Calculation of Optical Efficiency for the First Central-receiver Solar Concentrator System in Korea

In 2011, the first Korean central-receiver solar thermal plant of 200 kWe was developed as a government research project. Its solar field consists of 450 heliostats in the northern half to a 49 m tall tower, and each heliostat is made of 4 flat mirror facets with a 1 m2 reflecting area. In this paper, we present its optical efficiency calculated with a Monte Carlo ray-tracing code. The code enables to break down the optical efficiency into its six components, that is, cosine, air transmission, shadowing, reflectivity, blocking, and spillage, while taking into account the solar limb darkening without circumsolar radiation as well as reflector surface slope error. We carried out calculations at specific times on summer and winter solstices and autumn equinox. Negligible block efficiency demonstrates that the no-blocking heliostat field layout is well realized. The shadowing efficiency, which is due mainly to the tower rather than neighboring heliostats, is also insignificant except winter solstice. Net optical efficiency is best on autumn equinox but worst on summer solstice mainly because of the cosine efficiency.