OTHER
POWER PLANTS AND ECONOMICS OF POWER PLANTS
GEOTHERMAL POWER
PLANT:
Geothermal
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 2000 GW. Current worldwide
installed capacity is 10,715 megawatts (MW), with the largest capacity in the United States (3,086 MW), Philippines, and Indonesia.
Geothermal
power is considered to be sustainable because the heat extraction is small
compared with the Earth's heat content. The emission intensity of existing geothermal
electric plants is on average 122 kg of CO2
per megawatt-hour (MW·h) of electricity, about one-eighth of a conventional
coal-fired plant.
OTEC:
Ocean
thermal energy conversion (OTEC
)uses the difference between cooler deep and warmer shallow or surface ocean waters to run a
heat
engine and produce useful work, usually in the form of electricity.
A heat
engine gives greater efficiency and power when run with a large temperature
difference. In the oceans the temperature difference between surface and deep
water is greatest in the tropics, although still a modest 20oC to 25oC.
It is therefore in the tropics that OTEC
offers the greatest possibilities. OTEC
has the potential to offer global amounts of energy that are 10 to 100 times
greater than other ocean energy options such as wave power.
OTEC plants can operate
continuously providing a base load supply for an electrical power generation
system.
The main
technical challenge of OTEC is to
generate significant amounts of power efficiently from small temperature
differences. It is still considered an emerging technology. Early OTEC systems were of 1 to 3% thermal efficiency, well below the theoretical
maximum for this temperature difference of between 6 and 7%.[2]
Current designs are expected to be closer to the maximum. The first operational
system was built in Cuba in 1930 and generated 22 kW. Modern designs allow
performance approaching the theoretical maximum Carnot
efficiency and the largest built in 1999 by the USA generated 250 kW .
The most
commonly used heat cycle for OTEC
is the Rankine cycle using a low-pressure turbine. Systems
may be either closed-cycle or open-cycle. Closed-cycle engines use working
fluids that are typically thought of as refrigerants
such as ammonia
or R-134a.
Open-cycle engines use vapour from the seawater itself
as the working fluid.
OTEC can also supply quantities of cold
water as a by-product . This can be used for air conditioning and refrigeration
and the fertile deep ocean water can feed biological technologies. Another
by-product is fresh water distilled from the sea.
Cycle types
Cold
seawater is an integral part of each of the three types of OTEC systems: closed-cycle, open-cycle, and hybrid.
To operate, the cold seawater must be brought to the surface. The primary
approaches are active pumping and desalination. Desalinating seawater near the
sea floor lowers its density, which causes it to rise to the surface.
The
alternative to costly pipes to bring condensing cold water to the surface is to
pump vaporized low boiling point fluid into the depths to be condensed, thus
reducing pumping volumes and reducing technical and environmental problems and
lowering costs.
Closed
Diagram of a closed cycle OTEC
plant
Closed-cycle
systems use fluid with a low boiling point, such as ammonia, to power
a turbine to
generate electricity. Warm surface seawater is
pumped through a heat exchanger to vaporize the fluid. The expanding
vapor turns the turbo-generator. Cold water, pumped through a second heat
exchanger, condenses the vapor into a liquid, which is then recycled through
the system.
In 1979,
the Natural Energy Laboratory and several private-sector partners developed the
"mini OTEC" experiment,
which achieved the first successful at-sea production of net electrical power
from closed-cycle OTEC.[12]
The mini OTEC vessel was moored
1.5 miles (2 km) off the Hawaiian coast and produced enough net
electricity to illuminate the ship's light bulbs and run its computers and
television.
Open
Diagram of an open cycle OTEC
plant
Open-cycle
OTEC uses warm surface water
directly to make electricity. Placing warm seawater in a low-pressure container
causes it to boil. The expanding steam drives a low-pressure turbine attached to an electrical generator. The steam, which has
left its salt and
other contaminants in the low-pressure container, is pure fresh water.
It is condensed into a liquid by exposure to cold temperatures from deep-ocean
water. This method produces desalinized
fresh water, suitable for drinking water or irrigation.
In 1984,
the Solar Energy Research Institute (now the National Renewable Energy
Laboratory) developed a vertical-spout evaporator to convert warm seawater
into low-pressure steam for open-cycle plants. Conversion efficiencies were as
high as 97% for seawater-to-steam conversion (overall efficiency using a
vertical-spout evaporator would still only be a few per cent). In May 1993, an
open-cycle OTEC plant at Keahole
Point, Hawaii, produced 50,000 watts of electricity during a net power-producing experiment.
This broke the record of 40 kW set by a Japanese system in 1982.
Hybrid
A hybrid
cycle combines the features of the closed- and open-cycle systems. In a hybrid,
warm seawater enters a vacuum chamber and is flash-evaporated, similar to the
open-cycle evaporation process. The steam vaporizes the ammonia working
fluid of a closed-cycle loop on the other side of an ammonia
vaporizer. The vaporized fluid then drives a turbine to produce electricity.
The steam condenses within the heat exchanger and provides desalinated
water.
Working fluids
A
popular choice of working fluid is ammonia, which
has superior transport properties, easy availability, and low cost. Ammonia,
however, is toxic and flammable. Fluorinated carbons such asCFCs and HCFCs are not toxic or
flammable, but they contribute to ozone layer depletion. Hydrocarbons too are
good candidates, but they are highly flammable; in addition, this would create
competition for use of them directly as fuels. The power plant size is
dependent upon the vapor pressure of the working fluid. With increasing vapor
pressure, the size of the turbine and heat exchangers decreases while the wall
thickness of the pipe and heat exchangers increase to endure high pressure
especially on the evaporator side.
TIDEL
POWER PLANT:
Tidal
power, also called tidal energy, is a form of hydropower
that converts the energy of tides into electricity or other useful forms of power. The first
large-scale tidal power plant (the Rance Tidal Power Station) started
operation in 1966.
Although
not yet widely used, tidal power has potential for future electricity generation. Tides are more
predictable than wind energy and solar power.
Among sources of renewable energy, tidal power has traditionally
suffered from relatively high cost and limited availability of sites with
sufficiently high tidal ranges or flow velocities, thus constricting its total
availability. However, many recent technological developments and improvements,
both in design (e.g. dynamic
tidal power, tidal lagoons) and turbine technology (e.g. new axial turbines, crossflow turbines), indicate that the total
availability of tidal power may be much higher than previously assumed, and
that economic and environmental costs may be brought down to competitive
levels.
Historically,
tide mills
have been used, both in Europe and on the Atlantic coast of North America. The
earliest occurrences date from the Middle Ages,
or even from Roman times.
Tidal
power is extracted from the Earth's oceanic tides; tidal
forces are periodic variations in gravitational attraction exerted by
celestial bodies. These forces create corresponding motions or currents in the
world's oceans. The magnitude and character of this motion reflects the
changing positions of the Moon and Sun relative to the Earth, the effects
of Earth's rotation, and local geography of
the sea floor and coastlines.
Tidal
power is the only technology that draws on energy inherent in the orbital
characteristics of the Earth–Moon
system, and to a lesser extent in the Earth–Sun system. Other natural
energies exploited by human technology originate directly or indirectly with
the Sun, including fossil fuel, conventional
hydroelectric, wind, biofuel, wave and solar
energy. Nuclear energy makes use of Earth's mineral deposits
of fissionable elements, while geothermal
power taps the Earth's internal heat, which comes from a combination of residual heat from planetary accretion
(about 20%) and heat produced through radioactive
decay (80%).
A tidal
generator converts the energy of tidal flows into electricity. Greater tidal
variation and higher tidal current velocities can dramatically increase the
potential of a site for tidal electricity generation.
Because
the Earth's tides are ultimately due to gravitational interaction with the Moon
and Sun and the Earth's rotation, tidal power is practically inexhaustible and
classified as a renewable energy resource. Movement of tides
causes a loss of mechanical energy in the Earth–Moon
system: this is a result of pumping of water through natural restrictions
around coastlines and consequent viscous
dissipation at the seabed
and in turbulence.
This loss of energy has caused the rotation of the Earth to slow in the
4.5 billion years since its formation. During the last 620 million
years the period of rotation of the earth (length of a day) has increased from
21.9 hours to 24 hours;[4]
in this period the Earth has lost 17% of its rotational energy. While tidal
power may take additional energy from the system, the effect is negligible and
would only be noticed over millions of years.
Generating methods
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.
Top-down view of a DTP dam. Blue and dark red colors indicate low and high
tides, respectively.
Tidal
power can be classified into three generating methods:
Tidal stream generator
Tidal
stream generators (or TSGs) make use of the kinetic
energy of moving water to power turbines, in a similar way to wind
turbines that use moving air.
Tidal barrage
Tidal
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.
Dynamic tidal power
Dynamic
tidal power (or DTP) is a theoretical generation technology that would exploit
an interaction between potential and kinetic energies in tidal flows. It
proposes that very long dams (for example: 30–50 km length) be built from
coasts straight out into the sea or ocean, without enclosing an area. Tidal phase
differences are introduced across the dam, leading to a significant
water-level differential in shallow coastal seas – featuring strong
coast-parallel oscillating tidal currents such as found in the UK, China and
Korea.
PUMPED
STORAGE:
Pumped-storage
hydroelectricity is a type of hydroelectric
power
generation used by some power plants for load balancing. The method
stores energy in the form of water, pumped from a lower elevation reservoir to
a higher elevation. Low-cost off-peak electric power is used to run the pumps.
During periods of high electrical demand, the stored water is released through turbines.
Although the losses of the pumping process makes the plant a net consumer of
energy overall, the system increases revenue by
selling more electricity during periods of peak demand,
when electricity prices are highest. Pumped storage is the largest-capacity
form of grid energy storage now available.
SOLAR
CENTRAL RECIVER SYSTEM:
The solar
power tower (also known as 'central tower' power plants or 'heliostat'
power plants or power towers) is a type of solar
furnace using a tower to receive the focused sunlight. It uses an array of
flat, movable mirrors (called heliostats) to focus the sun's rays upon a
collector tower (the target). Concentrated solar thermal is seen as one viable
solution for renewable, pollution free energy production with currently
available technology.
Early
designs used these focused rays to heat water, and used the resulting steam to power a turbine. Newer
designs using liquid sodium has been demonstrated, and systems using molten salts
(40% potassium nitrate, 60% sodium nitrate) as the working fluids are now in
operation. These working fluids have high heat
capacity, which can be used to store the energy before using it to boil
water to drive turbines. These designs allow power to be generated when the sun
is not shining.
COST OF ELECTRICAL
ENERGY:
Electric
power transmission or "high voltage electric transmission"
is the bulk transfer of electrical energy, from generating power
plants to substations located near to population centers. This is distinct
from the local wiring between high voltage substations and customers, which is
typically referred to as electricity distribution. Transmission lines,
when interconnected with each other, become high voltage transmission networks.
In the US, these are typically referred
to as "power grids" or just "the grid", while in the UK the
network is known as the "national grid." North
America has three major grids: The Western Interconnection; The Eastern Interconnection and the Electric Reliability Council of
Texas (or ERCOT) grid.
Historically,
transmission and distribution lines were owned by the same company, but over
the last decade or so many countries have liberalized the electricity market in ways that have led to the
separation of the electricity transmission business from the distribution
business.
Transmission
lines mostly use three-phase alternating current (AC), although single phase AC is sometimes used in railway electrification systems. High-voltage direct-current (HVDC) technology is used only for very long
distances (typically greater than 400 miles, or 600 km); submarine power cables (typically longer than
30 miles, or 50 km); or for connecting two AC networks that are not
synchronized.
Electricity
is transmitted at high voltages (110 kV or above) to reduce the
energy lost in long distance transmission. Power is usually transmitted through
overhead power lines. Underground power
transmission has a significantly higher cost and greater operational
limitations but is sometimes used in urban areas or sensitive locations.
A key
limitation in the distribution of electricity is that, with minor exceptions,
electrical energy cannot be stored, and therefore must be generated as needed.
A sophisticated system of control is therefore required to ensure electric
generation very closely matches the demand. If supply and demand are not in
balance, generation plants and transmission equipment can shut down which, in
the worst cases, can lead to a major regional blackout, such as occurred in California
and the US Northwest in 1996 and in the US Northeast in 1965, 1977 and 2003. To
reduce the risk of such failures, electric transmission networks are
interconnected into regional, national or continental wide networks thereby
providing multiple redundant alternate routes for power to
flow should (weather or equipment) failures occur. Much analysis is done by
transmission companies to determine the maximum reliable capacity of each line
which is mostly less than its physical or thermal limit, to ensure spare
capacity is available should there be any such failure in another part of the
network.
ENERGY
RATES:
Electricity
pricing (sometimes referred to as electricity tariff or
the price of electricity) varies widely from country to country, and may
vary signicantly from locality to locality within a particular country. There
are many reasons that account for these differences in price. The price of power generation depends largely on the type
and market
price of the fuel used, government subsidies, government and industry
regulation, and even local weather patterns.
Basis of electricity rates
Electricity
prices vary all over the world, even within a single region or power-district
of a single country. In standard regulated monopoly markets, they typically vary
for residential, business, and industrial customers, and for any single
customer class, might vary by time-of-day or by the capacity or nature of the
supply circuit (e.g., 5 kW, 12 kW, 18 kW, 24 kW are typical in some
of the large developed countries); for industrial customers, single-phase vs.
3-phase, etc. If a specific market allows real-time
dynamic pricing, a more recent option in only a few
markets to date, prices can vary by a factor of ten or so between times of low
and high system-wide demand.
TYPES OF
TARIFFS:
In
economic terms, electricity (both power and energy) is a commodity
capable of being bought, sold and traded. An electricity market is a
system for effecting purchases, through bids to buy; sales, through offers to
sell; and short-term trades, generally in the form of
financial or obligation swaps. Bids and offers use supply
and demand principles to set the price. Long-term trades are contracts
similar to power purchase agreements and generally
considered private bi-lateral transactions between counterparties.
Wholesale transactions (bids and
offers) in electricity are typically cleared and settled by the market operator
or a special-purpose independent entity charged exclusively with that function.
Market operators do not clear trades but often require knowledge of the trade
in order to maintain generation and load balance. The commodities within an
electric market generally consist of two types: Power
and Energy. Power is the metered net electrical
transfer rate at any given moment and is measured in Megawatts (MW).
Energy is electricity that flows through a metered point for a given period and
is measured in Megawatt Hours (MWh).
Markets for power related
commodities are net generation output for a number of intervals usually in
increments of 5, 15 and 60 minutes. Markets for energy related commodities
required by, managed by (and paid for by) market operators to ensure
reliability, are considered Ancillary Services and include such names as
spinning reserve, non-spinning reserve, operating
reserves, responsive reserve, regulation up, regulation down, and installed capacity.
In addition, for most major
operators, there are markets for transmission congestion and electricity derivatives, such as electricity futures
and options, which are actively traded. These markets
developed as a result of the restructuring
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