Solar heats water by heating a second coil, (a radiator), in your cylinder, in much the same way as your central heating does. Both are closed systems which heat a liquid and pump it through pipes to seperate dedicated coils in your cylinder where the heat transfers into the water. The central heating coil is on top to heat the top half of your cylinder and the solar coil at the bottom, where the water is the coldest to allow for maximum heat transfer.
Solar water heating simply converts light into heat and uses that heat to heat your domestic water. The systems do not need direct sunlight to work effectively!
1. Light is absorbed and heats a solution in the solar collector (the solution is a mix of water and glycol).
2. The heated solution is pumped into a second coil at the bottom of your cylinder in your hot press (this is a closed system so the solution does not mix with the water in your cylinder).
3. The heat is transferred through the copper coil into your water.
4. The heated water rises to the top of the cylinder for domestic use.
5. The solution is pumped to the roof again for reheating.