Are You Specifying Your Solar Thermal Cylinders Correctly?

The lure of ‘free’ hot water, the potential to cut energy bills and the potential to earn money via the government’s Renewable Heat Incentive (RHI), is making solar thermal installations an increasingly attractive proposition.

And whilst our solar thermal cylinders have been successfully installed for decades, clients continue to have challenges when it comes to specifying cylinders to maximise the savings delivered by the project.

Solar CylinderSolar Cylinders – The Basics As most people will know the solar thermal circuit is linked to a high efficiency coil located in the bottom of the cylinder. As the solar energy is transferred through the coil and to the water, heat rises, and the draw-off point for the water to the taps is at the top. This means on a sunny day, a well-designed and efficient solar system is capable of heating the whole volume of water stored in the cylinder. Even on gloomier days, where there is little solar gain, an efficient system can actually generate a decent amount of heat with water temperatures reaching as much as 30 to 40 degrees.

This will need to be ‘topped up’ by a boiler, immersion or additional fuel source to deliver the required household temperature.

Sizing of Solar Cylinders

As a general rule of thumb, the typical consumption of hot water is approximately 50 litres per person per day.  However, in addition to the normal factors such as number of people, bathrooms and water demand, the size of a solar thermal cylinder will also need to take into consideration the property type and the number of solar panels.

But at the very minimum, solar cylinders must allow 25 litres of designated solar volume per square metre of solar collector.

Cylinder Manufacture

When it comes to the efficiency of the cylinder, the coil is without question the most critical part of the system.

To maximise the heat transfer process, it is therefore vital to maximise the specification of the coil.

Most manufacturers of solar hot water cylinders, use high efficiency finned or ribbed coils and attempt to maximise the length of solar coil in the cylinder, with a best practice ratio of 0.3 Metres Square of coil, for every square metre of solar panel.

So whilst solar cylinders can be made from various different materials, including copper and stainless steel, copper coils are proven to transfer the heat more effectively creating a far more efficient system and therefore providing the most energy savings.

Clearly every solar thermal installation will require its own individual specification to maximise the performance and the potential savings.

To discuss your project with our technical sales team call us now on 01592 611123 or email

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