We often get asked why converting your existing geyser is preferrable to installing a solar geyser.  There are indeed a number reasons why.

With a geyser retrofit (conversion), you make use of your own geyser and it stays where it is (normally in the roof space in the house) whereas for a solar geyser you basically throw away your old geyser making it less cost effective.

Solar geysers aesthetically look rather large and unattractive on the roof while with solar geyser retrofits you only see the evacuated tubes (EVT) which are much more attractive and minimal looking (see photos).

Having the solar geyser on the roof is also much more troublesome and can even be dangerous as the heavy weight of the geyser drum and the water inside can weaken or damage the roof.  In order to support such weight, modifications to the roof for a solar geyser are often necessary.

Solar geysers are less efficient because they do not benefit from the insulation that your own geyser has by being inside your house.  Solar geysers lose a lot of heat this way which is wasted and you end up with less hot water, especially in the morning after a cold night.  While with a solar geyser retrofit, your geyser stays much warmer inside the roof or elsewhere in the house resulting in hotter water for longer and bigger savings.

The amount of hot water a solar geyser or geyser retrofit produces is proportional to the number of evacuated tubes (EVT) in the system (see the number tubes in the photos).  Solar geysers generally produce less hot water than solar retrofits because the number of tubes is limited to the width of the solar geyser, with a geyser retrofit, you can get more tubes tailored to your household size, bathing patterns and geyser size.

Finally, most solar geysers are low pressure systems and not enough pressure is available for showers and baths can only be taken.  This is quite inefficient at showers use less water than a bath and severely restricts the amount of bathing possible for a family.  Solar geyser retrofits are high pressure systems with much faster flowing water facilitating hard hot showers and generous hot water from the bath, kitchen and other taps.