Similar to microbial fuel cells, biological photovoltaic systems which employ whole organisms have the advantage over non-biological fuel cells and photovoltaic systems of being able to self-assemble and self-repair (i.e. the photosynthetic organism is able to reproduce itself). The ability of the organism to store energy allows for power generation from biological photovoltaic systems in the dark, circumventing the grid supply and demand problems sometimes faced by conventional photovoltaics.[5] Additionally, the use of photosynthetic organisms that fix carbon dioxide means the 'assembly' of the light harvesting material in a biological photovoltaic system could have a negative carbon footprint.