Effect of heliostat design wind speed on the levelised cost of electricity from concentrating solar thermal power tower plants

This paper assesses the influence on the levelised cost of electricity (LCOE) of the design wind speed at which heliostats in concentrating solar thermal (CST) power tower (PT) plants are stowed. Lowering the design wind speed for parking heliostats in the stow position reduces the cost of the heliostat field at the expense of a reduction in the energy harvested. However, both influences are highly non-linear and also vary from site to site, so that new understanding is needed to guide the optimisation of this parameter. The capacity factor and the power output for a PT plant without thermal storage are calculated for six locations by mapping hourly solar irradiance data to the Weibull probability distribution of mean wind speed. The cost of materials for the heliostat components and their sensitivity to heliostat size are estimated as a function of the design (stow) wind speed based on the specification of the structural design for quasi-static wind loads. The sensitivity of the LCOE to the design is assessed statistically. The results show that the materials cost of structural components in larger heliostats are most sensitive to the design wind speed, so that a 34% reduction in cost can be achieved by lowering the design wind speed from 15 m/s to 10 m/s. In contrast, the optimum design wind speed for smaller heliostats between 20 m2 and 50 m2 is typically above 10 m/s. The LCOE can be reduced by as much as 18% by lowering the design wind speed from the maximum recorded wind speeds at the three Australian sites. Hence there is significant economic benefit from optimising the minimum design at sites with high wind speeds.