Optical Analysis of a Heliostat Array With Linked Tracking

Abstract

The optical performance of a novel solar concentrator consisting of a 400 spherical heliostat array and a linked two-axis tracking system is analyzed using the Monte Carlo ray-tracing technique. The optical efficiency and concentration ratio are compared for four different heliostat linkage configurations, including linkages of 1 × 1, 1 × 2, 2 × 2, 4 × 4, and 5 × 5 heliostats for 7-hour operation and the selected months of June and December. The optical performance of the concentrator decreases with the increasing number of heliostats in the individual groups due to increasing optical inaccuracies. In June, the best-performing linked configuration, in which 1 heliostat in the east-west direction and 2 heliostats in the north-south direction are linked, provides a monthly-averaged 7-hour optical efficiency and average concentration ratio of 79% and 511 suns, respectively. In December, the optical efficiency and the average concentration ratio decreases to 61% and 315 suns, respectively.

Development of an Elevation–Fresnel Linked Mini-Heliostat Array

“…With the information obtained here, we have found a loss of energy of 7.7% for arrays of 8 mini-heliostats with respect to individual tracking. Also, the H2 arrays have a loss of 4.4% in comparison with the two-heliostat arrays of Dunham et al [14] with a loss of only 1.4%, Bear in mind that no effort for optimization of the present arrays has been attempted. Such an analysis could be made based on more reliable data provided by the present prototype.…”

“…As input value for the Direct Normal Irradiance (DNI) at different times and days, values obtained from a clear sky model [14] were used:…”

“…It is not clear if the cause of this behavior is absorption by the glass or low reflectivity of the silver film, but this is low even compared to 6 mm mirrors from other brands. A value of 72.48% was obtained for the broadband solar reflectance ρ s , by using Equation (14). A photograph of the prototype is shown in Figure 15.…”

“…Another direction of research is the reduction of control units by way of linking nearby heliostats mechanically, to reduce the overall number of actuators [6,[14][15][16]. This approach logic is that small heliostats require quite similar movements due to their proximity.…”

“…For instance, a concept proposed by Göttsche et al [6] consist of very small mirrors (10 × 10 cm) mounted on ball-in-socket joints driven by a stepper motor. Dunham et al [14] analyzed the effect of linking heliostats in different numbers, when they are distributed on a square mesh over a flat land surface. They calculated the monthly energy efficiency of the coupled heliostats as compared to independent tracking units.…”