ERC Researchers Quantify Potential Increase in Energy Production by Using Spectrum Splitting
Researchers at the NSF-funded Engineering Research Center (ERC) for Quantum Energy and Sustainable Solar Technologies (QESST), which is headquartered at Arizona State University, were able to quantify the potential increase in energy production from use of spectrum-splitting, multiple-junction solar cells connected independently versus in series.
Because efficiency is one of the primary parameters used to evaluate photovoltaic (PV) systems, it is important to understand how various solar-cell configurations affect efficiency. The researchers learned, under specific conditions examined, that the independent ensembles have an efficiency advantage over the series-connected cells, a result that translates to a large difference in annual energy production (see figure).
The traditional $/Wp metric combines module performance and cost into a single number. It is critical to remember that all energy production technologies ultimately compete on the cost of the energy they produce. Evaluating different technologies requires an estimate of performance under the widely varying conditions that deployed systems will experience. For many single-junction solar modules the system efficiency will be very stable regardless of irradiance. However, for spectral-splitting approaches that use multiple junctions, any change in the spectral composition can have a large impact on efficiency.
Measuring the impact on efficiency was the focus of the QESST researchers' work, which showed that the electricity production advantage for independent cells over series-connected cells ranges from almost 10% for the two-cell ensembles to approximately 25% for the 20-cell ensembles. The performance penalty for the series-connected ensembles comes from the current matching enforced by the electrical configuration.