RENEWABLE AND ALTERNATIVE ENERGY SOURCES Mrs. Paul Environmental Science Chapter 17 (pgs )

Renewable Energy Today  Renewable Energy: energy from sources constantly being formed.  Include: solar energy, wind energy, water energy, Earth’s heat.  Even renewable energy affects the environment.

Solar Energy  Solar energy: energy from the sun; absorbed by plants and used as fuel.  Sun  Medium-sized star.  Radiates energy from nuclear fusion reaction in its core. High temperatures cause hydrogen nuclei to fuse, forming helium nuclei and a loss of mass occurs. Lost mass converted to heat and light energy.  Only little bit (2-billionth) of energy reaches Earth.  All renewable energy comes from the sun.  Energy reaches us as visible light and infrared radiation.

 Pros  Free, clean, nonpolluting.  Savings on fuel bills  Collected energy can be stored.  Cons  Energy source is not constant (limited sunlight on cloudy or rainy days, none at night).

Passive Solar Heating  Passive solar heating: sun’s energy is collected, stored, and distributed naturally in an enclosed dwelling.  Not used to produce electricity.  Example: Northern Hemisphere-windows facing south receive most solar energy; passive solar buildings have windows facing south. Energy enters windows and warms the house! Heat released slowly at night.  Buildings must be well insulated with thick walls and floors to prevent heat loss.  Oriented to sun’s yearly movement.

Passive Solar Features:

Active Solar Heating  Active solar heating: energy from sun gathered by collectors and used to heat water or buildings.  Solar collectors capture sun’s energy.  Liquid heated as it passes through collectors.  Hot liquid pumped through heat exchanger, which heats water for building.

 Photovoltaic cells: solar cells; convert the sun’s energy into electricity, using thin wafers of semiconductor material.  No moving parts, electric current generated when electrons on negative side move to positively charged side.  Nonpolluting  Produce little electrical current, need extended sunshine to produce electricity (stored in batteries when not shining).  Energy production from solar cells has doubled every 4 years from 1985.

Wind Power-Cheap and Abundant  Wind: movement of air masses as Earth’s surface is warmed unevenly by the sun.  Wind power: converts the movement of wind into electric energy.  Wind turbines are cost effective and can by constructed quickly.  Aerogenerators: windmills used to generate electricity; also called wind turbine generators.

Wind Farms  Wind farms: large arrays of wind turbines.  Take up little space.  Land can still be used for farming.

Biomass-Power from Living Things  Biomass Fuel: organic material that is used as an energy source.  Renewable  Ex: wood, dung, plant material.  Wood Used for heating and cooking Renewable Careful-can lead to habitat loss, deforestation, soil erosion; pollution from burning

 Methane Produced when bacteria decompose organic wastes. Burned to generate heat or electricity  Alcohol Can be made from fermenting fruit or agricultural waste. Gasohol (gasoline and ethanol) produces less pollution.

Hydroelectricity-Power from Moving Water  Hydroelectric energy: energy produced from moving water.  Dam across river to hold back water.  Water released to turn a turbine.  Motion of turbine transferred to coils of wire inside generators. Coils spin in magnetic field.  Benefits: Inexpensive to operate No air pollution Last long

 Disadvantages: Dam changes river flow. Resevoir floods habitat above the dam. Water flow below dam is reduced. Dam failure can kill or injure people.  Modern Trends Micro-hydropower: electricity produced in a small stream without having to build a big dam.

 Energy from the Tides  Generate electricity similarly to how generated in river.  Turbine must be able to turn in BOTH directions.

Geothermal Energy-Power from the Earth  Geothermal Energy: energy from heat in the Earth’s crust; can be used to generate electricity.  Geothermal heat pump: a loop of piping that circulates a fluid underground, using the stable underground temperatures to warm and cool homes.

 Enough heat present in the earth to melt rock.  Magma: molten rock. When it reaches the surface it is called lava.

Alternative Energy and Conservation  Alternative energy: energy sources that are still in development.  To become viable, source must prove to be cost effective, and environmental effects must be acceptable.

 Tidal Power  Movement of water in oceans caused by gravitational attraction between the sun, Earth and moon.  Marked by rising and falling of sea level.  As tide rises, water trapped behind the dam. Released to turn turbine and generate electricity.  High cost to build, not many good locations.

 Ocean Thermal Energy Conversion (OTEC)  Warm surface water is used to boil sea water in a vacuum chamber. The water turns to steam and turns a turbine, generating electricity.  Pumping the water up uses about 1/3 of the generated electricity.

 Hydrogen  Burned as a fuel.  When burned, it combines with oxygen to form water.  Current production of hydrogen is not efficient and a LOT of hydrogen is needed to produce energy.