Heat Pumps
A heat pump works like an inverse air conditioner. It takes heat particles from the atmosphere, compresses them, pumps them into your geyser and circulates the water round.
Heat pumps are efficient in how they use electricity and 1 kw input of electricity generally translates to a 4kw output of electricity. This means that savings on your geyser will be similar to that of a solar geyser.
Aesthetically speaking, heat pumps look like air conditioners so there is little resistance from consumers to placing a heat pump on the wall.