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Solar Water Heating

The cost of heating water makes up a significant amount of an average household’s energy consumption. One way to reduce this cost is through the use of solar water heaters. Energy Star reports that solar water heaters can cut the average family’s water heating costs in half, which means they will more than pay for themselves over time.

Active vs. Passive Systems

There are two basic types of solar water heaters: active and passive. The primary difference is their construction, with active models having circulating pumps and mechanical controls, while passive ones are more basic. Both have a water storage tank and a solar collector that is used to heat water with. Passive models are less expensive than active ones, but will not work well in every situation, hence the need for active water heaters.

Active Water Heaters

Active solar water heaters consist of two different types:

  • Direct or open loop circulation systems, which pump water that has already been heated through the collectors and then into the home.
  • Indirect or closed-loop circulation systems, which circulate a heat transfer fluid through a heat exchanger before allowing water to flow into the home.

Direct circulation systems work well in areas where the temperature rarely dips below freezing, while indirect circulation systems are needed in colder areas. Both of these types require a source of electricity in order to operate, and will not produce hot water during a blackout. Even so, water already stored in the tanks of active solar water heaters can expect to stay warm for up to 24 hours, depending on conditions outside.

Active systems may also have different types of collectors, with the two most common ones being:

  • Flat plate, consisting of weatherproof boxes containing a dark-colored absorber plate that attracts sunlight. This absorber plate is placed under one or more layers of glass or plastic.
  • Evacuated tubes, which are actually rows of glass tubes. Each tube consists of an outer glass tube and an inner metal absorber tube that is attached to a fin that collects heat.

Active direct systems with flat plate collectors are ideal for moderate climates where temperatures rarely get below freezing. Active indirect systems with flat plate collectors can be used in moderate climates, or in areas where temperatures sometimes dip below freezing. Active indirect systems with evacuated tube collectors are typically used in colder climates or for commercial applications.

Passive Systems

Passive solar water heaters do not require a form of electricity in order to operate. They also have no moving parts to wear out over time, which means they will also last longer. These systems are appropriate for year-round use in very warm climates, but may only be used seasonally in other areas. When used in very cold climates, the system must be drained during the winter months to prevent it from freezing and cracking.

There are also two different types of passive water heating systems as well:

  • Thermosyphon systems, which allow water to flow through them when warm water rises and colder water sinks. These require the collector to be installed below the storage tank to allow warm water to rise.
  • Integral collector storage systems allow cold water to flow through the collector and become heated by the sun. Hot water is then drawn from the top of the collector, at which time new water enters the collector from the bottom and in turn becomes heated.


Solar water heaters are normally installed on the roof of a building in order to ensure they receive the maximum amount of sunlight possible. In multi-storied buildings, or when the stability of the roof is an issue, these tanks can be installed on an exterior south-facing wall instead. Installing a system in this way is more difficult, and can therefore lead to additional costs. Regardless of where they are installed, solar heaters can be placed in a manner that allows them to blend with the aesthetics of the home rather nicely.

Backup System

Solar water heaters are unable to produce hot water on cloudy days. In addition, some may only be used seasonally, and active systems will not operate during a power outage. For this reason, homeowners will still need to use a conventional water heater as a backup. Many people elect to install a tankless hot water heater at the same time they install a solar one, since it takes up very little room and is also energy efficient.


Most solar water heaters will require very little maintenance over their lifetime. Most manufacturers recommend an annual service be performed, which includes a tank and panel flush and a complete inspection of the system. A system flush can often be performed as a DIY project, meaning that hiring a professional is not always needed. The annual inspection should include a check for:

  • Leaking pipes
  • Loose wires and connections
  • Secure panel mounting bolts
  • Dirty panels
  • Cracked insulation

Minor repairs can typically be made by the homeowner, but others such as loose wires or leaking pipes could require the assistance of a professional. In addition, a solar service technician should perform a major tune-up every five years, which involves:

  • Inspecting the sensors and wiring, and replacing as needed
  • Flushing tank and solar panels
  • Replacing tank anode rod
  • Re-caulking as needed
  • Inspecting for and repairing leaks

With the proper maintenance, owners can expect to increase the life of their solar water heater by as much as 50%. Most people can expect a well maintained system to last for between 20 and 30 years, and to begin paying for itself in as little as three years.

Solar water heaters are a great way for people to save money on their energy bill without having to sacrifice hot water in the process. The amount of money one can save will depend on a number of factors; however, everyone can benefit in some way from having these water heaters installed. Since they will pay for themselves over time, they are an excellent investment, both now and in the future.