Any Solar Geyser System will only operate as good as it is installed. A very good and effective Solar Geyser system will become poor and ineffective if it is installed poorly and or incorrectly. 90% of manufactures and supplier’s complaints and service calls are as a result of poor installations. The following are basic considerations that need to consider when a Solar Geyser System is installed.
Before one can consider a Solar Water Heating system one needs to ascertain if your home is suitable for a Solar Water Heating system. The most important question that one needs to answer is if the solar collectors when placed on your roof will be exposed to the suns solar radiation unobstructed for most part of the day, usually between 9am and 3pm.
To achieve this, a solar collector must be placed or orientated on a roof structure in South Africa that is facing true north. Variation of up to 45° east or west of true north have little effect on the system and if these variations cannot be achieved, additional solar collectors could be added or solar frames could be introduced, both at additional costs.
Once you have ascertained if your houses roof orientation is suitability for a solar wtaer heating system the following needs to be consideration when positioning the system
Positioning of the Solar Collector
During summer months the sun is located high in the sky, while in winter months it is low in the sky. To optimise the solar radiation falling on the face of the solar collectors one will need to tilt the collectors to receive the full face of the sun as the sun’s angle changes throughout the year. By inclining the solar collector to the same angle of latitude of the location where the solar collector is being installed the face of the solar collector receives the sun’s optimum though out the year. The inclined angle from the horizontal in South Africa and vary 25 degrees in Pretoria to 33 degress in Cape Town. However the pitch for roofs in South Africa is commonly between 22° and 35°. A few degrees extra tilt above or below the optimum angle of latitude tilt makes virtually no annual difference. So in most situations, attaching the solar collectors directly to a north facing roof, even if the roof pitch angle or inclination is not ideal, is the cheapest and simplest option. If the roof pitch is not optimal, it is generally cheaper and neater to install an extra collector than to use a frame to achieve the optimum inclination and thus performance.
It almost goes without saying that the solar collectors need to be installed in a position that is shade free all year long. As a minimum, it is recommended that shading be avoided between 9am and 3pm, since most of the solar radiation is received during this period. Shading generally has the biggest effect in winter, when the sun is lower in the sky all day and its path and solar intensity is lower.
In the case of a close coupled solar configuration, the closer the unit to the area of water usage in the home the more efficient. As for the split unit configuration the further away the solar collectors are from the solar storage cylinder the greater the chance of heat loss through the pipework can occur.
Suitability of the roof
One may neglect to consider the amount of weight a roof has to carry when installing a SWH system which could lead to catastrophic results. Not only do the solar collectors add weight but, in addition, a fully filled storage cylinder does too – giving a combined weight in excess of 300kg. This causes tremendous strain on the roof, which it was, in most cases, not designed for.
Consideration must not only given to the actual roof design and its ability to carry the anticipated loads but also that the roof covering such as the roof tiles can do the same.
Sizing of solar system
Sizing a Solar Water Heating system is based on the volume of hot water required by members of the house hold including appliances that make use of hot water. The sizing of the system involves the selecting and sizing of two components being the solar storage cylinder and the solar collector area.
Hot Water Storage Cylinder Sizing (i.e. Hot Water Usage)
With solar it is desirable to have one-and-a-half to two days of hot water usage in storage, thereby ensuring that if hot water is used in the evening, there is still solar-heated water available for the morning or first half of the following day.
The following table is a guide to the recommended hot water storage required depending on number of household members and hot water usage appliances. However one needs to refer to the relevant manufacturers specifications for their Solar Water Heating system performances and their recommendations.
Number of Household Members and hot water appliances Daily of Household Hot Water Consumption (litres)
1 100 to 150
2 150 to 200
3 200 to 250
4 250 to 300
5 plus 300 plus
Solar Collectors Sizing
A rough rule of thumb is that a one square meter area of a solar collector is required per person, plus 1m2 for each appliance that uses hot water from the solar system. Most solar collectors are approximately 2m2 in area but it must be pointed out, that there is a vast difference between different types of solar collectors and their ability to convert the sun’s energy into hot water.
It is important to use information provided by the solar collector manufacturers, who will have tested their product and are aware of how their collectors perform.