Energy Accounting for a Renewable Energy Future

For millennia, humans relied almost entirely on renewable energy (RE), largely biomass, for their energy needs. Over the past century, fossil fuels (FFs) have not only largely replaced RE, but have enabled a many-fold rise in total energy use. This FF dominance changed the way we think about and accounted for energy use. If (as at present) the world essentially continues to ignore climate change, eventual resource depletion will force conversion to RE and, perhaps, nuclear energy will once again have to provide most of the world's energy use. However, the change is more likely to come about because of the urgent need for climate change mitigation. At present, primary RE electricity accounting is done by calculating the FF energy that would be needed to produce it. But as FFs disappear, this approach makes less sense. Instead, a new approach to energy accounting will be needed, one that allows for the intermittent nature of the two most abundant RE sources, wind and solar power. Surplus intermittent RE might be converted to H-2, further complicating energy accounting. An additional complication will be the treatment of energy reductions, especially from passive solar energy, likely to be more important in the coming decades. This paper is a review of the evidence to try to determine the best approach to future energy accounting.