What is the difference between copper heat pipes and glass heat pipes?
The gravity system has glass heat pipes; high pressure systems have copper heat pipes. In practice, this means that the gravity system has to go up on the roof or have a pump downstream, to get high water pressure at the tap. The pressure system can be put anywhere, even below the point of use and high flow can be achieved simply by increasing the input pressure. Both systems heat up their tanks of water in the same time-about 3 or 4 hours in full sun. The difference in price comes about because the pressure system has to have everything made stronger.
