5.7C Alternative Energy
Key Concept 1: Alternative energy resources rely on natural processes
and can be used to produce energy.
Alternative energy is any energy that does not come from nonrenewable
resources, such as coal, oil, or natural gas (fossil fuels). For a resource to
be considered “green” (environmentally friendly), the energy source must
be renewable and “clean.” This means the supply must be continually
available, have few or zero carbon emissions, and produce few toxic byproducts.
Nonrenewable resources are materials of which there is a finite or fixed
amount, and once they are consumed, they cannot be replaced by the
Earth in any reasonable time. Fossil fuels, such as oil, coal, and natural
gas, are irreplaceable once they are burned or manufactured into a
human-made product (like gasoline). For many years, humans have relied
on nonrenewable energy resources, which unfortunately have produced
hydrocarbon pollutants that harm our environment. Overdependence on
nonrenewable energy cannot protect future generations from running out
of fuel or energy, nor reduce pollution. With a nonrenewable resource,
excessive consumption only hastens the day when that resource will no
longer be available.
Renewable resources are materials that can be replenished by nature in a
relatively short time, like lumber, which comes from trees. In the United
States, for every tree felled to be made into building materials, a new
seedling is planted to take its place. Although air, water, soil, plants, and
animals are renewable resources, proper conservation and management
policies need to be in place to insure we do not use these resources
faster than they can be replenished. There are two solutions: dramatically
reduce our consumption or find alternative resources. Students will
explore alternative resources that are renewable, nonpolluting, come from
Earth’s natural processes, and can be transformed into usable energy.
Key Concept 2: Alternative energy resources include wind, solar,
hydroelectric, geothermal, and biofuels.
Wind Energy - Wind energy comes from changing the power of moving
air into a useful form. Windmills have been used to pump water and grind
grains for hundreds of years. Modern windmills sit atop 30-foot towers to
harness wind energy by rotating three enormous turbine blades, which
turn a shaft connected to an electric generator. When more power is
needed, wind farms, consisting of hundreds of wind turbines, are
connected to produce large quantities of electricity. Meteorologists help
engineers identify appropriate sites with suitable wind conditions, such as
hill tops, coastal areas, or offshore (to catch ocean winds). Although wind
energy is renewable, cost effective, and environmentally friendly, there are
limited areas in which frequent windy conditions exist.
Solar Energy - Solar panels made of photovoltaic (PV) cells produce
electricity directly from sunlight. Solar collectors concentrate the Sun’s
rays in the form of heat, which can then be used directly or converted
into electricity using a generator. Solar panels are nonpolluting, make no
noise, and have no moving parts that require maintenance. Passive solar
energy can be used where buildings have walls that absorb sunlight and
radiate that heat instead of burning fuel in a furnace. The disadvantages
of solar energy are: the high cost of producing and installing solar panels,
the limited areas of use at Earth latitudes where sufficient hours of
sunlight can be captured, and overcast weather days that block sunlight.
Hydroelectric Energy - The force of moving water from dammed up
rivers, free flowing rivers, or ocean tides can provide unlimited
hydroelectric power. The gush of flowing water turns the blades of a
turbine, which generates electricity. Hydroelectric energy offers the
advantage of having constantly moving water. The disadvantage is the
limited availability to only communities near water sources.
Geothermal Energy - Geothermal energy is a renewable energy source
because the heat is continuously produced inside Earth where magma
deep underground heats overlying rocks and water, which creates hot
spots. Geothermal power plants drill down to that heat source to make
steam used to heat homes, or to turn a turbine, which generates
electricity. In the United States, most geothermal reservoirs of hot water
are located in California, Alaska, and Hawaii. Newer geothermal power
plants use the hot water source to boil a working fluid that vaporizes and
then turns a turbine.
Biofuel Energy - Humans have burned wood for fuel for thousands of
years. Modern technology can now convert other sources of “biomass,”
organic material made from plants and animals, into usable sources of
fuel. Biofuel contains stored energy from the Sun that plants absorbed.
Biofuel is a renewable energy source because we can always grow more
trees and crops, and waste will always exist. Biofuels, such as ethanol and
methane gas, are produced from sugar cane or corn. Biodiesel is made
from vegetable oil or animal fat. Other sources of biofuel are algae and
animal manure. Although biofuels are renewable, some pollution is
produced from biofuel engines or biofuel power plants.