Solar- and nuclear-electricity-generation technologies often are deemed "carbon-free" because their operation does not generate any carbon dioxide. However, this is not so when considering their entire lifecycle of energy production; carbon dioxide and other gases are emitted during the extraction, I processing, and disposal of associated materials. We determined the greenhouse gas (GHG) emissions, namely, CO2, CH4. N2O, and chlorofluorocarbons due to materials and energy flows throughout all stages of the life of commercial technologies for solar-electric- and nuclear-power generation, based on data from 12 photovoltaic (PV) companies, and reviews of nuclear-fuel life cycles in the United States, Europe, and Japan. Previous GHG estimates vary widely, from 40 to 180 CO2-eq./kWh for PV. and 3.5-100 CO2-eq./kWh for nuclear power. Country-specific parameters account for many of these differences, which are exacerbated by outdated information. We conclude, instead, that lifetime GHG emissions from solar- and nuclear-fuel cycles in the United States are comparable under actual production conditions and average solar irradiation, viz., 22-49 g CO2-eq./kWh (average US) 17-39 g CO2-eq./kWh (south west) for solar electric, and 16-55 g CO2-eq./kWh for nuclear energy. However, several factors may significantly change this picture within the next 5 years, and there are unanswered questions about the nuclear fuel cycle that warrant further analyses. Published by Elsevier Ltd.