Seite - 98 - in Water, Energy, and Environment - A Primer

○ Direct use ○ Ground source heat pumps • Biomass energy ○ Plantmaterial ○ Wastematerials ○ Algae • Hydropower ○ Traditional technology ○ Barrage technology • Ocean energy ○ Wave ○ Tidal ○ Ocean current ○ OTEC What might be noted is that most of the entries are direct or indirect forms of solar energy. PV and solar thermal are direct forms.Wind is an indirect form arising from uneven heating of the Earth’s surface. Biomass is organic matter grown with the aid of sunlight. Hydropower depends on water delivered by the hydrological cycle which is solar-driven. OTEC (ocean thermal energy conversion) depends on solar heating of the ocean’s surface.Wave energy is partly wind-driven, but is also affected by the gravitational attraction between the Earth and theMoon. Tidal energy is water energy that is driven by ocean heating as well as gravitational effects. The one exception is geothermal energy that derives from radioactive decay in the Earth’s core. 8.1 THESUN’SENERGYSOURCEAND RADIATIONSPECTRUM As an introduction to a more detailed look at each renewable energy technology in subsequent sections of this chapter, let us beginwith abrief discussionof the source of theSun’s energy. Water,Energy, andEnvironment–APrimer98