Transitioning to a sustainable energy supply will be critical to meeting future economic and environmental goals. This transition will require optimizing and commercializing a portfolio of new clean energy technologies. However, many promising clean energy technologies are based on materials with inherent risks in their supply; these risks include scarcity, price volatility, criticality, and other potential supply-chain disruptions. Using tellurium use in CdTe photovoltaics as a case study, this paper presents analysis of some of the key challenges associated with modeling byproduct systems (a supply-chain where a key material is actually a byproduct of extraction of another material, copper in the case of tellurium). This work presents a novel modeling approach; the results of the case study are used to identify potential supply risks facing this clean technology, with a unique focus on sensitivity to changes in the preliminary lifecycle stages. Supply-chain sensitivities are connected with direct environmental impacts to frame the implications in a broader sustainability context and to emphasize the future role of recycling. Ultimately, it was shown that if historical supply and demand trends continue, supply gap conditions will emerge before the end of the current decade. However, improvements in byproduct yield, end-use recycling rate, and end-use material intensity exhibit significant leverage to minimize risk in the energy-critical tellurium supply-chain. (C) 2014 Elsevier Ltd. All rights reserved.