Difference between revisions of "Solar water heater tank"

Revision as of 04:25, 20 November 2012

A Solar water heater is installed on several rooftops in South Africa. Photo: AFP

A solar water heater is any system that uses the thermal energy of the sun to heat water. They are usually aimed at heating water to a temperature hot enough for washing clothes, washing dishes, and personal hygiene, but not hot enough to cook with straight away. However, as long as it is clean, the hot water can also be used in cooking to save time and fuel.

The basic idea behind the solar water heater is a piece of black piping, filled with water, and laid in the sun for the water to heat up. To heat up more water you increase the number of pipes to make a “collector” and add a tank to store the heated water in. The whole system is insulated to minimize heat-loss. Water is cycled through the collector several times to raise the temperature. Some systems use electric pumps to pump water through the system, but this increases the cost. Alternatively, water can be made to pass through the pipes without a pump using the thermosyphon effect.

Thermosyphons use the fact that hot water rises above cold water. In a passive thermosyphon system, the tank is always above the collector. As the water in the pipes heats up, it rises up into the top of the tank, causing cold water from the bottom of the tank to flow down into the collector. The flow continues until the water in the pipes and the tank is at the same temperature. One-way valves are fitted to stop water flowing back the other way when the temperature drops at night.

Suitable conditions

Benefits

• Heating water with sunshine costs you less. Once you have paid for it, your water heating costs will be zero.
• A solar water heater cannot give you a shock or set fire to your house like electrical or flame-based water heating systems.
• Solar water heaters do not make any smoke, so they don’t make your home smell or get dirty.
• If you usually heat water with gas or electricity from fossil fuels, a solar water heater helps reduce the carbon dioxide produced by your household, helping in the fight against global warming.

Construction, operations and maintenance

How a solar water heater works. Drawing: PACE.

Costs

The cost will vary widely around Africa, depending on the size of the system and whether the materials used have to be imported. Import taxes and taxes on business sometimes add to the expense. Governments could help promote solar water heating by reducing taxes for businesses selling solar water heaters. In South Africa in 2005, a 70 litre solar water heating system cost R3000 (US$455). Larger systems with electric back-up cost up to R10000 (US$1520).

Acknowledgements

• Solar Water Heating, Action Sheet 64. PACE. Paceproject.net.