Economics of tandem flat plate photovoltaic modules

Tandem modules, formed by stacking two PV cells, either monolithically or mechanically, can offer higher solar conversion efficiency than modules that use only one type of PV cell. Such modules necessarily cost more per unit area than either single-junction alternative, but the increased efficiency leverages area-related costs to potentially reduce system cost per watt. High-efficiency, low-cost tandems could arise if the cost of III-V cells is reduced to approach the cost of silicon cells, or if stable large-area perovskite cells are demonstrated with efficiency approaching that of today's best laboratory devices. Within the scope given by these optimistic assumptions, future costs and performance still have a substantial range of uncertainty. A probabilistic Monte Carlo model is presented that generates a large number of cost and performance scenarios based on a range of values for each input parameter. The results can be used to assign a probability, within the scope of the assumptions, that the tandem will be more cost-effective than either single-junction alternative. Four types of tandem modules are analyzed: (1) III-V on silicon, (2) III-V on thin film, (3) perovskite on silicon, and (4) perovskite on thin film. All of these tandems have a reasonable chance (>10%) of providing slightly lower cost per watt for residential systems, and the two thin-film options might also slightly benefit utility-scale systems. Achieving a substantial cost benefit is less likely. Only the perovskite on thin film tandem has a reasonable chance of reducing system cost per watt by more than 10% for residential systems, or of reducing system cost per watt by more than 5% for utility-scale systems.