While many of us can remember the solar craze of the late-1970s, not many of us can remember when solar water heating was quite common, at least in sunny California and Florida.

“Back in the 19th century, there was no easy way to heat water,” says solar historianJohn Perlin, author of “A Golden Thread - 2,500 Years of Solar Architecture.” “First, you had to chop wood or lift heavy hods of coal, and then you had to kindle the fuel and stoke the fire, typically in a wood stove.”

Wealthier city dwellers heated tanks of water with gas derived from coal. The fuel naturally didn’t burn clean. And if you forgot to put out the flame, the tank had the unfortunate habit of blowing up.

We met Perlin in a much more modern way: by Googling “history, solar, hot water,” and found him at the California Solar Center,www.californiasolarcenter.org.

To get around all that work to heat water, the first advancement came by simply painting a metal tank black. Set that in the sun and, well, even on a sunny day, you’d wait until afternoon to get hot water.

Perlin points to Clarence Kemp as the first manufacturer of solar water heating equipment. The Baltimore inventor patented the Climax, an insulated box around a metal tank with a glass top in 1891.

The Climax was widely used throughout sunny Southern California at the end of the 19th century. The price tag: $25. Perlin says other inventors made other improvements throughout the beginning of the 20th century, but none proved better than the Day and Night heaters, an innovation ofWilliam J. Baileyof the Carnegie Steel Co.

“Bailey was the first manufacturer to really modernize solar hot water in a way we’d still recognize today - by separating the collector from the storage tank,” Perlin told us.

Bailey’s heating element consisted of a set of 1/2-inch copper pipe attached to a black-painted metal backing inside a glass-covered box. In this way, a smaller amount of water was heated faster and then flowed into an insulated storage tank installed inside.

Soon Kemp was out of business and Bailey sold more than 4,000 Day and Night heaters between 1909 and 1918.

Plentiful supplies of natural gas, however, put an end to the California market. Perlin says Bailey sold his patent rights to a Florida firm, which did quite well as that part of the country developed. As America was about to enter WW II, the Florida company had installed more than 60,000 heaters and more than half of the population of Miami used the sun to heat domestic water.

Cheaper electricity rates, however, brought that market to end as America modernized after the war.

Perlin’s site also features more information on solar developments throughout the 1980s and 1990s as manufacturers soldiered on after the end of the Carter administration’s tax credits.