Retrofit solar thermal and reduce energy consumption

Energy prices are rising and ever more households are looking for ways to become independent of oil or gas. You can do this with a solar thermal system from Viessmann, which harnesses free solar energy for heating and/or domestic hot water heating. The following guide explains how this works and how you can retrofit solar thermal.

Convert solar radiant heat into thermal energy with high efficiency  

Solar thermal systems operate almost completely without consumption costs. This is made possible by collectors that capture light from the sun. They heat up and transfer thermal energy to the solar medium. Driven by a pump, this flows to a cylinder in the house that is filled with DHW or heating water. Once here, the liquid gives off its heat. It heats up the cylinder and then flows back to the collectors at a lower temperature.

Retrofit a solar system and combine with other heating systems

If you would like to use the principle for yourself, you can retrofit solar thermal. The technology can then support a conventional system, such as gas or oil heating, thus consuming less energy. In addition to fossil heat generators, biomass heating systems and heat pumps can be combined with solar thermal also, to help you save on heating costs.

There is a choice between flat-plate collectors or vacuum tube collectors

When it comes to the efficiency of the system, the collectors play an important role. In practice, there are two main types in use: 

  • Flat-plate collectors, such as the Vitosol 200-FM, have a robust design. They score highly with a very good price-performance ratio and are used in numerous projects. 

  • Vacuum tube collectors, such as the Vitosol 300-TM, are more efficient. They gain more heat from the same surface area and are used when conditions are not optimal or space is limited.

The intended use determines the design of the technology

You can retrofit solar thermal for DHW or for central heating backup. In the first case, the system feeds free solar heat into a DHW cylinder. This covers around 60 percent of the annual DHW heating demand and saves around five percent in heating costs. If the system is used for central heating backup, it heats the heating water in the buffer cylinder, which then transports heat to all rooms in the house. On average, this covers around 20 percent of the energy consumption for heating and domestic hot water.

The right size Viessmann solar thermal system for retrofitting

DHW solar thermal systems, such as the Vitosol 141-FM DHW solar package, are comparatively small. They manage with a collector area of 1.0 to 1.5 square metres per person and require a DHW cylinder with a capacity of 60 to 80 litres per person.

If you want to retrofit solar thermal for central heating backup, more space is needed. For this system, you need a collector area of around one square metre per ten square metres of living space. In addition, there is also a buffer cylinder that holds at least 60 litres per square metre of collector area or 750 litres.

Technical requirements for a solar thermal system

Solar thermal cannot be retrofitted in every house. Pipes need sufficient space, roof surfaces must support the collectors and a cylinder must be installed in the building. Other requirements relate to orientation and location:

  • The pitch and orientation of the roof surfaces determine how much sun hits the collectors. Around 35 degrees with a southern orientation is favourable.

  • Shading of the collectors on the roof should be avoided as far as possible as this reduces the yield. Typical sources of shade are other buildings, trees or mountains nearby. Note that the sun is lower in the sky in winter.

Do you meet the requirements? Then you can retrofit a Viessmann solar thermal system and save on heating costs right away.


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