The present edition has been updated in a number of renewable energy technology areas (Chapter 4 and 5), where progress have been made over the recent years. New solar simulation studies have been added to Chapter 6, and market considerations have been included in the overview in Chapter 1, and in discussing industry liberalisation in Chapter 7. The remarks on advanced subjects made in the preface to the 2nd edition are still valid. A new growth area is fuel cells for stationary and mobile uses of hydrogen and other fuels. Only modest updates have been done in this area, as it is the subject of a new, companion.