than that claimed by the manu- facturer). Fig. 3(b) shows that the high efficiency is maintained over a wide range of solar array currents.
4. CONCLUSIONS
Using these techniques it appears to be possible to raise the day-average efficiency of the pump/motor/ controller system from 40%, a good figure for current systems, to 60-70%, reducing the demand for elec- tricity by a factor of 1.5. Using the concentrating collector should halve the cost of the electricity. The combined system should reduce the cost for a given flow of water by a factor of between 2 and 3.
Acknowledgement~We are indebted to the British Council for a link with Zhengzhou University, China, for water pump work, and to the European Community for a grant for work on concentrator systems.
REFERENCES