The term “biogas” is used for a gas produced by anaerobic
fermentation of different forms of organic matter. This anaerobic process is
driven by different varieties of bacteria, in anaerobic digester tanks this is
usually at a temperature of 30 – 40° C.
FEEDSTOCK FOR
PRODUCTION OF BIOGAS
Typical feedstock’s for biogas production are manure and
sewage, residues of crop production (i.e., straw), the organic fraction of the
waste from cities and municipalities, be it sewage sludge, waste from the food
industry or collected from household organic waste bins, as well as energy
crops including maize and grass silage. The process itself occurs in airtight
biogas digesters without oxygen.The
rate of the process depends on the feedstock and several other parameters. The
digestion time varies from several hours (for sugars, and alcohol) to several
weeks (in case of hemicelluloses, fat, and protein).
TYPE
Nm3 biogas
1 milking cow 20m³ liquid manure/a
500
1 pig 1.5 – 6 m³ liquid manure/a
42-168
1 cattle (beef) 3 -11t solid manure/a
240 – 880
100 chicken -1,8m³ dry litter
242
Maize silage 40 -60 green weight/ha
7040 - 10560
Grass 24 – 43 t fresh matter/ha
4118 - 6811
COMPOSITION OF
BIOGAS
During this biological process a major portion of the carbon
compounds are converted to CH4, CO2 and water. Biogas consists mainly of
methane, carbon dioxide, and some other minor components.
Composition of bio gas
MATTER
%
CH4
50-75
CO2
25-45
H20
2-7
N2
<2
O2
<2
NH3,H2,H2S,trace gases
WORKING OF BIO GAS
PLANT
Manure and sewage, residue of crop, the organic waste from
cities and municipalities are collected together in preliminary tank & from
there they are disposed into fermenter.
Fermenter or digester is a large cylindrical container with
a conical or dome shape at top in which temperature is maintained at 30-40
degree in which anaerobic fermentation occurs which produce biogas.
This biogas is heated & supplied to CHP plant which
contain a gas operated engine or motor coupled with a generator which produces
electrical power which is delivered to grid.
Biogas is directly used as a fuel in gas operated auto mobs
or for cooking at home.
REASON FOR SLOW
DEVELOPMENT
Reasons for the slow deployment of biogas include: a lack of
information about the possibilities of biogas, a lack of a trained labor force,
high capital cost for the setting up of commercial plants, generally inadequate
and unreliable government support policies and the competition of natural gas
as a cheaper alternative in many parts of the world.
ADVANTAGE OF
BIOGAS ENERGY
A specific advantage of biogas technology is in the utilization
of organic wastes and other organic byproducts for energy production, as
opposed to disposal via landfills, which inevitably leads to further emissions
of greenhouse gases by the process of slow decomposition.
Reference : "WBA factsheet-Biogas- an important Renewable energy source"
Solar, or photovoltaic (PV), cells are electronic devices
that essentially convert the solar energy of sunlight into electric energy or
electricity. The physics of solar cells is based on the same semiconductor
principles as diodes and transistors, which form the building blocks of the
entire world of electronics.
In the later part of the century, physicists discovered a phenomenon:
when light is incident on liquids or metal cell surfaces, electrons are
released. However, no one had an explanation for this bizarre occurrence. At
the turn of the century, Albert Einstein provided a theory for this which won
him the Nobel Prize in physics and laid the groundwork for the theory of the photoelectric
effect. Figure 1 shows the photoelectric effect experiment. When light is shone
on metal, electrons are released. These electrons are attracted toward a
positively charged plate, thereby giving rise to a photoelectric current.
Einstein explained the observed phenomenon by a contemporary theory of
quantized energy levels, which was previously developed by Max Planck. The
theory described light as being made up of miniscule bundles of energy called
photons. Photons impinging on metals or semiconductors knock electrons off
atoms. In the 1930s, these theorems led to a new discipline in physics called
quantum mechanics, which consequently led to the discovery of transistors in
the 1950s and to the development of semiconductor electronics.
fig 1
Most solar cells are constructed from semiconductor
material, such as silicon (the fourteenth element in the Mendeleyev table of
elements). Silicon is a semiconductor that has the combined properties of a
conductor and an insulator. Metals such as gold, copper, and iron are
conductors; they have loosely bound electrons in the outer shell or orbit of
their atomic configuration. These electrons can be detached when subjected to an
electric voltage or current. On the contrary, atoms of insulators, such as
glass, have very strongly bonded electrons in the atomic configuration and do
not allow the flow of electrons even under the severest application of voltage
or current. Semiconductor materials, on the other hand, bind electrons midway
between that of metals and insulators. Semiconductor elements used in
electronics are constructed by fusing two adjacently doped silicon wafer
elements. Doping implies impregnation of silicon by positive and negative
agents, such as phosphor and boron. Phosphor creates a free electron that
produces so-called N-type material. Boron creates a “hole,” or a shortage of an
electron, which produces so-called P-type material. Impregnation is
accomplished by depositing the previously referenced dopants on the surface of
silicon using a certain heating or chemical process. The N-type material has a
propensity to lose electrons and gain holes, so it acquires a positive charge.
The P-type material has a propensity to lose holes and gain electrons, so it
acquires a negative charge. When N-type and P-type doped silicon wafers are
fused together, they form a PN junction. The negative charge on P-type material
prevents electrons from crossing the junction, and the positive charge on the
N-type material prevents holes from crossing the junction. A space created by
the P and N, or PN, wafers creates a potential barrier across the junction.
This PN junction, which forms the basic block of most electronic components,
such as diodes and transistors, has the following specific operational uses when
applied in electronics:
In diodes, a PN device allows for the flow of electrons and,
therefore, current in one direction. For example, a battery, with direct
current, connected across a diode allows the flow of current from positive to
negative leads. When an alternating sinusoidal current is connected across the
device, only the positive portion of the waveform is allowed to pass through.
The negative portion of the waveform is blocked. In transistors, a wire secured
in a sandwich of a PNP-junction device (formed by three doped junctions), when
properly polarized or biased, controls the amount of direct current from the
positive to the negative lead, thus forming the basis for current control,
switching, and amplification, as shown in Fig 2
fig 2
In light-emitting diodes (LEDs), a controlled amount and
type of doping material in a PN-type device connected across a dc voltage
source converts the electric energy to visible light with differing frequencies
and colors, such as white, red, blue, amber, and green. In solar cells, when a
PN junction is exposed to sunshine, the device converts the stream of photons
(packets of quanta) that form the visible light into electrons (the reverse of
the LED function), making the device behave like a minute battery with a unique
characteristic voltage and current, which is dependent on the material dopants
and PN-junction physics. This is shown in Fig 3
The bundles of photons that penetrate the PN junction
randomly strike silicon atoms and give energy to the outer electrons. The
acquired energy allows the outer electrons to break free from the atom. Thus, the
photons in the process are converted to electron movement or electric energy as
shown in Figure 1.4. It should be noted that the photovoltaic energy conversion
efficiency is dependent on the wavelength of the impinging light. Red light,
which has a lower frequency, produces insufficient energy, whereas blue light,
which has more energy than needed to break the electrons, is wasted and
dissipates as heat.
Wind is a form of solar energy and is a result of the uneven heating of the atmosphere by the sun, the irregularities of the earth's surface, and the rotation of the earth.
TYPES OF WIND TURBINES
Modern wind turbines classify into two basic groups: the horizontal-axis and the vertical-axis design. Horizontal-axis wind turbines typically either have two or three blades. These three-bladed wind turbines are operated "upwind," with the blades facing into the wind.
SIZES OF WIND TURBINES
Utility-scale turbines range in size from 100 kilowatts to as large as several megawatts. Larger wind turbines are more cost effective and are grouped together into wind farms, which provide bulk power to the electrical grid. In recent years, there has been an increase in large offshore wind installations in order to harness the huge potential that wind energy,
How does a turbine generate electricity?
A turbine is a machine that spins around in a moving fluid (liquid or gas) and catches some of the energy passing by. All sorts of machines use turbines, from jet engines to hydroelectric power plants and from diesel railroad locomotives to windmills. Even a child's toy windmill is a simple form of turbine.
The huge rotor blades (propellers) on the front of a wind turbine are the "turbine" part. As wind passes by, the kinetic energy (energy of movement) it contains makes the blades spin around (usually quite slowly). The blades have a special curved shape so they capture as much energy from the wind as possible.
Although we talk about "wind turbines," the turbine is only one of the three main parts inside these giant machines. The second part is a gearbox whose gears convert the slow speed of the spinning blades into higher-speed rotary motion—turning the drive shaft quickly enough to power the electricity generator.
The generator is the third main part of a turbine and it's exactly like an enormous, scaled-up version of the dynamo on a bicycle. When you ride a bicycle, the dynamo touching the back wheel spins around and generates enough electricity to make a lamp light up. The same thing happens in a wind turbine, only the "dynamo" generator is driven by the turbine's rotor blades instead of by a bicycle wheel, and the "lamp" is a light in someone's home dozens of miles away.
The application of
direct current (dc) electric power is a century-old technology that took a
backseat to alternating current (ac) in early 1900s when Edison and Tesla were
having a feud over their energy transmission and distribution inventions-“WAR
OF CURRENTS”. The following are some interesting historical notes that were
communicated by two of the most brilliant inventors in the history of
electrical engineering.
Nicola Tesla: “Alternating Current will allow the
transmission of electrical power to any point on the planet, either through
wires or through the air, as I have demonstrated.”
Thomas Edison: “Transmission of ac over long distances
requires lethally high voltages, and should be outlawed. To allow Tesla and
Westinghouse to proceed with their proposals is to risk untold deaths by
electricide.”
Tesla: “How will the dc power a 1,000 horsepower electric
motor as well as a single light bulb? With AC, the largest as well as the
smallest load may be driven from the same line.”
Edison: “The most efficient and proper electrical supply for
every type of device from the light bulb to the phonograph is Direct Current at
low voltage.”
Tesla: “A few large AC generating plants, such as my
hydroelectric station at Niagara Falls, are all you need: from these, power can
be distributed easily wherever it is required.”
Edison: “Small dc generating plants, as many as are
required, should be built according to local needs, after the model of my power
station in New York City.”
Relive that era & feel the charge
EARLY AC DOMINANCE
After Edison introduced his dc power stations, the first of
their kind in the world, the demand for electricity became overwhelming. Soon,
the need to send power over long distances in rural and suburban America was
paramount.
How did the two power systems compare in meeting this need?
Alternating current
could be carried over long distances, via a relatively small line given an
extremely high transmission voltage of 50,000 volts (V) or above.
The high voltage could then be transformed down to lower
levels for residential, office, and industrial use.
While higher in
quality and more efficient than alternating current, dc power could not be
transformed or transmitted over distances via small cables without suffering
significant losses through resistance. AC power became the standard of all
public utilities, overshadowing issues of safety and efficiency and forcing
manufacturers to produce appliances and motors compatible with the national
grid.
THE 100-YEAR-OLD
POWER SCHEME
With ac power the
only option available from power utilities, the world came to rely almost
exclusively on ac-based motors and other appliances, and the efficiencies and
disadvantages of ac power became accepted as unavoidable. Nicola Tesla’s
development of the polyphase induction ac motor was a key step in the evolution
of ac power applications. His discoveries contributed greatly to the
development of dynamos, vacuum bulbs, and transformers, strengthening the
existing ac power scheme 100 years ago. Compared to direct current and Edison’s
findings, ac power is inefficient because of the energy lost with the rapid
reversals of the current’s polarity. We often hear these reversals as the
familiar 60 cycles per second [60 hertz (Hz)] or 50 cycles per second [50
hertz(Hz)] of an appliance. AC power is also prone to harmonic distortion,
which occurs when there is a disruption in the ideal ac sinusoidal power
wave shape.
Since most of today’s technologically advanced on-site power
devices use direct current, there is a need to use inverters to produce
alternating current through the system and then convert it back to direct
current into the end source of power. These inverters are inefficient; energy is
lost (up to 50 percent) when these devices are used. This characteristic is
evident in many of today’s electronic devices that have internal converters,
such as fluorescent lighting.
ALTERNATING AND
DIRECT CURRENT:
1950 TO 2000 The
discovery of semiconductors and the invention of the transistor, along with the
growth of the American economy, triggered a quiet but profound revolution in
how we use electricity. Changes over the last half-century have brought the
world into the era of electronics with more and more machines and appliances
operating internally on dc power and requiring more and more expensive
solutions for the conversion and regulation of incoming ac supply. The
following table reflects the use of ac and dc device applications of the
mid-twentieth and twenty-first centuries.
Sr.no
AC DEVICES—1950
DC DEVICES—2000
1
Electric typewriters
Computers, printers, CRTs, scanners
2
Adding machines
CD-ROMs, photocopiers
3
rotary telephones
Wired, cordless, mobile phones
4
Teletypes
machines, modems, faxes
5
Early fluorescent lighting
fluorescent lighting with electronic ballasts
6
Radios, early TVs
HDTVs, CD players, videocassettes
7
Record players
Microwave ovens, DC vehicles
8
Fans, furnaces
Electronically controlled HVAC systems
As seen from the preceding table, over the last 50 years we
have moved steadily from an electromechanical to an electronic world—a world
where most of our electric devices are driven by direct current and most of our
non-fossil-fuel energy sources (such as photovoltaic cells and batteries) deliver
their power as a dc supply. Despite these changes, the vast majority of today’s
electricity is still generated, transported and delivered as alternating
current. Converting alternating current to direct current and integrating
alternative dc sources with the mainstream ac supply are inefficient and
expensive activities that add significantly to capital costs and lock us all
into archaic and uncompetitive utility pricing structures. With the advent of
progress in solar power technology, the world that Thomas Edison envisioned
(one with clean, efficient, and less costly power) is now, after a century of
dismissal, becoming a reality.
The following exemplify the significance of dc energy
applications from solar photovoltaic systems: first, on-site power using direct
current to the end source is the most efficient use of power; second, there are
no conversion losses resulting from the use of dc power which allows maximum
harvest of solar irradiance energy potential.
