Organic Solar Cells-Coupled Electrochromic Windows: A Comparative Energy, Emissions, and Costs Analysis

Abstract

Electrochromic windows (ECW) dynamically control the transmittance of solar radiation under applied voltage, allowing for selective utilization of the incident spectral energy to reduce lighting, heating and cooling loads in buildings. Energy demands attributed to such uses have been estimated to account for approximately 30% of the total end-use energy demand in the United States. The Loo group at Princeton combines ECW technology with organic photovoltaics (OPV), which are transparent and lightweight, while allowing ECWs to be energy self-sufficient. This work explores two main comparisons, one between OPV-ECWs and static low-e glazings, and another between OPV-ECWs and ECWs externally powered via conventional photovoltaics, as a function of material costs, energy savings, carbon price, and state-average emission factors.

In addition to material costs and energy savings, we found that the economics of EC coatings is sensitive to state-average emissions profiles for electricity generation and the price per ton of carbon dioxide equivalent emitted. This dynamic underscores the role of carbon pricing in the evaluation of emerging technologies, particularly the higher threshold for profitability as the world moves towards decarbonization. Between OPV-powered and conventional PV-powered ECWs, we report comparable performance in economic terms at current cost assumptions. Whereas conventional PVs are more efficient than their organic counterparts, they face the inherent disadvantage of capital-intensive wiring processes, which pose a barrier to adoption in a relatively young market. An OPV + ECW system that is relatively easy to retrofit would show increasing competitive advantage as the cost of electrochromic and OPV materials fall in the future, and wiring costs become a growing fraction of total expenses.