Case study of a central-station grid-intertie photovoltaic system with V-trough concentration

A case study of an installed, central-station (no storage), utility-intertie photovoltaic (PV) system in Sede Boger, Israel (latitude 30.9 degrees N), is presented. This PV system was constructed with 189 polycrystalline silicon solar cell modules mounted on inexpensive, horizontal north-south axis trackers with V-trough mirrors for low-level concentration. The power conditioning unit operates at a fixed voltage rather than at maximum power point (MPP). Although design output of this system was a nominal 12 kW peak, the measured output was significantly less, occasionally dropping to zero on clear summer days. The major task was to pinpoint the causes of this deficiency and recommend system modifications. As part of this investigation, quantitative assessments of fixed-voltage operation as well as the energetic value of V-trough concentration and one-axis tracking were performed for this system and similar systems. The sample results show that fixed-voltage operation at the best fixed voltage (BFV) can achieve 96% of the yearly energy of MPP operation. The results also show the sensitivity of the yearly energy delivery to the selection of fixed voltage and its marked asymmetry about the BFV; the influences of inverter current constraints on yearly energy delivery and the BFV; and how the separate effects of tracking and optical concentration increase yearly energy delivery.<
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