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Solar Water Heating

Solar Water HeaterSolar hot water refers to the use of the sun's energy to heat water for household and industrial use. Solar water heating systems generally consist of the following components:

  1. A solar collector
  2. A storage vessel
  3. A heat exchange fluid in the case of indirect systems*
  4. A pump in the case of an active system*

Southern Africa has an ideal climate for the use of solar water heaters and, given that the heating of water is the biggest single consumer of electricity for the average household and thus contributes to the bulk of the electricity bill (up to 50%), the installation of a solar water heating system can go a long way towards saving the homeowner money and alleviating the strain on the electricity supply in the region.

 

Traditionally, flat-plate solar collectors have consisted of a simple glass-topped, insulated box with a flat absorber made of metal and attached to copper pipes. The copper is painted black to maximise the amount of sun's energy absorbed. Another type of collector is the evacuated tube collector consisting of metal pipes surrounded by glass cylinder that houses a vacuum. This type of collector is very efficient at capturing the sun's energy. Both flat-plate and evacuated tube systems work well in South African conditions.
Last Updated on Thursday, 15 October 2009 13:17
 

Frequently Asked Questions About Solar Water Heating

Besides cost savings, what are the other benefits of solar water heating?
In today’s beleaguered world, installing a SWH is simply the right thing to do. A domestic SWH with a two square metre collector could harvest up to 2,000 kWh (kilowatt hours) of energy from the sun every year. By displacing the Eskom electricity that would otherwise have been used to heat the water, 1,080 kg of coal and 2,800 litres of water are saved, while 1,956 kg of Carbon Dioxide, 320 kg of ash, 17.9 kg of Sulphur Dioxide and 8.4 kg of Nitrous Oxide are not discharged to add to the Planet’s growing burden of pollution. That’s an important gift to the Earth for any good citizen to consider!
What is the difference between a direct and indirect solar water heating system?

“Indirect” systems use a heat transfer fluid (glycol) to move the heat from the solar collector to the tank, thus heating the water indirectly. Indirect systems are freeze resistant, but require maintenance because the glycol may evaporate over time. "Direct" systems may break in sub-zero temperatures (unless they are freeze-resistant) and should thus be installed in frost-free areas. Direct systems are simple and reliable and do not require regular servicing.

Definition of a frost area


Rule of thumb is if the temperature ever drops below 4°C then you will get frost.

Further; the area between the South African escarpment (high areas) and the coast (low area) is deemed to be generally frost free. Although there are pockets within the coastal band that do get frost, these areas should be known by residents. 

All inland areas, which are those from the escarpment inwards (most of the country ) are definitely deemed to be frost prone areas. Therefore only indirect or direct systems that have been tested and confirmed frost resistant by SABS should be installed.

The following areas in the coastal provinces are frost areas:

In Kwa-Zulu Natal:

  • Pietermaritzburg
  • Inland

In the Western Cape

  • Karoo

In the Eastern Cape

  • Umtata
  • Inland

 

What happens when there is not enough sun to heat the water to the desired temperature?
Solar water heating system's tanks are much better insulated than conventional geysers. They therefore ensure that the water stays hotter for longer. If the water does drop below the desired temperature (which is governed by a thermostat like with conventional geysers), most solar systems have a backup element which will automatically switch on. It is desirable to have a timer on the element to ensure that it does not turn on during periods of peak electricity consumption or when hot water is not needed such as in the middle of the night.
How long will a solar water heating system last?
We know of flat plate direct systems that are still working after 27 years. Theoretically, a flat plate system made of copper, aluminium or stainless steel should have an unlimited life, and even those with galvanized steel casings have good durability inland. As with vintage aircraft and motor cars, preventive maintenance will prolong their lives.
How to decide on a supplier?
You are strongly advised to install a system that is on the Eskom list of approved suppliers as well as being a SESSA Solar Water Heating Division member. Our Solar Water Heating Division members are listed here. Not only could you qualify for a rebate, but Eskom will check on the installation to ensure it has been done correctly. If you decide to buy a system that is not yet on the Eskom list (some suppliers are still in the process of testing at the SABS), you must look at the track record of the product, and talk to several owners of the system.
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