Appropriate Technology

Solar energy

Many developing countries have an abundance of sun, so there is great potential for harnessing its energy to address basic needs such as lighting and cooking.

Since the 1980s a variety of solar technologies have been tried, tested and adapted, some successfully and others not proving to be as useful as they might first appear.  So here I would like to share my own experience, and also that of colleagues working with solar in development contexts in India.

...but first - solar bottle lighting - a brilliant idea from South America - do watch this video

Photovoltaic (PV) cells convert sunlight into electricity, which can be used directly or stored in either directly by charging batteries to store the energy for later use.  In India small photovoltaic panels, although initially fairly expensive, have been used very successfully to light schools, streets, market stalls, homes and even nomad tents.  Small solar lanterns are also readily available in the shops.  Larger arrays have been successfully used to charge batteries to power refrigerators, for example to store medicines in remote locations. Photovoltaics can also be used to power pumps for drinking water provision and irrigation for small scale farming.

In my experience, of all the solar technologies available, small scale photovoltaics have proved the most adaptable to developing situations, especially where systems are simple and easily maintained.  One inspiring organisation, the Barefoot College, has developed and delivers training courses in the assembly of simple solar lanterns and home lighting units.  The majority of trainees have been illiterate women from many developing countries in India and Africa, who have learnt how to electrify their home communities using solar technology.

Another inspiring organization working with photovoltaics in India is Aurore, winner of the prestigious Ashden Award in 2004.  And a 2012 Ashden Award winner is Australia's Barefoot Power

Solar water heaters
A solar water heater functions on the thermosyphon, or forced circulation, principle, where water circulation depends on variable density.  Basic solar heating panels consist of glazed units containing pipes fed from a cold water source and linked to an insulated hot water storage tank.  When sunlight falls on the panels it warms the water in the pipes which increases in density and thus rises under pressure into the insulated storage tank, displacing any colder water inside so that it re-circulates.  The hot water can be used directly from the storage tank or used to heat water in a secondary storage tank via a coil. 

The efficiency of these systems is determined by the quality and regularity of maintenance.  In particular, the glazing on the panels must be kept very clean.  Unfortunately, where there is a poor maintenance culture, efficiency quickly declines and the water heating systems often fall into disrepair and disuse because they are perceived to be malfunctioning, when all they need is agood clean! – see photo below of a relatively new system seen recently in south India! 

Concentrated solar power systems
Lenses or mirrors and tracking systems can be used to focus a large area of sunlight into a small beam, which may be used to heat large quantities of water to provide steam for cooking, or large quantities of hot water for washing and cleaning.  The solar bowl is an example of such a system.  It is most appropriate to use by large institutions and maintenance is critical to maintaining efficiency.

Solar box cookers and parabolic solar cookers
This type of cooker is relatively cheap and efficient and would seem to be an ideal solution where fuel is scarce, but for the cookers to work at maximum efficiency, they need to be intermittently turned to track the sun’s path across the heavens.  Sadly, even the modest cost puts the cookers out of reach of the poorest and, as family members may need to work long hours away from home to survive, there is often nobody available to turn the cookers during the day. 

...and it seemed like a good idea at the time - Photovoltaic elephant fencing!  

In south India, where there is an interface between humans and  elephants, this can result in serious crop damage and even human fatalities.  In an effort to keep elephants out of areas of human habitation, photovoltaic electrified fencing was introduced as an experiment, with limted success - because as we all know elephants have thick skins!

The appropriateness of innovative solar technologies in any given situation is dependent upon an in-depth understanding of the daily lives of those that they are intended to benefit.
Photovoltaic panel, Ladakh
Solar water heater, Karnataka
Solar bowl (Auroville image)
Parabolic solar cooker, Ladakh
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