Optimal cell connections for improved shading, reliability, and spectral performance of microsystem enabled photovoltaic (MEPV) modules

Microsystems enabled photovoltaics (MEPV) is a recently developed concept that promises benefits in efficiency, functionality, and cost compared to traditional PV approaches. MEPV modules consist of heterogeneously integrated arrays of ultra-thin (~2 to 20 μm), small (~100 μm to a few millimeters laterally) cells with either one-sun or micro-optics concentration configurations, flexible electrical configurations of individual cells, and potential integration with electronic circuits. Cells may be heterogeneously stacked and separated by dielectric layers to realize multi-junction designs without the constraints of lattice matching or series connections between different cell types. With cell lateral dimensions of a few millimeters or less, a module has tens to hundreds of thousands of cells, in contrast to today's PV modules with less than 100. Hence, MEPV modules can operate at high voltages without module DC to DC converters, reducing resistive losses, improving shading performance, and improving robustness to individual cell failures. Because these 'multi-junction' cells are integrated heterogeneously versus monolithically, different cell types need not be directly connected in series, improving the efficiency under conditions where different cell outputs are not ideally matched, for example with high incident angles in late afternoon. Instead, different numbers of same cell types are first connected in series, producing an intermediate common voltage, and then these 'microstrings' of different cell types are connected in parallel. Further series and parallel connections enable module voltages of a few hundred volts in small areas (~ 18 × 20 cm) and allow nearly ideal linear degradation with shading across an installation of multiple modules. We present details of these cell interconnection designs and performance under spectral and shading variations of the incident solar radiation for MEPV modules designed with heterogeneously stacked cells and single cell designs, and simulations of the relative efficiency of MEPV modules versus the probability of open and shorted cells.