The fixed position of the mirror arrays in the heliostat field is a limiting factor for the optical perform­ance. Each single mirror has the same characteristics as a classical heliostat. Because of the close spac­ing, the main problem of the MMA is shading.

To evaluate the characteristics of a MMA and compare its performance to that of a conventional (ref­erence) heliostat of the same size, its performance was evaluated in a raytracing model. The instanta­neous reflection efficiency and the annual reflection efficiency are defined as

DNIi and DNIa stand for the instantaneous and annual direct normal insolation respectively. “Pre — flected” and “Ereflected” are respectively the power and energy reflected by the heliostat towards the receiver. Ah is the frontal area of the MMA heliostat box and the mirror area of the conventional helio — stat.