Design and Construction of a ∼7× Low-Concentration Photovoltaic System Based on Compound Parabolic Concentrators

We report on the design, construction, and initial performance measurements of a low-concentration photovoltaic system based on compound parabolic concentrators (CPCs). The system is approximately a 7× concentration system and uses commercially available laser groove buried contact monocrystalline silicon photovoltaic cells. The CPCs are fabricated using a second-surface aluminized acrylic mirror with proven weather durability. The asymmetric CPC optical design was driven by a balance between concentration factor, thermal issues, and optical angle of acceptance and was thoroughly evaluated by optical ray tracing. The design was targeted for a single-axis tracking system, with extruded aluminum heat sinks doubling as structural components. We fabricated a 120-cell (10 × 12) prototype array, and over three months of operation, we estimated an approximate peak total system power efficiency of 7.9%, limited mostly by the CPC optical efficiency (∼55%) and the cell conversion efficiency. We discuss several issues regarding system performance, reliability, and cost.