Hydroelectric power, or hydropower as it’s generally called, is the dominant source of renewable energy used to produce electricity—accounting for almost two thirds of the electricity generated from all renewable sources of energy worldwide. However, global additions to capacity in 2017 were a modest 21.9 GW—a lot less than the additional capacity registered by solar and wind. In other words, solar energy and wind power are the fastest growing sources of clean renewable energy.
The top ten countries for installed hydroelectric power capacity are shown in the table 
Together these countries account for 68 % of the global total installed hydropower capacity. The East Asia and Pacific region added the most capacity in 2017—mainly as a result of the 9.1 GW brought online by China. Next in line was Brazil (+3.4 GW), India (+1.9 GW), Portugal (+1.1 GW) and Angola (+1.0 GW). R
In North and Central America, the increase in hydropower capacity was modest compared to the other regions—but a notable feature was the increased focus on pumped storage projects. About 510 MW of new capacity was brought online in 2017, about a quarter of which was pumped storage. In Canada, major storage projects under construction include the Keeyask plant in Manitoba, Site C in British Columbia (1100 MW), Muskrat Falls in Newfoundland and Labrador, and Romain-4 in Quebec.
In the US, 140 MW of capacity was added through retrofits to existing facilities. 139 MW of pumped storage capacity was added at the Northfield Mountain Unit in Massachusetts and the Ludington plant in Michigan. In the Dominican Republic, work was underway on a small 10.7 MW installation at Hatillo on the Rio Yuna.
In South America, over 4 GW of capacity was added in 2017. In Brazil, although 3.38 GW was added, the country decommissioned several large installations from its 1-year pipeline of projects—reportedly in favour of pursuing more decentralized renewable energy.
In Africa—the continent with the largest untapped potential for hydropower development, development is slow but steady. Only 1.9 GW of capacity was added. Angola commissioned power generation units for the 2 GW Lauca hydropower plant, and a second power plant at Cambambe. Cote d’Ivoire commissioned the 275 MW Soubre plant; in Sudan the Upper Atbara and Seitt dam project was completed; while across in Zimbabwe, the first unit of the Kariba South extension project was commissioned.
Hydropower is the largest source of renewable energy in Europe—and an additional 2.3 GW of capacity came online in 2017. About half of this capacity was pumped storage. For instance, Portugal commissioned two pumped storage projects: Foz Tua (263 MW) and Frades II (780 MW).
South and Central Asia saw over 3.2 GW of capacity added in 2017, with over half of this capacity commissioned in India—including the 1.2 GW Teesta II project in the north-east state of Sikkim. Other hydropower projects were commissioned in Russia, Iran, Georgia and Nepal.
In East Asia and the Pacific region, the narrative is all about China. Over 90 % of the total added capacity of 9.8 GW was commissioned in China—which increased its total installed capacity to 341 GW. Australia announced plans to expand the 4.1 GW Snowy Mountains Scheme—a pumped storage installation that links two large dams and which would effectively operate as a giant 2 GW battery. Smaller projects are underway in Vietnam, Cambodia, and Papua New Guinea.P
The energy storage capability of hydropower installations has always been a crucial component of modern energy infrastructure. Hydropower reservoirs can store energy by reducing output when other sources of power are available, or alternatively, pumped storage can directly absorb surplus power from the grid.
The growing penetration of variable renewable energy (mainly wind and solar) is raising interest in pumped storage capacity—due to its ability to absorb excess power generated by wind and solar, and to avoid curtailment of wind farm power when the grid is overloaded. Global pumped storage capacity rose by more than 3 GW in 2017 for a year-end total of 153 GW. New capacity was installed in China, Portugal, and Switzerland.
In China, two large pumped storage plants were completed in 2017. The five remaining reversible turbine generators of the Liyang facility were operational by the end of 2017 for a total of 1.5 GW of pumping capacity. China also completed the first of 300 MW of a 1.2 GW storage plant in Shenzhen City—the country’ first large scale pumped storage facility too be built within an urban environment.
Also in 2017, Portugal’s 780 MW Frades II and the 263 MW Foz Tua pumped storage plants both came online. The larger Frades II plant has two variable-speed turbines—which respond faster to voltage variations on the grid. Many projects in Europe are now incorporating variable speed turbines for flexibility, and a wider operating range—characteristics useful for accommodating increased levels of variable renewable energy.
Scotland is the location of over 90% of the UK’s hydropower. Two of the UK’s four pumped storage hydro facilities are located in Scotland. The Cruachan installation is located within the 1126 meter high Ben Cruachan mountain on the shore of Loch Awe, and the Foyers installation is on the shore of Loch Ness. The two sites have a generating capacity of 440 MW and 300 MW respectively.
Greenhouse gas emissions
Does hydropower produce greenhouse gases? It seems unlikely if you just consider the electrical power generation—where no fuel is burned and there are no emissions. But large reservoirs of water that have inundated extensive areas of land can potentially produce emissions of methane.
The question has always been : how much? A 2014 article in Scientific American claimed that global methane emissions from hydropower reservoirs could be about the same as methane emissions from burning fossil fuels—somewhere around 100 million tonnes a year. If that estimate is correct, then utility-scale hydropower plants requiring large reservoirs and pumped storage installations are very significant sources of methane which is a strong greenhouse gas.
Attempting to answer this question more precisely, in 2017 the International Hydropower Association (IHA) conducted a study of 498 reservoirs worldwide. The study measured emissions from hydropower reservoirs in boreal, temperate, subtropical and tropical climates in more than 50 countries. The results of the study showed a very large range of values: from less than 1 gram of GHG emissions per kWh of energy output to as much as 1000 g per kWh. For reference, the table shows the median values for GHG emissions for several sources of energy .
The value shown for hydropower in the table is the median value—which means that half the measured values were below 18.5—and half were above. But the majority of installations, 84 % of reservoirs, showed emissions of less than 100 gCO2e/kWh.
The IHA study confirms what we knew–that hydropower can produce significant emissions of greenhouse gases—but at a level that is, on average, considerably less than fossil fuel power plants. The range of values however is very large—which means that some hydropower plants around the world emit just as much greenhouse gases as natural gas and coal-fired power plants.
Flooding extensive areas of land nearly always comes with very considerable environmental, social, and economic impacts. Large dams are notorious for creating long-lasting conflicts, and sparking protests from the communities that are displaced, and by people whose livelihoods are disrupted by the flooded land. Where a river runs through several countries—like the Nile, constructing a large dam upstream–like the Grand Ethiopian Renaissance Dam the Ethiopian government is building on the Blue Nile–can also create serious international disagreements: Egypt is legitimately worried that the flow of the River Nile will be disrupted and diminished, and that this will cause social and economic problems for farmers dependent on the river for irrigation—particularly in the Nile delta .
The Grand Ethiopian Renaissance Dam project is huge. When completed it will have an installed capacity of 6450 MW and will be the largest hydropower plant in Africa. It will flood about 1700 km2 of forested land and displace about 20,000 people.
Writing in the 2018 Hydropower Status Report, the Ethiopian Minister of Water, Irrigation and Electricity, Seleshi Bekele, stated:
By 2025, electricity access is expected to reach 100 percent in both rural and urban areas of Ethiopia. To attain this, electrification enables the provision of affordable electricity to poor households who are forced to use fuelwood to meet their energy needs. 
But massive hydropower projects are not the solution to providing electricity to rural communities. The cost of the transmission and distribution of centrally generated electricity to poor villagers is nearly always totally uneconomic. Only distributed systems—like photovoltaic minigrid systems—can realistically provide power to dispersed rural communities in a country as large as Ethiopia.
Closer to home in North America, the Site C hydroelectric plant in British Columbia, Canada, continues to be hugely controversial. The Site C dam is a large earth-fill dam on the Peace River near Fort St. John in northwest British Columbia. The plant has a rated capacity of 1100 MW and will cost at least $9 billion CAD. The dam will flood about 93 km2 of land. It is due for completion in 2020.
The project has generated considerable opposition because of the flooding of a large area of agricultural land, the lack of support from First Nations groups and local landowners, the high cost of the project compared to alternatives, and its environmental impact.
Two Treaty 8 First Nations and local landowners made legal challenges to the dam; these were eventually dismissed by a Federal Court of Appeal. In an unprecedented move, 250 Canadian scholars as well as the President of the Royal Society of Canada wrote to the Canadian government in May 2016 expressing their concerns about the approval procedures and the environmental assessment process. However, the Federal government refused to review the approval of the project, and in December 2017, the Premier of British Columbia decided finally to authorize the completion of the project.
But what is evident is that practically all large hydroelectric projects create conflicts that can seriously delay construction and substantially increase costs. The number of people displaced by large dams can run into the hundreds of thousands . Cost overruns on large hydropower projects are the norm—not the exception.
Hydropower used to be the only renewable energy technology capable of generating hundreds of megawatts of power—apart from nuclear energy. But this is no longer the case. Utility-scale photovoltaic power plants, concentrating solar power systems, and offshore and onshore wind farms are capable of generating almost as much power—at less cost, with quicker completion (months not years), and with much less social, cultural, and environmental impact and disruption.
For more information check out these sources:
 See the Hydropower Status Report 2018. International Hydropower Association. Available at: //www.hydropower.org/publications/2018-hydropower-status-report
 Hydropower Status Report 2018. Op. cit
 Hydropower Status Report 2018. Op. cit. page 12.
 Hydropower Status Report 2018. Op.cit.
 Renewables 2018 Global Status Report. Op. cit.
 Renewables 2018 Global Status Report. Op.cit
8] See: Methane emissions may swell from behind dams. Accessed at : //scientificamerican.com/article/methane-emissions-may-swell-from-behind-dams/
 Hydropower Status Report 2018. Op.cit.
 See: Egypt’s rice farmers see rough times downstream of new Nile mega-dam, at : //www.yahoo.com/news/egypts-rice-farmers-see-rough-times-downstream-nile-1603341997.html
 See the Wikipedia article: Site C dam. Also the letter from the President of the Royal Society of Canada, available here: //rsc-src.ca/sites/default/files/pdf/PM_Trudeau_19.05.2016.pdf
 The record is held by China’s Three Gorges dam which reportedly displaced as many as 1.2 million people. See: //theguardiancom/environment/blog/2015/jan/12/12-dams-that-changed-the-world-hoover-sardar-sarovar-three-gorges