechanical energy that can be abstracted. Heat pumps have hitherto been designed to utilize a constant work input and a source of heat at variable temperature. But in order to harness renewable energy effectively, a heat pump is required that will utilize variable shaft work to upgrade heat from a source at near-constant temperature.