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Designing a Solar Water Heater

Each component of a solar water heater has a distinct function and is important for the design of an efficient hot water system. Homeowners should decide which type of system best fits their needs. They can select from various designs, inluding cylinder sizes, types of collectors, and orientations of the solar heater system.
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First, the system for a solar water heater should be selected. There are both active and passive solar hot water systems, either with a direct or indirect water distribution. Next, the type of collector for the solar water heater should be chosen. The most common types are the flat plate and the evacuated tube collectors. In regard to the position of the collectors, one should consider that collectors are at an optimal position when they face south at a tilt of 35 degrees.

Then, the storage cylinder for a solar water heater has to be sized - it should be able to provide 40-60 liters per day per person in the household. There are three types of storage cylinders: vented, mains pressure, and thermal cylinders. For pre-heating water storage, the most common cylinders are single cylinders with twin coils or a distinct pre-heat tank which is placed before the conventional cylinder of a solar water heater.

It is also important to consider the right size of the pipe line. When pipes are too wide, up to 50% of the heat can be lost. The pipes in a correctly installed solar water heater should control the flow of the heat transfer fluid with minimum power requirements.

An active solar water heater requires a circulation pump that circulates the water or heat transfer fluid through the pipes. An efficient pump should provide the required flow rate with the minimum amount of electricity.

Active and Passive Solar Heaters(A) Passive Solar Heater; (B) Active Solar Heater, Image: Jwhferguson via Wikimedia Commons


A solar water heater can provide sufficient hot water during warm, summer months, but generally must be supported by other heating systems during cold, winter months. There are a number of options for supporting systems, including electrical resistance heating or a gas powered boiler.

Before installing a solar water heater, the energy efficiency of a system should be calculated. This can be accomplished with the greatest accuracy with the help of a professional installer.

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Written by: Christian Märtel, Editor
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