Conversion steps in bioenergy production – analysis of the energy flow from photon to biofuel

Abstract

The overall goal for bioenergy systems is to transfer as much solar energy as possible into the desired product (i.e. biofuel). While the energy flow from photon to biomass is relatively well documented in algae, the energy conversion efficiency in higher plants is less well understood. In addition to the efficiency losses defined by nature, inevitable losses occur due to the technical processing steps necessary to convert the biomass into a biofuel. Against this background the aim of the following explanations is the assessment of the energy flow from solar insulation to a technically usable and storable biofuel (here: biomethane from maize and algae; bioethanol from wheat grains); this is similar to the flow of organic carbon from the ambient air via the plant to the bioenergy carrier (CH₄, C₂H₅OH). To allow for a critical review the results are compared with the use of photovoltaics and the subsequent conversion of the electricity to a storable fuel with similar characteristics.