In 1980, he joined Brookhaven National Laboratory, working as a research engineer and senior scientist across departments focused on sustainable energy and environmental sciences.

He received a PhD in fluid dynamics and atmospheric science from New York University in 1991, with a focus on toxic gas release modeling and mitigation using water spray systems.

[14] Fthenakis has led collaborations on silane safety and lead-free solder technologies, conducted foundational life-cycle studies on thin-film photovoltaics and PV recycling, and anticipated regulatory trends concerning lead and cadmium, supporting industry adaptation.

[19] From 2002 to 2005, he established a laboratory focused on recycling spent photovoltaic modules and manufacturing scrap, employing hydrometallurgical separation technologies and resulting in a patented method for separating copper, cadmium, and tellurium, with applications in cadmium telluride (CdTe) and copper indium gallium selenide (CIGS) technologies.

[21] Recognizing the environmental concerns surrounding the growth of the CdTe and CIGS markets, he designed experiments simulating fire effects on photovoltaics using techniques such as NSLS-x ray diffraction analysis.

[22] In 2005, he led a European Union workshop, organized with the Joint Research Center and the German Ministry of the Environment, facilitating a US company's establishment of a manufacturing facility in Germany.

Fthenakis' research on photovoltaics and the environment has led to approximately 300 journal and conference papers, contributing to over 450 publications on energy and environmental topics.