The application of the exergy methodology reveals the system components where high exergy dissipation occurs and improvements may be accomplished to conserve energy resources. The method is applied to several systems: heat exchangers, including boilers and condensers; vapor and gas power cycles, including cogeneration units; jet engines; and geothermal units. Calculations on exergy dissipation identify the processes and components where improvements would save energy resources. The calculations reveal that combustion processes waste a great deal of exergy, leading to the conclusion that direct energy conversion devices, such as fuel cells, utilize fossil fuels in a sustainable way. The exergy method is also applied to photovoltaic cells and thermal solar power plants, as well as to solar collectors that deliver heat. Significant exergy destruction occurs in wind turbines because of Betz’s limit and the wind turbine characteristics. A large number of examples in this chapter elucidate the exergy calculations and provide guidance and resources for the application of the exergy methodology to power and heat generation systems and processes.

SDG 7 aims to ensure access to affordable, reliable, sustainable and modern energy for all. Forests contribute to SDG 7 through four pathways: sustainable use of traditional wood fuels, processed wood fuels, liquid biofuels and biopower. We hypothesise that the role of traditional wood fuels (e.g. firewood and charcoal) in household energy portfolios will decline in most low- and middle-income countries, but will not be completely replaced with modern fuels. In the transition to affordable clean fuels, processed wood fuels (e.g. pellets), liquid biofuels produced from forest feedstock, and biopower will play an increasing role in energy service provision. How forest-based transitions to clean energy will fare relative to other renewable energy technologies (including solar, wind and micro-hydro) will depend on how renewable energy policy evolves, and on relative costs and storage capacity. Reaching SDG 7 through the promotion of large-scale hydro and agricultural commodity derived biofuels can threaten forests and forest-based livelihoods. In general, promoting transitions to sustainable forest-based clean energy supports the realisation of other SDGs, highlighting the potential for forests to play a significant role in discourse and action on the SDGs.