The photosynthesis process generates beside carbon hydrates also complex chemical compounds. The artificial synthesis of such compounds is often impossible or may require high energy input compared with their heating value. In other words, the entropy of energy crops is low compared with that of fossil fuels. This fact is usually neglected in energy analysis of bio fuels resulting in questionable political decisions concerning renewable energy. This paper demonstrates that the energy saving and the GHG mitigation potential of fibre crops may be enhanced using them first used as raw material for commercial products before processing to fuel at the end of their lifetime. For example reed canary grass may be used for paper production and after recycling the used paper can be processed to insulation material in buildings before thermal use. Such a chain of usage trades off both, the low entropy as raw material for pulp and the heat value of the carbon hydrates. A calculation model is presented to estimate the reduction of CO2 equivalents of the following two options: Alternative A: Production of reed canary grass + processing to fuel for heating. Alternative B: Production of reed canary grass + processing to paper + recycling of paper + processing to insulation material + installation of insulation material in buildings + recycling of insulation material + processing for heating. The results show that alternative B is outclassing alternative A. Pulp made of reed canary grass for paper and insulation material saves between ten and hundred times or more energy compared with the energy yield of burning. However, fossil fuels render a higher energy return on investment and are for the time being more competitive than both options.