Techno-economic viability of silicon-based tandem photovoltaic modules in the United States

Abstract

Tandem photovoltaic modules with silicon bottom cells offer a promising route to exceed the single-junction photovoltaic efficiency limit and further lower the levelized cost of solar electricity. However, it is unclear whether continued improvements in efficiency will render tandem modules cost-competitive with their two constituent sub-cells, and with silicon technology in particular. Here, we construct a simple and versatile techno-economic model that, for a given balance-of-systems scenario, calculates the tandem module efficiency and cost from assumed sub-cell module efficiencies and costs. To understand which input conditions are likely to be representative of the future photovoltaic market, we calculate learning rates for both module and area-related balance-of-system costs, and find that the slower learning rate of the latter means that high-efficiency tandems will become increasingly attractive. Further, in the residential market in 2020, the model indicates that top-cell modules could cost up to US$100 m–2—over twice that of the projected silicon module cost—and the associated tandem module would be cost-competitive if its energy yield, degradation rate, service life and financing terms are similar to those of silicon. One way to overcome the theoretical efficiency limit of silicon photovoltaics is to use them as the bottom cell in a tandem photovoltaic module. Here a model for tandem module efficiency and cost is presented, based on assumed sub-cell efficiencies and costs, and used to examine possible paths for different tandem markets.