Two Worldwatch institute researchers survey ""the major sources of renewable energy with the most potential."" After a gloomy review of non-renewable energies (coal, oil, gas, nuclear), their supply and hazards, Deudney and Flavin focus on: solar energy--and forms thereof (passive architectural design, water heaters, stills, collectors, solar ponds, ocean thermal energy conversion, photovoltaics); wood--and methanol; biomass conversion (ethanol, biogas, utilizing urban waste); water, wind, and geothermal energies. They look into how existing systems are working; consider the ways modern technology might improve efficiency, and discuss possible and actual environmental drawbacks. (Whether the wood-supply will hold up as well as they think is questionable.) They also take pertinent note of how these technologies, applied on a small scale, might help the energy-poor Third World. Certain other renewables, however (hydrogen, wave and tidal power, nuclear fusion), are dismissed or omitted, which seems to reflect authorial bias rather than objective assessment. Useful as a wrap-up, then, within bounds--and where books on the individual forms of energy, combined with broad environmental studies, don't suffice.