Integrated solar tracker positioning unit in distributed grid-feeding inverters for CPV power plants
The total amount of photovoltaic (PV) energy production in the global energy mix has been increasing strongly all over the world in the last decade. This phenomenon has been mainly driven by the promotion of renewable energies, as well as by the well known feed-in tariffs. Although the major part of PV installations consists in roof mounted panels in private, collective or commercial buildings, the amount of large scale PV power plants, from 200 kW to 10 MW or more is increasing drastically. Such large scale PV power plants already represent nearly 20 % of the total installed PV capacity. Indeed, by reducing of the overall system costs, they are becoming serious alternatives to fossil fuel or nuclear power plants for utilities. [GRAPHICS] Taking into account that a sun tracking system can substantially improve the daily energy production of flat plate modules (approx. 10% to 50%), and that such a tracking unit is absolutely necessary for concentrating photovoltaic systems (CPV), one understands its crucial role for solar power plants. One or two axis solar trackers already represent 27% of the total power plant capacity worldwide in 2008. This part is increasing constantly since the additional investment costs for the mechanics are relatively inexpensive compared to PV. Especially for CPV systems, the control unit of a solar tracker has to provide reliable and precise positioning; hence controlling one or two drives to move the panels in a restricted angle window to the sun (typ. 1 degrees to 0.1 degrees). In principle, such a positioning unit consists of a calculation unit (e.g.: mu C or DSP), a power unit driving the motors and a feed-back circuit for different kinds of sensors (e.g.: position or irradiance sensors). Consequently, integrating those functions into an already existing inverter, which feeds the PV power of one tracking unit (typ. 5 kW(p) to 40 kW(p)) into the grid, allows plenty of interesting advantages that will be pointed out in this paper.