by Nick Jefferies
In poor rural communities around the world, one of the only ways of earning extra income is by growing vegetables and fruits to sell at the local market. The key to growing these crops is irrigation. Most current irrigation methods use either labour intensive manual pumps or expensive, carbon-emitting diesel engines. While undertaking my Masters at CAT in Renewable Energy, I came across a small-scale solar thermal technology being developed that offers an alternative method for irrigation pumping.
The system uses a parabolic dish to focus the sun’s heat onto a boiler to produce steam power that drives a simple type of reciprocating engine pump. Having contacted the inventor, I travelled to Holland to see the pump in operation and determine whether I could contribute to further development. This led me to travel to Ethiopia last September where I spent two months monitoring the engineering performance and socioeconomic issues related to pumps installed on ten farms around the town of Ziway.
Data indicated that the system could produce 2,500-5,000 litres/day from a depth of 5-13m, allowing for a cultivated area of 500-800 sq m. If good growing practices are followed, this means the cost of the pump could be paid back in less than one year. Monitoring also showed that the equipment was simple enough to allow farmers to operate the system independently. One key finding was that the overall efficiency of the system, calculated by comparing incoming solar energy to hydraulic energy output, was about three times less than expected. The main reason for this under-performance was identified as an incorrect sizing of one of the steam engine components.
This issue will be addressed in the next development stage, leading to a large increase in daily pumped volume, and thus directly improving the income potential and marketability of the solar steam pump.