Present solar power technology (based on photo voltaic conversion) is often too costly for water pumping in developing countries. The thermal conversion system presented here has the potential to do the same work for less than half the cost. A further advantage is that it can be locally produced and maintained.

The technology
The Solar Pump works on the Rankine principle i.e. a fluid is evaporated through heat from the sun; the pressurized vapor drives a motor; the vapor is then condensed in a cooler and returned to the evaporator through a condenser pump. The evaporation takes place at 70C and the condensation at 35C. With these temperatures a maximum theoretical efficiency can be obtained of 10%.

Efforts in the past usually obtained no more than 1% final efficiency. Extensive research by PRACTICA has discovered that “entrance condensation” is the reason for these low efficiencies.

With this knowledge, the expander (motor) has been designed to minimize entrance condensation losses and make otherwise optimum use of the vapor energy. On the test bench, overall efficiencies were 3%, sunlight to shaft power.


The design
The solar motor uses simple flat plate collectors for the evaporation of the working fluid (Pentane). The vapor coming from the collectors at a pressure of 1.5bar is led to the motor (expander). The motor is a single cylinder, oscillating machine. All parts coming into contact with the hot gas are made of heat insulating material. The design of the motor is such that it requires little investment in “tooling” for production. It is also very simple so that with very little training maintenance can be done by existing rural mechanics.
The motor is designed to work with the Volanta pump (see separate product sheet), forming together the Solar Pump.

Production
The simplicity of the solar thermal pump allows local production / assembling. This reduces cost, generates local employment and provides a good guarantee for spares availability and long term maintenance. It is estimated that the Solar Pump can work at 30-50% of the cost of solar photovoltaic pumps. For example: for a daily capacity of 10m³ from a depth of 30m, the total cost of the pump plus the solar motor, collector etc. will be in the order of US$ 3000. Of this, 50% is the cost of the pump and 50% of the solar system.
 
Applications
At first, the Solar Pump will be introduced for water pumping. Later a dual purpose system will be developed which has as basic function water pumping but which will have enough extra capacity to drive a grain mill at the same time. The mill will be driven by a belt from the flywheel of the pump. In this case a large water tank will be used as a heat store for the system.
Eventually it may be possible to drive also a generator to provide basic electric power. This will be of particular interest to remote villages.

Source: http://www.practicafoundation.nl/technologies/solarpump.html