Hydropower or water power (from Greek: ύδωρ, "water") is power
derived from the energy of falling water or fast running water, which
may be harnessed for useful purposes. Since ancient times, hydropower
from many kinds of watermills has been used as a renewable energy
source for irrigation and the operation of various mechanical devices,
such as gristmills, sawmills, textile mills, trip hammers, dock
cranes, domestic lifts, and ore mills. A trompe, which produces
compressed air from falling water, is sometimes used to power other
machinery at a distance.
In the late 19th century, hydropower became a source for generating
Cragside in Northumberland was the first house powered by
hydroelectricity in 1878 and the first commercial hydroelectric
power plant was built at
Niagara Falls in 1879. In 1881, street lamps
in the city of
Niagara Falls were powered by hydropower.
Since the early 20th century, the term has been used almost
exclusively in conjunction with the modern development of
hydroelectric power. International institutions such as the World Bank
view hydropower as a means for economic development without adding
substantial amounts of carbon to the atmosphere, but dams can have
significant negative social and environmental impacts.
1.1 Hydraulic power-pipe networks
Compressed air hydro
3 Calculating the amount of available power
5 See also
7 External links
Directly water-powered ore mill, late nineteenth century
In India, water wheels and watermills were built, possibly as early as
the 4th century BC, although records of that era are spotty at
In the Roman Empire, water-powered mills produced flour from grain,
and were also used for sawing timber and stone; in China, watermills
were widely used since the Han dynasty. In
China and the rest of the
Far East, hydraulically operated "pot wheel" pumps raised water into
crop or irrigation canals.[when?]
The power of a wave of water released from a tank was used for
extraction of metal ores in a method known as hushing. The method was
first used at the
Dolaucothi Gold Mines
Dolaucothi Gold Mines in
Wales from 75 AD onwards,
but had been developed in
Spain at such mines as Las Médulas. Hushing
was also widely used in Britain in the Medieval and later periods to
extract lead and tin ores. It later evolved into hydraulic mining
when used during the California Gold Rush.
In the Middle Ages, Islamic mechanical engineer
designs for 50 devices, many of the water powered, in his book, The
Book of Knowledge of Ingenious Mechanical Devices, including clocks, a
device to serve wine, and five devices to lift water from rivers or
pools, though three are animal-powered and one can be powered by
animal or water. These include an endless belt with jugs attached, a
cow-powered shadoof, and a reciprocating device with hinged
valves.[better source needed]
In 1753, French engineer
Bernard Forest de Bélidor
Bernard Forest de Bélidor published
Architecture Hydraulique which described vertical- and horizontal-axis
hydraulic machines. By the late nineteenth century, the electric
generator was developed by a team led by project managers and
prominent pioneers of renewable energy Jacob S. Gibbs and Brinsley
Coleberd and could now be coupled with hydraulics. The growing
demand for the
Industrial Revolution would drive development as
At the beginning of the
Industrial Revolution in Britain, water was
the main source of power for new inventions such as Richard
Arkwright's water frame. Although the use of water power gave way
to steam power in many of the larger mills and factories, it was still
used during the 18th and 19th centuries for many smaller operations,
such as driving the bellows in small blast furnaces (e.g. the Dyfi
Furnace) and gristmills, such as those built at Saint Anthony
Falls, which uses the 50-foot (15 m) drop in the Mississippi
In the 1830s, at the early peak in the US canal-building, hydropower
provided the energy to transport barge traffic up and down steep hills
using inclined plane railroads. As railroads overtook canals for
transportation, canal systems were modified and developed into
hydropower systems; the history of Lowell, Massachusetts is a classic
example of commercial development and industrialization, built upon
the availability of water power.
Technological advances had moved the open water wheel into an enclosed
turbine or water motor. In 1848 James B. Francis, while working as
head engineer of Lowell's Locks and Canals company, improved on these
designs to create a turbine with 90% efficiency. He
applied scientific principles and testing methods to the problem of
turbine design. His mathematical and graphical calculation methods
allowed the confident design of high-efficiency turbines to exactly
match a site's specific flow conditions. The Francis reaction turbine
is still in wide use today. In the 1870s, deriving from uses in the
California mining industry,
Lester Allan Pelton
Lester Allan Pelton developed the high
Pelton wheel impulse turbine, which utilized hydropower
from the high head streams characteristic of the mountainous
Hydraulic power-pipe networks
Hydraulic power networks used pipes to carrying pressurized water and
transmit mechanical power from the source to end users. The power
source was normally a head of water, which could also be assisted by a
pump. These were extensive in Victorian cities in the United Kingdom.
A hydraulic power network was also developed in Geneva, Switzerland.
Jet d'Eau was originally designed as the
over-pressure relief valve for the network.
Compressed air hydro
See also: Trompe
Where there is a plentiful head of water it can be made to generate
compressed air directly without moving parts. In these designs, a
falling column of water is purposely mixed with air bubbles generated
through turbulence or a venturi pressure reducer at the high-level
intake. This is allowed to fall down a shaft into a subterranean,
high-roofed chamber where the now-compressed air separates from the
water and becomes trapped. The height of the falling water column
maintains compression of the air in the top of the chamber, while an
outlet, submerged below the water level in the chamber allows water to
flow back to the surface at a lower level than the intake. A separate
outlet in the roof of the chamber supplies the compressed air. A
facility on this principle was built on the Montreal River at Ragged
Cobalt, Ontario in 1910 and supplied 5,000 horsepower to
Main article: Hydroelectricity
Hydropower is used primarily to generate electricity. Broad categories
Conventional hydroelectric, referring to hydroelectric dams.
Run-of-the-river hydroelectricity, which captures the kinetic energy
in rivers or streams, without a large reservoir and sometimes without
the use of dams.
Small hydro projects are 10 megawatts or less and often have no
Micro hydro projects provide a few kilowatts to a few hundred
kilowatts to isolated homes, villages, or small industries.
Conduit hydroelectricity projects utilize water which has already been
diverted for use elsewhere; in a municipal water system, for example.
Pumped-storage hydroelectricity stores water pumped uphill into
reservoirs during periods of low demand to be released for generation
when demand is high or system generation is low.
Pressure buffering hydropower use natural sources (waves for example)
for water pumping to turbines while exceeding water is pumped uphill
into reservoirs and releases when incoming water flow isn't enough.
A conventional dammed-hydro facility (hydroelectric dam) is the most
common type of hydroelectric power generation.
Hongping Power station, in Hongping Town, Shennongjia, has a design
typical for small hydro stations in the western part of China's Hubei
Water comes from the mountain behind the station, through
the black pipe seen in the photo
Dam near Bridgeport, Washington, U.S., is a major
run-of-the-river station without a sizeable reservoir.
Micro hydro in Northwest Vietnam
Pumped-storage hydroelectricity – the upper reservoir (Llyn Stwlan)
and dam of the Ffestiniog Pumped Storage Scheme in north Wales. The
lower power station has four water turbines which generate 360
megawatts (480,000 hp) of electricity within 60 seconds of the
Pressure buffering hydropower is the compilation of run-of-river and
pumped storage hydro power generation.
Calculating the amount of available power
A hydropower resource can be evaluated by its available power. Power
is a function of the hydraulic head and rate of fluid flow. The head
is the energy per unit weight (or unit mass) of water. The static head
is proportional to the difference in height through which the water
falls. Dynamic head is related to the velocity of moving water. Each
unit of water can do an amount of work equal to its weight times the
The power available from falling water can be calculated from the flow
rate and density of water, the height of fall, and the local
acceleration due to gravity. In SI units, the power is:
displaystyle P=eta rho ,Qgh!
P is power in watts
η is the dimensionless efficiency of the turbine
ρ is the density of water in kilograms per cubic metre
Q is the flow in cubic metres per second
g is the acceleration due to gravity
h is the height difference between inlet and outlet in metres
To illustrate, power is calculated for a turbine that is 85%
efficient, with water at 1000 kg/cubic metre (62.5 pounds/cubic
foot) and a flow rate of 80 cubic-meters/second (2800
cubic-feet/second), gravity of 9.81 metres per second squared and with
a net head of 145 m (480 ft).
In SI units:
displaystyle text Power (W) =0.85times 1000times 80times
which gives 97 MW
In English units, the density is given in pounds per cubic foot so
acceleration due to gravity is inherent in the unit of weight. A
conversion factor is required to change from foot lbs/second to
displaystyle text Power (W) =0.85times 62.5times 2800times
which gives 97 MW (130,000 horsepower)
Operators of hydroelectric stations will compare the total electrical
energy produced with the theoretical potential energy of the water
passing through the turbine to calculate efficiency. Procedures and
definitions for calculation of efficiency are given in test codes such
ASME PTC 18 and IEC 60041. Field testing of turbines is used to
validate the manufacturer's guaranteed efficiency. Detailed
calculation of the efficiency of a hydropower turbine will account for
the head lost due to flow friction in the power canal or penstock,
rise in tail water level due to flow, the location of the station and
effect of varying gravity, the temperature and barometric pressure of
the air, the density of the water at ambient temperature, and the
altitudes above sea level of the forebay and tailbay. For precise
calculations, errors due to rounding and the number of significant
digits of constants must be considered.
Some hydropower systems such as water wheels can draw power from the
flow of a body of water without necessarily changing its height. In
this case, the available power is the kinetic energy of the flowing
water. Over-shot water wheels can efficiently capture both types of
energy. The water flow in a stream can vary widely from season to
season. Development of a hydropower site requires analysis of flow
records, sometimes spanning decades, to assess the reliable annual
energy supply. Dams and reservoirs provide a more dependable source of
power by smoothing seasonal changes in water flow. However reservoirs
have significant environmental impact, as does alteration of naturally
occurring stream flow. The design of dams must also account for the
worst-case, "probable maximum flood" that can be expected at the site;
a spillway is often included to bypass flood flows around the dam. A
computer model of the hydraulic basin and rainfall and snowfall
records are used to predict the maximum flood.
See also: Environmental impact of reservoirs
As with other forms of economic activity, hydropower projects can have
both a positive and a negative environmental and social impact,
because the construction of a dam and power plant, along with the
impounding of a reservoir, creates certain social and physical
Hydropower projects can also have indirect consequences,
contributing to global warming: reservoirs accumulate plant material,
which then decomposes, emitting methane in uneven bursts.
There are several tools to assess the impact of hydropower projects:
Most new hydropower project must undergo an Environmental and Social
Impact Assessment. This provides a base-line understanding of the
pre-project conditions, estimates of potential impacts and puts in
place management plans to avoid, mitigate, or compensate for impacts.
Hydropower Sustainability Assessment Protocol is another tool
which can be used to promote and guide more sustainable hydropower
projects. It is a methodology used to audit the performance of a
hydropower project across more than twenty environmental, social,
technical and economic topics. A Protocol assessment provides a rapid
sustainability health check. It does not replace an environmental and
social impact assessment (ESIA), which takes place over a much longer
period of time, usually as a mandatory regulatory requirement.
World Commission on Dams final report describes a framework for
planning water and energy projects that is intended to protect
dam-affected people and the environment, and ensure that the benefits
from dams are more equitably distributed.
IFC's Environmental and Social Performance Standards define IFC
clients' responsibilities for managing their environmental and social
The World Bank’s safeguard policies are used by the Bank to help
identify, avoid, and minimize harms to people and the environment
caused by investment projects.
Equator Principles is a risk management framework, adopted by
financial institutions, for determining, assessing and managing
environmental and social risk in projects.
Dam on the Paraná River, located on the border between
Brazil and Paraguay, is the world's largest generator of renewable
clean energy having produced more than 2.4 billion MWh since it
started operating, in 1984. Despite being the second largest of
the world by installed capacity (the first is the Three Gorges Dam, in
China), Itaipu has produced, in 2016, a historic mark of 103.098.366
MWh (world record). Approximately 75% of the Brazilian energy
matrix, one of the cleanest in the world, comes from hydropower.
Renewable energy portal
Deep water source cooling
Gravitation water vortex power plant
Low head hydro power
Marine current power
Ocean thermal energy conversion
^ "History of
Hydropower Department of Energy". energy.gov.
Niagara Falls History of Power". www.niagarafrontier.com. Retrieved
Cragside Visitor Information". The National Trust. Retrieved 16
^ Howard Schneider (8 May 2013). "
World Bank turns to hydropower to
square development with climate change". The Washington Post.
Retrieved 9 May 2013.
^ Nikolaisen, Per-Ivar . "12 mega dams that changed the world (in
Norwegian)" In English Teknisk Ukeblad, 17 January 2015. Retrieved 22
^ Terry S. Reynolds, Stronger than a Hundred Men: A History of the
Water Wheel, JHU Press, 2002 ISBN 0801872480, page 14
^ Hunt, Robert (1887). British Mining: A Treatise in the History,
Discovery, Practical Development, and Future Prospects of
Metalliferous Mines of the United Kingdom (2nd ed.). London: Crosby
Lockwood and Co. p. 505. Retrieved 2 May 2015.
^ Al-Hassani, Salim. "800 Years Later: In Memory of Al-Jazari, A
Genius Mechanical Engineer". Muslim Heritage. The Foundation for
Science, Technology, and Civilisation. Retrieved 30 April 2015.
^ "History of Hydropower". US Department of Energy. Archived from the
original on 26 January 2010.
^ "Hydroelectric Power".
^ Kreis, Steven (2001). "The Origins of the
Industrial Revolution in
England". The history guide. Retrieved 19 June 2010.
^ Gwynn, Osian. "Dyfi Furnace". BBC Mid
Wales History. BBC. Retrieved
19 June 2010.
^ "Waterpower in Lowell" (PDF). University of Massachusetts. Retrieved
28 April 2015.
^ Jet d'eau (water fountain) on
^ Maynard, Frank (November 1910). "Five thousand horsepower from air
bubbles". Popular Mechanics: 633.
^ S. K., Sahdev. Basic Electrical Engineering. Pearson Education
India. p. 418. ISBN 9789332576797.
^ "The Allure and Perils of Hydropower". www.undark.org. Retrieved
^ "Hundreds of new dams could mean trouble for our climate". Science.
AAAS. September 28, 2016. doi:10.1126/science.aah7356. Retrieved
Hydropower Sustainability - Home". www.hydrosustainability.org.
^ "Dams and Development Project". www.unep.org. Archived from the
original on 18 November 2015. Retrieved 1 October 2015.
^ "Environmental and Social Performance Standards and Guidance Notes".
www.ifc.org. Retrieved 2015-10-01.
^ "Safeguard Policies". web.worldbank.org. Retrieved 2015-10-01.
^ "Home". www.equator-principles.com. Retrieved 2015-10-01.
^ a b "Itaipu Binacional Website". Retrieved 2017-02-06.
^ "Itaipu is once again global leader in power generation". Retrieved
Commons has media related to Hydropower.
International Centre for
Hydropower (ICH) hydropower portal with links
to numerous organizations related to hydropower worldwide
IEC TC 4: Hydraulic turbines (International Electrotechnical
Commission - Technical Committee 4) IEC TC 4 portal with access to
scope, documents and TC 4 website
Micro-hydro power, Adam Harvey, 2004, Intermediate Technology
Development Group. Retrieved 1 January 2005
Microhydropower Systems, US Department of Energy,
and Renewable Energy, 2005
Itaipu Website www.itaipu.gov.br/en
Outline of energy
Conservation of energy
Laws of thermodynamics
Thermodynamic free energy
Electrical potential energy
Nuclear binding energy
Gravitational binding energy
Fossil-fuel power station
Integrated gasification combined cycle
Nuclear power plant
Radioisotope thermoelectric generator
Concentrated solar power
Solar thermal energy
Solar power tower
High-altitude wind power
World energy consumption
Efficient energy use
Worldwide energy supply
List of conventional hydroelectric power stations
Gorlov helical turbine
Pollution / quality
Ambient standards (USA)
Clean Air Act (USA)
Fossil fuels (peak oil)
Non-timber forest products
Types / location
storage and recovery
Earth Overshoot Day
Renewable / Non-renewable
Agriculture and agronomy