Bring me sunshine
Buderus’s capability in exploiting solar energy extends to large-scale solar thermal installations.
The amount of solar irradiation that falls on Britain is very similar to Germany, Europe’s largest market for solar collectors, which is why Buderus is targeting the UK for the next stage in expanding its solar-thermal business.The environmental benefits of using solar energy to generate domestic hot water in the UK are quite simple. A collector area of just 6 m2 reduces carbon-dioxide emissions by about 1000 kg a year. However, the expertise of Buderus extends much further than installations with just one or two panels. Its solar pumping stations, for example, cater for installations of up to 50 collectors per field, with up to 10 collectors in per row. That is also why the company, which describes itself as Europe’s largest heating brand, is targeting the UK as the next stage in developing its business for exploiting solar energy in commercial buildings. Among projects already carried out in the UK is an installation of 20 panels for a hotel in Cornwall and one of 450 panels for a housing development. Buderus has been established in the UK boiler market for several years and is now looking to build on its success with solar energy in the German market. Richard Evans is sales director for Buderus Commercial in the UK and tells us that the amount of solar radiation available in the UK is similar to Germany, which is the largest market for solar collectors in Europe. Indeed, the amount of solar radiation that falls on the UK in a year is as high as 60% of what falls at the Equator. He sees market opportunities as being hotels, and leisure centres. Schools with outdoor swimming pools are another market opportunity, where an installation of 50 panels could enable the pool to be used from May through to the Autumn. Generating domestic hot water using solar thermal collectors does not require prolonged periods of exposure to direct sunlight or, even, continual high temperatures. While direct radiation from full sunlight amounts to about 1000 W/m2, as much as 300 to 600 W/m2 is still available with partial cloud cover and about 100 W/m2 from an overcast sky. Richard Evans is keen to explain that the key to successfully exploiting solar energy in the UK is efficient collection and efficient control to maximise the benefit of that solar energy so as to minimise the use of supporting boiler plant. Furthermore, it is crucial that a solar thermal system is correctly sized. ‘Nothing is worse than wrongly sizing a solar system,’ says Richard Evans. The ideal to aim for is that all the heat for generating domestic hot water for commercial buildings between April and September should be largely provided by solar collectors. If a system is over-sized, the water/glycol mixture that transports solar energy from the panels on the roof vaporises so that the system goes into stagnation and delivers no energy at all. Inevitably, a solar-thermal system requires the support of a boiler, but it is important that the boiler is not allowed to operate to achieve quick recovery when hot water is drawn off if demand is such that there is time for solar energy to do the job. The Buderus approach to controlling an installation is based on maximising the use that is made of solar energy. One aspect of the control philosophy is to vary the speed of a fully modulating pump to maintain a constant temperature differential between the collector and the solar storage cylinder. On a cloudy day, the speed of the pump would be reduced to enable the circulating fluid to absorb enough energy to reach an effective flow temperature.
The efficiency of a solar thermal system starts with a panel that is designed to make the maximum us of the solar energy that falls on it. The Buderus SKS flat panel enables up to 97% of light irradiation to be captured and converted to useful heat.
Buderus’s integrated approach to control links the support boiler with the solar system to prevent the boiler firing if the solar system has time to reheat the hot-water store. The result is the boiler firing 24% fewer times. The benefit of such control is to further improve the energy savings of a solar thermal system by up to 10%. The efficient use of solar energy must, of course, be associated with its efficient collection. Buderus offers flat-plate collectors that are constructed from a highly translucent 3.2 mm toughened solar safety glass that is 15% more effective than window glass in optimising light capture. The collectors are hermetically sealed and filled with dry argon, an inert gas, to ensure that no mist, condensation or corrosion forms inside them. Energy is never used to evaporate condensation that may otherwise occur early in the morning. A vacuum-applied PVD coating minimises heat loss from the absorber and enables up to 97% of light irradiation to be captured and converted to useful heat. This layer of mineral-wool insulation minimise heat loss, from, say, the collector to the roof space. Installation is simplified by the flexible design of the system hydraulics, with a rapid plug-and socket connection system for linking multiple collectors without tools. Bellowed joints between each collector accommodate expansion, a particular benefit for older roofs that may not be flat or level. The aluminium collector frames are light and robust. A frame system has been devised for installation on flat roofs. Richard Evans explains that solar comes into its own in commercial installations where there is a large demand for hot water. Examples include frequent showering in hotels and heating swimming pools.
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