Ron Smith's Yale course The Atmosphere, the Ocean and Environmental Change turns to renewable energy sources: wind, solar, biomass, and geothermal. Smith explains how large wind turbines depend on strong, steady wind with low turbulence, and how solar power is harvested either through photovoltaic cells or concentrated solar collectors. He covers two routes for biomass energy, direct combustion for electricity and fermentation into fuel ethanol, then describes geothermal plants that pump water into hot rock to generate steam for turbines. The lecture closes with a broader look at electricity sources. Recorded in Fall 2011 as lecture 34 of the course, it runs about 48 minutes and moves through each technology's physical mechanics rather than policy debates, giving a technical grounding in how each renewable source actually converts natural energy into usable power.