Entropy of energy crops and GHG mitigation

Summary

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 to their heat value. In other words, the entropy of energy crops is low compared to fossil fuels. This fact is usually neglected in energy analysis of bio fuels resulting in questionable political decisions concerning renewable energy. The objective of this paper is to demonstrate that the GHG mitigation potential of e.g. fibre crops may be enhanced using them first 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 used to estimate the reduction of CO2 equivalents of 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. However, fossil fuels render a higher energy return of investment and are for the time being more competitive than both options.