The function of evacuated tube solar water heating systems are:

Step 0ne: Solar energy is absorbed by the evacuated tubes, converted into thermal energy and then conveyed to the heat pipe.

Step Two: The copper heat pipe contains a small amount of acetone and/or refrigerant as the working fluid. The hollow centre of the heat pipe is a vacuum, so that even at temperatures of around 25 - 30^oC the acetone / refrigerant will be boiling. The vapor rises to the tip (condenser) of the heat pipe where there is a lower temperature, caused by the water flowing through the manifold. This causes the vapor to condense and transfer it's heat into the manifold. The condensed vapor then flows back down the heat pipe where the process is once again repeated.

Step Three: During pump cycling, water is circulated through the manifold. Each time the water circulates through the manifold the temperature is increased by 5-10^oC in the cylinder.