There is a need for heat operated refrigeration systems in areas of the world which have a warm climate and also have no firm electricity supply. Research is underway on carbon -ammonia refrigerators driven by the heat of steam condensing in a thermosyphon heat pipe. The heat source can be solar energy, biomass, or some combination of the two. New monolithic carbon adsorbent-aluminium composites have been developed which promise power densities of 1kW cooling per kg carbon. The high power density leads to much lower first costs.