Small hydro is the generation of hydroelectric power on a smaller scale as compared to traditional large-scale hydro. Exact definitions vary by country, but small hydro power (SHP) projects are typically less than 50 megawatts (MW) and can be further subdivided by scale into "mini" (<500 kW), "micro" (<100 kW), and "pico" (<10 kW). Maximum power generation capacity is the primary factor of SHP classification. Factors like dam height, weir height, reservoir area, outlet structures and operating procedures are not standardized under this metric. SHP projects have grown rapidly in the past two decades. Quicker permitting processes can make them easier to develop and contribute to distributed generation in a regional electricity grid. Small hydro projects may be built in isolated areas that would be uneconomic to serve from a national electricity grid, or in areas where a national grid does not exist. They produce power on a scale suitable for local community use, promoting energy independence. Rural areas face challenges in SHP integration due to an absence of political focus, accurate data, and sustainable funding. The exact socio-environmental effects of smaller scale hydro are not yet fully understood. Many countries do not require environmental impact assessments for smaller installations.
Description The use of the term "small hydro" varies considerably around the world. In India, hydro projects with up to 25 MW capacities are categorized as Small Hydro Power (SHP) projects. In California, hydroelectric generating stations with a maximum capacity of less than 30 MW are classified as small and are eligible for inclusion in the state's renewable portfolio standard. The maximum limit is usually somewhere between 10 and 30 MW and is stretched up to 50 MW in Canada, China, Pakistan, and the United States.
A variety of project designs can be implemented for hydro projects with similar energy capacities. Some SHP projects utilize a run-of-river system. Others, such as the Iron Gate Dam, utilize impoundment systems which host the disadvantages associated with reservoirs. For investors, environmentalists, and policy makers small hydro projects are considered most viable when there is little ecological impact and projected profit after construction.
Advantages and disadvantages The primary advantages of small hydro development include low costs to build and the ability to remain disconnected from centralized power grids. Contentious points within small hydropower development include issues in environmental justice, regulatory oversight, and environmental impacts. In a number of communities which lack essential electricity access, small hydro offers a reliable source of decentralized electricity. Small hydro projects do not always require significant government assistance and gaps in governance allow them to be built fairly easily. Given these policy gaps, small hydropower as a renewable, climate mitigation strategy can also negatively affect local livelihoods in the absence of community-minded policy.
The environmental impacts of small hydropower projects are understudied. Within run-of-river design projects, the greatest harm for water systems are flow regime alteration, loss of river cohesion and connectivity, and habitat degradation affecting fish and macroinvertebrates.
Growth Between 2005 and 2010, China planned to electrify a further 10,000 villages under their China Village Electrification Program, including further investments in small hydro and photovoltaics. By 2010, China had 45,000 small hydro installations, especially in rural areas, producing 160 Twh annually. Over 50% of the world's potential small hydro power was found in Asia; however, a report noted that "It is possible in the future that more small hydropower potential might be identified both on the African and American continents". In the mountains and rain forests of British Columbia, Canada there are a great many sites suitable for hydro development. However environmental concerns towards large reservoirs after the 1980s halted new dam construction. The solution to coping with increased demand was to offer contracts to independent power producers, who have built 100 run of the river projects under 50 MW. Power production without reservoirs varies dramatically, but older conventional dams retain or release water to average out production though the year. In 2014 these independent producers generated 18,000 GWh from 4,500 MW of capacity.
As of 2022, the global capacity (for projects ≤10 MW) is approximately 79.0 GW, with China holding over 53% of the world's SHP installed capacity. Under this definition (≤10 MW), installed SHP capacity increased by 11% in the Americas from 2019 to 2022. Because of local differences in SHP definitions, it is likely that the installed capacity of SHPs across the globe is higher than these totals. Countries such as China, India, and Brazil, are significantly expanding their small hydro capacity in the 21st century. The continents of Asia, Africa and the Americas hold the most potential for small hydro power growth.
History Wood water wheels along riversides may be considered the first examples of "small hydro". Up to the 17th century the efficiency of water wheels neared 70%. However, as the need for power generation increased small hydropower projects were phased out in favor of the large scale dams using newly designed turbines. Post 20th century environmental doctrine is moving away from large-scale hydropower construction due to increased awareness of ecological problems associated with dams. Examples of previous dam deconstruction projects include the Restoration of the Elwha River and Un-Dam the Klamath river movement in the United States. Both of these projects deconstructed dams with generation capacities less than 30 MW.
Generation
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