5 - Innovative working fluids for parabolic trough collectors

Abstract

This chapter describes the state of the art of working fluids for parabolic trough collectors, starting with thermal oil as the option already implemented in most of the commercial parabolic trough plants, and then continuing with alternative working fluids that could lead to significant cost reduction and/or overall increase in plant efficiency. Three alternative working fluids are analyzed in this chapter: (1) water/steam (the so-called direct steam generation technology); (2) molten salts; and (3) pressurized gases. Thermo-hydraulic aspects, cost-related issues, and open questions associated with the use of these three alternative working fluids are dissected in this chapter, together with the current status of associated technologies. Since pressure drop in the solar field piping and heat transfer in the receiver tubes are key issues because of their impact on solar field pumping power and thermal stress in the receivers these two parameters are analyzed for each working fluid. This analysis is completed with a proposal of research and development activities that should be undertaken to fully clarify the technical and operational feasibility of these three innovative working fluids.