Energy Input-Output Meta-Analysis Reveals Algal Diesel Struggles to Break Even (Supplemental Information)

Algal biofuels have been investigated as an alternative to traditional fossil fuels for transportation in the United States since the 1970s. Yet after five decades of development, scalability and implementation remain limited. To evaluate the state of progress, this study harmonized energy inputs and outputs across 39 papers, encompassing 508 observations on the production of algal biofuel energy return on energy investment (EROEI) in the United States. The analysis produced a mean EROEI of 1.01—essentially the break-even point—irrespective of system boundaries. This is lower than bioethanol (2.8) and far below oil (8.7). Life-cycle analysis results showed that hydrothermal liquefaction in algal diesel production yielded a slightly higher mean EROEI (0.67) than transesterification (0.51). Co-products were found to play a significant role in reported EROEI values, particularly those recycled into production processes. Collectively, these findings indicate that investment to date has not produced a competitive technology. This evidence suggests that continuing to invest heavily in algal biofuels as a primary pathway for the energy transition is unlikely to yield competitive results in the near to medium term. For this reason, algal biofuels show little potential to alleviate the ongoing decline in the EROEI of petroleum and are not a promising renewable energy option for reducing greenhouse gas emissions from the transportation sector. They also show little promise for alleviating the land use, food vs fuel and other controversies that have plagued first and second-generation biofuels.