Several renewable and (claimed) sustainable energy sources have been introduced into the market during the last century in an attempt to battle pollution from fossil fuels. Especially biomass energy technologies have been under debate for their sustainability. A new biomass energy technology was introduced in 2008: the plant‐microbial fuel cell (P‐MFC). In this system, electricity can be generated with living plants and thus bioelectricity and biomass production can be combined on the same surface. A green roof producing electricity with a P‐MFC could be an interesting combination. P‐MFC technology is nearing implementation in the market and therefore we assessed the environmental performance of the system with an early stage life cycle assessment (LCA). The environmental performance of the P‐MFC is currently worse than that of conventional electricity production technologies. This is mainly due to the limited power output of the P‐MFC and the materials presently used in the P‐MFC. Granular activated carbon (anode material), gold wires (current collectors), and Teflon‐coated copper wires (connecting anode and cathode) have the largest impact on environmental performance. Use of these materials needs to be reduced or avoided and alternatives need to be sought. Increasing power output and deriving co‐products from the P‐MFC will increase environmental performance of the P‐MFC. At this stage it is too early to compare the P‐MFC with other (renewable) energy technologies since the P‐MFC is still under development. © 2013 Society of Chemical Industry and John Wiley & Sons, Ltd