Hydropower

Archaeological evidence dates water wheels and watermills in the ancient Near East to the 4th century BC, with related irrigation machinery attributed to Sumer and Babylonia. Studies suggest the water wheel was the initial form of water power, the ancestor of all later hydropower machinery.

The Roman writer Vitruvius set out descriptions of water-powered mills by the first century BC. Roman practice scaled up substantially: the Barbegal mill in modern France ran 16 water wheels and processed up to 28 tons of grain a day.

The Jijiupian dictionary of 40 BC, followed by Yang Xiong's Fangyan and Huan Tan's Xin Lun, describe the Hun waterwheel used in Han China. Historians argue waterwheels rather than water scoops drove blast furnace bellows, since scoops would have lacked the motive force.

The Han engineer Du Shi, active around AD 31, connected waterwheels to piston-bellows in iron forging. This marked one of the earliest industrial applications of hydropower to metallurgy.

From AD 75 onwards, torrents of water were released at Dolaucothi in Wales to strip ground and reveal ore. The technique spread to Spanish mines such as Las Medulas, was used in medieval Britain for lead and tin, and evolved into hydraulic mining during the 19th-century California Gold Rush.

The Hierapolis sawmill used a waterwheel driving two crank-and-connecting rods to power two marble saws, converting rotary into linear motion. Comparable Eastern Roman sawmills were excavated at Ephesus and Gerasa from the 6th century.

Greek sources record the transfer of Roman water mills and bath technology to India in the early 4th century AD. Dams, spillways, reservoirs, channels and water balance works subsequently developed under the Mauryan, Gupta and Chola empires.

During the Islamic Golden Age and the Arab Agricultural Revolution hydropower was widely developed, with fulling, paper, sugar, steel, stamp and tide mills, plus early tidal power and large hydraulic factory complexes. Muslim engineers used water turbines, gearing, and pioneered dams as a source of water power. By the 11th century every province of the empire had such industrial mills in operation.

The Muslim mechanical engineer Al-Jazari documented water-powered clocks, wine-serving automata and five water-lifting machines. His designs included an endless belt with jugs attached and a reciprocating device with hinged valves, codifying hydraulic engineering knowledge.

At the start of the Industrial Revolution water drove new textile machinery such as the water frame. Even after steam displaced water in larger mills, water power persisted through the 18th and 19th centuries in small blast furnaces and gristmills, including those exploiting the 50-foot drop at Saint Anthony Falls on the Mississippi.

The French engineer's treatise systematised the design of hydraulic machinery on both axis orientations. It provided an engineering reference as water power entered the industrial era.

The French engineer's turbine design established the basic machine of hydroelectric generation. A Fourneyron unit was installed in the commercial plant at Niagara Falls in 1895 and is reported still to be operating.

As head engineer of Lowell's Locks and Canals company, Francis applied scientific principles and systematic testing to turbine design, moving hydropower from the open water wheel to the enclosed turbine. His mathematical and graphical methods allowed turbines to be matched confidently to a site's flow conditions, and the Francis turbine remains in use.

Deriving from Californian mining practice, Pelton's impulse wheel exploited the high-head streams of the Sierra Nevada. It complemented reaction turbines by making steep, low-flow sites economically usable.

After the British occupation of Egypt in 1882 the two states constructed the first Aswan Dam, raising it in 1912 and again in 1934 to hold back Nile floods. This established the Nile as a contested site of hydropower and water control by both riparian and foreign actors.

Small hydropower was central to early electrification in parts of Africa, powering South African gold mines and the region's first electric railway. Zimbabwean farmers installed their own small hydropower stations in the 1930s before national grids displaced them.

The company struggled to transmit electricity far enough from the falls to reach enough customers to justify installation. The project succeeded largely because of Nikola Tesla's alternating current motor, which made long-distance delivery of hydroelectricity viable and inspired bolder schemes worldwide.

Hydropower remained the leading renewable electricity source by installed capacity. As of 2019 the five largest power stations in the world were all conventional hydroelectric plants with dams.

Ethiopia had sought US assistance for Nile irrigation and hydropower in the 1960s, but progress stalled with the 1974 coup and the 17-year civil war. Construction from 2011 revived its claim on Nile hydropower.

The study examined rain power as a potential hydropower niche. Commentators judged collecting roof runoff to drive a turbine more practical, with an estimated 3 kWh a year from a 185 square metre roof.

Capacity at the Inga plant on the Congo River had declined under Mobutu's failure to maintain it; the power pool introduced coordinated maintenance and cross-border transmission. States with abundant hydropower such as the DRC and Ghana sell excess power to neighbours through such arrangements.

Opposition deterred government and private investors and gave rise to NGOs dedicated to fighting dams. Together with rising costs, this checked the mid-century era of large-dam expansion.

Over this period the dam supplied a third of national power. It demonstrated the scale of national dependence a single hydropower scheme could create.

Countries had largely abandoned small hydropower systems by the 1930s in favour of large dams and national grids. Government subsidies and a push for more independent energy producers revived small plants in the 1970s.

Costs climbed because of rising construction expense and the dwindling supply of high-quality sites, while other energy sources became cheaper. By the 1990s only 18% of the world's electricity came from hydropower.

Tidal schemes appeared as a new branch of hydropower in the 1960s. It has not since taken hold as a strong energy contender.

Campaigns based on environmental concerns defeated proposed dams in Dinosaur National Monument and the Grand Canyon, even as the Reclamation Bureau and Army Corps built over 150 new dams across the American West into the 1970s. Environmental legislation of the 1970s gave opponents further tools, and hydropower gradually faded in American importance as nuclear and fossil fuels grew.

Nasser's government adopted engineer Adriano Daninos's plan, modelled on the Tennessee Valley Authority's multipurpose dams, and publicised it as economic development. American refusal to fund and British withdrawal left Soviet finance decisive, making hydropower a Cold War instrument. The dam flooded part of Sudan and triggered a Nile-sharing dispute between Sudan and Egypt.

The dam symbolically linked hydropower to the job creation and economic growth priorities of the New Deal. The federal government followed quickly with the Shasta and Grand Coulee dams, and electricity from all three fed war production during the Second World War.

The scheme was prompted in part by the loss of coal reserves after the First World War. German dams originally built for flood control and irrigation, such as the Urft, Mohne and Eder, found hydropower an added benefit, especially in the coal-poor south.

Despite the valley's protection within a national park, the city defeated the Sierra Club and secured rights after a prolonged fight with the federal government. Hetch Hetchy hydropower and water reached San Francisco a decade later at twice the promised cost, with power sold to PG&E and resold at a profit.

Built near Cobalt, Ontario, the plant used falling water to produce compressed air that was transmitted to mines. It showed hydropower could be delivered as pneumatic rather than electrical energy.

The English engineer's hydro-powered station at his Northumberland house was the first private electrical power station. It demonstrated domestic-scale hydroelectric generation.

Some 12,000 watermills operated in the Po watershed in the 1890s, but the 1898 plant marked the transition from mechanical to electrical hydropower. Large plants shifted power from rural mountain areas to urban centres on the plain, and Italy pursued near-nationwide electrification almost entirely from hydropower.