Rattenberg was built just north of the Rat Mountain for defensive reasons in the Middle Ages. But the height of the mountain means that local inhabitants must seek sun outside their town during the cold winter months from November to mid February. The depressive effect of this lack of natural light has led to a steady reduction in the population over recent years.
"We have worked with the town authorities on various street and monument lighting projects," explains Wilfried Pohl of Austrian project leader Bartenbach LichtLabor. This lighting design bureau has long specialised in the use of natural light to illuminate windowless offices and underground areas. "Use of natural light not only saves electrical energy but also raises the environmental quality of the areas being illuminated. This led to the idea of using optical reflector technology to provide sunny spots within the town."
Three main elements
Heliostats are used extensively for solar energy generation, but had not been used for lighting previously. The system proposed in the EUREKA project consists of three main elements:
- Heliostats sited 400 metres north of the city to redirect sunlight precisely towards secondary reflectors. The heliostats would be mounted on ball joints and computer controlled to trace the movement of the sun automatically;
- Secondary reflectors on top of the castle hill just above the town, designed and shaped precisely to project sunlight from the heliostats towards specific locations; and
- Components to distribute the reflected sunlight.
Illumination would have all the properties of natural light in terms of accentuated spots, sharp contrast between light and shadow, brilliance, spectral colour resolution and sparkling effects. "We can't light the whole town," explains Pohl. "But we would provide five or six large sunny spots." Residents and visitors would be aware of the sunshine wherever they were, and so receive the impression of a 'sunny town', a very important psychological benefit.
"We intend to illuminate around 100 m2 in all," adds Pohl. "This would not be economical with artificial lighting, as it would require some 10 million lumens - equivalent to around 100 kW of electrical power." Help with funding Neither the town authorities nor the lighting designer could afford to develop the technology required, so Bartenbach turned to the EUREKA Initiative for help. The resulting project also involves German solar energy equipment manufacturer Bomin Solar Herstellung und Vertrieb Solartechnischer Anlagen, with which Bartenbach has realised many lighting projects, and the University of Catania and SME Cogei that are keen to develop the benefits of such natural light illumination in Italy.
"Stage one involves determining if the project is feasible according both to the laws of physics and technically," says Pohl. "More importantly, we need to establish if it makes sense to provide such a system and to justify the cost." This latter point has involved psychological tests as people often expect too much from such systems. The feasibility studies should lead to the engineering phase early in 2006. This would involve developing mirrors and other optical elements that are much more precise in terms of flatness and tolerances than now possible. A full-scale mock-up is planned for mid 2006.
Success of this prototype could lead to the scheme becoming a reality in Rattenberg and perhaps other towns with similar problems as early as 2007. Current estimates are that the overall investment required for the Rattenberg installation would be some €1.5 million. Once the benefits of this natural lighting system can be experienced in a trial installation, the decision to provide funding for implementation should be much easier.