Optimisation of the size and cost of heliostats in a concentrating solar thermal power tower plant

Abstract

Concentrating solar thermal (CST) power tower (PT) is one of the most promising renewable technologies for large-scale electricity production, however the main limitation of PT systems is their significantly larger levelised cost of electricity (LCOE) relative to base load energy systems. One opportunity to lower the LCOE is to reduce the capital cost of heliostats through optimisation of the size and position of heliostat mirrors to withstand maximum wind loads during high-wind conditions when aligned parallel to the ground in the stow position. Wind tunnel experiments were carried out to measure the forces on thin flat plates of various sizes at a range of heights in a simulated part-depth atmospheric boundary layer (ABL). Calculated peak wind load coefficients on the stowed heliostat showed an inverse proportionality with the chord length of the heliostat mirror, which suggests that the coefficients could be optimised by increasing the size of the heliostat mirror relative to the sizes of the relevant eddies approaching the heliostat. The peak lift coefficient and peak hinge moment coefficient on the stowed heliostat could be reduced by as much as 23% by lowering the elevation axis height of the heliostat mirror by 30% in the simulated ABL. A significant linear increase of the peak wind load coefficients occurred at longitudinal turbulence intensities greater than 10% in the simulated ABL. Hence, the critical scaling parameters of the heliostat should be carefully considered depending on the turbulence characteristics of the site.