Solar Power to Electricity—A Photovoltaic Perspective on the Plant Microbial Fuel Cell

The keywords solar power and electricity combined evidently point our minds toward photovoltaics. However, plant microbial fuel cells (PMFCs) have a similar working principle. The technology – which emerged in 2008 – combines living plants and microorganisms in an <i>in situ</i> fuel cell configuration, also converting sunlight into electricity [1]. But how do these two technologies compare? In this study, PMFCs were approached from a photovoltaic perspective. A rough upper limit for the overall energy conversion efficiency was estimated and compared to various classes of photovoltaics. To this end, each intermediate step in the working principle of plant microbial fuel cells was investigated, and of each step, the maximum efficiency found in literature was used to calculate the maximum power conversion efficiency. This approach estimated the maximum efficiency to be around 1%, more than one order of magnitude lower than traditional and emerging photovoltaics [2].<br/>Going from theory to practice, the corresponding maximum power density was compared to the historical evolution of reported power output values. However, no apparent increase through time could be seen since their emergence. The application of the technology may explain this as the plant microbial fuel cell has many dedicated niche applications ranging from sensing to remediation, where power output might not be of interest [3]. Even though various routes toward increased power output are still being proposed, it is clear that PMFCs are intrinsically limited and dwarfed in comparison to photovoltaics when looking at power output alone. Nonetheless, the various niche applications - together with certain advantages the technology has over photovoltaics, i.e., aesthetics, price, straightforwardness, etc. - provide an added value to the technology.<br/>This critical discussion aids in placing the plant microbial fuel cells, their applications, and expectations in the world of green, and particularly of solar energy-related research.<br/><br/>[1] Strik D.P.B.T.B. et al., <i>Int. J. Energy Res</i>. <b>32</b> (2008)<br/>[2] NREL - Best Research-Cell Efficiency Chart (2022)<br/>[3] Ebrahimi A. et al., <i>J. Environ. </i><i>Chem. Eng</i>. <b>9</b> (2021)