ABSTRACT
Solar pump systems are often backed 100 percent by auxiliary power-either by a directly coupled electric motor or by a separate motor-driven pump. Generally, heat engines are used to convert solar energy to mechanical energy to power the solar pumps. Several basic types of power systems, or working cycles, can be selected to convert the thermal energy from the solar collectors into useful shaft power. The Rankine cycle is the only one of these systems to use both the liquid and vapor phases of a working fluid. Most solar power systems will operate more efficiently at constant temperature corresponding to design-point conditions; there is considerable effort underway in the United States to develop phase-change storage units, particularly for solar space heating and cooling and solar power generation. Such systems are experimental in nature and are costly, requiring large areas for transfer of heat into and out of the solid-phase material.
