INTRODUCTION

Discussion of renewable sources of energy is where you will find the largest collection of half-truths and exaggerations. The Renewables covered in this chapter include wind-, solar-, geothermal-, hydro-, ocean-, and biomass-energy systems (biofuels are treated in the next chapter). According to the OECD Factbook (2008), renewables made up about 13% of world total primary energy supply (TPES), but the only two that make a significant contribution to emission-free energy today are large-scale hydroelectric dams and biomass. Large hydropower systems supply 18% of world electricity and 4% of TPES, but are often not included in the definition of renewables for reasons that involve value judgments that have nothing to do with greenhouse gases and global warming. Biomass, which contributes 7% of TPES, is the use of waste plant and forest materials for energy and is the fuel that the poorest people have available for heat and cooking as well as supplemental fuel for energy in more developed nations; I will come back to it briefly in the chapter on biofuels..

When large hydro and biomass are excluded, only a tiny part of TPES comes from wind, solar electrical, geothermal, ocean, and biofuel systems: less than 1% in the Unites States and less than 2% worldwide. Of these, wind is the largest, supplying about 1% of US electricity in 2008, but has problems because it is intermittent and the best sites are often not where the largest demand is.