A traditional argument for the continued use of fossil fuels has been their high energy efficiency in energy investment. This refers to the proportion of how much energy a source, such as coal or oil, will produce compared to the amount of energy needed to extract it.
Previously, estimated ratios for return on energy investment (ROI) have favoured fossil fuels over renewable energy sources. For oil, coal and gas, ratios of more than 25:1 are generally calculated, meaning that approximately one barrel of used oil produces 25 barrels to return to the energy economy. Renewable energy sources often have much lower estimated ratios, below 10:1.
However, these fossil fuel relationships are measured at the extraction stage, when oil, coal or gas are removed from the ground. These ratios do not take into account the energy needed to transform oil, coal and gas into finished fuels, such as gasoline used in cars or electricity used by households.
A new study, in collaboration with scientists at the University of Leeds Sustainability Research Institute (UK), has calculated the EROI for fossil fuels over a 16-year period and found that at the finished fuel stage, the ratios are much closer to renewables, about 6:1, and potentially as low as 3:1 for electricity.
The study, carried out as part of the UK Energy Research Centre programme and published in Nature Energy on Thursday, warns that the rising energy costs of fossil fuel extraction will cause proportions to continue to decline, pushing energy resources towards a precipice of net energy’, i.e. when the net energy available to society decreases rapidly due to the growing amounts of ‘parasitic’ energy required in energy production.
The researchers emphasize that these findings are a good argument for rapidly accelerating investment in renewable energy sources and that the transition from renewable energy can halt, or reverse, the decline of the global EROI in the finished fuel stage.
Co-author of the study, Dr. Paul Brockway, an expert in energy economics models at the School of Earth and Environment in Leeds, points out that “measuring the energy efficiency of fossil fuel investment at the extraction stage gives the misleading impression that we have plenty of time for a renewable energy transition before energy constraints are a concern.
These measurements essentially predict potential energy production from newly extracted sources, such as crude oil,” he adds in a statement. But crude oil is not used to heat our homes or feed our cars. It makes more sense for the calculations to take into account where energy enters the economy, and it doesn’t bring us much closer to the precipice.
Therefore, he believes that “the proportions will only continue to decline because we are rapidly reaching the point where all easily accessible fossil fuel sources are being depleted. By increasing investment in renewable energy sources, we can help ensure that we don’t fall to the limit.
Study co-author Dr. Lina Brand-Correa, an expert on social aspects of energy use at the Living Well within Limits (LiLi) project in Leeds, believes that too much emphasis is being placed on the initial economic costs of transitioning to renewable energy.
Renewable infrastructure, such as wind farms and solar panels, requires a large initial investment, which is one of the reasons why their rates of return on energy investment have been so low so far,” she admits.
But the average energy return on investment for all fossil fuels in the finished fuel stage fell by about 23 percent in the 16-year period we consider. This decline will result in restrictions on the energy available to society in the not-so-distant future, and these restrictions can develop quickly and unexpectedly.
Once renewable infrastructure is built and dependence on fossil fuels decreases, the return on investment in energy from renewable sources should increase,” she says. This must be considered for future investment decisions in energy policies and infrastructure, not only to meet climate change mitigation commitments but to ensure that society continues to have access to the energy it needs.