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ENERGY PRINCIPLES
Basic Energy Principles: Energy is the driving force for the universe. Energy is a quantitative property of a
system which may be kinetic, potential, or other in form. There are many different
forms of energy. One form of energy can be transferred to another form. The laws of
thermodynamics govern how and why energy is transferred. Before the different types
of energy resources and their uses are discussed, it is important to understand a little
about the basic laws of energy.
The Three Laws of Thermodynamics
- The first law of thermodynamics, also called conservation of energy, states
that the total amount of energy in the universe is constant. This means that all of the
energy has to end up somewhere, either in the original form or in a different from. We
can use this knowledge to determine the amount of energy in a system, the amount
lost as waste heat, and the efficiency of the system.
-The second law of thermodynamics states that the disorder in the universe
always increases. After cleaning your room, it always has a tendency to become messy
again. This is a result of the second law. As the disorder in the universe increases, the
energy is transformed into less usable forms. Thus, the efficiency of any process will
always be less than 100%.
- The third law of thermodynamics tells us that all molecular movement stops
at a temperature we call absolute zero, or 0 Kelvin (-273oC). Since temperature is a
measure of molecular movement, there can be no temperature lower than absolute
zero. At this temperature, a perfect crystal has no disorder.
When put together, these laws state that a concentrated energy supply must be used
to accomplish useful work.
ENERGY HISTORY
Energy has a long history. Beginning back
before people could read and write, fire was
discovered to be good for cooking, heating and
scaring wild animals away. Fire was civilization's
first great energy invention, and wood was the
main fuel for a long time.
Energy is essential to life. Living creatures
draw on energy flowing through the
environment and convert it to forms they can use. The most fundamental energy flow for
living creatures is the energy of sunlight,
and the most important conversion is the act of biological primary production, in which
plants and sea-dwelling phytoplankton convert sunlight into biomass by photosynthesis.
The Earth's web of life, including human beings, rests on this foundation.
Over millennia, humans have found ways to
extend and expand their energy harvest,
First by harnessing draft animals and later
by inventing machines to tap the power of
wind and water. Industrialization, the
watershed social and economic development
of the modern world, was enabled by the
widespread and intensive use of fossil fuels.
This development freed human society from
the limitations of natural energy flows by unlocking the Earth's vast stores of coal, oil,
and natural gas. Tapping these ancient, concentrated deposits of solar energy enormously
multiplied the rate at which energy could be poured into the human economy.
The result was one of the most profound social transformations in history. The new
river of energy wrought astonishing changes and did so with unprecedented speed.
The energy transformations experienced by traditional societies--from human labor
alone to animal muscle power and later windmills and watermills--were very slow, and
their consequences were equally slow to take effect. In contrast, industrialization
and its associated socioeconomic changes took place in the space of a few generations.
PREHISTORIC ERA
Horse Animated Before the Industrial Revolution
of the 1890s, human beings had only a moderate
need for energy. Man mostly relied on the energy
from brute animal strength to do work.
Man first learn to control fire around 1 million BC.
Man has used fire to cook food and to warm his
shelters ever since. Fire also served as protection
against animals.
Thousands of years ago, human beings also
learned how to use wind as an energy source.
Wind is produced by an uneven heating by the
sun on the surface of the earth because of the
different specific heats of land and water. Hot air
has lower pressure than cold air and since high
pressure tries to equalize with low pressure the
current called wind is produced. Around 1200 BC, in Polynesia, people learned to use this
wind energy as a propulsive force for their boats by using a sail.
About 5 thousand years ago, magnetic energy was discovered in China. Magnetic force
pulled iron objects and it also provided useful information to navigators since it always
pointed North because of the Earth's magnetic field.
Electric energy was discovered by a Greek philosopher named Thales, about 2500
years ago. Thales found that, when rubbing fur against a piece of amber, a static force
that would attract dust and other particles to the amber was produced which now we
know as the "electrostatic force".
Around 1000 BC, the Chinese found coal and started using it as a fuel. It burned
slower and longer than wood and gave off more heat. It served as an excellent fuel
and continued to be used for centuries thereafter. When Marco Polo returned to Italy
after an exploration to China in 1275, he introduce coal to the Western world.
EVOLUTION OF ENERGY SOURCES The economic and technological development of societies is linked with shifts in sources
of energy. The tendency has been the adoption of increasingly energy dense sources, as
the shift from coal (solid) to oil (liquid) and natural gas (gas) indicates. This shift can be
simplified into 5 major phases, one being speculative:
- From the beginning of history up to the industrial revolution (18th century),
mankind's sources of energy relied only on muscular and biomass sources. Most work
was provided by manual labor and animals, while the biomass (mainly wood) provided for
heating and cooking energy needs. Other sources of energy, such as windmills and
watermills were present but their overall contribution was marginal.
- By the mid 19th century, the industrial revolution brought a major shift in energy
sources with the usage of coal, mainly for steam engines, but increasingly for power
plants.
- As the 20th century began, the major reliance was on coal, but a gradual shift
towards higher energy content sources like oil began. This second major shift
inaugurated the era of the internal combustion engine and of oil-powered ships.
- In the late 20th century, the emphasis on petroleum products as the main provider
of energy has reached the point where the world economy highly depends on the
internal combustion engine and supporting industries. As its level of technical expertise
increased, mankind was able to tap on more efficient sources of fossil fuels, mainly
natural gas, and energy released by matter itself (nuclear fission).
- The 21st century will be characterized by major shifts in energy sources with a
gradual obsolescence of polluting fossil fuels, like coal and oil, for more efficient fossil
fuels such as natural gas. Advances in biotechnologies let anticipate the growing usage
of biofuels. Nuclear energy, if nuclear fusion becomes commercially possible, may also
play a significant role. A very important change in energy sources is likely to be the
usage of hydrogen, mainly for fuel cells powering vehicles, small energy generators and
numerous portable devices.
WHAT IS ENERGY
Energy is Ability to do work.
The energy can take a wide variety of forms - heat (thermal), light (radiant), mechanical,
electrical, chemical, and nuclear energy. There are two types of energy - stored
(potential) energy and working (kinetic) energy. For example, the food you eat contains
chemical energy, and your body stores this energy until you release it when you work or
play.
All forms of energy are stored in different ways, in the energy sources that we use
every day. These sources are divided into two groups -- renewable (an energy source
that we can use over and over again) and nonrenewable/conventional (an energy source
that we are using up and cannot recreate in a short period of time). Renewable energy
sources include solar energy (which comes from the sun and can be turned into
electricity and heat), wind energy, geothermal energy (from inside the earth), biomass
from plants, and hydropower from water are also renewable energy sources.
However, we get most of our energy from nonrenewable energy sources, which include
the fossil fuels -- oil, natural gas, and coal. They're called fossil fuels because they
were formed over millions and millions of years by the action of heat from the Earth's
core and pressure from rock and soil on the remains (or "fossils") of dead plants and
animals. Another nonrenewable energy source is the element uranium, whose atoms we
split (through a process called nuclear fission) to create heat and ultimately electricity.
We use all these energy sources to generate the electricity we need for our homes,
businesses, schools, and factories. Electricity "energizes" our computers, lights,
refrigerators, washing machines, and air conditioners, to name only a few uses.
We use energy to run our cars. The gasoline we burn in our cars is made from oil.
We use energy to cook on an outdoor grill or soar in a beautiful hot-air balloon. The
propane for these recreational activities is made from oil and natural gas.
Energy is in everything. We use energy to do everything we do, from making a jump
shot to baking our favorite cookies to sending astronauts into space -- energy is there,
making sure we have the power to do it all.
NON-RENEWABLE ENERGY SOURCES
We get most of our energy from nonrenewable energy sources, which include the fossil
fuels - oil, natural gas, and coal. They're called fossil fuels because they were formed
over millions and millions of years by the action of heat from the Earth's core and
pressure from rock and soil on the remains (or "fossils") of dead plants and animals.
Another nonrenewable energy source is the element uranium, whose atoms we split
(through a process called nuclear fission) to create.
OIL (PETROLEUM)
Oil was formed from the remains of
animals and plants that lived millions of
years ago in a marine (water) environment
before the dinosaurs. Over the years, the
remains were covered by layers of mud.
Heat and pressure from these layers
helped the remains turn into what we
today call crude oil. The word "petroleum"
means "rock oil" or "oil from the earth."
Where does Oil come from? Crude oil is a smelly, yellow-to-black liquid and is usually found in underground areas
called reservoirs. Scientists and engineers explore a chosen area by studying rock
samples from the earth. Measurements are taken, and, if the site seems promising,
drilling begins. Above the hole, a structure called a 'derrick' is built to house the tools
and pipes going into the well. When finished, the drilled well will bring a steady flow of
oil to the surface.
Oil was formed from the remains of animals and plants that lived millions of years ago
in a marine (water) environment before the dinosaurs. Over the years, the remains
were covered by layers of mud. Heat and pressure from these layers helped the
remains turn into what we today call crude oil. The word "petroleum" means "rock oil"
or "oil from the earth."
How we get Oil? Crude oil is a smelly, yellow-to-black liquid and is usually found in underground areas
called reservoirs. Scientists and engineers explore a chosen area by studying rock
samples from the earth. Measurements are taken, and, if the site seems promising,
drilling begins. Above the hole, a structure called a 'derrick' is built to house the tools
and pipes going into the well. When finished, the drilled well will bring a steady flow
of oil to the surface.
COAL
How coal was formed? Coal is a combustible black or brownish-black
sedimentary rock composed mostly of carbon
and hydrocarbons. It is the most abundant
fossil fuel produced in the United States.
Coal is a nonrenewable energy source because it
takes millions of years to create. The energy in
coal comes from the energy stored by plants
that lived hundreds of millions of years ago,
when the earth was partly covered with swampy
forests. For millions of years, a layer of dead
plants at the bottom of the swamps was covered by layers of water and dirt, trapping the
energy of the dead plants. The heat and pressure from the top layers helped the plant
remains turn into what we today call coal.
How we get coal? Coal miners use giant machines to remove coal from the ground. They use two methods:
surface or underground mining. Many U.S. coal beds are very near the ground's surface,
and about two-thirds of coal production comes from surface mines. Modern mining
methods allow us to easily reach most of our coal reserves. Due to growth in surface
mining and improved mining technology, the amount of coal produced by one miner in
one hour has more than tripled since 1978.
Surface mining is used to produce most of the coal in the U.S. because it is less
expensive than underground mining. Surface mining can be used when the coal is
buried less than 200 feet underground. In surface mining, giant machines remove the
top-soil and layers of rock to expose large beds of coal. Once the mining is finished,
the dirt and rock are returned to the pit, the topsoil is replaced, and the area is
replanted. The land can then be used for croplands, wildlife habitats, recreation, or
offices or stores. Underground mining , sometimes called deep mining, is used when
the coal is buried several hundred feet below the surface. Some underground mines
are 1,000 feet deep. To remove coal in these underground mines, miners ride elevators
down deep mine shafts where they run machines that dig out the coal.
ELECTRICITY
Electricity is the flow of electrical power or charge. It
is a secondary energy source which means that we get it
from the conversion of other sources of energy, like
coal, natural gas, oil, nuclear power and other natural
sources, which are called primary sources. The energy
sources we use to make electricity can be renewable or
non-renewable, but electricity itself is neither
renewable or non-renewable.
Electrical phenomena have been studied since antiquity, though advances in the science
were not made until the seventeenth and eighteenth centuries. Practical applications for
electricity however remained few, and it would
not be until the late nineteenth century that engineers were able to put it to industrial
and residential use. The rapid expansion in electrical technology at this time
transformed industry and society.
Electricity's extraordinary versatility as a source of energy means it can be put to
an almost limitless set of applications which include transport, heating, lighting,
communications, and computation. The backbone of modern industrial society is, and
for the foreseeable future can be expected to remain, the use of electrical power.
In general usage, the word "electricity" is adequate to refer to a number of physical
effects. In scientific usage, however, the term is vague, and these related, but distinct,
concepts are better identified by more precise terms:
Electric charge – a property of some subatomic particles, which determines
their electromagnetic interactions. Electrically charged matter is influenced by,
and produces, electromagnetic fields.
Electric current – a movement or flow of electrically charged particles,
typically measured in amperes.
Electric field – an influence produced by an electric charge on other charges
in its vicinity.
Electric potential – the capacity of an electric field to do work on a electric
charge, typically measured in volts.
Electromagnetism – a fundamental interaction between the magnetic field
and the presence and motion of an electric charge.
NATURAL GAS
Where does Natural Gas come from? Millions of years ago, the remains of plants and animals decayed
and built up in thick layers. This decayed matter from plants
and animals is called organic material -- it was once alive. Over
time, the mud and soil changed to rock, covered the organic
material and trapped it beneath the rock. Pressure and heat
changed some of this organic material into coal, some into oil
(petroleum), and some into natural gas -- tiny bubbles of
odorless gas. The main ingredient in natural gas is methane, a
gas (or compound) composed of one carbon atom and four
hydrogen atoms.
In some places, gas escapes from small gaps in the rocks into the air; then, if there is enough activation
energy from lightning or a fire, it burns. When people first saw the flames, they experimented with them
and learned they could use them for heat and light.
How we get Natural Gas?
The search for natural gas begins with geologists (people who study the structure of the earth) locating
the types of rock that are usually found near gas and oil deposits.
Today their tools include seismic surveys that are used to find the right places to drill wells. Seismic
surveys use echoes from a vibration source at the earth's surface (usually a vibrating pad under a truck
built for this purpose) to collect information about the rocks beneath. Sometimes it is necessary to use
small amounts of dynamite to provide the vibration that is needed.
Scientists and engineers explore a chosen area by studying rock samples from the earth and taking
measurements. If the site seems promising, drilling begins. Some of these areas are on land but many
are offshore, deep in the ocean. Once the gas is found, it flows up through the well to the surface of
the ground and into large pipelines. Some of the gases that are produced along with methane, such as
butane and propane (also known as 'by-products'), are separated and cleaned at a gas processing plant.
The by-products, once removed, are used in a number of ways. For example, propane can be used for
cooking on gas grills.
Because natural gas is colorless, odorless and tasteless, mercaptan (a chemical that has a sulfur like
odor) is added before distribution, to give it a distinct unpleasant odor (smells like rotten eggs). This
serves as a safety device by allowing it to be detected in the atmosphere, in cases where leaks occur.
Most of the natural gas consumed in the United States is produced in the United States. Some is
imported from Canada and shipped to the United States in pipelines. Increasingly natural gas is also
being shipped to the United States as liquefied natural gas(LNG).
We can also use machines called "digesters" that turn today's organic material (plants, animal wastes,
etc.) into natural gas. This replaces waiting for thousands of years for the gas to form naturally.
URANIUM (NUCLEAR)
Nuclear energy is energy in the nucleus (core)
of an atom. Atoms are tiny particles that
make up every object in the universe. There is
enormous energy in the bonds that hold atoms
together.
Nuclear energy can be used to make
electricity. But first the energy must be
released. It can be released from atoms in
two ways: nuclear fusion and nuclear fission.
In nuclear fusion, energy is released when atoms are combined or fused together
to form a larger atom. This is how the sun produces energy.
In nuclear fission, atoms are split apart to form smaller atoms, releasing energy.
Nuclear power plants use nuclear fission to produce electricity.
Nuclear Fuel
Atoms are made up of three major particles: protons, neutrons and electrons. The
most common fissionable atom is an isotope (the specific member of the atom's
family) of uranium known as uranium-235 (U-235 or U 235 ), which is the fuel used in
most types of nuclear reactors today. Although uranium is quite common, about 100
times more common than silver, U-235 is relatively rare.
Nuclear power plants generate electricity
Most power plants burn fuel to produce electricity, but not nuclear power plants.
Instead, nuclear plants use the heat given off during fission as fuel. Fission takes
place inside the reactor of a nuclear power plant. At the center of the reactor is the
core, which contains the uranium fuel.
The uranium fuel is formed into ceramic pellets. The pellets are about the size of your
fingertip, but each o .
HYDROGEN Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At
standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly
flammable diatomic gas with the molecular formula H2. With an atomic weight of 1.00794 u, hydrogen is
the lightest element. Hydrogen is the simplest element known to man. Each atom of hydrogen has only one proton. It
is also the most plentiful gas in the universe. Stars are made primarily of hydrogen.
The sun is basically a giant ball of hydrogen and helium gases. In the sun's core, hydrogen atoms combine to form helium atoms. This process—called fusion gives off radiant energy.
This radiant energy sustains life on earth. It gives us light and makes plants grow. It makes
the wind blow and rain fall. It is stored as chemical energy in fossil fuels. Most of the energy we use today came from the sun's radiant energy.
Hydrogen gas is lighter than air and, as a result, it rises in the atmosphere. This is why hydrogen as a gas (H2) is not found by itself on earth. It is found only in compound form with
other elements. Hydrogen combined with oxygen, is water (H2O). Hydrogen combined with carbon, forms different compounds such as methane (CH4), coal, and petroleum. Hydrogen is
also found in all growing things—biomass. It is also an abundant element in the earth's crust. Hydrogen has the highest energy content of any common fuel by weight(about three times
more than gasoline), but the lowest energy content by volume (about four times less than gasoline). It is the lightest element, and it is a gas at normal temperature and pressure.
Hydrogen gas, H2, was first artificially produced and formally described by T. Von Hohenheim
(also known as Paracelsus, 1493–1541) via the mixing of metals with strong acids. He was unaware that the flammable gas produced by this chemical reaction was a new chemical
element. In 1671, Robert Boyle rediscovered and described the reaction between iron filings and dilute acids, which results in the production of hydrogen gas. In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, by identifying the gas from a
metal-acid reaction as "inflammable air" and further finding in 1781 that the gas produces water when burned. He is usually given credit for its discovery as an element. In 1783, Antoine
Lavoisier gave the element the name hydrogen (from the Greek hydro meaning water and genes meaning creator) when he and Laplace reproduced Cavendish's finding that water is
produced when hydrogen is burned.
RENEWABLE ENERGY SOURCES
Renewable energy sources include all fuel types and energy carriers, different from
the fossil ones. Renewable energy sources include solar energy (which comes from the
sun and can be turned into electricity and heat), wind energy, geothermal energy (from
inside the earth), biomass from plants, and hydropower from water are also renewable
energy sources.
SOLAR ENERGY
“Solar” is the Latin word for “sun” – and it’s a powerful
source of energy. In fact, the sunlight that shines on the
Earth in just one hour could meet world energy demand for
an entire year!
We can use solar power in two different ways: as a heat
source, and as an energy source. People have used the sun as
a heat source for thousands of years. Families in ancient
Greece built their homes to get the most sunlight during
the cold winter months.
Where does solar come from? The sun has produced energy for billions
of years. Solar energy is the solar
radiation that reaches the earth.
Solar energy can be converted directly
or indirectly into other forms of energy,
such as heat and electricity. The major
drawbacks (problems, or issues to
overcome) of solar energy are:
(1) the intermittent and variable manner in which it arrives at the earth's surface and,
(2) the large area required to collect it at a useful rate.
Solar energy is used for heating water for domestic use, space heating of buildings,
drying agricultural products, and generating electrical energy.
In the 1830s, the British astronomer John Herschel used a solar collector box to cook
food during an expedition to Africa. Now, people are trying to use the sun's energy for
lots of things.
Electric utilities are are trying photovoltaics, a process by which solar energy is
converted directly to electricity. Electricity can be produced directly from solar energy
using photovoltaic devices or indirectly from steam generators using solar thermal
collectors to heat a working fluid.
WIND ENERGY
Wind is air in motion. It is produced by the uneven
heating of the earth’s surface by the sun. Since the
earth’s surface is made of various land and water
formations, it absorbs the sun’s radiation unevenly.
When the sun is shining during the day, the air over
landmasses heats more quickly than the air over
water. The warm air over the land expands and rises,
and the heavier, cooler air over water moves in to take
its place, creating local winds. At night, the winds are
reversed because the air cools more rapidly over land
than over water.
Similarly, the large atmospheric winds that circle the earth are created because the
surface air near the equator is warmed more by the sun than the air over the North and
South Poles. Wind is called a renewable energy source because wind will continually be
produced as long as the sun shines on the earth. Today, wind energy is mainly used to
generate electricity.
Wind turbines:
Windmills work because they slow down the speed of the wind. The wind flows over the
airfoil shaped blades causing lift, like the effect on airplane wings, causing them to turn.
The blades are connected to a drive shaft that turns an electric generator to produce
electricity.
Today’s wind machines are much more technologically advanced than those early
windmills. They still use blades to collect the wind’s kinetic energy, but the blades are
made of fiberglass or other high-strength materials.
Modern wind machines are still wrestling with the problem of what to do when the wind
isn’t blowing. Large turbines are connected to the utility power network—some other
type of generator picks up the load when there is no wind. Small turbines are sometimes
connected to diesel/electric generators or sometimes have a battery to store the extra
energy they collect when the wind is blowing hard.
BIOMASS ENERGY
Biomass is organic material which has
stored sunlight in the form of chemical
energy. Biomass fuels include wood, wood
waste, straw, manure, sugar cane, and
many other byproducts from a variety of
agricultural processes.
Biomass is a renewable energy source
because the energy it contains comes
from the sun. Through the process of
photosynthesis, chlorophyll in plants
captures the sun's energy by converting
carbon dioxide from the air and water
from the ground into carbohydrates,
complex compounds composed of carbon,
hydrogen, and oxygen. When these
carbohydrates are burned, they turn
back into carbon dioxide and water and
release the sun's energy they contain. In this way, biomass functions as a sort of
natural battery for storing solar energy. As long as biomass is produced sustainably—
with only as much used as is grown—the battery will last indefinitely.
From the time of Prometheus to the present, the most common way to capture the
energy from biomass was to burn it, to make heat, steam, and electricity. But advances
in recent years have shown that there are more efficient and cleaner ways to use
biomass. It can be converted into liquid fuels, for example, or cooked in a process called
"gasification" to produce combustible gases. And certain crops such as switchgrass and
willow trees are especially suited as "energy crops," plants grown specifically for energy
generation.
HYDRO ENERGY
Hydropower is a clean, renewable and reliable energy source which converts kinetic
energy from falling water into electricity, without consuming more water than is
produced by nature.
Quite simply the oldest method by which renewable energy has been harnessed by the
human race. The first water wheels were used well over 2000 years ago, and the
technology has since been refined to become very efficient in the production of
electricity.
The potential energy stored
in a body of water held at a
given height is converted to
kinetic energy (movement
energy) which is used to turn
a turbine and create
electricity.
Mechanical energy is derived
by directing, harnessing, or
channeling moving water. The
amount of available energy in
moving water is determined
by its flow or fall.
In either instance, the water
flows through a pipe, or
penstock, then pushes against
and turns blades in a turbine to spin a generator to
produce electricity. In a run-of-the-river system, the force of the current applies the
needed pressure, while in a storage system, water is accumulated in reservoirs created
by dams, then released when the demand for electricity is high.
Meanwhile, the reservoirs or lakes are used for boating and fishing, and often the
rivers beyond the dams provide opportunities for whitewater rafting and kayaking.
GEOTHERMAL ENERGY
Geothermal energy can be used as an efficient heat source in small end-use applications
such as greenhouses, but the consumers have to be located close to the source of heat.
Geothermal energy - heat from the earth (in most cases mineral water)- is an important
energy source having environmental and economic advantages over fossil and nuclear
energy sources.
Heat from the earth can be used as an energy source in many ways, from large and
complex power stations to small and relatively simple pumping systems. This heat
energy, known as geothermal energy, can be found almost anywhere—as far away as
remote deep wells in Indonesia and as close as the dirt in our backyards. Tapping
geothermal energy is an affordable and sustainable solution to reducing our dependence
on fossil fuels, and the global warming and public health risks that result from their use.
OCEAN ENERGY
Generating technologies for
deriving electrical power from
the ocean include tidal
power, wave power, ocean
thermal energy conversion,
ocean currents, ocean winds
and salinity gradients. Of
these, the three most well-
developed technologies are
tidal power, wave power and
ocean thermal energy
conversion.
Tidal energy Tides are caused by the gravitational pull of the moon and sun, and the rotation of the earth.
Near shore, water levels can vary up to 40 feet. Only about 20 locations have good inlets and a large enough tidal range- about 10 feet- to produce energy economically. The simplest generation
system for tidal plants involves a dam, known as a barrage, across an inlet. Sluice gates on the barrage allow the tidal basin to fill on the incoming high tides and to empty through the turbine system on the outgoing tide, also known as the ebb tide. There are two-way systems that
generate electricity on both the incoming and outgoing tides.
Tidal barrages can change the tidal level in the basin and increase turbidity in the water. It can also affect navigation and recreation. Potentially the largest disadvantage of tidal power is the
effect a tidal station can have on plants and animals in the estuaries.
Tidal fences can also harness the energy of tides. A tidal fence has vertical axis turbines mounted in a fence. All the water that passes is forced through the turbines. They can be used in areas such as channels between two landmasses. Tidal fences have less impact on the
environment than tidal barrages although they can disrupt the movement of large marine animals. They are cheaper to install than tidal barrages too. A tidal fence is planned for the San
Bernardino Strait in the Philippines.
Tidal turbines are a new technology that can be used in many tidal areas. They are basically wind turbines that can be located anywhere there is strong tidal flow. Because water is about 800 times denser than air, tidal turbines will have to be much sturdier than wind turbines. They will
be heavier and more expensive to build but will be able to capture more energy.