Pump or no pump?
The water or fluid can be circulated around the solar water heating system using a pump, or it can be circulatenaturally using a thermosiphon system.
Systems that use natural circulation by thermosiphon d are often called 'passive' systems. In this type of system, the hot water cylinder has to be located above the collector panels, usually on the roof. Cold water or fluid moves down from the cylinder into the collector panels; then, once it is heated by the sun, it rises back up into the cylinder.
Systems that use pumps to circulate the water or fluid are often called 'active' systems.
Thermosiphon circulation (image from EECA).
Natural circulation by thermosiphon has the advantage that it does not require a pump and therefore is not dependent on electricity, whereas a pump system is.
With a pump system, the hot water cylinder can be located at a level below the collector panels. This can be helpful if you're installing a solar water heating system in an existing home and you want to use the existing cylinder, or if you would rather not see the cylinder on the roof. It is essential that the pump is used in conjunction with a controller (see below) to ensure the pump operates only when necessary.
A controller manages the use of supplementary ('booster') gas or electric heating, and controls the pump in a pump system. The heating controller has a significant effect on overall system performance, so it is important this is set up correctly.
There are two types of supplementary heating controllers: time trigger controllers and minimum temperature controllers.
A time trigger controller can be used to keep the booster heating turned off during the day, to ensure you're not paying for electricity or gas to heat your water when the sun could be doing the job for free. The timer can also be set to turn on the supplementary heating before periods of high water use. This can greatly increase the system's efficiency.
Minimum temperature controllers simply trigger the supplementary heating whenever the cylinder temperature drops below a minimum pre-defined temperature.
Open loop system with pump circulation and controller (image from EECA).
A controller will ensure that you'll never be without hot water, regardless of the time of day. Make sure you talk to the installer or supplier about the type of controller you need.
The Building Code requires that the temperature of the water in your cylinder must reach 60 degrees at least once a day. Make sure your system is set up to meet that requirement.
It's also worth reviewing your electricity tariff when you install a solar water heating system to ensure you are paying the best rate for supplementary heating.