Domestic Water Heating

The Pulpit Rock

A 50 sq ft solar water heater sealed into the roof

Solar water heating for domestic use is not a recent idea - it goes back over 100 years. We have evaluated and serviced dozens of systems in the Madison area that are still working great after 30 years. Today, the technology is more advanced than ever. Developments have made systems more efficient, reliable, visually attractive and user-friendly.

Solar thermal systems are used to supplement a building's heating loads, such as domestic water heating, winter space heating, or pool heating. Domestic water heating systems are the most common type of solar thermal system installed in Wisconsin. Solar thermal systems that are used for winter space heating and pool heating are often also used to heat domestic water year-round.

How it Works

Solar thermal collectors absorb radiant heat energy from the sun. Full Spectrum Solar most commonly installs flat-plate collectors. Flat-plate collectors are manufactured with a strong, insulated, anodized aluminum frame and tempered glass, which gives them an appearance similar to skylights and an excellent track record for durability. Inside the collector frames, copper tubing is attached to an absorber that is specially coated for maximum energy gain. The collectors are typically mounted on a relatively shade-free, south-facing roof area or structure built on the ground.

When the sun shines, a small pump circulates a non-toxic antifreeze solution (solar fluid) through insulated piping between the collectors and a heat exchanger. In a domestic water heating system, the heat exchanger transfers the collected heat from the solar fluid to a storage tank and is often as simple as a coil of tubing immersed in the tank.

The solar storage tank looks like a standard tank water heater but is typically a little larger. It is plumbed inline before the existing gas or electric water heater, which remains in service as a backup for stretches of cloudy weather. Whenever hot water is used in the home or building, solar heated water is drawn from the storage tank into the backup water heater, which eliminates or reduces the need for conventional heating. The solar storage tank is necessary because most domestic hot water use occurs in the morning or evening hours, when it’s not necessarily sunny. A well-insulated storage tank allows for water that was heated during the day to be utilized later that evening and the next morning.

The Pulpit Rock

Image Courtesy Velux Corporation

Operation of a solar water heating system:
  1. Sunlight heats fluid in solar collectors
  2. Heated fluid pumped via heat exchanger to water storage
  3. Solar heated water supplemented by auxiliary heat source
  4. Hot water to taps
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