Jeffrey Yago gives a brief history of solar hot water heaters:
With continued shortages of wood for home heating, the Greeks built the North Hill section of Olympus in the 5th century B.C. This planned community had all streets running east and west, with each parallel street at a higher elevation as you went north. In this way every home had a large south-facing window which allowed the sun to heat up the uninsulated heavy masonry walls during the day, while heavy drapes were drawn at night to seal in this solar heat. If a neighbor later built an addition that blocked the warming sun, the offended homeowner could sue in court to remove the shading construction.Around the 1st century A.D., the Romans improved on this design by splitting mica into thin sheets or using hand-formed sheet glass to cover open skylights and south-facing windows. This made it more efficient to warm their many public baths using the sun’s rays, while holding in the heat. By the 1800s many upscale London homes included solar greenhouses or conservatories, and glass-covered insulated wood boxes were being used to heat water with the sun.
By the early 1900s, many upscale homes in the United States were able to buy solar water heaters for the huge price of $25 including installation. These insulated glass-covered boxes contained multiple metal water tanks which were installed on a south-facing roof. Valves were located next to the bathtub so the homeowner could route the cold water supply up through the solar-heated tanks then back into the bathtub. Through most of the 1930s many homes in California and Florida had commercially-made solar water heaters to heat hot water where utility natural gas was not available.
These early solar water heaters were very simple to operate and did not require pumps or controls. A solar panel was installed at the lowest part of a south-facing roof just above the roof eave. An insulated storage tank was mounted as high up in the attic as possible. Since heat rises, the heated water in the lower solar panel pushed its way up to the top of the upper tank, and the colder water at the bottom returned to the solar panel to be reheated as a result of this thermo-siphon effect.
When an attic was too small to house the tank, or the roof slope was too shallow to provide enough tank elevation, the installer would cut a hole in the roof peak and the hot-water tank would be mounted upright sticking up out of the roof. A fake chimney was then built around the tank to provide insulation and camouflage. Once low-cost oil and gas was available and piped throughout the towns and cities, solar hot water heaters were gradually replaced with cheap gas-fired hot water heaters and the solar industry in the United States disappeared until a revival in the late 1970s after an energy crisis brought on by two oil embargos.