Abstract Biomass has been used as a fuel source ever since humanity learned to make fire and served as the primary source of energy before fossil fuels became common in the twentieth century. Biomass is still the dominant source of energy for one billion of the poorest people. Biofuels are attractive for a number of reasons - plants act as `solar panels', capture carbon, and store energy. Their large-scale adaptation as energy source for modern industrial societies hinges on the solar utilization efficiency of plants. Plants appear to have similar efficiencies in capturing solar radiation as the most efficient solar panels that can be deployed at large scale, but the plants' own metabolism combined with the 'metabolism' of the infrastructure to produce biofuel from biomass yields a very low solar utilization. The climate vulnerability of biomass as renewable energy source is largely similar to food crops. Slight differences might be expected for different biofuel types. First generation biofuels might be more vulnerable due to constrains on deploying often energy intensive agricultural practices that can offset adverse climate impacts. Second generation biofuels are likely to be more resilient than food crops since their feedstock comes from marginal lands that are more close to natural vegetation.