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A Solar Powered Water Heater

Understand how a solar powered water heater works in three steps. A solar water heating system is not very complicated, at least in theory.

solar powered water heater
Solar water heating uses the power of the sun instead of electricity to heat the water you use in your home or business.

There are three basic steps that occur in a solar power water heating system:

  • In a solar powered water heating system a collector is mounted on your roof (most commonly) or on a south facing wall.

  • The sunlight is filtered through a plastic or glass cover and it strikes an absorbent material such as rubber.

  • The absorbent material converts the sunlight into heat, and the glazing (glass or plastic top layer) stops heat from escaping. To better understand this concept think about how hot the inside of your car becomes when it is left standing in the sun with all the windows closed. A solar collector box functions in the same way. It is a closed, tightly sealed box where heat collects. Internal temperatures in a collector can rise to over 3000 F degrees.

The most common types of solar collectors used for solar powered water heaters are generally glazed flat plate collectors. This type of collector uses a rectangular box with a transparent plastic or glass pane. This "window" covers a flat black plate. The black plate connects to a series of parallel tubes or one longer serpentine tube. Water or another heat transferring fluid like anti freeze circulates through the tube(s).

In the second step of the process heat is transferred from the collector to a fluid and finally to a water storage tank. In some types of solar powered water heaters, hot fluid is pumped directly from the collector to a storage tank. In many cases, the pump which moves the fluid between the collector and storage tank is powered by electricity that comes from another source or in some cases it is powered by a small solar photovoltaic module that is located beside the collector.

Water that has been heated is stored in an insulated tank so it is ready to be used when it is needed. Hot water is drawn off the top of the tank when you turn on a hot water spigot and cold water enters at the bottom of the tank to replace the volume of water that has been consumed.

What do you need for a fully functioning solar hot water system?

A solar hot water system consists of the following equipment:

  • A solar collector where water is heated from the energy of the sun)

  • A collection box where the heated water is stored

  • A heat exchanger ( a system which enables heat to be exchanged between two different mediums i.e. the sun and water)

  • A pump (active system) or

  • A natural convection system (passive) to move water between the collection point and the solar collector where it is heated

  • A hot water tank to store the solar heated water until required for use

A solar powered water heater can be used alone or in combination with another source of water heating. In both cases it can help save money as well as the environment by reducing the need for gas or electricity generated from fossil fuels.

To learn more about how to install and use a solar powered water heater, I can really recommend the book Solar Water Heating: A Comprehensive Guide to Solar Water and Space Heating Systems. The book does a good job in both explaining how different solar powered water heating systems work and showing step by step how to build and install such a system.

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