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© Paradigma/Ritter XL Solar GmbH
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Using vacuum to bundle the sun

Evacuated tube collectors are constructed from two layers of solar glass in a similar way to a thermos flask. The cavity is evacuated and enables a very high insulating effect. The inner tube has a vapor-deposited, highly selective absorber layer which faces the cavity. The centre contains the aluminium absorber sheet and the curved solar pipes made of stainless steel which feed the heat to the collector tubes which are arranged vertically in relation to them. A CPC aluminium mirror behind the tubes with a special coating diverts the sun’s rays onto the absorber tube, even with different irradiation angles and diffuse light conditions. As a result, high temperatures can even be achieved in the solar circuit during the winter when outside temperatures are low.

Using solar energy to cool buildings

The facade system with evacuated tube collectors achieves particularly high temperatures during the summer. This provides the ideal conditions for solar thermal cooling. In moderate climate zones, but also in central Europe, the need for cooling in buildings is growing. Standards of comfort are increasing, and ever larger portions of building envelopes are being glazed. Despite more modern technology, the waste heat from computers and electronic equipment in office buildings has remained at the same high level as before. Solar energy systems could frequently meet this requirement in an efficient and environmentally friendly way. Naturally, export to southern climate zones is of particular interest.

In terms of technology, German research institutions and small and medium-sized companies have become international leaders thanks to their intensive research. However, this young industry sector is facing double competition. On the one hand, well-known companies from the cooling sector, particularly from Asia, are surging onto the international markets. On the other hand, new competition is growing with regard to technology. The significant decrease in the cost of photovoltaics has also made solar electricity systems with vapour compression chillers increasingly attractive. However, representatives from the industry and the majority of researchers remain optimistic. The consensus of opinion is that there is room for both technologies. One advantage of solar thermal systems is apparently that they can also be flexibly combined with other heat sources. In this way, industrial waste heat or energy from the combined heat and power generation could be used.

According to scientists, more research needs to be conducted on the components as well as on the system technology. For example, the recooling systems are in need of significant improvement. The German Federal Ministry for the Environment has initiated a complex joint project to further develop this technology, with three scientific institutions and three companies. Other components such as the collectors are of a sufficiently high quality, but must become significantly cheaper. In the joint project “Evaluierung der Chancen und Grenzen von solarer Kühlung im Vergleich zu Referenztechnologien” (evaluation of the opportunities and limits of solar cooling compared to reference technologies), the researchers will demonstrate the prospects for solar thermal cooling for different areas of application, in particular also a comparison of systems which use solar electricity methods.

Projektinfo 07/2013:
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Addresses

Measurement of the prototypes and 0 series of the facade collector
Universität Stuttgart, ITW

Simulation and yield assessment
Solites

Industrial partner for collectors, test collector facility Langensteinbach
Ritter XL Solar GmbH

Industrial partner for facade
Wicona

Industrial partner for facade construction
FRENER & REIFER GmbH

Industrial partner for facade construction
Metallbau Früh GmbH