You can think of energy
as the ability to do work. All heterotrophic organisms derive chemical
energy from the food they eat to do biological work: growing, reproducing,
controlling body temperature, moving, avoiding predators, and acquiring
more food. Humans, by using technology, have figured out how to use
energy from other sources to help them do biological work. For instance,
we use heaters and make clothes to keep us warm, drive or fly from place
to place powered by engines, and use machines to increase our crop yields.
All this technology has made human civilization possible and allowed
us to live longer lives. But it comes with a price.
Most of our technologies
are powered by fossil fuels: coal, oil, and natural gas. These are non-renewable
sources of energy which will eventually run out. In the meantime, our
fossil fuel consumption is the main cause of environmental problems
such as global warming, acid precipitation, smog, and many types of
water and soil pollution. Burgeoning environmental awareness in the
1970s led scientists, especially in the US and Europe, to look for viable
alternatives to fossil fuels to meet the majority of our energy needs.
The aerospace and transportation industries have also participated in
developing new energy technologies. Today, several alternatives to fossil
fuels are available to heat our homes, provide electricity for our appliances,
power industrial processes, and propel our cars, trains, boats, and
planes. In addition, we have made major strides in the area of energy
efficiency and conservation, though US citizens continue to consume
and waste more energy than the citizens of any other nation, while renewable
energy sources account for a tiny fraction of our energy use.
Before we begin looking at
the some of these alternative technologies, we need to understand a
little about of the physics of energy. Remember that everything we do
is constrained by the laws of thermodynamics, so we would do well to
keep them in mind when we develop energy technologies.
Where does our
energy come from?
Because of the first law of thermodynamics, we must acquire energy since
we can never "make” it. Of course sunlight is the only source
of energy that is constantly being added to the earth’s system,
so solar panels for heat or electricity leap to mind when we think of
harvesting the sun’s energy, but many other energy technologies
also depend on energy from the sun. For instance, the energy in fossil
fuels, most likely the fossilized remains of plants and animals that
lived millions of years ago, is actually solar energy that ancient photosynthetic
organisms captured and stored in chemical bonds. So when you cozy up
to the heater, if it is fueled by oil, coal, or natural gas, you are
actually being warmed by solar energy that arrived on the earth many
millions of years ago. But remember that in modern times very little
energy is being stored in the earth’s crust in this way, so fossil
fuels are not being replaced as we use them up: they are non-renewable.
The sun also drives the winds
and the water cycle, so when we use hydroelectric dams or windmills
to generate electricity, we are actually using solar energy. When we
burn wood to keep warm, we are using solar energy stored in the process
A few energy sources do not rely on light from the sun. Geothermal technologies
use heat from the earth’s mantle to heat water and homes or to
generate electricity. Nuclear energy technologies use nuclear fission--splitting
atoms apart--to harvest the enormous amount of energy stored in matter
What forms of
energy do we need?
Think about the ways you use energy in your home. Chances are that you
use electrical energy for many of your energy needs, such as operating
appliances, cooling your food, and lighting your rooms. You also use
heat energy to warm your home and heat your water. This heat energy
may be generated by burning fossil fuels or wood in a furnace or stove,
harvested by capturing solar or geothermal energy, or it may be converted
from electrical energy in an electric heater. So you use energy primarily
in two forms: heat and electricity.
How much energy
is lost to entropy?
Efficiency is the percent of available energy that is actually used
to do work. For instance, if your car’s internal combustion engine
converts 15% of the chemical energy in gasoline into mechanical energy
to propel your car along the highway, it is said to have an efficiency
of 15%. The remaining 85% of energy is wasted as heat--that is why your
car’s engine is hot after you drive it. Every time energy is transformed,
some is lost as useless heat (remember the second law of thermodynamics?).
So your car’s engine will never be able to convert all of the
energy in the gasoline to propel your car; no energy technology can
be 100% efficient. But your car can be much more efficient than it is;
in recent years, internal combustion engines have been developed that
are twice as efficient as older models.
Let’s perform a thought
experiment to illustrate the importance of efficiency: Suppose you are
using an electric heater in your home. Most traditional methods of generating
electricity involve burning fossil fuels, catching falling water, or
splitting atoms to power electrical generators. If your heater uses
electricity generated at the power plant in Sandwich, the heat it gives
off began as chemical energy stored in crude petroleum which was pumped
from deep wells and carried in pipelines and ships to a refinery. The
drills, pumps, and ships which transport the petroleum all require energy
to operate. Refining removes impurities and separates the oil into several
useful chemicals; this process requires energy and some of the chemical
energy in the fuel itself is lost in refining. After refining, #6 fuel
oil, a thick black substance sometimes called bunker fuel, is shipped
to Canal Electric, using more energy to run the ship and the pumps.
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