2.2.2. Evaluation of life-cycle energy conversion efficiency
Measuring sustainability of the energy supply systems is a major issue as well as a driving force for the development of sustainable systems, and assessment of energy efficiency in respect to the consumption of primary energy to the energy output is a key technical consideration (Wang et al., 2009). Compatible savings in primary energy consumption can be reached by conversion technologies using renewable energy sources, or reduction of final energy consumptions, under the same operating conditions. Biogas production and utilization pathways were evaluated on the basis of Primary Energy Input to Output (PEIO) ratio. Input was the sum of energy used in; crop cultivation and feedstock pre-treatment, feedstock collection and transport, biogas plant operation, biogas utilization and digestate processing and handling. Energy output
was the sum of potential energy conversion from the biogas yield from the respective feedstock. A detailed description of the analyses is presented by Pöschl et al. 2010.