On the calculation of the optimum position of a horizontal single axis tracker under any sky conditions

Many current PV installations incorporate solar tracking systems that always seek to orient the surface of the modules as perpendicular as possible to the Sun (astronomical tracking). This position of the trackers is easy to calculate and allows to maximize the beam irradiance captured, which is by far the largest component of irradiance on a sunny day. However, under other sky conditions, this positioning strategy does not necessarily maximize the total irradiance captured by the PV modules and other tracking strategies could increase the PV generation at no additional cost. The proper design and evaluation of such strategies requires to know the optimum position of a PV tracker as a function of the sky conditions, but the analytical calculation of that position is still an open question in the state of the art. In this paper, two analytical expressions have been developed to calculate the optimal position of a horizontal single-axis tracker under any sky condition. One of them uses a new isotropic-diffuse transposition factor developed in this paper to consider the influence of adjacent trackers in the diffuse irradiance received by modules. All the expressions proposed here have been experimentally validated in a PV installation specifically designed to measure the optimal position of a horizontal single-axis tracker. The experimental results not only allow to determine which of the proposed expressions better approaches the measured optimal position, but also to properly compare their impact on the total irradiation received by the PV modules.