Solar Water Heaters built in the late eighteenth-and nineteenth-century were bare metal tanks painted black and tilted to face the sun to absorb heat. These early solar water heaters took a long time to heat water on a hot sunny day and quickly lost the heat at night. Later on they improved on these solar water heaters by putting the tank in an insulated box. Still most of the heat gained was lost at night. The Romans invented glass and this trapped the solar energy as heat inside their houses. When glass was applied between the black tank and the sun on these early solar water heaters they were much more efficient. In 1909, William J. Bailey patented a solar water heater that took advantage of the fact that when water is heated it becomes less dence or lighter. His idea was to improve on the solar collector (black tank) and have a seperate insulated hot water storage tank. He rebuilt the solar collector (black tank) and made it very thin. I understand he used a system of black riser pipes that rose up to a header pipe, they were attached onto a black metal plate where the sun rays were absorbed as heat. An Insulated header tank for the solar heated water was installed above the solar collector. Two pipes connected this tank to the solar collector, one from the bottom of the tank to the bottom of the collector and one from the top of the tank to the top of the solar collector.

A day & night thermosyphon

SOLAR WATER HEATER.