evacuated heat pipe

In simple terms it is a glass tube that is sealed and all the air is sucked out. Inside the tube is a long corrugated aluminium fin that heats up a pipe in the middle of the fin. Inside the pipe is an ether solution which has a very low boiling point.

As a vacuum insulates 93% of the sun's radiation, the tube gets very hot inside which in turn heats the aluminium fin which heats the pipe which heats the Ether solution. The Ether solution then evaporates, the hot gases travel up the pipe and condense against a condenser node which can get up to 250 Degrees hot!! The nodes(from 10 -25, depending on your geyser size) then transfer heat onto the manifold. It is the hot manifold that heats the water as it passes through en route to the geyser.

So in summary so that you can impress your friends and family: The Sun's radiation beats down and heats up the evacuated tube which heats up the'fin' which heats up the pipe in its core which heats up the Ether solution inside the pipe which evaporates and heats up the condenser nodes which then in turn heat up the manifold which finally heats up you water as it passes through!