Use and Management of Energy Sources Efficiently
Fossil fuelFossil fuels are fuels formed by natural processes
such as anaerobic decomposition of buried dead organisms. The age
of the organisms and their resulting fossil fuels is typically
millions of years, and sometimes exceeds 650 million years. Fossil
fuels contain high percentages of carbon and include coal,
petroleum, and natural gas. They range from volatile materials with
low carbon:hydrogen ratios like methane, to liquid petroleum to
nonvolatile materials composed of almost pure carbon, like
anthracite coal. Methane can be found in hydrocarbon fields, alone,
associated with oil, or in the form of methane clathrates. The
theory that fossil fuels formed from the fossilized remains of dead
plants by exposure to heat and pressure in the Earth's crust over
millions of years (see biogenic theory) was first introduced by
Georg Agricola in 1556 and later by Mikhail Lomonosov in the 18th
century.Strictly speaking, fossil fuels are a renewable resource.
They are continually being formed via natural processes as plants
and animals die and then decompose and become trapped beneath
sediment. However, fossil fuels are generally considered to be
non-renewable resources because they take millions of years to
form, and known viable reserves are being depleted much faster than
new ones are being made.The use of fossil fuels raises serious
environmental concerns. The burning of fossil fuels produces around
21.3 billion tonnes (21.3 gigatonnes) of carbon dioxide (CO2) per
year, but it is estimated that natural processes can only absorb
about half of that amount, so there is a net increase of 10.65
billion tonnes of atmospheric carbon dioxide per year (one tonne of
atmospheric carbon is equivalent to 44/12 or 3.7 tonnes of carbon
dioxide). Carbon dioxide is one of the greenhouse gases that
enhances radiative forcing and contributes to global warming,
causing the average surface temperature of the Earth to rise in
response, which the vast majority of climate scientists agree will
cause major adverse effects. A global movement towards the
generation of renewable energy is therefore under way to help
reduce global greenhouse gas emissions.Oil refinery
The oil refinery in Haifa, Israel is capable of processing about
9 million tons (66 million barrels) of crude oil a year. Its two
cooling towers are landmarks of the city's skyline.An oil refinery
or petroleum refinery is an industrial process plant where crude
oil is processed and refined into more useful products such as
petroleum naphtha, gasoline, diesel fuel, asphalt base, heating
oil, kerosene and liquefied petroleum gas. Oil refineries are
typically large, sprawling industrial complexes with extensive
piping running throughout, carrying streams of fluids between large
chemical processing units. In many ways, oil refineries use much of
the technology of, and can be thought of, as types of chemical
plants. The crude oil feedstock has typically been processed by an
oil production plant. There is usually an oil depot (tank farm) at
or near an oil refinery for the storage of incoming crude oil
feedstock as well as bulk liquid products.Raw or unprocessed crude
oil is not generally useful in industrial applications, although
"light, sweet" (low viscosity, low sulfur) crude oil has been used
directly as a burner fuel to produce steam for the propulsion of
seagoing vessels. The lighter elements, however, form explosive
vapors in the fuel tanks and are therefore hazardous, especially in
warships. Instead, the hundreds of different hydrocarbon molecules
in crude oil are separated in a refinery into components which can
be used as fuels, lubricants, and as feedstocks in petrochemical
processes that manufacture such products as plastics, detergents,
solvents, elastomers and fibers such as nylon and
polyesters.Petroleum fossil fuels are burned in internal combustion
engines to provide power for ships, automobiles, aircraft engines,
lawn mowers, chainsaws, and other machines. Different boiling
points allow the hydrocarbons to be separated by distillation.
Since the lighter liquid products are in great demand for use in
internal combustion engines, a modern refinery will convert heavy
hydrocarbons and lighter gaseous elements into these higher value
products.Oil can be used in a variety of ways because it contains
hydrocarbons of varying molecular masses, forms and lengths such as
paraffins, aromatics, naphthenes (or cycloalkanes), alkenes,
dienes, and alkynes. While the molecules in crude oil include
different atoms such as sulfur and nitrogen, the hydrocarbons are
the most common form of molecules, which are molecules of varying
lengths and complexity made of hydrogen and carbon atoms, and a
small number of oxygen atoms. The differences in the structure of
these molecules account for their varying physical and chemical
properties, and it is this variety that makes crude oil useful in a
broad range of several applications.Once separated and purified of
any contaminants and impurities, the fuel or lubricant can be sold
without further processing. Smaller molecules such as isobutane and
propylene or butylenes can be recombined to meet specific octane
requirements by processes such as alkylation, or less commonly,
dimerization. Octane grade of gasoline can also be improved by
catalytic reforming, which involves removing hydrogen from
hydrocarbons producing compounds with higher octane ratings such as
aromatics. Intermediate products such as gasoils can even be
reprocessed to break a heavy, long-chained oil into a lighter
short-chained one, by various forms of cracking such as fluid
catalytic cracking, thermal cracking, and hydrocracking. The final
step in gasoline production is the blending of fuels with different
octane ratings, vapor pressures, and other properties to meet
product specifications.Oil refineries are large scale plants,
processing about a hundred thousand to several hundred thousand
barrels of crude oil a day. Because of the high capacity, many of
the units operate continuously, as opposed to processing in
batches, at steady state or nearly steady state for months to
years. The high capacity also makes process optimization and
advanced process control very desirable.Fossil-fuel power stationA
fossil fuel power station burns fossil fuels such as coal, natural
gas or petroleum (oil) to produce electricity. Central station
fossil-fuel power plants are designed on a large scale for
continuous operation. In many countries, such plants provide most
of the electrical energy used. Fossil-fuel power stations have
rotating machinery to convert the heat energy of combustion into
mechanical energy, which then operates an electrical generator. The
prime mover may be a steam turbine, a gas turbine or, in small
plants, a reciprocating internal combustion engine. All plants use
the energy extracted from expanding gas - steam or combustion
gases. Very few MHD generators have been built which directly
convert the energy of moving hot gas into electricity.Byproducts of
thermal power plant operation must be considered in their design
and operation. Waste heat energy, which remains due to the finite
efficiency of the Carnot, Rankine, or Diesel power cycle, is
released directly to the atmosphere, directly to river or lake
water, or indirectly to the atmosphere using a cooling tower with
river or lake water used as a cooling medium. The flue gas from
combustion of the fossil fuels is discharged to the air. This gas
contains carbon dioxide and water vapor, as well as other
substances such as nitrogen oxides (NOx), sulfur oxides (SOx),
mercury, traces of other metals, and, for coal-fired plants, fly
ash. Solid waste ash from coal-fired boilers must also be removed.
Some coal ash can be recycled for building materials.Fossil fueled
power stations are major emitters of CO2, a greenhouse gas (GHG)
which according to a consensus opinion of scientific organisations
is a contributor to global warming as it has been observed over the
last 100 years. Per unit of electric energy, brown coal emits about
3 times as much CO2 as natural gas, and black coal emits about
twice as much CO2. Carbon capture and storage of emissions is not
expected to be available until technology is safe and deployable.In
a fossil fuel power plant the chemical energy stored in fossil
fuels such as coal, fuel oil, natural gas or oil shale and oxygen
of the air is converted successively into thermal energy,
mechanical energy and, finally, electrical energy. Each fossil fuel
power plant is a complex, custom-designed system. Construction
costs, as of 2004, run to US$1,300 per kilowatt, or $650 million
for a 500 MWe unit. Multiple generating units may be built at a
single site for more efficient use of land, natural resources and
labour. Most thermal power stations in the world use fossil fuel,
outnumbering nuclear, geothermal, biomass, or solar thermal
plants.Heat into mechanical energyThe second law of thermodynamics
states that any closed-loop cycle can only convert a fraction of
the heat produced during combustion into mechanical work. The rest
of the heat, called waste heat, must be released into a cooler
environment during the return portion of the cycle. The fraction of
heat released into a cooler medium must be equal or larger than the
ratio of absolute temperatures of the cooling system (environment)
and the heat source (combustion furnace). Raising the furnace
temperature improves the efficiency but complicates the design,
primarily by the selection of alloys used for construction, making
the furnace more expensive. The waste heat cannot be converted into
mechanical energy without an even cooler cooling system. However,
it may be used in cogeneration plants to heat buildings, produce
hot water, or to heat materials on an industrial scale, such as in
some oil refineries, plants, and chemical synthesis plants.Coal as
fuelCoal is the most abundant fossil fuel on the planet. It is a
relatively cheap fuel, with some of the largest deposits in regions
that are relatively stable politically, such as China, India and
the United States. This contrasts with natural gas and petroleum,
the largest deposits of which are located in the politically
volatile Persian Gulf. Solid coal cannot directly replace natural
gas or petroleum in most applications, petroleum is mostly used for
transportation and the natural gas not used for electricity
generation is used for space, water and industrial heating. Coal
can be converted to gas or liquid fuel, but the efficiencies and
economics of such processes can make them unfeasible. Vehicles or
heaters may require modification to use coal-derived fuels. Coal
can produce more pollution than petroleum or natural gas.As of 2009
the largest coal-fired power station is Taichung Power Plant in
Taiwan. The world's most energy-efficient coal-fired power plant is
the Avedre Power Station in Denmark.
Taichung coal-fired power plant in Taiwan, the world's largest
carbon dioxide emitterGas turbine plants
Currant Creek Power Plant near Mona, Utah is a natural gas fired
electrical plant.One type of fossil fuel power plant uses a gas
turbine in conjunction with a heat recovery steam generator (HRSG).
It is referred to as a combined cycle power plant because it
combines the Brayton cycle of the gas turbine with the Rankine
cycle of the HRSG. The thermal efficiency of these plants has
reached a record heat rate of 5690 Btu/(kWh), or just under 60%, at
a facility in Baglan Bay, Wales.The turbines are fueled either with
natural gas, syngas or fuel oil. While more efficient and faster to
construct (a 1,000 MW plant may be completed in as little as 18
months from start of construction), the economics of such plants is
heavily influenced by the volatile cost of fuel, normally natural
gas. The combined cycle plants are designed in a variety of
configurations composed of the number of gas turbines followed by
the steam turbine. For example, a 3-1 combined cycle facility has
three gas turbines tied to one steam turbine. The configurations
range from (1-1), (2-1), (3-1), (4-1), (5-1), to (6-1)Simple-cycle
or open cycle gas turbine plants, without a steam cycle, are
sometimes installed as emergency or peaking capacity; their thermal
efficiency is much lower. The high running cost per hour is offset
by the low capital cost and the intention to run such units only a
few hundred hours per year. Other gas turbine plants are installed
in stages, with an open cycle gas turbine the first stage and
additional turbines or conversion to a closed cycle part of future
project plans.Greening of fossil fuel power plantsSeveral methods
exist to improve the efficiency of fossil fuel power plants. A
frequently used and cost-efficient method is to convert a plant to
run on a different fuel. This includes conversions for biomass and
waste. Conversions to waste-fired power plants have the benefit of
reducing landfilling. In addition, waste-fired power plants can be
equipped with material recovery, which is also beneficial to the
environment.Regardless of the conversion, a truly green fossil fuel
power plant implements carbon capture and storage (CCS). CCS means
that the exhaust CO2 is not released into the environment and the
fossil fuel power plant becomes an emissionless power plant. A 2006
example of a CCS fossil fuel power plant is the pilot Elsam power
station near Esbjerg, Denmark.Low NOx BurnersA common retrofit in
fossil fueled power stations is the replacement of original burners
with Low NOx burners. Careful consideration of fluid dynamics and
flame thermodynamics has enabled substantial reduction in flame
temperature, leading to reduced formation of Nitrous Oxides.Clean
coal"Clean coal" is the name attributed to a process whereby coal
is chemically washed of minerals and impurities, sometimes
gasified, burned and the resulting flue gases treated with steam,
with the purpose of removing sulfur dioxide, and reburned so as to
make the carbon dioxide in the flue gas economically recoverable.
The coal industry uses the term "clean coal" to describe
technologies designed to enhance both the efficiency and the
environmental acceptability of coal extraction, preparation and
use, but has provided no specific quantitative limits on any
emissions, particularly carbon dioxide. Whereas contaminants like
sulfur or mercury can be removed from coal, carbon cannot be
effectively removed while still leaving a usable fuel, and clean
coal plants without carbon sequestration and storage do not
significantly reduce carbon dioxide emissions. James Hansen in an
open letter to U.S. President Barack Obama has advocated a
"moratorium and phase-out of coal plants that do not capture and
store CO2". In his book Storms of My Grandchildren, similarly,
Hansen discusses his Declaration of Stewardship the first principle
of which requires "a moratorium on coal-fired power plants that do
not capture and sequester carbon dioxide".
Hydropower
The 22,500 MW Three Gorges Dam in the People's Republic of
China, the largest hydroelectric power station in the
world.Hydro-power or water power is power derived from the energy
of falling water and running water, which may be harnessed for
useful purposes. Since ancient times, hydro-power has been used for
irrigation and the operation of various mechanical devices, such as
watermills, sawmills, textile mills, dock cranes, domestic lifts,
power houses and paint making.Since the early 20th century, the
term has been used almost exclusively in conjunction with the
modern development of hydro-electric power, which allowed use of
distant energy sources. Another method used to transmit energy is
by using a trompe, which produces compressed air from falling
water. Compressed air could then be piped to power other machinery
at a distance from the waterfall. Hydro power is a renewable energy
source.Water's power is manifested in hydrology, by the forces of
water on the riverbed and banks of a river. When a river is in
flood, it is at its most powerful, and moves the greatest amount of
sediment. This higher force results in the removal of sediment and
other material from the riverbed and banks of the river, locally
causing erosion, transport and, with lower flow, sedimentation
downstream.Generating methodsHydropower is used primarily to
generate electricity. Broad categories include:Conventional
(dams)
Turbine row at Los Nihuiles Power Station in Mendoza,
ArgentinaMost hydroelectric power comes from the potential energy
of dammed water driving a water turbine and generator. The power
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. A large pipe (the
"penstock") delivers water to the turbine.Pumped-storageThis method
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 most commercially
important means of large-scale grid energy storage and improve the
daily capacity factor of the generation system. Pumped storage is
not an energy source, and appears as a negative number in
listings.Run of the riverRun of the river hydroelectric stations
are those with small or no reservoir capacity, so that the water
coming from upstream must be used for generation at that moment, or
must be allowed to bypass the dam. In the United States, run of the
river hydropower could potentially provide 60,000 MW (about 13.7%
of total use in 2011 if continuously available).TideA tidal power
plant makes use of the daily rise and fall of ocean 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. Tidal power is viable in a relatively
small number of locations around the world. In Great Britain, there
are eight sites that could be developed, which have the potential
to generate 20% of the electricity used in 2012.
The world's first commercial-scale and grid-connected tidal
stream generator SeaGen in Strangford Lough. The strong wake shows
the power in the tidal current.UndergroundAn underground power
station makes use of a large natural height difference between two
waterways, such as a waterfall or mountain lake. An underground
tunnel is constructed to take water from the high reservoir to the
generating hall built in an underground cavern near the lowest
point of the water tunnel and a horizontal tailrace taking water
away to the lower outlet waterway.
Geothermal energy
Steam rising from the Nesjavellir Geothermal Power Station in
Iceland.Geothermal energy is thermal energy generated and stored in
the Earth. Thermal energy is the energy that determines the
temperature of matter. The geothermal energy of the Earth's crust
originates from the original formation of the planet (20%) and from
radioactive decay of minerals (80%). The geothermal gradient, which
is the difference in temperature between the core of the planet and
its surface, drives a continuous conduction of thermal energy in
the form of heat from the core to the surface. Earth's internal
heat is thermal energy generated from radioactive decay and
continual heat loss from Earth's formation. Temperatures at the
coremantle boundary may reach over 4000 C (7,200 F). The high
temperature and pressure in Earth's interior cause some rock to
melt and solid mantle to behave plastically, resulting in portions
of mantle convecting upward since it is lighter than the
surrounding rock. Rock and water is heated in the crust, sometimes
up to 370 C (700 F).From hot springs, geothermal energy has been
used for bathing since Paleolithic times and for space heating
since ancient Roman times, but it is now better known for
electricity generation. Worldwide, 11,400 megawatts (MW) of
geothermal power is online in 24 countries in 2012. An additional
28 gigawatts of direct geothermal heating capacity is installed for
district heating, space heating, spas, industrial processes,
desalination and agricultural applications in 2010.Geothermal power
is cost effective, reliable, sustainable, and environmentally
friendly, but has historically been limited to areas near tectonic
plate boundaries. Recent technological advances have dramatically
expanded the range and size of viable resources, especially for
applications such as home heating, opening a potential for
widespread exploitation. Geothermal wells release greenhouse gases
trapped deep within the earth, but these emissions are much lower
per energy unit than those of fossil fuels. As a result, geothermal
power has the potential to help mitigate global warming if widely
deployed in place of fossil fuels.The Earth's geothermal resources
are theoretically more than adequate to supply humanity's energy
needs, but only a very small fraction may be profitably exploited.
Drilling and exploration for deep resources is very expensive.
Forecasts for the future of geothermal power depend on assumptions
about technology, energy prices, subsidies, and interest rates. But
as a result of government assisted research and industry
experience, the cost of generating geothermal power has decreased
by 25% over the past two decades. In 2001, geothermal energy cost
between two and ten US cents per kWh.As Thermal energy
Ground source heating and coolingLower temperature sources
produce the energy equivalent of 100M BBL per year. Sources with
temperatures from 30-150 C are used without conversion to
electricity for as district heating, greenhouses, fisheries,
mineral recovery, industrial process heating and bathing in 75
countries. Heat pumps extract energy from shallow sources at 10-20
C in 43 countries for use in space heating and cooling. Home
heating is the fastest-growing means of exploiting geothermal
energy, with global annual growth rate of 30% in 2005 and 20% in
2012.Approximately 270 petajoules (PJ) of geothermal heating was
used in 2004. More than half went for space heating, and another
third for heated pools. The remainder supported industrial and
agricultural applications. Global installed capacity was 28 GW, but
capacity factors tend to be low (30% on average) since heat is
mostly needed in winter. Some 88 PJ for space heating was extracted
by an estimated 1.3 million geothermal heat pumps with a total
capacity of 15 GW.Heat for these purposes may also be extracted
from co-generation at a geothermal electrical plant.Heating is
cost-effective at many more sites than electricity generation. At
natural hot springs or geysers, water can be piped directly into
radiators. In hot, dry ground, earth tubes or downhole heat
exchangers can collect the heat. However, even in areas where the
ground is colder than room temperature, heat can often be extracted
with a geothermal heat pump more cost-effectively and cleanly than
by conventional furnaces. These devices draw on much shallower and
colder resources than traditional geothermal techniques. They
frequently combine functions, including air conditioning, seasonal
thermal energy storage, solar energy collection, and electric
heating. Heat pumps can be used for space heating essentially
anywhere.Iceland is the world leader in direct applications. Some
92.5% of its homes are heated with geothermal energy, saving
Iceland over $100 million annually in avoided oil imports.
Reykjavk, Iceland has the world's biggest district heating system.
Once known as the most polluted city in the world, it is now one of
the cleanest.As Electrical energyGeothermal electricity is
electricity generated from geothermal energy. Technologies in use
include dry steam power plants, flash steam power plants and binary
cycle power plants. Geothermal electricity generation is currently
used in 24 countries, while geothermal heating is in use in 70
countries.Estimates of the electricity generating potential of
geothermal energy vary from 35 to 2,000 GW. Current worldwide
installed capacity is 10,715 megawatts (MW), with the largest
capacity in the United States (3,086 MW). El Salvador, Kenya, the
Philippines, Iceland and Costa Rica generate more than 15 percent
of their electricity from geothermal sources.Geothermal power is
considered to be sustainable because the heat extraction is small
compared with the Earth's heat content. The life cycle greenhouse
gas emissions of geothermal electric plants are on average 45 grams
of CO2 per kilowatt-hour of electricity, or less than 5 percent of
that of conventional coal-fired plants.Geothermal power stations
are similar to other steam turbine thermal power stations heat from
a fuel source (in geothermal's case, the earth's core) is used to
heat water or another working fluid. The working fluid is then used
to turn a turbine of a generator, thereby producing electricity.
The fluid is then cooled and returned to the heat source.Dry steam
power plantsDry steam plants are the simplest and oldest design.
They directly use geothermal steam of 150C or greater to turn
turbines.Flash steam power plantsFlash steam plants pull deep,
high-pressure hot water into lower-pressure tanks and use the
resulting flashed steam to drive turbines. They require fluid
temperatures of at least 180C, usually more. This is the most
common type of plant in operation today.Binary cycle power
plantsBinary cycle power plants are the most recent development,
and can accept fluid temperatures as low as 57C. The moderately hot
geothermal water is passed by a secondary fluid with a much lower
boiling point than water. This causes the secondary fluid to flash
vaporize, which then drives the turbines. This is the most common
type of geothermal electricity plant being constructed today. Both
Organic Rankine and Kalina cycles are used. The thermal efficiency
of this type plant is typically about 1013%.Wind power
Burbo Bank Offshore Wind Farm, at the entrance to the River
Mersey in northwest England.Wind power is the conversion of wind
energy into a useful form of energy, such as using wind turbines to
produce electrical power, windmills for mechanical power, windpumps
for water pumping or drainage, or sails to propel ships.Large wind
farms consist of hundreds of individual wind turbines which are
connected to the electric power transmission network. For new
constructions, onshore wind is an inexpensive source of
electricity, competitive with or in many places cheaper than fossil
fuel plants. Offshore wind is steadier and stronger than on land,
and offshore farms have less visual impact, but construction and
maintenance costs are considerably higher. Small onshore wind farms
can feed some energy into the grid or provide electricity to
isolated off-grid locations.Wind power, as an alternative to fossil
fuels, is plentiful, renewable, widely distributed, clean, produces
no greenhouse gas emissions during operation and uses little land.
The effects on the environment are generally less problematic than
those from other power sources. As of 2011, Denmark is generating
more than a quarter of its electricity from wind and 83 countries
around the world are using wind power to supply the electricity
grid. In 2010 wind energy production was over 2.5% of total
worldwide electricity usage, and growing rapidly at more than 25%
per annum.Wind power is very consistent from year to year but has
significant variation over shorter time scales. As the proportion
of windpower in a region increases, a need to upgrade the grid, and
a lowered ability to supplant conventional production can occur.
Power management techniques such as having excess capacity storage,
geographically distributed turbines, dispatchable backing sources,
storage such as pumped-storage hydroelectricity, exporting and
importing power to neighboring areas or reducing demand when wind
production is low, can greatly mitigate these problems. In
addition, weather forecasting permits the electricity network to be
readied for the predictable variations in production that occur.
Wind power can be considered a topic in applied eolics.Wind farmsA
wind farm is a group of wind turbines in the same location used for
production of electricity. A large wind farm may consist of several
hundred individual wind turbines distributed over an extended area,
but the land between the turbines may be used for agricultural or
other purposes. A wind farm may also be located offshore.Almost all
large wind turbines have the same design a horizontal axis wind
turbine having an upwind rotor with three blades, attached to a
nacelle on top of a tall tubular tower.In a wind farm, individual
turbines are interconnected with a medium voltage (often 34.5 kV),
power collection system and communications network. At a
substation, this medium-voltage electric current is increased in
voltage with a transformer for connection to the high voltage
electric power transmission system.Feeding into gridInduction
generators, often used for wind power, require reactive power for
excitation so substations used in wind-power collection systems
include substantial capacitor banks for power factor correction.
Different types of wind turbine generators behave differently
during transmission grid disturbances, so extensive modelling of
the dynamic electromechanical characteristics of a new wind farm is
required by transmission system operators to ensure predictable
stable behaviour during system faults (see: Low voltage ride
through). In particular, induction generators cannot support the
system voltage during faults, unlike steam or hydro turbine-driven
synchronous generators. Doubly fed machines generally have more
desirable properties for grid interconnection. Transmission systems
operators will supply a wind farm developer with a grid code to
specify the requirements for interconnection to the transmission
grid. This will include power factor, constancy of frequency and
dynamic behavior of the wind farm turbines during a system
fault.Offshore wind powerOffshore wind power refers to the
construction of wind farms in large bodies of water to generate
electricity. These installations can utilise the more frequent and
powerful winds that are available in these locations and have less
aesthetic impact on the landscape than land based projects.
However, the construction and the maintenance costs are
considerably higher.Siemens and Vestas are the leading turbine
suppliers for offshore wind power. DONG Energy, Vattenfall and E.ON
are the leading offshore operators. As of October 2010, 3.16 GW of
offshore wind power capacity was operational, mainly in Northern
Europe. According to BTM Consult, more than 16 GW of additional
capacity will be installed before the end of 2014 and the UK and
Germany will become the two leading markets. Offshore wind power
capacity is expected to reach a total of 75 GW worldwide by 2020,
with significant contributions from China and the US.At the end of
2012, 1,662 turbines at 55 offshore wind farms in 10 European
countries are generating 18 TWh, which can power almost five
million households. As of August 2013 the London Array in the
United Kingdom is the largest offshore wind farm in the world at
630 MW. This is followed by the Greater Gabbard Wind Farm (504 MW),
also in the UK. The Gwynt y Mr wind farm (576 MW) is the largest
project currently under construction.
BiomassBiomass is biological material derived from living, or
recently living organisms. It most often refers to plants or
plant-based materials which are specifically called lignocellulosic
biomass. As an energy source, biomass can either be used directly
via combustion to produce heat, or indirectly after converting it
to various forms of biofuel. Conversion of biomass to biofuel can
be achieved by different methods which are broadly classified into:
thermal, chemical, and biochemical methods.Wood remains the largest
biomass energy source to date; examples include forest residues
(such as dead trees, branches and tree stumps), yard clippings,
wood chips and even municipal solid waste. In the second sense,
biomass includes plant or animal matter that can be converted into
fibers or other industrial chemicals, including biofuels.
Industrial biomass can be grown from numerous types of plants,
including miscanthus, switchgrass, hemp, corn, poplar, willow,
sorghum, sugarcane, bamboo, and a variety of tree species, ranging
from eucalyptus to oil palm (palm oil).Plant energy is produced by
crops specifically grown for use as fuel that offer high biomass
output per hectare with low input energy. Some examples of these
plants are wheat, which typically yield 7.58 tonnes of grain per
hectare, and straw, which typically yield 3.55 tonnes per hectare
in the UK. The grain can be used for liquid transportation fuels
while the straw can be burned to produce heat or electricity. Plant
biomass can also be degraded from cellulose to glucose through a
series of chemical treatments, and the resulting sugar can then be
used as a first generation biofuel.Biomass can be converted to
other usable forms of energy like methane gas or transportation
fuels like ethanol and biodiesel. Rotting garbage, and agricultural
and human waste, all release methane gasalso called "landfill gas"
or "biogas." Crops, such as corn and sugar cane, can be fermented
to produce the transportation fuel, ethanol. Biodiesel, another
transportation fuel, can be produced from left-over food products
like vegetable oils and animal fats. Also, biomass to liquids
(BTLs) and cellulosic ethanol are still under research.The biomass
used for electricity generation varies by region. Forest
by-products, such as wood residues, are common in the United
States. Agricultural waste is common in Mauritius (sugar cane
residue) and Southeast Asia (rice husks). Animal husbandry
residues, such as poultry litter, are common in the UK.
A cogeneration plant in Metz, France. The station uses waste
wood biomass as an energy source, and provides electricity and heat
for 30,000 dwellings.Biomass conversion process to useful
energyThermal conversionThermal conversion processes use heat as
the dominant mechanism to convert biomass into another chemical
form. The basic alternatives of combustion (torrefaction,
pyrolysis, and gasification) are separated principally by the
extent to which the chemical reactions involved are allowed to
proceed (mainly controlled by the availability of oxygen and
conversion temperature).Energy created by burning biomass (fuel
wood) is particularly suited for countries where the fuel wood
grows more rapidly, e.g. tropical countries. There are a number of
other less common, more experimental or proprietary thermal
processes that may offer benefits such as hydrothermal upgrading
(HTU) and hydroprocessing. Some have been developed for use on high
moisture content biomass, including aqueous slurries, and allow
them to be converted into more convenient forms. Some of the
applications of thermal conversion are combined heat and power
(CHP) and co-firing. In a typical dedicated biomass power plant,
efficiencies range from 727% (HHV basis). Biomass cofiring with
coal, by contrast, typically occurs at efficiencies near those of
the coal combustor (3040%, HHV basis).Chemical conversionA range of
chemical processes may be used to convert biomass into other forms,
such as to produce a fuel that is more conveniently used,
transported or stored, or to exploit some property of the process
itself. Many of these processes are based in large part on similar
coal-based processes, such as Fischer-Tropsch synthesis, methanol
production, olefins (ethylene and propylene), and similar chemical
or fuel feedstocks. In most cases, the first step involves
gasification, which step generally is the most expensive and
involves the greatest technical risk. Biomass is more difficult to
feed into a pressure vessel than coal or any liquid. Therefore,
biomass gasification is frequently done at atmospheric pressure and
causes combustion of biomass to produce a combustible gas
consisting of carbon monoxide, hydrogen, and traces of methane.
This gas mixture, called a producer gas, can provide fuel for
various vital processes, such as internal combustion engines, as
well as substitute for furnace oil in direct heat applications.
Because any biomass material can undergo gasification, this process
is far more attractive than ethanol or biomass production, where
only particular biomass materials can be used to produce a fuel. In
addition, biomass gasification is a desirable process due to the
ease at which it can convert solid waste (such as wastes available
on a farm) into producer gas, which is a very usable
fuel.Conversion of biomass to biofuel can also be achieved via
selective conversion of individual components of biomass. For
example cellulose can be converted to intermediate platform
chemical such a sorbitol, glucose, hydroxymethylfurfural etc. These
chemical are then further reacted to produce hydrogen or
hydrocarbon fuels.Biomass also has the potential to be converted to
multiple commodity chemicals. Halomethanes have successfully been
by produced using a combination of A. fermentans and engineered S.
cerevisiae. This method converts NaX salts and unprocessed biomass
such as switchgrass, sugar cane, corn stover, or poplar into
halomethanes. S-adenosylmethionine which is naturally occurring in
S. cerevisiae allows a methyl group to be transferred. Production
levels of 150 mg L-1H-1 iodomethane were achieved. At these levels
roughly 173000L of capacity would need to be operated just to
replace the United States need for iodomethane. However, an
advantage of this method is that it uses NaI rather than I2; NaI is
significantly less hazardous than I2. This method may be applied to
produce ethylene in the future.Biochemical conversionAs biomass is
a natural material, many highly efficient biochemical processes
have developed in nature to break down the molecules of which
biomass is composed, and many of these biochemical conversion
processes can be harnessed.Biochemical conversion makes use of the
enzymes of bacteria and other microorganisms to break down biomass.
In most cases, microorganisms are used to perform the conversion
process: anaerobic digestion, fermentation, and composting.
Solar energy
Part of the 354 MW SEGS solar complex in northern San Bernardino
County, California, USASolar energy is radiant light and heat from
the sun harnessed using a range of ever-evolving technologies such
as solar heating, solar photovoltaics, solar thermal electricity,
solar architecture and artificial photosynthesis.Solar technologies
are broadly characterized as either passive solar or active solar
depending on the way they capture, convert and distribute solar
energy. Active solar techniques include the use of photovoltaic
panels and solar thermal collectors to harness the energy. 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.In
2011, the International Energy Agency said that "the development of
affordable, inexhaustible and clean solar energy technologies will
have huge longer-term benefits. It will increase countries energy
security through reliance on an indigenous, inexhaustible and
mostly import-independent resource, enhance sustainability, reduce
pollution, lower the costs of mitigating climate change, and keep
fossil fuel prices lower than otherwise. These advantages are
global. Hence the additional costs of the incentives for early
deployment should be considered learning investments; they must be
wisely spent and need to be widely shared".Solar thermalSolar
thermal technologies can be used for water heating, space heating,
space cooling and process heat generation.Water heatingSolar 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.
Solar water heaters facing the Sun to maximize gain.Heating,
cooling and ventilationIn 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
heatheat 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 in the northern hemisphere or the
northern side in the southern hemisphere, 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 Equator facing 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.Water
treatmentSolar distillation can be used to make saline or brackish
water potable. The first recorded instance of this was by
16th-century Arab alchemists. A large-scale solar distillation
project was first constructed in 1872 in the Chilean mining town of
Las Salinas. The plant, which had solar collection area of 4,700
m2, could produce up to 22,700 L per day and operated for 40 years.
Individual still designs include single-slope, double-slope (or
greenhouse type), vertical, conical, inverted absorber, multi-wick,
and multiple effect. These stills can operate in passive, active,
or hybrid modes. Double-slope stills are the most economical for
decentralized domestic purposes, while active multiple effect units
are more suitable for large-scale applications.Solar water
disinfection (SODIS) involves exposing water-filled plastic
polyethylene terephthalate (PET) bottles to sunlight for several
hours. Exposure times vary depending on weather and climate from a
minimum of six hours to two days during fully overcast conditions.
It is recommended by the World Health Organization as a viable
method for household water treatment and safe storage. Over two
million people in developing countries use this method for their
daily drinking water.Solar energy may be used in a water
stabilisation pond to treat waste water without chemicals or
electricity. A further environmental advantage is that algae grow
in such ponds and consume carbon dioxide in photosynthesis,
although algae may produce toxic chemicals that make the water
unusable.
Solar water disinfection in IndonesiaProcess heatSolar
concentrating technologies such as parabolic dish, trough and
Scheffler reflectors can provide process heat for commercial and
industrial applications. The first commercial system was the Solar
Total Energy Project (STEP) in Shenandoah, Georgia, USA where a
field of 114 parabolic dishes provided 50% of the process heating,
air conditioning and electrical requirements for a clothing
factory. This grid-connected cogeneration system provided 400 kW of
electricity plus thermal energy in the form of 401 kW steam and 468
kW chilled water, and had a one hour peak load thermal
storage.Evaporation ponds are shallow pools that concentrate
dissolved solids through evaporation. The use of evaporation ponds
to obtain salt from sea water is one of the oldest applications of
solar energy. Modern uses include concentrating brine solutions
used in leach mining and removing dissolved solids from waste
streams.Clothes lines, clotheshorses, and clothes racks dry clothes
through evaporation by wind and sunlight without consuming
electricity or gas. In some states of the United States legislation
protects the "right to dry" clothes.Unglazed transpired collectors
(UTC) are perforated sun-facing walls used for preheating
ventilation air. UTCs can raise the incoming air temperature up to
22 C and deliver outlet temperatures of 4560 C. The short payback
period of transpired collectors (3 to 12 years) makes them a more
cost-effective alternative than glazed collection systems. As of
2003, over 80 systems with a combined collector area of 35,000 m2
had been installed worldwide, including an 860 m2 collector in
Costa Rica used for drying coffee beans and a 1,300 m2 collector in
Coimbatore, India used for drying marigolds.CookingSolar cookers
use sunlight for cooking, drying and pasteurization. They can be
grouped into three broad categories: box cookers, panel cookers and
reflector cookers. The simplest solar cooker is the box cooker
first built by Horace de Saussure in 1767. A basic box cooker
consists of an insulated container with a transparent lid. It can
be used effectively with partially overcast skies and will
typically reach temperatures of 90150 C. Panel cookers use a
reflective panel to direct sunlight onto an insulated container and
reach temperatures comparable to box cookers. Reflector cookers use
various concentrating geometries (dish, trough, Fresnel mirrors) to
focus light on a cooking container. These cookers reach
temperatures of 315 C and above but require direct light to
function properly and must be repositioned to track the Sun.
The Solar Bowl in Auroville, India, concentrates sunlight on a
movable receiver to produce steam for cooking.Electricity
productionSolar power is the conversion of sunlight into
electricity, either directly using photovoltaics (PV), or
indirectly using concentrated solar power (CSP). CSP systems use
lenses or mirrors and tracking systems to focus a large area of
sunlight into a small beam. PV converts light into electric current
using the photoelectric effect.Commercial CSP plants were first
developed in the 1980s. Since 1985 the eventually 354 MW SEGS CSP
installation, in the Mojave Desert of California, is the largest
solar power plant in the world. Other large CSP plants include the
150 MW Solnova Solar Power Station and the 100 MW Andasol solar
power station, both in Spain. The 250 MW Agua Caliente Solar
Project, in the United States, and the 221 MW Charanka Solar Park
in India, are the worlds largest photovoltaic plants. Solar
projects exceeding 1 GW are being developed, but most of the
deployed photovoltaics are in small rooftop arrays of less than 5
kW, which are grid connected using net metering and/or a feed-in
tariff.Concentrated solar powerConcentrating Solar Power (CSP)
systems use lenses or mirrors and tracking systems to focus a large
area of sunlight into a small beam. The concentrated heat is then
used as a heat source for a conventional power plant. A wide range
of concentrating technologies exists; the most developed are the
parabolic trough, the concentrating linear fresnel reflector, the
Stirling dish and the solar power tower. Various techniques are
used to track the Sun and focus light. In all of these systems a
working fluid is heated by the concentrated sunlight, and is then
used for power generation or energy storage.PhotovoltaicsA solar
cell, or photovoltaic cell (PV), is a device that converts light
into electric current using the photoelectric effect. The first
solar cell was constructed by Charles Fritts in the 1880s. In 1931
a German engineer, Dr Bruno Lange, developed a photo cell using
silver selenide in place of copper oxide. Although the prototype
selenium cells converted less than 1% of incident light into
electricity, both Ernst Werner von Siemens and James Clerk Maxwell
recognized the importance of this discovery. Following the work of
Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller
and Daryl Chapin created the silicon solar cell in 1954. These
early solar cells cost 286 USD/watt and reached efficiencies of
4.56%. By 2012 available efficiencies exceed 20% and the maximum
efficiency of research photovoltaics is over 40%.Fuel
productionSolar chemical processes use solar energy to drive
chemical reactions. These processes offset energy that would
otherwise come from a fossil fuel source and can also convert solar
energy into storable and transportable fuels. Solar induced
chemical reactions can be divided into thermochemical or
photochemical. A variety of fuels can be produced by artificial
photosynthesis. The multielectron catalytic chemistry involved in
making carbon-based fuels (such as methanol) from reduction of
carbon dioxide is challenging; a feasible alternative is hydrogen
production from protons, though use of water as the source of
electrons (as plants do) requires mastering the multielectron
oxidation of two water molecules to molecular oxygen. Some have
envisaged working solar fuel plants in coastal metropolitan areas
by 2050- the splitting of sea water providing hydrogen to be run
through adjacent fuel-cell electric power plants and the pure water
by-product going directly into the municipal water system. Another
vision involves all human structures covering the earth's surface
(i.e., roads, vehicles and buildings) doing photosynthesis more
efficiently than plants.Hydrogen production technologies been a
significant area of solar chemical research since the 1970s. Aside
from electrolysis driven by photovoltaic or photochemical cells,
several thermochemical processes have also been explored. One such
route uses concentrators to split water into oxygen and hydrogen at
high temperatures (2300-2600 C). Another approach uses the heat
from solar concentrators to drive the steam reformation of natural
gas thereby increasing the overall hydrogen yield compared to
conventional reforming methods. Thermochemical cycles characterized
by the decomposition and regeneration of reactants present another
avenue for hydrogen production. The Solzinc process under
development at the Weizmann Institute uses a 1 MW solar furnace to
decompose zinc oxide (ZnO) at temperatures above 1200 C. This
initial reaction produces pure zinc, which can subsequently be
reacted with water to produce hydrogen.