sterilisator01In rural areas of India Institutions depending on oil, gas and electricity try to switch to renewable energies. Reasons are the high costs of conventional fuel and the unreliability of the electric grid. Photovoltaic is often too expensive and therefore only used for small applications like lamps or small refrigerators for vaccine. For applications that draw more power oil burners and diesel generators are used. The high cost of the fuel and the transport of the fuel often present a big problem.

Looking at the energy needs of a rural hospital it gets clear that most of the energy provided by diesel generators is used in form of thermal energy. Laundry and autoclaves (run by steam) are the main consumers.

For those applications thermal solar devices like flat plate collectors or concentrating solar reflectors are ideal, as they transform solar energy into thermal energy at the necessary temperature level.

For laundry rural hospitals more and more switch to flat plate collectors. Those are robust, simple to manufacture and efficient. Because of government subsides the amortise in 3 to 5 years.

To sterilise medical equipment saturated steam at a minimum temperature of 121 °C is needed. Flat plate collectors can only provide water up to 80°C. For sterilization vacuum tube collectors or concentrating systems have to be used.

Since 2002 a sterilizer at a Hospital in Patna is run with steam produced by 4 Scheffler Reflectors of 8m² each. This system was installed by Solar Alternatives, based on the experience with large steam kitchens.

For rural hospitals a smaller system was developed by the author. The idea was to optimise the efficiency and to provide a system that does not store energy in form of pressurised steam. One Scheffler Reflector of 10m² heats an iron block of 230kg up to 400°C. At any time of the day steam can be created by the hot iron block to run a 76 litre standard autoclave. Clouds will not interfere the sterilisation process, as the energy is extracted from the storage.

At Holy Family Hospital in Mandar (150 beds) such a system was installed in autumn 2004 and is running without problems since. In the dry season the autoclave is run up to four times a day. In rainy season the electric boiler of the autoclave is used.

After this promising experience Solar Alternatives is now producing two more solar autoclave system for further hospitals.

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Together with Solar Alternatives (India) a solar steriliser was developed in 2003 . A prototype of a steam generator was built which is able to run an ordinary autoclave of 67l volume 3 to 4 times a day.

The system is designed in a way that makes construction and maintenance easy.
Only locally available materials are used. When the weather is bad the gas or electric boiler of the autoclave can be used.

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The system is based on a 230 kg block of iron which is heated in the focal point of a 10 sqm Scheffler Reflectors. The iron block has boreholes which function as a once-through steam generator.

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Heat losses were reduced by using 200mm thick rock wool insultion and a suspension of the iron block with strips of stainless steel. Heatresistant glas is reducing the energy loss through convection at the focal point.At night the absorber area is closed with an insulated lid.

Several experimental setups showed that the system is most efficient and easy to use when it has a closed cycle with natural circuclation. To make the system robust the least amount of valves is used.

The valve conected with the condensate vessel regulates the complete solar steam cycle.Opening or closing the valve controls the flow of water into the iron block and therfore regulates the amount of steam generated. The system is run with destilled water, to avoid scaling. A small solar stil of 1,7 m² provides 5,5 l of destilled water a day.



sterilisator09The first system was installed in Holy Family Hospital in Mandar (150 beds) in winter 2004. The technical staff of the hospital was trained to solve any upcoming problems with the system on its own.The system has been running since its installation without problems.
As an example: in February 2005 57 solare and 5 electrical sterilisationens were performed. From the 28 days 5 were cloudy.

The development of the prototype is documented in a diploma thesis (in german), for questions please contact us.

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