ALTERNATIVE and RENEWABLE ENERGY n CO-GENERATION n WIND ENERGY n GEOTHERMAL ENERGY n SOLAR ENERGY n CONSERVATION

COGENERATION FROM TRASH Garbage is converted to useful energy in this solid waste plant. The plant generates energy for businesses in downtown Akron, Ohio, by burning certain types of refuse in a high-temperature furnace. Steam produced by incineration drives a turbine on a generator, and the energy from the generator is converted for use in the city.

WIND ENERGY Increasingly popular as alternative sources of energy, wind turbine generators produce electricity by harnessing the wind. A type of windmill, wind turbine generators are much less harmful to the environment than other sources of energy, but are not always practical because they require average wind speeds of at least 21 km/h (13 mph). This wind farm on the San Gorgonio Mountain Pass in California’s San Bernadino Mountains contains over 4000 separate windmills and provides enough electricity to power the entire Coachella Valley in southern California.

WIND ENERGY A water-pumping windmill in Spring, Arizona, provides water for agricultural use. The blades, or sails, are mounted at an oblique angle on the horizontal shaft. The fantail rudder steers the bladed wheel into the wind to maximize the windmill’s efficiency.

GEOTHERMAL ENERGY Geothermal energy plants generate electricity and heat by harnessing the heat energy contained within the earth. The earth transfers its energy to deep-lying circulating water, which the plants access with wells and pumps. Geothermal energy is attractive because it has a low impact on the environment; however, there are few sites where geothermal energy can be extracted.

SOLAR ENERGY In a photovoltaic cell, light excites electrons to move from one layer to another through semi-conductive silicon materials. This produces an electric current.

SOLAR ENERGY for HOT WATER

SOLAR ENERGY FOR HOT WATER Flat plate collectors utilize the sun’s energy to warm a carrier fluid, which in turn provides usable heat to a household. The carrier fluid, which in this case is water, flows through copper tubing in the solar collector, and in the process absorbs some of the sun’s energy. Next, the carrier fluid moves to the heat exchange, where the carrier fluid warms water that is used by the household. Finally, a pump moves the carrier fluid back to the solar collector to repeat the cycle.

SOLAR ENERGY for SPACE HEATING AND COOLING

Active solar heating systems involve installing special equipment that uses energy from the sun to heat or cool existing structures. Passive solar energy systems involve designing the structures themselves in ways that use solar energy for heating and cooling. For example, in this home, a "sun space" serves as a collector in winter when the solar shades are open and as a cooler in summer when the solar shades are closed. Thick concrete walls modulate wide swings in temperature by absorbing heat in winter and insulating in summer. Water compartments provide a thermal mass for storing heat during the day and releasing heat at night.

A RENEWABLE ENERGY HOUSE In this solar home in Corrales, New Mexico, a flat plate solar collector (lower right) provides energy to heat water pumped by the windmill. The water is stored in large drums on the side of the home.

“CONSERVATION” is an ENERGY CONSIDERATION A thermograph shows the large amount of heat lost through a house’s windows during winter. Replacing conventional windows with double- or triple-paned windows cuts down the amount of heat that can escape from the house; this conserves energy and reduces heating bills.