Fast and reliable flux map on cylindrical receivers

Abstract

The thermal design of external solar receivers is a complex problem, in which the main input is the flux caused by the entire heliostat field on the cylindrical receiver surface. In this work, a fast and reliable model of flux distribution on the cylindrical receiver is proposed. This new cylinder flux map is based on the HFLCAL model for the analytic flux density sent by a heliostat on its image plane and the projection, in the direction of the central reflected ray, of any point in the plane image onto the cylindrical surface. The heliostat flux density includes shading and blocking, cosine of the incidence angle, atmospheric attenuation and effective reflectivity. A differential energy balance supports the coherence of the new model, i.e. the power contained in a differential of area in the image plane has to be equal to the power contained in the projected differential of area onto the cylinder. As an application of this new flux distribution on cylindrical receivers, we present the receiver sizing for a Noor III-like 150 MWe plant, with 7400 heliostats, in which the minimum LCOE gives the receiver diameter and a preliminary receiver height. With the help of the new flux map, this height is analysed to verify the maximum allowable flux. A multi-aiming strategy suggested by Vant-Hull (2002) and put into practice by Sanchez-Gonzalez and Santana (2015) is used to spread the hot spots along the receiver height. The PC CPU time to produce a coherent flux map on the cylinder is around six seconds.