The present importance of fossil energy is recognized and the consequences of its exponential growth explained. The mechanism of global warming from increasing greenhouse gases in the atmosphere is summarised and the need for a transition to renewable energy is identified. The units that are usually used to describe energy are listed. The consequences of exponential growth are explained. Approaches to limiting energy use and the difficulties of reducing energy use are discussed. The consequences of applying discounted cash flow analysis in the economic appraisal of energy-efficiency measures are described. The challenges of low-carbon energy electricity generation are discussed and the carbon intensity of generation illustrated. The low-capacity factors of many renewable energy sources and the high-capacity margin of an electrical power system with renewable energy generation are described. Environmental and social impacts of renewable energy schemes are summarized. The chapter is supported by 4 examples, 13 questions with answers and full solutions in the accompanying online material. Further reading and online resources are identified.

Improvements in wind technology and reductions in cost mean that wind energy is now one of the most important sources of new electricity generation. This chapter looks at the history, physics and technological improvements leading to current wind turbine technology. Longer turbine blades and taller hub heights have played a key role in improving wind turbine performance. It also covers the development process required to build a wind farm including monitoring, energy assessment and financing aspects. A summary of pricing of recent wind energy projects from around the world demonstrates the economic competitiveness of the technology. We consider Denmark, and how it deals with the variability of obtaining more than 30% of its electricity from wind. Finally, it is demonstrated that a modest increase in wind installations to 72 gigawatts per year could see the world obtaining about 20% of electricity from wind power by 2040.