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 base on compound parabolic concentrators (CPCs). The system is approximately a 7× concentration system and uses commercially available laser-groove buried contact (LGBC) 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 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 have estimated an approximate total system power efficiency of 7.9%, limited mostly by the cell conversion efficiency and the CPC optical efficiency. We close with discussion of the overall performance of the prototype system and plans for the next system design.