SPECTRUM project

The name SPECTRUM (Project ID: JOR3970188) stands for Solar Power Exploitation by Collection and Transportation by fiber optics to Remote Utilization Modules, it was a European project of the FP4-NNE-JOULE C framework. The project started on 1st December 1997 and ended on 31st May 2000. The coordinator was Optronic Center of Excellence (CEO), Italy.
Official page on CORDIS site.

Several types of concentrators have been developed during the development of the project for the exploitation of solar energy. Various optical configurations were examined, from the simple parabolic collector to combinations of lenses and mirrors. The use of optical fibers for the transport of solar energy up to an utilization system has already been proposed: this technique has been suggested for operating theaters.

To maximize the light collected by the optical system and concentrate the solar power at the entrance of the optical fiber, it is necessary to pay attention to the design of the collection system so that the focused light corresponds to the diameter of the fiber and respects its opening angle . The use of an optical system implies the need to maintain a correct alignment of the system with the sun, which is usually maintained with a suitable tracking system. Normally a large paraboloid or a paraboloid coupled with one or more mirrors acting as heliostats is used. The first solution requires a mechanical system of large dimensions and considerable weight, due to the size of the system. The configuration with heliostats, on the other hand, requires systems of considerable size because the collection system is placed at a considerable distance from the mirrors. As part of the European "Joule" project we have studied a collection system composed of individual optical systems, each of which is coupled with an optical fiber. In this way the plant is formed by small units (tiles), which incorporate both the optics and the fibers. Each tile orientates itself autonomously with respect to the sun with its own tracking system. A prototype was built and tested for the project.

The basic element of the modular system is composed of a concentrator coupled to a fiber for the transport of energy. The choice of the optical element to be used as a concentrator was made considering as starting data the specifications of the quartz fiber with NA = 0.48 and core diameter 0.6 mm. The fiber was supplied by CeramOptec, a German partner. The choice of the fiber was made considering that the diameter chosen was the best to achieve the fiber-lens alignment; the numerical aperture chosen, which corresponds to a total acceptance angle of about 60 °, was judged to be sufficient for the purposes of the project. Typically quartz fibers have NA between 0.22 and 0.43 and are very expensive compared to other types of fibers.

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