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Learn About Evacuated Tube Solar Hot Water Collectors

Evacuated Tubes are a proven technology now widely accepted and adopted around the world. In fact, Evacuated Tube solar Hot Water System sold in the U.S out number flat plate collectors.


Evacuated Tubes are sleek, stylish and super-efficient. They work by absorbing the sun’s energy, trapping it like a giant thermos flask, and efficiently transferring heat to the water supply.


How Do Evacuated Tubes Work?


1/. Vacuum

Each Evacuated Tube consists of 2 layers of Borosilicate glass with a vacuum layer between them. This vacuum provides superb insulation and helps to retain an amazing amount of heat... up to 97% of the sun's thermal energy is held in the tube.

The secret to the brilliant performance of Evacuated Tubes in cold weather is the superb insulation provided by the vacuum in between the two layer of glass. This ensures that the sun’s energy you are catching is not lost. Other systems lose heat when it’s cool outside.

Solar Hot Water Evacuated Tube

2/. Absorber Coating

Evacuated Tubes have a special coating on the inner tube layer that absorbs radiation from the sun. The sun's energy is then trapped inside the tube by the vacuum and retained in the same way a Thermos Flask retains hot water for such long periods.


The absorber coating is formulated to catch as much of the sun's energy as possible, but at the same time not lose it through radiation. The performance between different brands of Evacuated Tubes can differ depending on the quality of the Absorber Coating.

Evacuated Tube - Clean Energy Centre


3/. The Heat Pipe

The sun's thermal energy is transferred to the water supply at the top of the solar collector via a heat pipe located in the centre of each tube. Inside the heat pipe there is a partial vacuum that contains a small amount of evaporative liquid.

As the Evacuated Tube is heated by the sun, the liquid in the heat pipe changes state and becomes a gas. The gas rises into the Heat Pipe Bulb positioned at the top of each pipe. The Heat Pipe Bulb is positioned in a Heat Exchanger that is fixed to the top of the collector.

Apricus Evacuated Tube

4/. The Heat Exchanger


The cold water in the tank is circulated through the Heat Exchanger and passes over the extremely hot Heat Pipe Bulbs which enables this water heat up at a rapid rate.

The heated water is then returned and stored in a storage vessel on the ground.


The result is an incredibly efficient system to harness the heat of the sun even in extremely cold areas. Because the system is so efficient it does not require full sun and it can work in cloudy or even rainy days.

Evacuated Tube Heat Exchanger Diagram

5/. Passive Sun Tracker


The round surface of each tube passively tracks the sun as it moves across the sky. This means that the face of the absorber in each tube is always perpendicular to the sun, and the round surface of the tube catches and re-directs the sun's energy inside.

Solar Hot Water Evacuated Tube - Clean Energy Centre

Evacuated Tubes are better at catching & retaining the sun's radiation. Evacuated Tubes reflect less of the sun's energy rays.


Solar Hot Water - Evacuated Tube