Introduction
Renewable energy is energy that is collected from renewable resources that are naturally replenished on
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a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat.
Although most renewable energy sources are sustainable, some are not. For example, some biomass sources are
considered unsustainable at current rates of exploitation. Renewable energy often provides energy for electricity
generation to a grid, air and water heating/cooling, and stand-alone power systems. Renewable energy
technology projects are typically large-scale, but they are also suited to rural and remote areas and developing
countries, where energy is often crucial in human development. Renewable energy is often deployed together
with further electrification, which has several benefits: electricity can move heat or objects efficiently, and is
clean at the point of consumption. In addition, electrification with renewable energy is more efficient and
therefore leads to significant reductions in primary energy requirements.
Between all this energy, we will talk about the hydroenergy or
hydropower.
I/Definition
Hydroelectricity, or hydroelectric power, is electricity
generated from hydropower (water power). Hydropower
supplies one sixth of the world's electricity, almost 4500 TWh
in 2020, which is more than all other renewable sources
combined and also more than nuclear power. Hydropower can
provide large amounts of low-carbon electricity on demand,
making it a key element for creating secure and clean
electricity supply systems. A hydroelectric power station that
has a dam and reservoir is a flexible source, since the amount
of electricity produced can be increased or decreased in
seconds or minutes in response to varying electricity demand.
Once a hydroelectric complex is constructed, it produces no
direct waste, and almost always emits considerably less
greenhouse gas than fossil fuel-powered energy plants.
However, when constructed in lowland rainforest areas, where
part of the forest is inundated, substantial amounts of
greenhouse gases may be emitted.
Construction of a hydroelectric complex can have significant
environmental impact, principally in loss of arable land and
population displacement. They also disrupt the natural ecology
of the river involved, affecting habitats and ecosystems, and
siltation and erosion patterns. While dams can ameliorate the
risks of flooding, dam failure can be catastrophic.
II/ The origin
Hydropower has been used since ancient times to grind flour
and perform other tasks. In the late 18th century hydraulic
power provided the energy source needed for the start of the
Industrial Revolution. In the mid-1770s, French engineer
Bernard Forest de Bélidor published Architecture
Hydraulique, which described vertical- and horizontal-axis
hydraulic machines, and in 1771 Richard Arkwright’s
combination of water power, the water frame, and continuous
production played a significant part in the development of the
factory system, with modern employment practices. In the
1840s the hydraulic power network was developed to generate
and transmit hydro power to end users.
By the late 19th century, the electrical generator was
developed and could now be coupled with hydraulics.[9] The
growing demand arising from the Industrial Revolution would
drive development as well.[10] In 1878, the world's first
hydroelectric power scheme was developed at Cragside in
Northumberland, England, by William Armstrong. It was used
to power a single arc lamp in his art gallery. The old
Schoelkopf Power Station No. 1, US, near Niagara Falls,
began to produce electricity in 1881. The first Edison
hydroelectric power station, the Vulcan Street Plant, began
operating September 30, 1882, in Appleton, Wisconsin, with
an output of about 12.5 kilowatts. By 1886 there were 45
hydroelectric power stations in the United States and Canada;
and by 1889 there were 200 in the United States alone.
At the beginning of the 20th century, many small hydroelectric
power stations were being constructed by commercial
companies in mountains near metropolitan areas. Grenoble,
France held the International Exhibition of Hydropower and
Tourism, with over one million visitors. By 1920, when 40%
of the power produced in the United States was hydroelectric,
the Federal Power Act was enacted into law. The Act created
the Federal Power Commission to regulate hydroelectric
power stations on federal land and water. As the power
stations became larger, their associated dams developed
additional purposes, including flood control, irrigation and
navigation. Federal funding became necessary for large-scale
development, and federally owned corporations, such as the
Tennessee Valley Authority (1933) and the Bonneville Power
Administration (1937) were created. Additionally, the Bureau
of Reclamation which had begun a series of western US
irrigation projects in the early 20th century, was now
constructing large hydroelectric projects such as the 1928
Hoover Dam. The United States Army Corps of Engineers
was also involved in hydroelectric development, completing
the Bonneville Dam in 1937 and being recognized by the
Flood Control Act of 1936 as the premier federal flood control
agency.
Conventional (dams)
Most 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. A large pipe
(the "penstock") delivers water from the reservoir to the
turbine.
A / Pumped-storage
This method produces electricity to supply high peak demands
by moving water between reservoirs at different elevations. At
times of low electrical demand, the excess generation capacity
is used to pump water into the higher reservoir, thus providing
demand side response. When the demand becomes greater,
water is released back into the lower reservoir through a
turbine. In 2021 pumped-storage schemes provided almost
85% of the world's 190 GW of 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.
C/Run-of-the-rive
Run-of-the-river hydroelectric stations are those with small or
no reservoir capacity, so that only the water coming from
upstream is available for generation at that moment, and any
oversupply must pass unused. A constant supply of water from
a lake or existing reservoir upstream is a significant advantage
in choosing sites for run-of-the-river.
B/Tide
A tidal power station 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 water wheels.
Tidal power is viable in a relatively small number of locations
around.
III/Advantages
A/Flexibility
Hydropower is a flexible source of electricity since stations
can be ramped up and down very quickly to adapt to changing
energy demands.[23] Hydro turbines have a start-up time of
the order of a few minutes.[29] Although battery power is
quicker its capacity is tiny compared to hydro.[3] It takes less
than 10 minutes to bring most hydro units from cold start-up
to full load; this is quicker than nuclear and almost all fossil
fuel power.[30] Power generation can also be decreased
quickly when there is a surplus power generation.[31] Hence
the limited capacity of hydropower units is not generally used
to produce base power except for vacating the flood pool or
meeting downstream needs.[32] Instead, it can serve as
backup for non-hydro generators.[31]
B/High value power
The major advantage of conventional hydroelectric dams with
reservoirs is their ability to store water at low cost for dispatch
later as high value clean electricity. In 2021 the IEA estimated
that the "reservoirs of all existing conventional hydropower
plants combined can store a total of 1 500 terawatt-hours
(TWh) of electrical energy in one full cycle" which was
"about 170 times more energy than the global fleet of pumped
storage hydropower plants".[3] Battery storage capacity is not
expected to overtake pumped storage during the 2020s.[3]
When used as peak power to meet demand, hydroelectricity
has a higher value than baseload power and a much higher
value compared to intermittent energy sources such as wind
and solar.
Hydroelectric stations have long economic lives, with some
plants still in service after 50–100 years.Operating labour cost
is also usually low, as plants are automated and have few
personnel on site during normal operation.
Where a dam serves multiple purposes, a hydroelectric station
may be added with relatively low construction cost, providing
a useful revenue stream to offset the costs of dam operation. It
has been calculated that the sale of electricity from the Three
Gorges Dam will cover the construction costs after 5 to 8
years of full generation. However, some data shows that in
most countries large hydropower dams will be too costly and
take too long to build to deliver a positive risk adjusted return,
unless appropriate risk management measures are put in place.
C/Suitability for industrial applications
While many hydroelectric projects supply public electricity
networks, some are created to serve specific industrial
enterprises. Dedicated hydroelectric projects are often built to
provide the substantial amounts of electricity needed for many
industrial applications.
D/Reduced CO2 emissions
Since hydroelectric dams do not use fuel, power generation
does not produce carbon dioxide. While carbon dioxide is
initially produced during construction of the project, and some
methane is given off annually by reservoirs, hydro has one of
the lowest lifecycle greenhouse gas emissions for electricity
generation. The low greenhouse gas impact of hydroelectricity
is found especially in temperate climates. Greater greenhouse
gas emission impacts are found in the tropical regions because
the reservoirs of power stations in tropical regions produce a
larger amount of methane than those in temperate areas
Like other non-fossil fuel sources, hydropower also has no
emissions of sulfur dioxide, nitrogen oxides, or other
particulates.
E/Other uses of the reservoir
Reservoirs created by hydroelectric schemes often provide
facilities for water sports, and become tourist attractions
themselves. In some countries, aquaculture in reservoirs is
common. Multi-use dams installed for irrigation support
agriculture with a relatively constant water supply. Large
hydro dams can control floods, which would otherwise affect
people living downstream of the project. Managing dams
which are also used for other purposes, such as irrigation, is
complicated.
IV/Disadvantages
A/Ecosystem damage and loss of land
Merowe Dam in Sudan. Hydroelectric power stations that use
dams submerge large areas of land due to the requirement of a
reservoir. These changes to land color or albedo, alongside
certain projects that concurrently submerge rainforests, can in
these specific cases result in the global warming impact, or
equivalent life-cycle greenhouse gases of hydroelectricity
projects, to potentially exceed that of coal power stations.
Large reservoirs associated with traditional hydroelectric
power stations result in submersion of extensive areas
upstream of the dams, sometimes destroying biologically rich
and productive lowland and riverine valley forests, marshland
and grasslands. Damming interrupts the flow of rivers and can
harm local ecosystems, and building large dams and reservoirs
often involves displacing people and wildlife.[23] The loss of
land is often exacerbated by habitat fragmentation of
surrounding areas caused by the reservoir.
Hydroelectric projects can be disruptive to surrounding
aquatic ecosystems both upstream and downstream of the
plant site. Generation of hydroelectric power changes 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 turbine
gates are often opened intermittently, rapid or even daily
fluctuations in river flow are observed.
B/Drought and water loss by evaporation
Drought and seasonal changes in rainfall can severely limit
hydropower. Water may also be lost by evaporation.
C/Siltation and flow shortage
When water flows it has the ability to transport particles
heavier than itself downstream. This has a negative effect on
dams and subsequently their power stations, particularly those
on rivers or within catchment areas with high siltation.
Siltation can fill a reservoir and reduce its capacity to control
floods along with causing additional horizontal pressure on the
upstream portion of the dam. Eventually, some reservoirs can
become full of sediment and useless or over-top during a flood
and fail.
Changes in the amount of river flow will correlate with the
amount of energy produced by a dam. Lower river flows will
reduce the amount of live storage in a reservoir therefore
reducing the amount of water that can be used for
hydroelectricity. The result of diminished river flow can be
power shortages in areas that depend heavily on hydroelectric
power. The risk of flow shortage may increase as a result of
climate change. One study from the Colorado River in the
United States suggest that modest climate changes, such as an
increase in temperature in 2 degree Celsius resulting in a 10%
decline in precipitation, might reduce river run-off by up to
40%.
D/Methane emissions (from reservoirs)
Lower positive impacts are found in the tropical regions. In
lowland rainforest areas, where inundation of a part of the
forest is necessary, it has been noted that the reservoirs of
power plants produce substantial amounts of methane. This is
due to plant material in flooded areas decaying in an anaerobic
environment and forming methane, a greenhouse gas.
According to the World Commission on Dams report, where
the reservoir is large compared to the generating capacity and
no clearing of the forests in the area was undertaken prior to
impoundment of the reservoir, greenhouse gas emissions from
the reservoir may be higher than those of a conventional oil-
fired thermal generation plant.
E/Relocation
Another disadvantage of hydroelectric dams is the need to
relocate the people living where the reservoirs are planned. In
2000, the World Commission on Dams estimated that dams
had physically displaced 40-80 million people worldwide.
Comparison and interactions with other methods of power
generation
Hydroelectricity eliminates the flue gas emissions from fossil
fuel combustion, including pollutants such as sulfur dioxide,
nitric oxide, carbon monoxide, dust, and mercury in the coal.
Hydroelectricity also avoids the hazards of coal mining and
the indirect health effects of coal emissions.
Nuclear power
Nuclear power is relatively inflexible; although it can reduce
its output reasonably quickly. Since the cost of nuclear power
is dominated by its high infrastructure costs, the cost per unit
energy goes up significantly with low production. Because of
this, nuclear power is mostly used for baseload. By way of
contrast, hydroelectricity can supply peak power at much
lower cost. Hydroelectricity is thus often used to complement
nuclear or other sources for load following. Country examples
where they are paired in a close to 50/50 share include the
electric grid in Switzerland, the Electricity sector in Sweden
and to a lesser extent, Ukraine and the Electricity sector in
Finland.
Wind power
Wind power goes through predictable variation by season, but
is intermittent on a daily basis. Maximum wind generation has
little relationship to peak daily electricity consumption, the
wind may peak at night when power isn't needed or be still
during the day when electrical demand is highest.
Occasionally weather patterns can result in low wind for days
or weeks at a time, a hydroelectric reservoir capable of storing
weeks of output is useful to balance generation on the grid.
Peak wind power can be offset by minimum hydropower and
minimum wind can be offset with maximum hydropower. In
this way the easily regulated character of hydroelectricity is
used to compensate for the intermittent nature of wind power.
Conversely, in some cases wind power can be used to spare
water for later use in dry seasons.
Conclusion
To sum up, we can keep in mind that hydroenergy is a
renewable energy which has such advantages and also
disadvantages. This energy like any others helps human in his
life and permit to do many things. Using renewable energy
can help to rebuild a new world where we could live
ecologically without destroying natural resources.
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