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Solar water pumps, based on electro-mechanical pumps powered by PV arrays, are commonly used and commercially available. However, one of the difficulties for their wider application in developing countries, where there is a high average insolation, is their relatively excessive cost. This arises mainly due to the high cost of the PV elements. Hence, this paper describes some developmental work and results of experimental tests on “low-tech” solar thermal water pumps which were built on the basis of Stirling engines with fluid pistons coupled to flat-plate solar collectors. Temperatures and pressures in the cycle are comparatively low, thus cheap design materials, such as glass and plastic, and a simple technology, available in the majority of mechanical workshops, can be used for their manufacture and consequently reduce their cost. Several design modifications of the above solar thermal water pumps have been developed and tested. The results obtained demonstrate that existing installations can be effectively applied for water pumping with a dynamic head which varies between 2-5 m. Furthermore, data from experimental tests shows that the pulsating motion of water in channels of the flat-plate solar collectors increases the collector’s efficiency by approximately 8-10%, which is a considerable advantage when a pump is used as part of a house solar heating system.

Solar thermal water pumps are low cost and low maintenance devices with a pumping capacity of 0.2-1m3/hour at a dynamic head of 1.5–5 m. The working fluid in the thermodynamic cycle is an air-steam mixture. In this paper we suggest a simple mathematical model to numerically simulate the internal processes in such a pump and determine the performance and physical dimensions of a preliminary design. The proposed mathematical model has been calibrated against experimental data and it provides the numerical simulation of the processes which occur in the cycle within an acceptable degree of accuracy for engineering purposes. The results of the analysis show that the performance of the solar water pump is mainly determined by the “steam” fraction of the cycle. The power of the solar thermal water pump increases with an increase in the maximum temperature in the cycle, while the indicated efficiency reduces because of the increase in the heat loss due to water vaporization and condensation processes.

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