Pete Mills, technical service manager at Buderus, comments on the growing specification of solar thermal systems and the need to avoid the pitfall of over sizing.
The UK's commitment to an 80% reduction in emissions by 2050, together with the development of the renewable energy strategy (RES) and European requirements on the energy performance of buildings, are clear indications of the drive towards higher levels of energy efficiency and the adoption of renewable technology for heating and hot water.

The tangible evidence of this development is Energy Performance Certificates for new buildings and large public buildings requiring Display Energy Certificates. Together, these create an incentive to ensure buildings are firstly built, and then used, in the most energy-efficient and sustainable way possible.

Of the various renewable options, solar thermal is generally regarded as the preferred choice. Although other renewable appliances are becoming more commonplace, there are a number
of design issues which can mean that opting for solar is the more practical solution.

All renewables by their nature tend to require space either for groundworks, storage or panels. In general, commercial buildings have an accessible and largely unused roof area and so lend themselves to the installation of solar on this vacant area of the building.

Used together, solar and modern condensing boilers make an extremely efficient partnership, combining free energy from the power of the sun, with a fuel-efficient boiler to satisfy any additional heat requirements.

Buderus high-specification solar thermal collector technology is the result of more than 25 years' experience in solar heating in Europe where more than 150,000 Buderus solar collectors have already been installed during this period.

To achieve maximum benefits from solar, however, requires much more than a high-specification solar collector. The Buderus range of solar equipment includes a range of pump stations, control systems and thermal storage devices, allowing for installation of up to 50 collectors in a single field - with multiple fields possible should demand require it.

In particular, the Buderus controls platform includes an intelligent solar optimisation function, which enables seamless integration between the Buderus solar collectors and Buderus boilers. This is essential if the heat generated by the solar collector field is to be fully maximised.
The controls ensure that solar energy is always fully utilised, only bringing the boiler into
operation if solar cannot meet the required heat demand. This significantly improves efficiency, reducing burner starts by up to 24% and providing additional energy savings of up to 10%.

Cloudy conditions

Buderus flat plate collectors are made from a highly translucent toughened solar safety glass, which optimises light capture even in cloudy conditions. To further improve efficiency and longevity, the Buderus SKS range of solar collectors are hermetically sealed and filled with dry argon to eliminate mist, condensation or corrosion from airborne pollutants.

Solar systems are especially suited for applications where there is a constant need for large amounts of stored hot water. But system size is a key issue in designing the most efficient system and each installation needs to be considered on its own requirements.

In circumstances where customers would require large amounts of hot water throughout the day (hotels and leisure centres for example), and a south-facing position is not available, it is also possible to install systems with an east-west split so that energy can be captured as the sun moves. Sadly there is a tendency towards oversizing solar systems in a bid to maximise the free energy gained.

This is not a good idea for solar panel installations, either from an efficiency viewpoint or for the general good of the panels themselves. Temperature sensors in the system protect it from overheating, particularly at the height of the summer months when the solar storage tanks quickly reach their maximum level.

In these circumstances, the sensors turn off the pump to avoid reaching temperatures which would be too high for the safety of the system.




This occurs because solar systems are filled with a fluid - usually a 50-50 mixture of glycol and water - to prevent freezing in the cold winter periods. But, in summer, if the sensors turn off the system because it is overheating, there is no flow and the solar fluid can eventually boil.
At this point, the steam and glycol would be likely to separate. If this occurs often, the solar fluid will start to deteriorate and thicken.

Efficient operation of the panels is compromised as the small-bore pipework contained within the panels can become blocked by the thickened fluid. Cleaning would therefore be rather impractical, especially as the panels are also totally sealed.

For these reasons, it is preferable to slightly undersize a solar system - unlike the boiler system - to retain durability and ensure reliable and efficient operation.

The critical detail required when designing a solar thermal installation is an accurate assessment of the domestic hot-water requirement on which information the optimum size of the system can be determined. This can be obtained either from existing records or by the temporary installation of a meter system. Accuracy is essential as larger commercial-sized solar system design can be complex.

Swimming pool

Abbots Bromley School for Girls in Staffordshire has recently completed the installation of a Buderus Solar thermal panel system to provide energy-efficient heating for its swimming pool complex, including hot-water needs. Vale Heating & Plumbing of Pershore specified and installed 32 solar panels in two fields, each of 16 panels. They chose Buderus solar panels for their build quality, energy yields and because they are designed especially for large-scale commercial applications.

The flat plate SKS 4.0 collectors have been installed using the Buderus in-roof mounting system providing an unobtrusive finish in keeping with the rest of the building. The swimming pool
will deliver significant savings in fuel costs and future maintenance. It will also reduce the school's carbon footprint.