The Different Solar Geyser Systems
A solar water heating system harnesses radiation energy from the sun to heat water and stores this hot water for use when required.
The dependence on sunshine means that a back-up electrical element is required for times when there is no sunshine – e.g. overcast weather or at night time.
Passive System (Thermosiphon)
This uses natural circulation of the water between the collector and the geyser. No pumps are required and because of its simplicity this system is the most reliable.
Hot water is lighter than cold water and will rise. Thermosiphon is the natural use of this principle.
Solar Collectors
Low Pressure Direct Evacuated Tube Systems (EVT)
These systems are generally used in situations such as low cost housing, farming and rural cases.
Features:
– Low cost
– Can only be used as close coupled system
High Pressure System Using Evacuated Tubes (EVT) With Heat Pipes
This system uses “heat pipes” within the vacuum tubes to conduct the heat from the EVT to the manifold and then to the geyser either by thermosiphon or a pump.
Frost resistant (if silicone inserts used for thermosiphon) or by controller with pumped system.
Tends to overheat in summer holidays.
Flat Plate Collector (FPC)
The flat plate collector consists of a network of copper pipes enclosed in a box like frame with a glass front panel.
The FPC is robust, efficient and simple which makes it the system of choice for South Africa. By nature of its design it has a “self regulating temperature” feature which eliminates the overheating problem of the EVT system.
Direct Geysers
The normal electric geyser is a direct geyser – there is no form of heat exchanger involved.
If used with solar collectors the potable water circulates through the collector. If used with solar collectors measures must be taken for protection against frost. (Indirect Geysers)
Indirect Geysers
Indirect geysers have a built in heat exchanger which separates the potable water from the fluid in the collectors. This fluid is a glycol and water mixture which protects the panel from freezing. The heat exchanger is either a double jacket or an internal copper coil.
If a coil type is used an expansion tank must be used in conjunction with it.
Jacketed geysers are designed to trap air in the geyser jacket which acts as an expansion tank.
When the geyser and collectors are mounted on a single frame the system is said to be “close coupled”.
Split Systems
Where the geyser is mounted remote from the panels such as inside the roof space the system is known as a “split system”.
Split systems can be either passive or pumped depending on whether the geyser can be mounted higher than the collectors.
Pumped Systems
A pumped system is used when the geyser is lower than the collectors. A pump is necessary to force the lighter hot water down into the geyser.
A non return valve must be installed to stop reverse siphon when the collector is cooler than the geyser (e.g. at night).
An air release valve at the highest point of the system.
Pre-feed System
To increase the amount of hot water available some clients opt to go for a pre-feed system to reduce the expense of putting in a large solar system.
The solar system is used to feed the client’s existing electric geyser with hot water. An electrical element is required to maintain the temperature of the electric geyser which is limited by a timer. The element in the solar geyser is normally left disconnected.
Solar Pre-feed with Heat Pump
A very efficient hybrid system can be built using a heat pump on the downstream geyser instead of the element.
