Solar water heating explained
Solar water heaters, which heat water for personal use, are classified as either being open (direct) or closed (indirect) systems. In an open/direct system the household (potable) water circulates through the collector panels. This system is ideal for locations where the ambient temperature never falls below 4˚C and where the water quality is good. Since most areas in South Africa are frost prone in winter, and because of the water's high mineral content in many areas, the open/direct system is generally not considered viable in most parts of this country.
In a closed/indirect system the household (potable) water used does not circulate through the collector panels. The heat exchange fluid used in the collector panels, generally a glycol and water mixture, is heated and that heat is then transferred indirectly, i.e. without coming into contact with the household water. Closed/indirect systems are typically used in areas where frost occurs and when water quality is poor. The glycol solution used in the collector panels contains USP propylene glycol. This specific glycol is considered generally safe for use in foods by the American FDA, meaning that even in the unlikely case of a leak and a consequent mixing of the glycol with the household water, there is no risk to humans or animals.
Advantages of solar heating:
- South Africa has very high solar irradiation, so using solar power makes sense.
- Other than buying the technology, solar is a money-saving long term investment. You save money on a day-to-day basis through greatly reduced electricity consumption.
- Heating water with solar energy is free, so there will be a 35 – 45% reduction in monthly electricity bills, depending on usage patterns.
- Some solar water heaters, but especially Solsquare Solar Water Heaters have much longer system lifespan than traditional geysers, thereby saving you money in future equipment replacement.
- Less vulnerable to electricity price increases and no lack of hot water during power outages.
- Financial rebates from Eskom.
- Using solar energy contributes to preserving the environment by reducing your environmental footprint, through reduced consumption of natural gas or coal.
- By more people converting to renewable energy, less and smaller new power plants will be needed, thus reducing the potential environmental damage caused by these power plants.
- Replacing your geyser with a Solsquare Solar Water Heater can save up to 3.5 tonnes of CO2 emissions or 6 kg of sulphur dioxide, which contributes to acid rain, annually - which is equivalent to taking 1.5 cars of the road.
Annual Solar Radiation in South Africa
Source: CSIR & ESKOM
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Annual global (Direct plus diffuse) solar radiation received on a level surface Legend
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What you need
Solar water heaters consist of three parts:
- Storage Tank (Solar Water Geyser) – this is where the hot water is kept.
- Collector – this is the collector that captures and transfers the sun's energy into hot water.
- Booster – the booster (Electrical element) is used to ensure that hot water is available during overcast days and at night. It is found inside the tank, similar to a normal electrical geyser.
The collector can either heat water directly, which is called an open (direct) system, or indirectly, called a closed (indirect) system. Direct systems are generally used where there is absolutely no chance of frost, outside temperatures don't drop below 4˚C, and the water quality is not a problem at all (equivalent to metropolitan areas). In other words, living in South Africa, you most probably want an indirect system. Such an Indirect system is a system where the domestic water does not circulate through the collector panels. A special heat transfer fluid used in the collector panels is heated, and that heat is then transferred indirectly, i.e. with-out coming into contact with the domestic water that will be used in a household, through the heat exchange jacket. A good quality Solar Water Heater such as the Solsquare system uses a full jacket heat exchange resulting in the highest possible degree of efficiency compared with other methods of heat exchanges.
How the system works
Thermosyphon vs. Split Systems
Thermosyphon systems are complete on-roof hot water systems, in which the storage tanks and solar collectors are mounted on the roof as a "close coupled" unit. Thanks to the sophisticated functional principle of the Thermosyphon, water is heated very economically and efficiently, without the need for any moving or potentially electricity consuming parts.
The cold and hot water supply lines are connected to the domestic water system. Thanks to the solar radiation water or heat exchange fluid is heated in the collector and as it is warmed up, its density decreases and therefore rises to the top of the collector from where it flows into the storage tank or heat exchange jacket and displaces the cold water. The cold water in turn flows into the collector and is heated there.
The heated water then flows into the hot water lines and can be used directly for cooking, washing or showering. Not only is this system often the most economical solution, but the technology is foolproof and requires virtually no maintenance.
Split systems separate the tank from the collectors and are therefore used where homeowners do not want the storage tank on the roof. They use a pump to move the liquid through the collectors and into the heat exchange in the storage tank, where the warm heat exchange fluid heats the domestic water through the heat exchange mechanism.
Though this system has more components and hence is slightly more expensive, its advantages are twofold:
- The storage tank does not need to be placed directly above the collectors, allowing the tank to be placed up to 20m away from the collectors.
- The system is very efficient as the pump regulates the flow rate of the glycol solution through the system.
If the sun does not shine for several days or the water consumption rate is abnormally high, the storage tank thermostat, used in both system types, automatically activates an additional electric heater. This ensures that hot water is always available.
Installation and Maintenance
The solar water heating system is covered by a 10 year warranty against defective factory parts or workmanship from the date of installation, which is subject to regular maintenance. The system must be installed by an approved installer, to ensure the quality and efficiency of the system.
The Solsquare Solar Water Heater is designed and installed so that there is minimal maintenance required by the owner. Personally inspecting or servicing of the system by the owner is not recommended.