Solar Water Heaters: What You Should Know

A solar water heater can save a household a lot of money and help reduce local and regional emissions that cause air pollution. Although the initial cost of the system and installation is higher (compared to replacing an existing electric or gas water heater), it can save 50-80% of water heating costs over time, according to the Department of Energy.1

Depending on which system you buy and how much hot water you use in your household, the purchase can pay for itself in just a few years. In addition, you can deduct the installation of such a system from your taxes.

What is a solar water heater?

Solar water heaters use the sun's energy to either directly heat water, which can then be used to heat water in the home, or to use the sun's energy to heat another liquid, which is then used to heat the water. They can be active or passive, and all systems require a storage tank.

Solar water heaters can be used in cold climates, in less sunny places and in a variety of conditions, but less effectively than in sunnier areas. But even if you live in a place where your solar water heater only preheats the water a little in winter, a little in autumn and spring, and a lot on summer days, you will still save money and reduce emissions.

At night and on cloudy days, when you don't have enough hot water stored, you need an extra heating element to raise the water temperatures. Most people with solar water heaters in mixed or seasonal climates use them in conjunction with an on-demand water heater to raise water temperatures a little further. Because these units heat water that has already been heated, they work even faster and more efficiently than if they were heating cold water.

Usually, solar water heaters are placed on the roof and face south to get the best quality of direct sunlight. However, they can also be placed in a garden, on a lawn or in other areas where they receive direct sunlight.

Types of solar water heaters

Active solar water heaters

An active solar water heater can be direct or indirect. In the direct system, pumps are used to circulate water through the solar panels (usually on the roof) where it is heated by the sun and then sent to a well-insulated tank for storage. These systems are useful in climates where it rarely freezes.

An indirect active solar water heater uses a special non-freezing heat transfer fluid that is heated by the sun and then heats the stored water. They are suitable for places where it freezes seasonally.

Passive solar water heaters

Passive systems are simpler and cheaper than active systems, but less efficient. There are several types, some of which use a hot-cold water gradient to move the water instead of pumps. The other type simply uses the available heat energy from the sun to preheat the water and then uses a conventional water heater to raise the temperature to the required level.

Parts of a solar water heater

Every solar water heater consists of at least two elements: a collector that captures the sun's energy and a storage tank. The other components of the system depend on the type of solar water heater used.

Solar collectors

The main components of any solar hot water system are one or more collectors to capture the solar energy and a well-insulated storage tank. There are, of course, different types of solar collectors for water heating.

Flat plate collectors have a glass or polymer cover with a dark plate underneath. When the sun shines on the plate, its heat is absorbed by the plate (and the dark pipes through which the water flows) and transferred to the water.

Integral storage systems are black tanks filled with water inside a transparent, well-insulated casing. This system is often used to preheat water, which is then fully heated by an additional system, such as a water heater, to the desired temperature for bathing or housework.

A third type, evacuated tube collectors, contain clear tubes with metal inside and are mostly used for commercial applications.

Storage tanks

Solar storage tanks for water heaters can vary depending on the size of the home, the number of solar collectors and the amount of hot water needed in the home. Typically, most systems have a large tank with a capacity of 80 gallons (or more) that can store hot water even on cloudy days. Some systems have two tanks, one for immediate use and the other for storage only.