box. The Climax was the precursor of all modern "batch" systems which heat water directly in a tank exposed to the sun. It was an instant hit in California, where it was usable all year round. Some 18 years later, in 1909, an engineer by the name of William Bailey invented the "Day and Night" solar thermal system, which had a separate collector and an insulated tank (among the first to appear). The collector was a set of pipes under a flat plate: the cold water entered the collector, was heated, rose naturally to the insulated tank and was replaced by falling cold water. Bailey's system is the precursor of all modern "flat plate" collector systems.

Unfortunately, a mere four years later, California suffered an abnormal cold snap... and a lot of Bailey's collectors froze and burst. He immediately changed the design to include an antifreeze-filled heat exchanger pipe. Instead of heating the tank's water directly, an antifreeze solution (made of alcohol and water) was heated in the pipe under the collector. The solution rose as it heated and entered the tank but, instead of mixing with the water, it remained in the heat exchanger pipe and warmed the water around it, eventually cooling and falling back to the collector. This system is the precursor of all modern "closed loop" solar thermal setups.

Bailey's water heaters were extremely popular in California and Florida but his own gas-powered heater of the 1920s and 1930s and the US's entry into World War II put an end to his solar success. He produced his last batch of solar thermal systems in 1941.