Replacing the cylinder with a twin coil solar cylinder is the most efficient way of receiving solar energy, but if economy and speed of installation is of a priority and the existing cylinder is in a perfectly good condition and size, and has a immersion blanking plug at the top of the cylinder, then a special drop in coil can be used. (27inch long only).
The coil is simply placed in the centre of the cylinder (through the immersion plug), and the flow and return pipework connected to the pump station.
As previously stated the heat exchange to the hot water cylinder would not be as effective, but time and money would be saved on the cost of the labour of replacing the cylinder.
The Drop in coil is £100.00, (deduct £200.00 from the solar package prices, if a new cylinder is not required).
NOTE – A mixing valve would also need to be fitted to the cylinder hot water outlet (as in all solar systems) to prevent the water from becoming scolding hot at the taps.