Alternative energy sources are seen by many people as potential solutions to the many economic and environmental challenges posed by the current dominance of world energy supply by fossil and nucler fuels. Just how realistic are these hopes? This unit summarises the technical and geographic challenges posed by each alternative source. It is left to you to judge the feasiibility of imploementing these changes against the claims for 'alternative' solutions to global energy challenges that are regularly made. This study unit is just one of many that can be found on LearningSpace, part of OpenLearn, a collection of open educational resources from The Open University. Published in ePub 2.0.1 format, some feature such as audio, video and linked PDF are not supported by all ePub readers.