Efficiency versus cost — A fundamental design conflict in energy science

Summary. — An essential design conflict in energy technology is the trade-off between efficiency and cost. The lecture introduces concepts that deal with this trade-off and discusses real world examples. Among the many definitions of efficiency, exergetic efficiency is the most rigorous and often the most adequate for analyzing the efficiency of a process. Exergy is the maximum work obtainable from a system as it comes into equilibrium with its environment. Exergetic efficiency is illustrated here with the heating of buildings. The right concept to analyze the trade-off between efficiency and the initial capital cost of equipment is the net present value analysis. We discuss two examples, overhead power lines and energy storage. Electrothermal energy storage is a new energy storage technology that builds on both concepts, optimization of exergetic efficiency and balancing of initial cost with that efficiency. Finally, non-technical barriers for energy efficiency are mentioned.