Active Solar Water Heating

Active Solar Hot Water Heating

Active solar hot water heaters use the sun's energy to heat water for domestic hot water. These systems can be very efficient, even on cloudy days.

Quick Links:
How to buy?
Energy-Saving Tips
What are my Options?
What do I ask a contractor?

How to buy?

Selecting a Solar Water Heater. Before you purchase and install a solar water heating system, you want to do the following:

Consider the economics of a solar water heating system.
Evaluate your site's solar resource.
Determine the correct system size.
Determine the system's energy efficiency.
Estimate and compare system costs.
Investigate local codes, covenants, and regulations.

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Energy-Saving Tips

After your water heater is properly installed and maintained, try some additional energy saving strategies to help lower your water heating bills, especially if you require a back-up system.  Some energy-saving devices and systems are more cost-effective to install with the water heater.  To lower your water heating bills, try one or more of these energy-saving strategies:

Reduce your hot water use.
Lower your water heating temperature.
Insulate your water heater tank.
Insulate hot water pipes.
Install heat traps on a water heater tank.
Install a timer and use off-peak power for an electric water heater.
Install a drain-water heat recovery system

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What are my Options?

Solar water heaters come in a variety of designs according to the circulation system and collector type and channel the sun's thermal energy to heat water.

Batch collectors, also known as Integrated Collector-Storage (ICS) systems, heat water in dark tanks or tubes within an insulated box, storing water until drawn. Water can remain in the collector for long periods of time if household demand is low. A tempering valve serves as protection from scalding at the tap by mixing in cold water with the heated water. Batch collectors are incompatible with indirect or closed loop systems (these systems use a non-freezing liquid to transfer heat from the sun to water in a storage tank) and are generally not recommended for cold climates.

Flat-plate collectors typically consist of copper tubes fitted to flat absorber plates. The most common configuration is a series of parallel tubes connected at each end by two pipes, the inlet and outlet manifolds. The flat plate assembly is contained within an insulated box, and covered with tempered glass. Flat plate collectors generally contain 40 gallons of water. Two collectors can provide roughly half of the hot water needed to serve a household of four.

Evacuated tube collectors are the most efficient collectors available. Each evacuated tube made of either glass or metal contains the water or heat transfer fluid and is surrounded by a larger glass tube. The space between them is a vacuum, so very little heat is lost from the fluid.These collectors can even work well in overcast conditions and operate in temperatures as low as -40°F. Individual tubes are replaced as needed. However, these are also the most expensive.

Two Types of Active Solar Water Heating Systems

Direct Circulation Systems.  Pumps circulate household water through the collectors and into the home. They work well in climates where it rarely freezes.   Drain down and drain back systems using water can avoid the problems of freezing and are becoming increasingly common in cold climates.

Indirect Circulation Systems.  Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures.

Passive solar water heating systems are typically less expensive than active systems, but they're usually not as efficient. However, passive systems can be more reliable and may last longer. There are two basic types of passive systems:

Integral Collector-Storage Passive Systems.  These work best in areas where temperatures rarely fall below freezing. They also work well in households with significant daytime and evening hot-water needs.

Thermosyphon Systems.  Water flows through the system when warm water rises as cooler water sinks. The collector must be installed below the storage tank so that warm water will rise into the tank. These systems are reliable, but contractors must pay careful attention to the roof design because of the heavy storage tank. They are usually more expensive than integral collector-storage passive systems.

Solar water heating systems almost always require a backup system for cloudy days and times of increased demand. Conventional storage water heaters usually provide backup and may already be part of the solar system package. A backup system may also be part of the solar collector, such as rooftop tanks with thermosyphon systems. Since an integral-collector storage system already stores hot water in addition to collecting solar heat, it may be packaged with a demand (tankless or instantaneous) water heater for backup.

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What do I ask a contractor?

The proper installation of solar water heaters depends on many factors. These factors include solar resource, climate, local building code requirements, and safety issues; therefore, it's best to have a qualified, solar thermal systems contractor install your system.
After installation, properly maintaining your system will keep it running smoothly. Passive systems don't require much maintenance.  For active systems, discuss the maintenance requirements with your system provider, and consult the system's owner's manual. Plumbing and other conventional water heating components require the same maintenance as conventional systems. Glazing may need to be cleaned in dry climates where rainwater doesn't provide a natural rinse.  Regular maintenance on simple systems can be as infrequent as every 3–5 years, preferably by a solar contractor. Systems with electrical components usually require a replacement part after or two after 10 years.

When screening potential contractors for installation and/or maintenance, ask the following questions:

Does your company have experience installing and maintaining solar water heating systems?
      Choose a company that has experience installing the type of system you want and servicing the applications you select.
How many years of experience does your company have with solar heating installation and maintenance?
      The more experience the better.  Request a list of past customers who can provide references.
Is your company licensed or certified?
      Having a valid plumber's and/or solar contractor's license is required in some states. Contact your city and county for more information. Confirm licensing with your state's contractor licensing board. The licensing board can also tell you about any complaints against state-licensed contractors.

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