Solar hot water can save you money

Anyone who has been on a roof in the Keys knows how hot it can get. Temperatures of 130 degrees, especially in the summer, are not uncommon.

Heating home hot water with the sun is one of the oldest ways to harness solar energy. It’s a relatively low-tech solution that can reduce power bills by as much as 15 percent or more for an average home.

Keith Kropf, manager of engineering for Florida Keys Electric Cooperative, said more than half of the houses in Miami had solar-heated water in the 1940s, and more than 80 percent of new-home owners planned to install it. But electricity became very cheap in the 1950s, and many residents had their solar units disconnected.

“People pay about $10 per month per person for hot water now,” Kropf said. “At these prices, people just don’t think about the cost.”

But times have changed. Oil is selling for double what it was just a year ago, and not only are gasoline prices increasing, but so are electric bills. Lower Keys utility Keys Energy just announced a 6 percent increase in rates, and more are sure to follow. Green is suddenly “in.”

Hawaii recently became the first state in the country to require installation of solar water heaters on new single-family homes by 2010. While neither Florida nor any Keys governmental agency has mandated solar hot water, the federal government provides tax rebates for installing the units. (Florida also sets aside money for rebates, but this year’s money has already run out.)

“People who install these units get the cheapest energy savings,” said Doug Gregory, director of the University of Florida/Monroe County Extension Service.

Gregory recently returned from a weeklong seminar put on by the Florida Solar Energy Center. While that seminar dealt with the more expensive and complex solar power systems, Gregory is most enthusiastic about the possibilities for solar water heater use in the Keys.

“The systems cost about $3,500, and [owners] get an immediate decrease in their electricity costs,” said Gregory, who is also a member of Green Living & Energy Education, the Keyswide nonprofit that focuses on sustainable living.

According to the Florida Keys Electric Cooperative, the average spent on hot water is about 8 percent of the electric bill, although that number varies by usage habits and number of people. It can be as high as 15 percent or more depending on the efficiency of the other appliances and air conditioning in the home. That translates into approximately $27.30 a month for two people and $45.50 for four.

Another benefit of solar hot water is that it doesn’t make any contribution to global warming.

According to the Florida Solar Energy Center, “Depending on the type of conventional fuel used, replacing an electric water heater with a solar heater can offset the equivalent of 40 percent to 100 percent of the carbon dioxide emissions of a modern passenger car.”

That’s significant.

How it works

Installing a solar hot water system is fairly straightforward, and experienced do-it-yourselfers can manage the process.

The best units for the Keys are called integral collector-storage systems, which are simple and reliable. The units are made of one or more black tanks or tubes in an insulated, glazed box.

Cold water first passes through the solar collector, which preheats the water, and then continues to the conventional backup water heater. The best systems use a small photovoltaic (solar) panel to power a small electric pump needed to push the water to the roof.

Gregory said that the most important and time-consuming portion of the installation is fastening the solar panel to the roof in our hurricane-prone zone.

“The roof penetrations for fastening the system to the home’s roof should be done by a roofer or a solar contractor as this is the most critical part of the installation,” he said. “The solar collector must be tied into the strongest parts of the roofing system, i.e., the trusses, and not just fastened to the roof sheathing.”

So why aren’t there more solar hot water heating units in the Keys? There haven’t been and, in general still aren’t, many installers. Gregory said he recently called around to plumbers in the area and few were interested.

“During our building boom, these companies were so busy remodeling homes that they just didn’t have time to think about a new venture,” Gregory said. “Now that building has slowed down, we may see more activity.”