The TROF (tower reflector with optical fibers): a new degree of freedom for solar energy systems

The integration of optical fibers into solar energy systems requires a trade-off between the cost, attenuation, and a limited flux carrying capability (due to limited numerical aperture) on one hand, and the flexibility in light distribution on the other hand. This paper presents a novel approach that minimizes the length of fibers in the system while fully utilizing the flexibility advantage. Optical fibers have been steadily improving and their cost has been declining as a result of the proliferation of their use in communication, and more recently in the lighting industry. The use of fibers in concentrating solar thermal systems has potential advantages of providing unprecedented flexibility in the final concentration and the receiver design. A central receiver system based on the tower reflector with optical fibers (TROF) is presented as a case study in a comparison between conventional concepts of solar thermal power generation, and new concepts employing optical fibers. Two new approaches to thermal conversion utilizing the flexibility of a fiber-based system, non-isothermal high-temperature receivers and distributed receivers, are presented. An approximate performance and cost analysis that assumes mass-produced solar-optimized fibers is presented. The effects of system size and several fiber types are discussed. The results show that the use of current optical fibers may become competitive for solar-driven electricity generation systems under optimistic assumptions. The analysis points to research and development directions that could lead to cost-effective TROF and other optical fiber-based systems in the future.