Exploitable results
More than a million villages world-wide, mostly in developing countries, lack a reliable low cost way of pumping water. Solar photovoltaic (PV) technology offers the opportunity to provide a reliable and robust way of mechanizing water pumping. However, there are few PV-powered pumps operational in developing countries, mainly because of the lack of awareness of purchasers to the benefits of PV pumps, and because of the high capital costs of current designs. At the small end of the scale in particular, there is too large a technology and cost gap between hand pumps and small PV mechanized pumps.
The work focused on 3 ways to improve PV pumps: high efficiency inverters, short-term energy storage and the development of a linear lift pump for small pumping applications. To increase system efficiency, a new concept of high voltage inverter was developed with a 300 V input voltage to suppress the need for a transformer and to reduce losses. The system studied had medium power (1 to 3 kW) with 20 PV modules in series to provide a high generator voltage. The reliability of the device was increased by constructing the inverter from a small number of fully integrated circuits.
The efficiency of a PV centrifugal pump was improved by designing a prototype for a short-term energy storage system. This device can store solar energy and then release it under cloudy or low irradiance conditions to allow the pump to operate near to its design point to achieve maximum efficiency. The third area of research focused on designing a prototype low cost linear-lift pump, based on the traditional chain and washer pump, to bridge the gap in technology and cost between hand pumps and mechanized pumps. A prototype was designed, built and tested successfully in the UK. The pump designers also wrote an operator's manual, which contains up to date information about the technology and its future prospects.
The high voltage inverter successfully reached efficiencies of 95% and demonstrated highest efficiencies over a large power range. An integrated DC current differential breaker prevented possible safety problems that could be encountered due to the high input voltage. The main advantages of the short-term energy storage system were seen under conditions of low and medium irradiance, where a standard system cannot overcome the initial irradiance threshold needed to get the pumping started. The linear lift pump prototype performed very promisingly, achieving efficiencies of about 40%.
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