Download Renewable energy is energy which comes from natural resources

Renewable energy is energy which comes from natural resources such as
sunlight, wind, rain, tides, and geothermal heat, which are renewable (naturally
replenished). About 16% of global final energy consumption comes from
renewables, with 10% coming from traditional biomass, which is mainly used
for heating, and 3.4% from hydroelectricity. New renewables (small hydro,
modern biomass, wind, solar, geothermal, and biofuels) accounted for another
3% and are growing very rapidly.[1] The share of renewables in electricity
generation is around 19%, with 16% of global electricity coming from
hydroelectricity and 3% from new renewables.[2]
Wind power is growing at the rate of 30% annually, with a worldwide installed
capacity of 238,000 megawatts (MW) at the end of 2011,[3] [4][5] and is
widely used in Europe, Asia, and the United States.[6] At the end of 2011 the
photovoltaic (PV) capacity worldwide was 67,000 MW, and PV power stations
are popular in Germany and Italy.[7] Solar thermal power stations operate in
the USA and Spain, and the largest of these is the 354 megawatt (MW) SEGS
power plant in the Mojave Desert.[8] The world's largest geothermal power
installation is the Geysers in California, with a rated capacity of 750 MW. Brazil
has one of the largest renewable energy programs in the world, involving
production of ethanol fuel from sugarcane, and ethanol now provides 18% of
the country's automotive fuel.[9] Ethanol fuel is also widely available in the
USA.
While many renewable energy projects are large-scale, renewable technologies
are also suited to rural and remote areas, where energy is often crucial in
human development.[10] As of 2011, small solar PV systems provide electricity
to a few million households, and micro-hydro configured into mini-grids serves
many more. Over 44 million households use biogas made in household-scale
digesters for lighting and/or cooking, and more than 166 million households
rely on a new generation of more-efficient biomass cookstoves.[11] United
Nations' Secretary-General Ban Ki-moon has said that renewable energy has
the ability to lift the poorest nations to new levels of prosperity.[12]
Climate change concerns, coupled with high oil prices, peak oil, and increasing
government support, are driving increasing renewable energy legislation,
incentives and commercialization.[13] New government spending, regulation
and policies helped the industry weather the global financial crisis better than
many other sectors.[14] According to a 2011 projection by the International
Energy Agency, solar power generators may produce most of the world’s
electricity within 50 years, dramatically reducing the emissions of greenhouse
gases that harm the environment.[15]
Contents
[hide]
* 1 Overview
* 2 Mainstream forms of renewable energy
o 2.1 Wind power
o 2.2 Hydropower
o 2.3 Solar energy
o 2.4 Biomass
o 2.5 Biofuel
o 2.6 Geothermal energy
* 3 Renewable energy commercialization
o 3.1 Growth of renewables
o 3.2 Economic trends
o 3.3 Hydroelectricity
o 3.4 Wind power market
o 3.5 New generation of solar thermal plants
o 3.6 Photovoltaic market
o 3.7 Biofuels for transportation
o 3.8 Geothermal energy commercialization
o 3.9 Developing country markets
o 3.10 Industry and policy trends
* 4 New and emerging renewable energy technologies
o 4.1 Cellulosic ethanol
o 4.2 Ocean energy
o 4.3 Enhanced geothermal systems
o 4.4 Experimental solar power
o 4.5 Artificial photosynthesis
* 5 Renewable energy debate
* 6 See also
* 7 References
* 8 Bibliography
* 9 External links
Overview
Global renewable power capacity excluding hydro[16]
Renewable energy flows involve natural phenomena such as sunlight, wind,
tides, plant growth, and geothermal heat, as the International Energy Agency
explains:[17]
Renewable energy is derived from natural processes that are replenished
constantly. In its various forms, it derives directly from the sun, or from heat
generated deep within the earth. Included in the definition is electricity and
heat generated from solar, wind, ocean, hydropower, biomass, geothermal
resources, and biofuels and hydrogen derived from renewable resources.
Renewable energy replaces conventional fuels in four distinct areas: electricity
generation, hot water/ space heating, motor fuels, and rural (off-grid) energy
services:[18]
* Power generation. Renewable energy provides 19% of electricity
generation worldwide. Renewable power generators are spread across many
countries, and wind power alone already provides a significant share of
electricity in some areas: for example, 14% in the U.S. state of Iowa, 40% in
the northern German state of Schleswig-Holstein, and 20% in Denmark. Some
countries get most of their power from renewables, including Iceland and
Paraguay (100%), Norway (98%), Brazil (86%), Austria (62%), New Zealand
(65%), and Sweden (54%).[19]
* Heating. Solar hot water makes an important contribution to renewable
heat in many countries, most notably in China, which now has 70% of the
global total (180 GWth). Most of these systems are installed on multi-family
apartment buildings and meet a portion of the hot water needs of an estimated
50–60 million households in China. Worldwide, total installed solar water
heating systems meet a portion of the water heating needs of over 70 million
households. The use of biomass for heating continues to grow as well. In
Sweden, national use of biomass energy has surpassed that of oil. Direct
geothermal for heating is also growing rapidly.[19]
* Transport fuels. Renewable biofuels have contributed to a significant
decline in oil consumption in the United States since 2006. The 93 billion liters
of biofuels produced worldwide in 2009 displaced the equivalent of an
estimated 68 billion liters of gasoline, equal to about 5% of world gasoline
production.[19]
Mainstream forms of renewable energy
Wind power
Main article: Wind power
A wind farm located in Manjil, Iran.
Airflows can be used to run wind turbines. Modern wind turbines range from
around 600 kW to 5 MW of rated power, although turbines with rated output of
1.5–3 MW have become the most common for commercial use; the power
output of a turbine is a function of the cube of the wind speed, so as wind
speed increases, power output increases dramatically.[20] Areas where winds
are stronger and more constant, such as offshore and high altitude sites, are
preferred locations for wind farms. Typical capacity factors are 20-40%, with
values at the upper end of the range in particularly favourable sites.[21][22]
Globally, the long-term technical potential of wind energy is believed to be five
times total current global energy production, or 40 times current electricity
demand. This could require wind turbines to be installed over large areas,
particularly in areas of higher wind resources. Offshore resources experience
average wind speeds of ~90% greater than that of land, so offshore resources
could contribute substantially more energy.[23]
Hydropower
See also: Hydroelectricity and Hydropower
Grand Coulee Dam is a hydroelectric gravity dam on the Columbia River in the
U.S. state of Washington. The dam supplies four power stations with an
installed capacity of 6,809 MW and is the largest electric power-producing
facility in the United States.
Energy in water can be harnessed and used. Since water is about 800 times
denser than air, even a slow flowing stream of water, or moderate sea swell,
can yield considerable amounts of energy. There are many forms of water
energy:
* Hydroelectric energy is a term usually reserved for large-scale
hydroelectric dams. Examples are the Grand Coulee Dam in Washington State
and the Akosombo Dam in Ghana.
* Micro hydro systems are hydroelectric power installations that typically
produce up to 100 kW of power. They are often used in water rich areas as a
remote-area power supply (RAPS).
* Run-of-the-river hydroelectricity systems derive kinetic energy from rivers
and oceans without using a dam.
Solar energy
See also: Solar energy, Solar power, and Solar thermal energy
Monocrystalline solar cell.
Solar energy is the energy derived from the sun through the form of solar
radiation. Solar powered electrical generation relies on photovoltaics and heat
engines. A partial list of other solar applications includes space heating and
cooling through solar architecture, daylighting, solar hot water, solar cooking,
and high temperature process heat for industrial purposes.
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.
Biomass
Biomass (plant material) is a renewable energy source because the energy it
contains comes from the sun. Through the process of photosynthesis, plants
capture the sun's energy. When the plants are burnt, they release the sun's
energy they contain. In this way, biomass functions as a sort of natural battery
for storing solar energy. As long as biomass is produced sustainably, with only
as much used as is grown, the battery will last indefinitely.[24]
In general there are two main approaches to using plants for energy
production: growing plants specifically for energy use (known as first and thirdgeneration biomass), and using the residues (known as second-generation
biomass) from plants that are used for other things. See biobased economy.
The best approaches vary from region to region according to climate, soils and
geography.[24]
Solar panel
A solar panel (also solar module, photovoltaic module or photovoltaic panel) is
a packaged, connected assembly of photovoltaic cells. The solar panel can be
used as a component of a larger photovoltaic system to generate and supply
electricity in commercial and residential applications.
Because a single solar panel can produce only a limited amount of power,
many installations contain several panels. A photovoltaic system typically
includes an array of solar panels, an inverter, and sometimes a battery and
interconnection wiring.
Theory and co
nstruction
See also: Solar cell
Polycrystalline PV cells connected in a solar panel.
Solar panels use light energy (photons) from the sun to generate electricity
through the photovoltaic effect. The structural (load carrying) member of a
module can either be the top layer or the back layer. The majority of modules
use wafer-based crystalline silicon cells or thin-film cells based on cadmium
telluride or silicon. The conducting wires that take the current off the panels
may contain silver, copper or other non-magnetic conductive transition metals.
The cells must be connected electrically to one another and to the rest of the
system. Cells must also be protected from mechanical damage and moisture.
Most solar panels are rigid, but semi-flexible ones are available, based on thinfilm cells.
Electrical connections are made in series to achieve a desired output voltage
and/or in parallel to provide a desired current capability.
Separate diodes may be needed to avoid reverse currents, in case of partial or
total shading, and at night. The p-n junctions of mono-crystalline silicon cells
may have adequate reverse current characteristics that these are not
necessary. Reverse currents waste power and can also lead to overheating of
shaded cells. Solar cells become less efficient at higher temperatures and
installers try to provide good ventilation behind solar panels.[1]
Some recent solar panel designs include concentrators in which light is focused
by lenses or mirrors onto an array of smaller cells. This enables the use of cells
with a high cost per unit area (such as gallium arsenide) in a cost-effective
way.[citation needed]
Depending on construction, photovoltaic panels can produce electricity from a
range of frequencies of light, but usually cannot cover the entire solar range
(specifically, ultraviolet, infrared and low or diffused light). Hence much of the
incident sunlight energy is wasted by solar panels, and they can give far higher
efficiencies if illuminated with monochromatic light. Therefore, another design
concept is to split the light into different wavelength ranges and direct the
beams onto different cells tuned to those ranges.[2] This has been projected to
be capable of raising efficiency by 50%.
Currently the best achieved sunlight conversion rate (solar panel efficiency) is
around 21% in commercial products,[3] typically lower than the efficiencies of
their cells in isolation. The energy density of a solar panel is the efficiency
described in terms of peak power output per unit of surface area, commonly
expressed in units of watts per square foot (W/ft2). The most efficient massproduced solar panels have energy density values of greater than 13 W/ft2
(140 W/m2).
[edit] Crystalline silicon modules
Main article: Solar cell
Most solar modules are currently produced from silicon photovoltaic cells.
These are typically categorized as monocrystalline or polycrystalline modules.
[edit] Thin-film modules
Main articles: Thin film solar cell, Third generation solar cell, and Low-cost
photovoltaic cell
Third generation solar cells are advanced thin-film cells. They produce highefficiency conversion at low cost.
[edit] Rigid thin-film modules
In rigid thin film modules, the cell and the module are manufactured in the
same production line.
The cell is created on a glass substrate or superstrate, and the electrical
connections are created in situ, a so called "monolithic integration". The
substrate or superstrate is laminated with an encapsulant to a front or back
sheet, usually another sheet of glass.
The main cell technologies in this category are CdTe, or a-Si, or a-Si+uc-Si
tandem, or CIGS (or variant). Amorphous silicon has a sunlight conversion rate
of 6-12%.
[edit] Flexible thin-film modules
Flexible thin film cells and modules are created on the same production line by
depositing the photoactive layer and other necessary layers on a flexible
substrate.
If the substrate is an insulator (e.g. polyester or polyimide film) then monolithic
integration can be used.
If it is a conductor then another technique for electrical connection must be
used.
The cells are assembled into modules by laminating them to a transparent
colourless fluoropolymer on the front side (typically ETFE or FEP) and a polymer
suitable for bonding to the final substrate on the other side. The only
commercially available (in MW quantities) flexible module uses amorphous
silicon triple junction (from Unisolar).
So-called inverted metamorphic (IMM) multijunction solar cells made on
compound-semiconductor technology are just becoming commercialized in July
2008. The University of Michigan's solar car that won the North American Solar
Challenge in July 2008 used IMM thin-film flexible solar cells.
The requirements for residential and commercial are different in that the
residential needs are simple and can be packaged so that as solar cell
technology progresses, the other base line equipment such as the battery,
inverter and voltage sensing transfer switch still need to be compacted and
unitized for residential use. Commercial use, depending on the size of the
service will be limited in the photovoltaic cell arena, and more complex
parabolic reflectors and solar concentrators are becoming the dominant
technology.
The global flexible and thin-film photovoltaic (PV) market, despite caution in
the overall PV industry, is expected to experience a CAGR of over 35% to 2019,
surpassing 32 GW according to a major new study by IntertechPira.[4]
[edit] Module embedded electronics
See also: Solar micro-inverter
Several companies have begun embedding electronics into PV modules. This
enables performing maximum power point tracking (MPPT) for each module
individually, and the measurement of performance data for monitoring and
fault detection at module level. Some of these solutions make use of power
optimizers, a DC-to-DC converter technology developed to maximize the power
harvest from solar photovoltaic systems. As of about 2010, such electronics
can also compensate for shading effects, wherein a shadow falling across a
section of a panel causes the electrical output of one or more strings of cells in
the panel to fall to zero, but not having the output of the entire panel fall to
zero.
[edit] Module performance and lifetime
Module performance is generally rated under standard test conditions (STC):
irradiance of 1,000 W/m², solar spectrum of AM 1.5 and module temperature at
25°C.
Electrical characteristics include nominal power (PMAX, measured in W), open
circuit voltage (VOC), short circuit current (ISC, measured in amperes),
maximum power voltage (VMPP), maximum power current (IMPP), peak power,
kWp, and module efficiency (%).
Nominal voltage refers to the voltage of the battery that the module is best
suited to charge; this is a leftover term from the days when solar panels were
used only to charge batteries. The actual voltage output of the panel changes
as lighting, temperature and load conditions change, so there is never one
specific voltage at which the panel operates. Nominal voltage allows users, at a
glance, to make sure the panel is compatible with a given system.
Open circuit voltage or VOC is the maximum voltage that the panel can
produce when not connected to an electrical circuit or system. VOC can be
measured with a meter directly on an illuminated panel's terminals or on its
disconnected cable.[5]
The peak power rating, kWp, is the maximum output according under standard
test conditions (not the maximum possible output).
Solar panels must withstand heat, cold, rain and hail for many years. Many
crystalline silicon module manufacturers offer a warranty that guarantees
electrical production for 10 years at 90% of rated power output and 25 years at
80%.[6]
[edit] Production
The "solar tree", a symbol of Gleisdorf, Austria
In 2010, 15.9 GW of solar PV system installations were completed, with solar
PV pricing survey and market research company PVinsights reporting growth of
117.8% in solar PV installation on a year-on-year basis. With over 100% yearon-year growth in PV system installation, PV module makers dramatically
increased their shipments of solar panels in 2010. They actively expanded their
capacity and turned themselves into gigawatt GW players. According to
PVinsights, five of the top ten PV module companies in 2010 are GW players.
Suntech, First Solar, Sharp, Yingli and Trina Solar are GW producers now, and
most of them doubled their shipments in 2010.[7]