| 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 book to be published about a year after this one (Sørensen: Hydrogen and fuel cells, Academic Press). Some older material has been omitted or tidied up, and manoeuvring through the book has been eased, both for reference and textbook uses.
The penetration of renewable energy into the energy system of human settlements on Earth is from one point of view nearly 100%. The energy system seen by the inhabitants of the Earth is dominated by the environmental heat associated with the greenhouse effect, which captures solar energy and stores it within a surface-near sheet of topsoil and atmosphere around the Earth. Only 0.02% of this energy system is currently managed by human society, as illustrated in Figure 1.1. Within this economically managed part of the energy sector, renewable energy sources currently provide about 25% of the energy supplied. As the Figure indicates, a large part of this renewable energy is in the form of biomass energy, either in food crops or in managed forestry providing wood for industrial purposes or for incineration (firewood used for heat and cooking in poor countries, or for mood-setting fireplaces in affluent countries, residue and waste burning in combined power and heat plants or incinerators). The additionally exploited sources of renewable energy include hydro, wind and solar. Hydropower is a substantial source, but its use no longer growing due to environmental limits identified in many locations with potential hydro resources. |