Solar Water Heating Frequently Asked Questions
A Solar Water Heating (SWH) system can take care of the bulk of your hot water needs however, in some instances, the SWH system may not be able to provide all the hot water you need e.g.:
- when it’s cloudy or rainy,
- when the solar heated water stored in the geyser is used in the evening and hot water is again required the next morning before the sun has had opportunity to heat the water
With a SWH system the electrical element remains in the geyser, but is controlled by a timer relay to only switch on at times chosen by the owner when hot water is needed and the SWH system might not be able to supply. If the water in the geyser is already hot the water will not be heated further and no power will be consumed.
Yes, if the geyser is not leaking and not very old, it can be converted to a SWH system. This is called a retrofit and the majority of SWH system installations that take place are of this type. The retrofit requires the fitment of different in and outlet fittings to the standard geyser as well as additional insulation.
A SWH water storage vessel has a thicker layer of insulation than a standard electrical geyser. This is to reduce energy/heat losses when the tank is located outside e.g. on top of the roof and is exposed to the elements as is many times the case for thermo-siphon type SWH systems (see picture on left below). In a pumped or split SWH system the storage vessel (geyser) is located inside of the roof space and even an old ‘E Class Energy Rated’ standard geyser is sufficiently insulated. ‘B Class Energy Rated’ geysers have insulation even thicker than solar geysers and are the only type installed by us. Geyser blankets fitted to ‘E Class’ geysers will save energy and the payback time on the investment is short and therefore recommended. When an existing ‘E Class’ geyser is not replaced SolarTech ZA will always install a geyser blanket and pipe insulating sleeves to reduce energy losses.
A thermo-siphon type SWH uses the principle that warm water rises (less dense) and cold water sinks (more dense) to accumulate the hot water in the storage vessel without
the use of a pump. These types of systems are less expensive than pumped systems but have some drawbacks:
- the water storage vessel must be located above the collector resulting (in most cases) that the vessel is located outside on the roof
- it is usually not cost effective to relocate an existing geyser from inside the roof space to outside in order to make such a system work
- systems are prone to overheating if hot water consumptions and/or storage size is not correctly matched to the size of the thermal collector panel
- requires a maintenance intensive indirect system containing Glycol if a flat plate collector panel is used is geographical locations where the night time temperature may drop to below the freezing point of water
In a pumped SWH system the storage vessel can be located in the roof space below the collector. A solar circulation pump circulates the geyser water through the thermal collector panel and may or may not have a controller. If the system does not have a controller with anti-freeze protection function the same limitations exists as for a thermo-siphon system.
In a direct SWH system the water in the storage vessel or geyser (which is also the same water that comes out of the tap) circulates through the thermal collector panel on the roof. In an indirect system a non-toxic Glycol (anti-freeze) mix referred to as the ‘Heat Transfer Fluid’ (HFT) is contained within a closed loop. The HTF circulates through the thermal collector panel, absorbing the solar energy, and transfers the heat to the water in the storage vessel (geyser) via a heat exchanger. In parts of the country where the ambient temperature drops to below freezing it is necessary to have an indirect system when installing a flat plate thermo-siphon SWH system to prevent freezing and subsequent bursting of the collector panel tubes. With a pumped SWH system that has a controller with a freeze protection function or with evacuated tube collectors this is not necessary.
In all SWH systems this situation cannot occur. In our pumped SWH system the controller monitors the temperature of the water in the collector and if the water temperature approaches the freezing point of water the solar circulation pump will be activated to pump a small amount of warm water from the storage vessel to the collector to maintain the collector water temperature above freezing. In our thermo-siphon SWH systems where no pump or controller is present we will always use evacuated tube collectors which do not contain water and therefore will not freeze. We do not like to install systems that require maintenance and therefore do not install indirect systems that contain a Glycol mix.
We supply and install both types of technologies. Flat plate collectors work very well in our warm and sunny South African conditions and have a higher efficiency than evacuated tube collectors at residential hot water temperatures. Evacuated tube collectors cost significantly more than flat plate collectors and work very well in cold, cloudy or otherwise unfavourable conditions. Evacuated tube systems may also work better where the position of the collector panel is such that it is not facing north.
SolarTech ZA supplies and installs SWH systems that work exceptionally well in cold, cloudy and winter conditions. At times, however, especially during long periods of cloud cover, some use of your backup system (the electrical element) may be required to meet hot water demands. This will be the case for all SWH systems where the electrical element remains in place as backup. In systems where the element is disconnected or removed, the owner will have to make do with lower temperature or even cold water in such cases.
The evacuated tubes in the SWH systems that SolarTech ZA installs are exceptionally strong. However, if one is broken, it can be easily replaced at a relatively low cost.
If there’s a broken tube, the rest of the collector will still function, although at a slightly lower performance. Since each tube is modular and separate from the system a broken tube does not result in a leak.
A SWH system requires very little maintenance but is not totally maintenance free no matter what any supplier claims. It is recommended that a trained person inspects the system once a year in order to determine whether it is still functioning optimally.
Solar Photovoltaic (PV) is a technology that uses solar photovoltaic (PV) panels to convert light energy from the sun into electricity. Thermal Solar or SWH is a technology that uses thermal energy from the sun to heat water.
Solar PV modules and certain types of solar thermal collector panels look very similar in appearance and may be confused. They are however vastly different in functionality and design.
All types of SWH systems installed are SABS approved and are designed to be very robust. The systems can for example resist impact from hail as large as 38mm in diameter.
Under normal circumstances an installation team can install a SWH system in one day.