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.