Global energy technology transitions.
Past energy technology transitions provide lessons for current efforts and can inform future visions of energy technology change in the twenty-first century . The global energy system is a planetary-scale complex network of energy converters and energy flows. Figure II.1 illustrates the associated global flows of “exergy”, that is, the energy available to be used, at the most aggregate level, from extraction at the primary level through the secondary, final and useful energy levels. It illustrates the dominance of fossil fuels and the low overall efficiency of the global system. It should also be noted that most greenhouse gas mitigation efforts focus on electricity supply, even though most losses are incurred from the final to the useful level. Useful energy is divided into motion (transport and machines), heat (mainly buildings) and non-energy (dominated by six materials). The underlying global reference energy system of interlinked energy technologies is even more complex. As the o...