Evacuated tube collectors contain a copper heat pipe, which is fitted into an absorber plate, inside a vacuum sealed glass tube. The heat pipe is hollow and the space inside is also evacuated. Inside the heat pipe is a small quantity of freeze resistant liquid. When sunlight falls onto the surface of the absorber, the liquid in the heat tube quickly turns to hot vapour and rises to the condenser top of the pipe. The condenser is plugged in to a manifold and water from the geyser flows through the manifold and absorbs the heat.
Heat pumps and solar water heaters can be retrofitted to work with an existing conventional storage water heater (geyser).