Solar water pumping

The principles of solar water pumping are briefly described. The mechanical energy needed for pumping water may be produced by thermodynamic, or direct-conversion methods. In thermodynamic conversion a fluid with high internal energy is produced in solar collectors or concentrators. The internal energy of the fluid may be utilized in Rankine-, Brayton-, or Stirling-cycles or in specially designed devices. The nature of irrigation in the arid regions calls for scattered water pumping stations, hence small solar pumps. These pumps may be mass produced and delivered to the site. The direct conversion includes photovoltaic, themoelectric and thermionic processes. With the current prices of solar cells photovoltaic water pumping seems to be economically competitive with the current solar Rankine-cycle system in the power ranges of below 5 kW, especially when both systems have to be imported by a developing country.