Solar Domestic Water Heating

Solar energy is most efficiently used for the low temperature water heating required for domestic or building service use. Examples include hot water for housing, dining facilities, laundries, and swimming pools. Solar energy has been used for more than 80 years in Florida and California for these applications.

A wide variety of solar energy systems are available to heat water. Small packaged systems designed to serve residential buildings are readily available. These systems include (1) integral collector storage units, which combine the collector and storage tank in a single unit, (2) thermosyphon systems with the tank located above the collectors, and (3) active solar systems using several different design strategies to prevent freezing.

Commercial, industrial and institutional buildings using moderate amounts of hot water require larger solar domestic water heating systems. These systems, normally sized to meet specific loads, are similar to the residential packaged active solar water heating systems, only larger. Typically, a multicollector array supplies a preheat tank with thermal energy and the entire system interconnects to the existing water heating system. Active solar water heating systems are typically mounted on the roof and use multicollector arrays in a closed loop, freeze protected systems.

Solar energy used to heat water directly displaces conventional energy sources, providing a positive environmental benefit. The installed cost of a typical solar water heating system used to heat domestic water is approximately $50.00 per square foot of collector area. Operation and maintenance costs over the life of the system effectively add a total of 12%, or $6.00 per square foot, to the installed cost of the solar system. A typical residential installation will require between 40 and 80 square feet depending on the water consumption (family size) expected. A commercial installation would be sized to the load.

The amount of hot water a solar system will provide depends on the type and size of the system, the site specific (micro) climate and the quality of the site in terms of solar access. In any installation aesthetics must be considered, orientation of the structure and solar access are critical issues. It may not be appropriate to install modern solar systems on some historical buildings.

The amount of energy each square foot of collector will deliver is site specific, in Florida, a typical solar thermal collector used to heat water will deliver between five and six million Btu's over its twenty year life. Dividing the total life cycle cost of $56.00 by the energy collected over the 20 year life results in a delivered energy cost of approximately $10.00 per million Btu's (Mbtu). This energy cost is equivalent to a guaranteed (fixed) price of $0.036 per Kwh (electric), $0.68 per gallon of LPG or $0.75 per therm of natural gas.

Businesses spending more than four cents per kWh or 75 cents per gallon of LPG to heat water should consider the solar option. They will find out for themselves that solar saves. Flaenergy has provided design for:

• Restaurants
• Recreational Facilities
• Process Water Heating System
• Many C&I Applications

Contact us if you are considering the solar alternative.