Energy is a scalar physical quantity that describes the amount of
work that can be performed by a force, an attribute of objects and systems that is
subject to a conservation law
Different forms of energy include kinetic, potential, thermal, gravitational, sound,
light, elastic, and electromagnetic energy. The forms of energy are often named
after a related force.
Any form of energy can be transformed into another form, but the total energy
always remains the same. This principle, the conservation of energy, was first
postulated in the early 19th century, and applies to any isolated system.
Types of Energy
There are two types of energy
Primary energy is energy found in nature that has not been subjected to any
conversion or transformation process.
Primary energy is energy contained in raw fuels and any other forms of energy
received by a system as input to the system.
The concept is used especially in energy statistics in the course of compilation of
energy balances. Primary energy includes non-renewable energy and renewable
Primary energies are transformed in energy conversion processes to more
convenient forms of energy, such as electrical energy, refined fuels, or synthetic
fuels such as hydrogen fuel. In energy statistics these forms are called energy.
Secondary energy is an energy form which has been transformed from another
one. Electricity is the most common example, being transformed from such
primary sources as coal, oil, natural gas, and wind.
The following are some of the energy sources
Solar energy is the radiant light and heat from the Sun that has been harnessed
by humans since ancient times using a range of ever-evolving technologies.
Solar radiation along with secondary solar resources such as wind and wave
power, hydroelectricity and biomass account for most of the available renewable
energy on Earth. Only a minuscule fraction of the available solar energy is used.
Solar power provides electrical generation by means of heat engines or
photovoltaics. Once converted, its uses are limited only by human ingenuity. A
partial list of solar applications includes space heating and cooling through solar
architecture, potable water via distillation and disinfection, daylighting, hot water,
thermal energy for cooking, and high temperature process heat for industrial
Solar technologies are broadly characterized as either passive solar or active
solar depending on the way they capture, convert and distribute sunlight. Active
solar techniques include the use of photovoltaic panels and solar thermal
collectors (with electrical or mechanical equipment) to convert sunlight into useful
outputs. Passive solar techniques include orienting a building to the Sun,
selecting materials with favorable thermal mass or light dispersing properties,
and designing spaces that naturally circulate air.
Types of Solar System
There are two types of solar system
Active Solar System
Passive Solar System
Active Solar System
An active solar system is a system that uses a mechanical device, such as
pumps or fans run by electricity in addition to solar energy, to transport air or
water between a solar collector and the interior of a building for heating or
Passive Solar System
A passive solar system is a system that distributes collected heat via direct
transfer from a thermal mass rather than mechanical power. Passive systems
rely on building design and materials to collect and store heat and to create
natural ventilation for cooling.
Application of Solar Energy
Heating, cooling and ventilation
In the 20th century artificial lighting became the main source of interior
illumination but daylighting techniques and hybrid solar lighting solutions are
ways to reduce energy consumption. Daylighting systems collect and distribute
sunlight to provide interior illumination. This passive technology directly offsets
energy use by replacing artificial lighting, and indirectly offsets non-solar energy
use by reducing the need for air-conditioning. Although difficult to quantify, the
use of natural lighting also offers physiological and psychological benefits
compared to artificial lighting. Daylighting design implies careful selection of
window types, sizes and orientation; exterior shading devices may be considered
as well. Individual features include sawtooth roofs, clerestory windows, light
shelves, skylights and light tubes. They may be incorporated into existing
structures, but are most effective when integrated into a solar design package
that accounts for factors such as glare, heat flux and time-of-use. When
daylighting features are properly implemented they can reduce lighting-related
energy requirements by 25%.
Hybrid solar lighting is an active solar method of providing interior illumination.
HSL systems collect sunlight using focusing mirrors that track the Sun and use
optical fibers to transmit it inside the building to supplement conventional lighting.
In single-story applications these systems are able to transmit 50% of the direct
Solar lights that charge during the day and light up at dusk are a common sight
Although daylight saving time is promoted as a way to use sunlight to save
energy, recent research has been limited and reports contradictory results:
several studies report savings, but just as many suggest no effect or even a net
loss, particularly when gasoline consumption is taken into account. Electricity use
is greatly affected by geography, climate and economics, making it hard to
generalize from single studies.
Solar hot water systems use sunlight to heat water. In low geographical latitudes
(below 40 degrees) from 60 to 70% of the domestic hot water use with
temperatures up to 60 °C can be provided by solar heating systems. The most
common types of solar water heaters are evacuated tube collectors (44%) and
glazed flat plate collectors (34%) generally used for domestic hot water; and
unglazed plastic collectors (21%) used mainly to heat swimming pools.
As of 2007, the total installed capacity of solar hot water systems is
approximately 154 GW. China is the world leader in their deployment with 70 GW
installed as of 2006 and a long term goal of 210 GW by 2020. Israel and Cyprus
are the per capita leaders in the use of solar hot water systems with over 90% of
homes using them. In the United States, Canada and Australia heating swimming
pools is the dominant application of solar hot water with an installed capacity of
18 GW as of 2005.
Heating Cooling and Ventilation
In the United States, heating, ventilation and air conditioning (HVAC) systems
account for 30% (4.65 EJ) of the energy used in commercial buildings and nearly
50% (10.1 EJ) of the energy used in residential buildings. Solar heating, cooling
and ventilation technologies can be used to offset a portion of this energy.
Thermal mass is any material that can be used to store heat—heat from the Sun
in the case of solar energy. Common thermal mass materials include stone,
cement and water. Historically they have been used in arid climates or warm
temperate regions to keep buildings cool by absorbing solar energy during the
day and radiating stored heat to the cooler atmosphere at night. However they
can be used in cold temperate areas to maintain warmth as well. The size and
placement of thermal mass depend on several factors such as climate,
daylighting and shading conditions. When properly incorporated, thermal mass
maintains space temperatures in a comfortable range and reduces the need for
auxiliary heating and cooling equipment.
A solar chimney (or thermal chimney, in this context) is a passive solar ventilation
system composed of a vertical shaft connecting the interior and exterior of a
building. As the chimney warms, the air inside is heated causing an updraft that
pulls air through the building. Performance can be improved by using glazing and
thermal mass materials in a way that mimics greenhouses.
Deciduous trees and plants have been promoted as a means of controlling solar
heating and cooling. When planted on the southern side of a building, their
leaves provide shade during the summer, while the bare limbs allow light to pass
during the winter. Since bare, leafless trees shade 1/3 to 1/2 of incident solar
radiation, there is a balance between the benefits of summer shading and the
corresponding loss of winter heating. In climates with significant heating loads,
deciduous trees should not be planted on the southern side of a building because
they will interfere with winter solar availability. They can, however, be used on
the east and west sides to provide a degree of summer shading without
appreciably affecting winter solar gain.
Sunlight can be converted into electricity using photovoltaics (PV), concentrating
solar power (CSP), and various experimental technologies. PV has mainly been
used to power small and medium-sized applications, from the calculator powered
by a single solar cell to off-grid homes powered by a photovoltaic array. For
large-scale generation, CSP plants like SEGS have been the norm but recently
multi-megawatt PV plants are becoming common. Completed in 2007, the
14 MW power station in Clark County, Nevada and the 20 MW site in
Beneixama, Spain are characteristic of the trend toward larger photovoltaic
power stations in the US and Europe. As an intermittent power source, solar
power requires a backup supply, which can partially be complemented with wind
power. Local backup usually is done with batteries, while utilities normally use
pumped-hydro storage. The Institute for Solar Energy Supply Technology of the
University of Kassel pilot-tested a combined power plant linking solar, wind,
biogas and hydrostorage to provide load-following power around the clock,
entirely from renewable sources.
Wind power is the conversion of wind energy into a useful form, such as
electricity, using wind turbines. At the end of 2008, worldwide nameplate capacity
of wind-powered generators was 121.2 gigawatts (GW). Wind power produces
about 1.5% of worldwide electricity use, and is growing rapidly, having doubled in
the three years between 2005 and 2008. Several countries have achieved
relatively high levels of wind power penetration, such as 19% of stationary
electricity production in Denmark, 11% in Spain and Portugal, and 7% in
Germany and the Republic of Ireland in 2008. As of May 2009, eighty countries
around the world are using wind power on a commercial basis.
Large-scale wind farms are typically connected to the local electric power
transmission network; smaller turbines are used to provide electricity to isolated
locations. Utility companies increasingly buy back surplus electricity produced by
small domestic turbines. Wind energy as a power source is attractive as an
alternative to fossil fuels, because it is plentiful, renewable, widely distributed,
clean, and produces no greenhouse gas emissions; however, the construction of
wind farms (as with other forms of power generation) is not universally welcomed
due to their visual impact and other effects on the environment.
Wind power is non-dispatchable, meaning that for economic operation all of the
available output must be taken when it is available, and other resources, such as
hydropower, and standard load management techniques must be used to match
supply with demand. The intermittency of wind seldom creates problems when
using wind power to supply a low proportion of total demand. Where wind is to be
used for a moderate fraction of demand, additional costs for compensation of
intermittency are considered to be modest.
A wind energy conversion device that produces electricity is known as wind
turbine. There are mainly two types of wind turbine
Horizontal Axis Wind Turbine
Vertical Axis Wind Turbine
Horizontal Axis Wind Turbine
A wind turbine in which the axis of the rotor's rotation is parallel to the wind
stream and the ground. All grid-connected commercial wind turbines today are
built with a propeller-type rotor on a horizontal axis (i.e. a horizontal main shaft).
Most horizontal axis turbines built today are two- or three-bladed, although some
have fewer or more blades. The purpose of the rotor is to convert the linear
motion of the wind into rotational energy that can be used to drive a generator.
The same basic principle is used in a modern water turbine, where the flow of
water is parallel to the rotational axis of the turbine blades.
The wind passes over both surfaces of the airfoil shaped blade but passes more
rapidly over the longer (upper) side of the airfoil, thus creating a lower-pressure
area above the airfoil. The pressure differential between top and bottom surfaces
results in aerodynamic lift. In an aircraft wing, this force causes the airfoil to rise,
lifting the aircraft off the ground. Since the blades of a wind turbine are
constrained to move in a plane with the hub as its center, the lift force causes
rotation about the hub. In addition to the lift force, a drag force perpendicular to
the lift force impedes rotor rotation. A prime objective in wind turbine design is for
the blade to have a relatively high lift-to-drag ratio. This ratio can be varied along
the length of the blade to optimize the turbine’s energy output at various wind
Vertical Axis Wind Turbine
A type of wind turbine in which the axis of rotation is perpendicular to the wind
stream and the ground. VAWTs work somewhat like a classical water wheel in
which water arrives at a right angle (perpendicular) to the rotational axis (shaft) of
the water wheel. Vertical-axis wind turbines fall into two major categories:
Darrieus turbines and Savonius turbines. Neither type is in wide use today.
The basic theoretical advantages of a vertical axis machine are:
The generator, gearbox etc. may be placed on the ground, and a tower is
not essential for the machine
A yaw mechanism isn't needed to turn the rotor against the wind.
The basic disadvantages are:
Wind speeds are very low close to ground level, so although a tower isn't
essential, the wind speeds will be very low on the lower part of the rotor
The overall efficiency of the vertical axis machines is not impressive
The machine is not self-starting, i.e. a Darrieus machine needs a "push"
before it will start. This is only a minor inconvenience for a grid-connected
turbine, however, since the generator may be used as a motor drawing
current from the grid to start the machine
Replacing the main bearing for the rotor necessitates removing the rotor
on both a horizontal and a vertical axis machine. In the case of the latter, it
means tearing the whole machine down
Hydroelectricity is electricity generated by hydropower, i.e., the production of
power through use of the gravitational force of falling or flowing water. It is the
most widely used form of renewable energy. Once a hydroelectric complex is
constructed, the project produces no direct waste, and has a considerably lower
output level of the greenhouse gas carbon dioxide (CO2) than fossil fuel powered
energy plants. Worldwide, hydroelectricity supplied an estimated 816 GWe in
2005. This was approximately 20% of the world's electricity, and accounted for
about 88% of electricity from renewable sources.
Most hydroelectric power comes from the potential energy of dammed water
driving a water turbine and generator. In this case the energy extracted from the
water depends on the volume and on the difference in height between the source
and the water's outflow. This height difference is called the head. The amount of
potential energy in water is proportional to the head. To obtain very high head,
water for a hydraulic turbine may be run through a large pipe called a penstock.
Pumped storage hydroelectricity produces electricity to supply high peak
demands by moving water between reservoirs at different elevations. At times of
low electrical demand, excess generation capacity is used to pump water into the
higher reservoir. When there is higher demand, water is released back into the
lower reservoir through a turbine. Pumped storage schemes currently provide the
only commercially important means of large-scale grid energy storage and
improve the daily load factor of the generation system. Hydroelectric plants with
no reservoir capacity are called run-of-the-river plants, since it is not then
possible to store water. A tidal power plant makes use of the daily rise and fall of
water due to tides; such sources are highly predictable, and if conditions permit
construction of reservoirs, can also be dispatchable to generate power during
high demand periods.
Less common types of hydro schemes use water's kinetic energy or undammed
sources such as undershot waterwheels.
A simple formula for approximating electric power production at a hydroelectric
plant is: P = hrgk, where P is Power in kilowatts, h is height in meters, r is flow
rate in cubic meters per second, g is acceleration due to gravity of 9.8 m/s2, and
k is a coefficient of efficiency ranging from 0 to 1. Efficiency is often higher with
larger and more modern turbines.
Annual electric energy production depends on the available water supply. In
some installations the water flow rate can vary by a factor of 10:1 over the course
of a year.
The major advantage of hydroelectricity is elimination of the cost of fuel. The cost
of operating a hydroelectric plant is nearly immune to increases in the cost of
fossil fuels such as oil, natural gas or coal, and no imports are needed.
Hydroelectric plants also tend to have longer economic lives than fuel-fired
generation, with some plants now in service which were built 50 to 100 years
ago. Operating labor cost is also usually low, as plants are automated and have
few personnel on site during normal operation.
Where a dam serves multiple purposes, a hydroelectric plant may be added with
relatively low construction cost, providing a useful revenue stream to offset the
costs of dam operation. It has been calculated that the sale of electricity from the
Three Gorges Dam will cover the construction costs after 5 to 8 years of full
Greenhouse gas emissions
Since hydroelectric dams do not burn fossil fuels, they do not directly produce
carbon dioxide (a greenhouse gas). While some carbon dioxide is produced
during manufacture and construction of the project, this is a tiny fraction of the
operating emissions of equivalent fossil-fuel electricity generation.
Reservoirs created by hydroelectric schemes often provide facilities for water
sports, and become tourist attractions in themselves. In some countries,
aquaculture in reservoirs is common. Multi-use dams installed for irrigation
support agriculture with a relatively constant water supply. Large hydro dams can
control floods, which would otherwise affect people living downstream of the
Geothermal power (from the Greek roots geo, meaning earth, and thermos,
meaning heat) is power extracted from heat stored in the earth. This geothermal
energy originates from the original formation of the planet, from radioactive decay
of minerals, and from solar energy absorbed at the surface. It has been used for
space heating and bathing since ancient roman times, but is now better known
for generating electricity. About 10 GW of geothermal electric capacity is installed
around the world as of 2007, generating 0.3% of global electricity demand. An
additional 28 GW of direct geothermal heating capacity is installed for district
heating, space heating, spas, industrial processes, desalination and agricultural
Geothermal power is cost effective, reliable, and environmentally friendly, but has
previously been geographically limited to areas near tectonic plate boundaries.
Recent technological advances have dramatically expanded the range and size
of viable resources, especially for direct applications such as home heating.
Geothermal wells tend to release greenhouse gases trapped deep within the
earth, but these emissions are much lower than those of conventional fossil fuels.
As a result, geothermal power has the potential to help mitigate global warming if
widely deployed instead of fossil fuels.
Geothermal electricity plants
Geothermal electric plants have until recently been built exclusively on the edges
of tectonic plates where high temperature geothermal resources are available
near the surface. The development of binary cycle power plants and
improvements in drilling and extraction technology has opened the hope that
enhanced geothermal systems might be viable over a much greater geographical
range. A demonstration project has recently been completed in Landau-Pfalz,
Germany, and others are under construction in Soultz-sous-Forêts, France and
Cooper Basin, Australia.
Non-electricity generation application
Approximately seventy countries made direct use of a total of 270 PJ of
geothermal heating in 2004. More than half of this energy was used for space
heating, and a third was used for heated pools. The remainder was used for
industrial and agricultural applications. The global installed capacity was 28 GW,
but capacity factors tend to be low (around 20%) since the heat is mostly needed
in the winter. The above figures include 88 PJ of space heating extracted by an
estimated million geothermal heat pumps with a total capacity of 15 GW. Global
geothermal heat pump capacity is growing by 10% annually.
Direct application of geothermal heat for space heating is far more efficient than
electricity generation and has less demanding temperature requirements. It may
come from waste heat supplied by co-generation from a geothermal electrical
plant or from smaller wells or heat exchangers buried in the shallow ground. As a
result it is viable over a much greater geographical range than electricity
generation. Where natural hot springs are available, the water may be piped
directly into radiators. If the shallow ground is hot but dry, earth tubes or
downhole heat exchangers may be used without a heat pump. But even in areas
where the shallow ground is too cold to provide comfort directly, it is still warmer
than the winter air. Seasonal variations in ground temperature diminish and
disappear completely below 10m of depth. That heat can be extracted with a
geothermal heat pump more efficiently than it can be generated by conventional
furnaces. Geothermal heat pumps can be used essentially anywhere.
Geothermal fluids drawn from the deep earth may carry a mixture of gases with
them, notably carbon dioxide and hydrogen sulfide. When released to the
environment, these pollutants contribute to global warming, acid rain, and
noxious smells in the vicinity of the plant. Existing geothermal electric plants emit
an average of 122 kg of CO2 per MWh of electricity, a small fraction of the
emission intensity of conventional fossil fuel plants. Some are equipped with
emissions-controlling systems that reduces the exhaust of acids and volatiles.
In addition to dissolved gases, hot water from geothermal sources may contain
trace amounts of dangerous elements such as mercury, arsenic, and antimony
which, if disposed of into rivers, can render their water unsafe to drink.
Geothermal plants can theoretically inject these substances, along with the
gases, back into the earth, in a form of carbon capture and storage.
Construction of the power plants can adversely affect land stability in the
surrounding region. Subsidence has occurred in the Wairakei field in New
Zealand and in Staufen im Breisgau, Germany. Enhanced geothermal systems
can trigger earthquakes as part of the hydraulic fracturing process. The project in
Basel, Switzerland was suspended because more than 10,000 seismic event
measuring up to 3.4 on the Richter Scale occurred over the first 6 days of water
Geothermal has minimal requirements for land use and freshwater. Existing
geothermal plants use 1-8 acres per megawatt (MW) versus 5-10 acres per MW
for nuclear operations and 19 acres per MW for coal power plants. They use 20
liters of freshwater per MWh versus over 1000 litres per MWh for nuclear, coal,
Biogas typically refers to a gas produced by the biological breakdown of organic
matter in the absence of oxygen. Biogas originates from biogenic material and is
a type of biofuel.
One type of biogas is produced by anaerobic digestion or fermentation of
biodegradable materials such as biomass, manure or sewage, municipal waste,
green waste and energy crops. This type of biogas comprises primarily methane
and carbon dioxide. The other principal type of biogas is wood gas which is
created by gasification of wood or other biomass. This type of biogas is
comprised primarily of nitrogen, hydrogen, and carbon monoxide, with trace
amounts of methane.
Biogas is practically produced as landfill gas (LFG) or digester gas.A biogas plant
is the name often given to an anaerobic digester that treats farm wastes or
Biogas can be produced utilizing anaerobic digesters. These plants can be fed
with energy crops such as maize silage or biodegradable wastes including
sewage sludge and food waste.
Landfill gas is produced by wet organic waste decomposing under anaerobic
conditions in a landfill. The waste is covered and compressed mechanically and
by the weight of the material that is deposited from above. This material prevents
oxygen from accessing the waste and anaerobic microbes thrive. This gas builds
up and is slowly released into the atmosphere if the landfill site has not been
engineered to capture the gas. Landfill gas is hazardous for three key reasons.
Landfill gas becomes explosive when it escapes from the landfill and mixes with
oxygen. The lower explosive limit is 5% methane and the upper explosive limit is
15% methane. The methane contained within biogas is 20 times more potent as
a greenhouse gas than carbon dioxide. Therefore uncontained landfill gas which
escapes into the atmosphere may significantly contribute to the effects of global
warming. In addition to this volatile organic compounds (VOCs) contained within
landfill gas contribute to the formation of photochemical smog.
Biogas can be utilized for electricity production on sewage works , in a CHP gas
engine, where the waste heat from the engine is conveniently used to heat the
digester; cooking, space heating, water heating and process heating. If
compressed, it can replace compressed natural gas for use in vehicles, where it
can fuel an internal combustion engine or fuel cells and is a much more effective
displacer of carbon dioxide than the normal use in on-site CHP plants.
Methane within biogas can be concentrated via a biogas upgrader to the same
standards as fossil natural gas, and becomes biomethane. If the local gas
network allows for this, the producer of the biogas may utilize the local gas
distribution networks. Gas must be very clean to reach pipeline quality, and must
be of the correct composition for the local distribution network to accept. Carbon
dioxide, Water, hydrogen sulfide and particulates must be removed if present. If
concentrated and compressed it can also be used in vehicle transportation.
Compressed biogas is becoming widely used in Sweden, Switzerland and
Germany. A biogas-powered train has been in service in Sweden since 2005.
Bates, an inventor, lived in Devon, UK, modified his car to run on biogas. A short
documentary film called "Sweet as a Nut" in 1974, talks through the simple
process and benefits of running a car on biogas, at which point he had run his
car for 17 years on gas he had produced by processing pig manure. The
conversion was simply made with an adapter attached to the combustion engine.
Solid biomass is most commonly used directly as a combustible fuel, producing
10-20 MJ/kg of heat. Biomass can also be used to feed bacteria, which can
transform it in another form of energy such as hydrogen, using a process called
Fermentative hydrogen production.
Its forms and sources include wood fuel, the biogenic portion of municipal solid
waste, or the unused portion of field crops. Field crops may or may not be grown
intentionally as an energy crop, and the remaining plant byproduct used as a
fuel. Most types of biomass contain energy. Even cow manure still contains two-
thirds of the original energy consumed by the cow. Energy harvesting via a
bioreactor is a cost-effective solution to the waste disposal issues faced by the
dairy farmer, and can produce enough biogas to run a farm.
With current technology, it is not ideally suited for use as a transportation fuel.
Most transportation vehicles require power sources with high power density, such
as that provided by internal combustion engines. These engines generally
require clean burning fuels, which are generally in liquid form, and to a lesser
extent, compressed gaseous phase. Liquids are more portable because they can
have a high energy density, and they can be pumped, which makes handling
Non-transportation applications can usually tolerate the low power-density of
external combustion engines, that can run directly on less-expensive solid
biomass fuel, for combined heat and power. One type of biomass is wood, which
has been used for millennia. Two billion people currently cook every day, and
heat their homes in the winter by burning biomass, which is a major contributor to
man-made climate change global warming. The black soot that is being carried
from Asia to polar ice caps is causing them to melt faster in the summer. In the
19th century, wood-fired steam engines were common, contributing significantly
to industrial revolution unhealthy air pollution. Coal is a form of biomass that has
been compressed over millennia to produce a non-renewable, highly-polluting
Wood and its byproducts can now be converted through processes such as
gasification into biofuels such as woodgas, biogas, methanol or ethanol fuel;
although further development may be required to make these methods affordable
and practical. Sugar cane residue, wheat chaff, corn cobs and other plant matter
can be, and are, burned quite successfully. The net carbon dioxide emissions
that are added to the atmosphere by this process are only from the fossil fuel that
was consumed to plant, fertilize, harvest and transport the biomass.
Processes to harvest biomass from short-rotation trees like poplars and willows
and perennial grasses such as switchgrass, phalaris, and miscanthus, require
less frequent cultivation and less nitrogen than do typical annual crops.
Pelletizing miscanthus and burning it to generate electricity is being studied and
may be economically viable.
Tidal power, sometimes called tidal energy, is a form of hydropower that converts
the energy of tides into electricity or other useful forms of power. Although not yet
widely used, tidal power has potential for future electricity generation. Tides are
more predictable than wind energy and solar power.
Categories of Tidal Power
Tidal power can be classified into three main types:
Tidal stream systems make use of the kinetic energy of moving water
to power turbines, in a similar way to windmills that use moving air.
This method is gaining in popularity because of the lower cost and
lower ecological impact compared to barrages.
Barrages make use of the potential energy in the difference in height
(or head) between high and low tides. Barrages are essentially dams
across the full width of a tidal estuary, and suffer from very high civil
infrastructure costs, a worldwide shortage of viable sites, and
Tidal lagoons, are similar to barrages, but can be constructed as self
contained structures, not fully across an estuary, and are claimed to
incur much lower cost and impact overall. Furthermore they can be
configured to generate continuously which is not the case with
Modern advances in turbine technology may eventually see large amounts of
power generated from the ocean, especially tidal currents using the tidal stream
designs but also from the major thermal current systems such as the Gulf
Stream, which is covered by the more general term marine current power. Tidal
stream turbines may be arrayed in high-velocity areas where natural tidal current
flows are concentrated such as the west and east coasts of Canada, the Strait of
Gibraltar, the Bosporus, and numerous sites in Southeast Asia and Australia.
Such flows occur almost anywhere where there are entrances to bays and rivers,
or between land masses where water currents are concentrated.
Tidal Stream Generators
A relatively new technology, tidal stream generators draw energy from currents in
much the same way as wind turbines. The higher density of water, 832 times the
density of air, means that a single generator can provide significant power at low
tidal flow velocities (compared with wind speed). Given that power varies with the
density of medium and the cube of velocity, it is simple to see that water speeds
of nearly one-tenth of the speed of wind provide the same power for the same
size of turbine system. However this limits the application in practice to places
where the tide moves at speeds of at least 2 knots (1m/s) even close to neap
Since tidal stream generators are an immature technology (no commercial scale
production facilities are yet routinely supplying power), no standard technology
has yet emerged as the clear winner, but a large variety of designs are being
experimented with, some very close to large scale deployment. Several
prototypes have shown promise with many companies making bold claims, some
of which are yet to be independently verified, but they have not operated
commercially for extended periods to establish performances and rates of return
Various turbine designs have varying efficiencies and therefore varying power
output. If the efficiency of the turbine "Cp" is known the equation below can be
used to determine the power output.
The energy available from these kinetic systems can be expressed as:
P = Cp x 0.5 x ρ x A x V³
Cp is the turbine coefficient of performance
P = the power generated (in watts)
ρ = the density of the water (seawater is 1025 kg/m³)
A = the sweep area of the turbine (in m²)
V³ = the velocity of the flow cubed (i.e. V x V x V)
Relative to an open turbine in free stream, shrouded turbines are capable of as
much as 3 to 4 times the power of the same rotor in open flow, depending on the
width of the shroud. However, to measure the efficiency, one must compare the
benefits of a larger rotor with the benefits of the shroud.
Wave power is the transport of energy by ocean surface waves, and the capture
of that energy to do useful work — for example for electricity generation, water
desalination, or the pumping of water (into reservoirs). Wave power is a
renewable energy source.
Waves are generated by wind passing over the sea: as long as the waves
propagate slower than the wind speed just above the waves, there is an energy
transfer from the wind to the most energetic waves. Both air pressure differences
between the upwind and the lee side of a wave crest, as well as friction on the
water surface by the wind shear stress causes the growth of the waves. The
wave height increases with increases in (see Ocean surface wave):
time duration of the wind blowing,
fetch — the distance of open water that the wind has blown over, and
water depth (in case of shallow water effects, for water depths less
than half the wavelength).
In general, large waves are more powerful. Specifically, wave power is
determined by wave height, wave speed, wavelength, and water density.
Wave size is determined by wind speed and fetch (the distance over which the
wind excites the waves) and by the depth and topography of the seafloor (which
can focus or disperse the energy of the waves). A given wind speed has a
matching practical limit over which time or distance will not produce larger waves.
This limit is called a "fully developed sea."
Oscillatory motion is highest at the surface and diminishes exponentially with
depth. However, for standing waves (clapotis) near a reflecting coast, wave
energy is also present as pressure oscillations at great depth, producing
microseisms. These pressure fluctuations at greater depth are too small to be
interesting from the point of view of wave power.
The waves propagate on the ocean surface, and the wave energy is also
transported horizontally with the group velocity. The mean transport rate of the
wave energy through a vertical plane of unit width, parallel to a wave crest, is
called the wave energy flux (or wave power, which must not be confused with the
actual power generated by a wave power device).
Wave Power Formula
In deep water, if the water depth is larger than half the wavelength, the wave
energy flux is
P the wave energy flux per unit wave crest length (kW/m);
Hm0 is the significant wave height (meter), as measured by wave buoys
and predicted by wave forecast models. By definition, Hm0 is four times the
standard deviation of the water surface elevation;
T is the wave period (second);
ρ is the mass density of the water (kg/m3), and
g is the acceleration by gravity (m/s2).
The above formula states that wave power is proportional to the wave period and
to the square of the wave height. When the significant wave height is given in
meters, and the wave period in seconds, the result is the wave power in kilowatts
(kW) per meter wavefront length.
Example: Consider moderate ocean swells, in deep water, a few kilometers off a
coastline, with a wave height of 3 meters and a wave period of 8 seconds. Using
the formula to solve for power, we get
Meaning there are 36 kilowatts of power potential per meter of coastline.
In major storms, the largest waves offshore are about 15 meters high and have a
period of about 15 seconds. According to the above formula, such waves carry
about 1.7 MW/m of power across each meter of wavefront.
An effective wave power device captures as much as possible of the wave
energy flux. As a result the waves will be of lower height in the region behind the
wave power device.
Wave Energy and Wave Energy Flux
In a sea state, the average energy density per unit area of gravity waves on the
water surface is proportional to the wave height squared, according to linear
where E is the mean wave energy density per unit horizontal area (J/m 2), the
sum of kinetic and potential energy density per unit horizontal area. The potential
energy density is equal to the kinetic energy, both contributing half to the wave
energy density E, as can be expected from the equipartition theorem. In ocean
waves, surface tension effects are negligible for wavelengths above a few
As the waves propagate, their energy is transported. The energy transport
velocity is the group velocity. As a result, the wave energy flux, through a vertical
plane of unit width perpendicular to the wave propagation direction, is equal to:
with cg the group velocity (m/s). Due to the dispersion relation for water waves
under the action of gravity, the group velocity depends on the wavelength λ, or
equivalently, on the wave period T. Further, the dispersion relation is a function
of the water depth h. As a result, the group velocity behaves differently in the
limits of deep and shallow water, and at intermediate depths
Deep water corresponds with a water depth larger than half the wavelength,
which is the common situation in the sea and ocean. In deep water, longer period
waves propagate faster and transport their energy faster. The deep-water group
velocity is half the phase velocity. In shallow water, for wavelengths larger than
twenty times the water depth, as found quite often near the coast, the group
velocity is equal to the phase velocity.
Energy planning software
Following are some of the energy planning softwares
LEAP: the Long range Energy Alternatives Planning system, is a Windows-based
software system for energy and environmental policy analysis. It is widely used
for integrated energy planning and climate change mitigation analysis and has
been applied in hundreds of different organizations in over 140 countries.
LEAP is developed and supported by the U.S. Center of the Stockholm
Environment Institute, a non-profit research institute based at Tufts University in
Somerville, Massachusetts. Most recently LEAP has been chosen by 85
countries as the main modeling tool for the climate change mitigation
assessments that will be presented to the United Nations Framework Convention
on Climate Change (UNFCCC)
LEAP is distributed at no charge to not-for-profit, academic and governmental
organizations based in developing countries.
Energy and Power Evaluation Program is distributed for use in over 70 countries.
The model provides state-of-the-art capabilities for use in energy policy
evaluation, energy pricing studies, assessing energy efficiency and renewable
resource potential, assessing overall energy sector development strategies, and
analyzing environmental burdens and greenhouse gas (GHG) mitigation options.
The European Union contracted an independent review of energy planning and
analysis software utilized in Mediterranean countries, which recommended
ENPEP as tool of choice for energy planning in the region.
Following are the key benefits of the market power
Perform Monte Carlo simulations around uncertain demand, generator
availability, hydro conditions, fuel prices, and economic conditions
Evaluate capacity mothballing, expansion, and retirement alternatives
based on economic analysis
Utilize market-driven algorithms, adaptive market simulations, flexible
data structure, and customized reports
Maximize profits by supporting market-based investment decisions
Evaluate deviations from economic equilibrium supply markets and
Following are the advantages of system optimizer
simultaneously consider of generation and transmission expansion
Develop long-term resource investment plans including type, size,
location, and timing of capital projects over a 20-year horizon Access
significant production and costing detail in results
Include a complete range of technologies, including renewables, DSM,
retirements, and transmission upgrades, today and in the future
Consider interactions with external markets and between internal regions