Hydropower is the capture of the energy of
moving water for some useful purpose. Prior to
the widespread availability of commercial electric
power, hydropower was used for irrigation,
milling of grain, textile manufacture, and the
operation of sawmills. The energy of moving
water has been exploited for centuries.
Imperial Rome used water powered mills to
produce flour from grain, and in China and the
rest of the Far East, hydraulically operated "pot
wheel" pumps that raised water into irrigation
canals. In the 1830s, at the peak of the canalbuilding era, hydropower was used to transport
barge traffic up and down steep hills using
inclined plane railroads.
Direct mechanical power transmission required
that industries using hydropower had to locate
near the waterfall. For example, during the last
half of the 19th century, many grist mills were
built at Saint Anthony Falls, utilizing the 50 foot
drop in the Mississippi River.
A water wheel is a hydropower
system; a machine for extracting
power from the flow of water.
Water wheels and hydropower
was widely used in the Middle
Ages, powering most industry in
Europe, along with the windmill.
The most common use of the
water wheel was to mill flour in
gristmills, but other uses included
foundry work and machining, and
pounding linen for use in paper.
A water wheel consists of a large
wooden or metal wheel, with a
number of blades or buckets
arranged on the outside rim
forming the driving surface.
Hydroelectricity is electricity produced by
hydropower. Most hydroelectric power comes
from the potential energy of dammed water
driving a water turbine and generator, although
less common variations use water's kinetic
energy or un-dammed sources such as run-ofthe-river, waterwheels, and tidal power.
Hydroelectricity is a renewable energy
source. Since no fossil fuel is consumed,
emission of C O 2 is eliminated. While some
carbon dioxide is produced during
manufacture and construction of the project,
this is a tiny fraction of the operating
emissions of equivalent fossil-fuel electricity
The energy extracted from water depends on the
volume and on the difference in height between
the source and the water's outflow. This height
difference is called the head. The amount of
potential energy in water is proportional to the
head. To obtain very high head, water for a
hydraulic turbine may be run through a large pipe
called a penstock. From there it runs into the
blades of the turbine.
Paraguay & Brazil
The control center of the 18 generators
Left half of it (in Brazil) controls the 60 Hz units, right
half (in Paraguay) controls the 50 Hz units.
Hydroelectric projects can be disruptive to
surrounding aquatic ecosystems. For instance,
studies have shown that dams along the Atlantic
and Pacific coasts of North America have reduced
salmon populations by preventing access to
spawning grounds upstream, even though most
dams in salmon habitat have fish ladders
installed. Salmon smolt are also harmed on their
migration to sea when they must pass through
turbines. This has led to some areas barging
smolt downstream during parts of the year.
Generation of hydroelectric power impacts on the
downstream river environment. Water exiting a
turbine usually contains very little suspended
sediment, which can lead to scouring of river beds
and loss of riverbanks. Since turbines are often
opened intermittently, rapid or even daily fluctuations
in river flow are observed.
For example, in the Grand Canyon, the daily
cyclic flow variation caused by Glen Canyon
Dam was found to be contributing to
erosion of sand bars. Dissolved oxygen
content of the water may change from preconstruction conditions. And water exiting
from turbines is typically much colder than
the pre-dam water, which can change
aquatic faunal populations, including many
endangered species.
Tidal Power
sometimes called tidal energy, is the power
achieved by capturing the energy contained in
moving water in tides and ocean currents.
The efficiency of tidal power generation in ocean
dams largely depends on the amplitude (height of
the rise and fall) of the tidal swell, which can be up
to 33 ft where the periodic tidal waves funnel into
rivers and fjords and extreme water velocities can
be up to 16 knots near Vancouver Island.
Amplitudes of up to 56 ft occur for example in the
Bay of Fundy, where tidal resonance amplifies the
tidal waves.
Tidal power is reliably predictable (unlike wind
energy and solar power). In Europe, tide mills have
been used for nearly a thousand years, mainly for
grinding grains. As with wind power, selection of
location is critical for a tidal power generator
Therefore, a tidal energy generator must be placed
in a location with very high-amplitude tides.
Suitable locations are found in the former USSR,
USA, Canada, Australia, Korea, the UK and other
Tidal energy has an efficiency of 80% in
converting the potential energy of the
water into electricity, which is efficient
compared to other energy resources
such as solar power. There are not
many effects on the environment, but it
can damage some fish.
The barrage method of extracting tidal energy involves
building a barrage and creating a tidal lagoon. The
barrage traps a water level inside a basin. Head is
created when the water level outside of the basin or
lagoon changes relative to the water level inside. The
head is used to drive turbines. The largest has been
working on the Rance river (France) since 1967 with
an annual production of 600 GWh (about 68 MW
average power)
Rance, France Tidal Power Plant
Scale model cross-section of tidal power plant
The basin is filled through the sluices until high tide.
Then the sluice gates are closed. The turbine gates
are kept closed until the sea level falls to create
sufficient head across the barrage, and then are
opened so that the turbines generate until the head is
again low. Then the sluices are opened, turbines
disconnected and the basin is filled again. The cycle
repeats itself. Ebb generation (also known as outflow
generation) takes its name because generation occurs
as the tide ebbs.
A tidal power scheme is a long-term source of
electricity that decreases the output of greenhouse
gases into the atmosphere. Tidal barrage power
schemes have a high capital cost and a very low
running cost. As a result, a tidal power scheme
may not produce returns for years, and investors
are thus reluctant to participate in such projects.
Governments may be able to finance tidal barrage
power, but many are unwilling to do so also due to
the lag time before investment return and the high
irreversible commitment.
Wave power
refers to the energy of ocean surface waves
and the capture of that energy to do useful
work, including electricity generation,
desalinization and the pumping of water into
reservoirs. Wave power is a form of
renewable energy. Though often co-mingled,
wave power is distinct from the diurnal flux of
tidal power and the steady gyre of ocean
Wave size is determined by wind speed and fetch (the distance
over which the wind excites the waves) and by the depth and
topography of the seafloor. A given wind speed has a matching
practical limit over which time or distance will not produce
larger waves. This limit is called a "fully developed sea.“ Wave
motion is highest at the surface and diminishes exponentially
with depth.
The rising and falling of the
waves moves the buoy-like
structure creating mechanical
energy which is converted into
electricity and transmitted to
shore over a submerged
transmission line. A 40kW buoy
has a diameter of 12 feet and is
52 feet long, with approximately
13 feet of the unit rising above
the ocean surface. Using the
three-point mooring system, they
are designed to be installed one
to five miles offshore in water
100 to 200 feet deep.
Pelamis Wave Energy Converter
The Pelamis is an attenuating wave device designed for
survivability at sea rather than highly efficient energy
conversion. This means that rather than absorbing all of
the energy available in a wave, it converts only a portion
of that energy to electricity. This is principally so that the
device can survive in dangerous storm conditions which
could do considerable damage to a wave device
attempting to absorb all the available energy.
The Pelamis device consists of a series of semisubmerged cylindrical sections linked by hinged
joints. The wave induced relative motion of these
sections is resisted by hydraulic rams which pump
high pressure oil through hydraulic motors via
smoothing hydraulic accumulators. The hydraulic
motors drive electrical generators to produce
electricity, 30 of these machines can power 20,000
Scottish homes. Several devices can be connected
together and linked to shore. Its operating efficiency
is approximately 15%.
What’s this?
Underwater Turbines
Underwater turbines are being developed that
can be placed in rivers that provide a constant
energy flow as long as the river maintains the
minimal flow required. Due to the increased
density of water when compared to air, those
turbines are said to be 80% more effective.

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