What Are The Different Types Of Solar Water Heaters?

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In the United States alone, there are more than a million residential solar hot water heaters installed in homes across the continent. Many commercial enterprises also make use of solar hot water heaters. In fact, it’s estimated that nearly a quarter million +solar water heaters are currently in commercial use. Solar water heaters are energy independent, and function extremely well in areas that receive plenty of annual sunshine. In many homes, solar water heaters account for eighty percent of the hot water use daily. 

It’s safe to say for many homeowners, especially ones seeking to live off grid or fossil-fuel independent, solar hot water heaters are an excellent option. Choosing the right type of hot water heater for your home can be a somewhat intimidating process, though. To that end,  we’ve assembled this guide to help you make the best choice for your needs. Read on to learn more about the different types of solar water heaters to make an informed choice for your home.

Different Types of Solar Water Heaters

Here’s a quick rundown of the most common types of solar hot water heaters:

1. Thermosiphon Systems

Water or an antifreeze fluid like glycol is heated by an absorber surface. The fluid or water rises by a process of natural convection from the collector panel to the storage tank. There is no pump required, as fluid movement and heat transfer increase as the overall system temperature increases. Thermosiphons are an excellent choice in regions that see high levels of solar radiation throughout the year.

2. Direct-Circulation Systems

Water is pumped from storage tanks to collectors during daylight hours when the collectors will absorb the most sunlight. These systems are more freeze resistant thanks to their recirculating hot water from the storage tank. Alternatively, freeze protection is accomplished by flushing collectors down through the system and back to the storage tank. While they can handle lower temperatures, direct-circulation systems are most effective where freezing temperatures are less frequent. They also require additional energy to run the electric pump.

3. Drain-Down Systems

A type of indirect water-heating system, drain-down solar water heaters circulate treated or untreated water through a closed loop. The heat is transferred to potable water via a heat exchange system. During non-daylight hours, gravity drains the system to avoid freezing and convection loops that can cool stored hot water in the storage tank. As with previously discussed hot water systems, these solar water heaters are best suited to areas with high daylight solar radiation levels.

4. Indirect Water-Heating Systems

The most efficient of solar water heaters, indirect water-heating systems circulate freeze-protected fluid through a closed loop. A heat exchanger transfers thermal energy to water in the storage tank with an eighty to ninety percent efficiency level. Most of these systems do require an electric water pump for circulation, but the power draw is typically minimal.

5. Air Systems

A variant of the indirect water-heating system, air systems use fans to move heated air from the collectors to a heat exchanger by the storage tank. Unlike a true indirect water heating system though, air systems have only a fifty percent efficiency transfer rate. Additionally, while the fans draw only minimal power, they still require an outside electrical power source.

Solar Collectors: Basic Types

Each type of solar water-heating system can use any of the following collector types. Here’s a brief overview of the options: 

1. Flat-plate Collectors

A panel-shaped box with fluid filled tubes is mounted to a dark-colored absorber. These are best for systems in humid climates where haze diffuses sunlight.

2. Evacuated-tube Collectors

Sidey-by-side tubes retain heating fluid. Each heating tube is encased in glass with a vacuum between the inner and outer tubes to provide superior insulation and reduce heat loss. These collectors operate at higher temperatures with better efficiency in direct or diffuse light.

3. Parabolic-Trough Collectors

A long U-shaped mirror focuses sunlight onto a fluid-filled tube along the length of the mirror. Tubes are insulated to reduce heat loss, though peak efficiency is best achieved in direct sunlight. 

Choosing a Solar Water Heater

  1. Active direct systems are best if you do not experience below-freezing temperatures.
  2. Indirect active systems are best for colder regions since these units are designed and built to resist severe cold weather damage.
  3. Homeowners who use more water during the day should choose an integral passive system since it produces batches of hot water.
  4. If you want to heat your swimming pool water as well as your washing water, the best choice is an indirect circulating system combined with heating fluid.
  5. Got more roof space than living space? Choose a thermosiphon system installed on the roof.
  6. Your choice of solar water heating system should be determined by the amount of daily sunlight your home receives, how much hot water you use daily, and how much you are willing to spend.


A solar water heater is an excellent way to reduce energy costs, live the off-grid life, and increase independence from fossil fuel energy. Choosing the best one for your home is a simple matter of calculating your daily hot water needs. Next, calculate the average daily hours of sunlight throughout the year. Then choose the system that best fits those variables, and you’re ready to install a solar hot water system. Don’t wait to start saving money and living greener: contact a solar power and hot water contractor today to get closer to energy independence and off-grid living.

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