There are two main components in a solar water heating system.
In this comment we only cover the tank, rather than the merits of solar collector types.
Most homes are fitted with electric geysers. They are typically 150litres or 200litres and are pressure tested to operate at 400kpa or 600kpa.
Although today the tanks can be located anywhere, (the water being pressurized, the water can go up as well as down) for historical reasons, when mains water was not pressurized, the geysers were located in the roof void. This resulted in gravity fed water to the taps.
With most geysers in the roof void, they make ideal opportunities for solar retrofitting. Put another way, use the existing plumbing infrastructure, and fit a solar system to it, where the solar collector will be on the roof, and the geyser below in the roof void.
All geysers, both electric and solar are tested to SANS 151. It is illegal to install a tank that has not been tested to 151, passed and SABS Marked.
In South Africa 400,000 to 500,000 electric geysers are manufactured per annum. They can all be retrofitted with solar by the home. In contrast solar water geysers are less than 20,000 units per annum and consequently considerably more expensive.
Are there other differences between solar geysers and electric geysers? The answer is ‘Yes’, but they are minor. An extra port into the geyser may be included making 4 or even 5 ports, rather than 3 or 4 on electric geysers. Insulation may be thicker, because on roof solar geysers are exposed to the elements and consequently are likely to suffer more heat loss, than one installed in the roof void.
Then depending on the type of solar collector, and the solar heat transfer process, the tanks may be fitted with holes for taking evacuated tubes. They may also be a double tank type, where the hot water for the home is the inside vessel, and an extra tank is wrapped around it so that heat is transferred to the inner vessel.
Does this make any type of tank better than another? Some people would claim so, but it is questionable, as the sole purpose of the tank is to store hot water.
On a solar system, whether it is an electric geyser that is retrofitted, or a solar geyser designed specifically for its solar collector, what really matters is the price and what you get for it.
Financial performance, along with hot water performance are the areas that matter.
Ubersolar solar collectors can be fitted to almost any tank of any size or volume.
Plug and play flexibility enables any volume of water to be heated by solar, with any required electricity or gas saving.
One reason we are cheaper is that we can both retrofit electric geysers, and use electric geysers for complete systems.
This improves the risk reward ratio, saving more electricity for less cost.