Frenchman Alexandre-Edmond Becquerel first demonstrated in 1839 that sunlight can induce an electrical current in a material, now called the photovoltaic effect.
Frenchman Alexandre-Edmond Becquerel first demonstrated in 1839 that sunlight can induce an electrical current in a material, now called the photovoltaic effect.
It was, however, over a century before a team of researchers at Bell Labs in the USA invented the first practical solar power unit in 1954. The first fully operational solar plant was built in Hawaii as recently as 1980, and the world’s largest solar power station, Solar One, was established in the Mojave Desert, California, in 1981.
South Africans have made many breakthroughs in the quest to harness solar power, including significant contributions by scientists from the University of Pretoria. Here we discuss three innovations in portable solar heater design.
In the 1990s Gerald Derby-Lewis designed the innovative Suntracker Dome, which converts light and heat from the sun into electricity. The heart of this combination solar electric generator/water heater is a dome-shaped Fresnel lens that captures sunlight irrespective of the position of the sun, and directs it in a straight line onto solar panels. A Fresnel lens is a flat lens with a concentrically-stepped surface that causes refraction as if by a much thicker and larger lens. Each step has the curvature of the corresponding part of the thick lens.
The Suntracker Dome operates like a giant solar magnifying glass and uses 20 times fewer solar cells than conventional flat plate collectors, yet it delivers more electricity and free water heating. The 50 watt Suntracker is ideal for domestic and outdoor use as it produces about 0.5kWh electricity per day and heats over 50 litres of water. It is a sealed unit, has no internal moving parts and is completely safe.
Another invention, the Turboheat Solar Spiral was invented by Alan Walton of Cape Town in 1996. It's a solar water heater with a heat exchange pipe wound around an inverted cone. Its 360º face eliminates the need to orientate it towards the sun, and it can be installed on the ground or on the roofs of concrete buildings.
The heat exchange pipe is made from inexpensive PVC plastic and the 3D spiral shape provides maximum length and a slow gradient over the cone-shaped heat collector, which maximizes heat gain. The insulated storage cylinder is mounted vertically to optimize natural convection and the action of a thermo-siphon.
The energy absorbed is the equivalent of 2kWh in full sunshine. The temperature of the stored water is 50-65ºC, and the unit may be connected in series to provide large quantities of hot water.
It is inexpensive to build as it is comprises only locally made materials and its simple construction makes it possible for semi-skilled labour to make and install it. The Turboheat Solar Spiral has the potential to improve the quality of life of rural people, create jobs, reduce dependence on fossil fuels, and promote better hygiene.
Then there's the Solo-Mobile Solar Water Heater, invented by Brian and Oliver Harmer of Johannesburg in 2000, which is a simple and practical device for heating water in rural areas. The solar heater is attached to a tank filled with water, and the whole device can be wheeled around so that the collector is positioned to face the sun. Cold water is heated in the collector, rises up pipes, and flows back into the tank. This cycle continues until all the water is hot.
This solar heater can produce hot water within an hour of being exposed to the sun. As hot water is tapped off, more cold water is added, which in turn heats up. Over 200 litres of hot water can be drawn from the Water Heater every day. It is ideal for people in rural areas who have no electricity or piped water, and has no negative environmental impacts. It can also be used by campers, hikers and the military in remote rural areas.
