More than 80 years ago, Miami was on the cutting edge of solar technology, using it to heat water.

''There was a company in Miami that was the biggest solar water heating company in the United States in the 1920s and '30s,'' said solar expert Jim Dunlop.

By the 1950s, however, the United States had begun an industrialization boom. Bigger power plants were built and electricity was cheap. There was a big push by electric utilities for homes to be all-electric, and soon everyone had electric water heaters and electric ranges, Dunlop said.

''So we got rid of all the other emerging technologies,'' he said. ``Solar, along with other alternative approaches to energy, went down the tubes.''

Then came the oil embargoes of the 1970s, and solar came back. Sort of.

PROBLEMS AROSE

Solar water heaters reappeared in the 1970s but they had problems.

''There were a lot of [installation] people who didn't understand what they were doing and there were not established standards in place,'' Dunlop said.

Solar water heaters got a bad reputation, and people quit buying them.

With the price of oil rising again, solar systems are especially attractive now for water heating, and the contemporary systems are better made and easier to install.

Materials today are far superior to the pre-1950s, said Dunlop. Freeze protection and system controls have been ''immensely improved,'' he said. Special coatings are used on absorber plates to improve solar radiation gain. The covers are made of highly transparent low-iron tempered glass.

Further, he said, there are international test standards for solar water heating systems, plus performance ratings that allow customers to compare products.

Most solar water heaters have a gas or electric booster for cloudy days when the sun won't heat a sufficient supply of water.

''Thermal hot water systems are very economical,'' said Bob Reedy with the Florida Solar Energy Center. ``They pay back very quickly.''

POOL HEATERS

The center calls solar swimming pool heaters ''one of the most economically attractive solar technologies in Florida today.'' The heaters cost $2,000 to $4,000. The center publishes a directory of solar contractors. Call 321-638-1000.

The 2005 U.S. Energy Policy Act also encourages use of solar water heating (and solar pool heating) with tax credits of 30 percent. Florida allows a $500 rebate.