Solar water heating is a technology that every homeowner can use to save dollars on utility bills. Questions most frequently addressed to the Florida Solar Energy Center in Cocoa about solar water heating are answered below.
Note that many of the replies are general and more explanation may be required for those with individual questions. For additional information, contact the FSEC Public Information Office or call a solar dealer.
What is solar water heating?
A solar water heater uses the sun's energy rather than electricity or gas to heat water, thus reducing your monthly utility bill. When installed properly, solar water heaters are more economical over the life of the system than heating water with electricity, dedicated heat pumps, heat recovery units or propane.
In Florida, three types of solar systems are used: Pumped, integral collector storage and thermo-siphon. The direct circulation system circulates potable water from the water storage tank through one or more collectors and back into the tank. The solar collector is the main component of the solar system. It is usually a metal box with insulation and a black absorber plate that collects solar radiation and heats the water. The circulating pump is regulated by either an electronic controller, a common appliance timer, or a photovoltaic panel.
In integral collector storage systems, the solar water storage system is built into the collector. The potable water in the collector unit is heated by the sun and delivered by city or well water pressure to an auxiliary tank (which contains non-solar back-up heating) or directly to the point of use.
A thermosiphon solar water heating system has a tank mounted above the collector (normally on the roof) to provide a natural gravity flow of water. Hot water rises through piping in the collector, which is mounted below the tank; heavier cold water sinks to the lowest point in the system (the collector), displacing the lighter hot water which rises to the tank.
The integral collector and thermosiphon systems are simple since they use no pumps or controllers and water always flows through the collector.
What size do I need?
For Florida homes with a dishwasher and automatic clothes washer, a rough rule of thumb is 10 square feet of collector area per person and 20 gallons of water storage per person. Thus, for a family of four, 40 square feet of collector and a total tank storage of 80 gallons are typical.
Families can also purchase a solar-assisted system that uses a 20- to 26-square-foot collector that is retrofitted to their existing 40- or 52-gallon water heater. Due to the reduced storage tank capacity and smaller collector size, these systems will only provide 50 to 60 percent of the hot water used. The installed price will of course be lower since the existing tank and smaller collector are used.
How much is saved?
Your monthly savings will depend on the amount of hot water you use, storage tank size and type and price of fuel used for backup water heating.
For a family of four, the typical hot water usage is 70 gallons per day, thus using 3990 kilowatt hours per year to heat the water electrically, or $399 per year worth of electricity at 10 cents per kilowatt hour.
A solar water heater should save between 50 percent and 85 percent of the hot water portion of the monthly utility bill, or $200 to $300 per year for a family of four, if the backup element is kept at 122 degrees.
A solar water heater can save even more if you turn off the backup and rely solely on the sun for your hot water. During summer months, when hot water demands are lower and the sun shines longer, most solar owners turn off the backup element circuit breaker, or switch. As electricity and other fuel prices go up, solar savings will increase accordingly.
What's the cost?
In Florida, an installed solar water heating system can cost anywhere from $3,500 to $5,500. Why the large range? System cost depends upon certain variables, such as the following:
Solar water heating is economically competitive with electrical and propane heating. It is also competitive with dedicated heat pumps and heat recovery units, depending upon the individual situation.
The Florida Solar Energy Center in Cocoa is a research institute of the University of Central Florida.