The sower's way quantifying the narrowing net energy pathways to a global energy transition
Planning the appropriate renewable energy (RE) installation rate should balance two partially contradictory objectives: substituting fossil fuels fast enough to stave off the worst consequences of climate change while maintaining a sufficient net energy flow to support the world's economy. The upfront energy invested in constructing a RE infrastructure subtracts from the net energy available for societal energy needs, a fact typically neglected in energy projections. Modeling feasible energy transition pathways to provide different net energy levels we find that they are critically dependent on the fossil fuel emissions cap and phase out profile and on the characteristic energy return on energy invested of the RE technologies. The easiest pathway requires installation of RE plants to accelerate from 0.12 TWp yr 1 in 2013 to peak between 7.3 and 11.6 TWp yr 1 in the late 2030s, for an early or a late fossil fuel phase out respectively in order for emissions to stay within the recommended CO2 budget.