Hydropower is a method of generating electricity that uses moving water (kinetic energy) to produce electricity. Small-scale hydropower has been used as a common way of generating electricity in isolated regions since end of 19th century. Small-scale hydropower systems can be installed in small rivers, streams or in the existing water supply networks, such as drinking water or wastewater networks. In contrast with large-scale hydropower systems, small-scale hydropower can be installed with little or negligible environmental impact on wildlife or ecosystems, mainly because the majority of small hydropower plants are run-of-river schemes or implemented in existing water infrastructure. Due to its versatility, low investment costs, and as a renewable energy source, small-scale hydropower is a promising option for producing sustainable, inexpensive energy in rural or developing areas.
Freshwater, Drinking Water, Energy
While water resources are valued for human health and for sustaining food production, the energy contained in moving water such as rivers or tides can also be harnessed to create energy through hydropower or mechanical uses. Hydropower schemes can either be small-scale or large scale, depending on the local conditions and the energy demand, and represent a renewable energy source that can be implemented wherever there is running water. Globally, 1.4 billion people lack access to electricity, with an additional 1 billion having only intermittent access (UNDP 2012). As running water is a resource that is globally available and renewable, harnessing its power to generate electricity can provide a sustainable source of energy to improve livelihoods and increase working productivity. Particularly in rural or developing areas, small-scale hydropower can represent a locally available, reliable source of energy where no other energy generation is feasible.
How Does it Work?
Regardless of size, the principle behind hydropower generation is the same: that the power of moving water can be harnessed to produce energy. The key elements for hydropower generation are “head” and “flow.” “Head” refers to the height of the gradient over which the water falls, while “flow” refers to the volume of water per unit time. To maximise energy production, both head and flow should be high. In other words, greater amounts of energy are generated when a large volume of water flows over a steep gradient. Hydropower plants generate electricity by directing water through a turbine, which in turn drives an electric generator. The electricity produced can either used directly, or fed into an electricity grid.
Adapted from SINGH (2009) and GAIUS-OBASEKI (2010)
Hydropower plants are classified according to their energy production capacity, expressed in megawatts. While large scale hydropower plants can produce well over 100 MW, small hydropower plants generally produce less than 10 MW. Based on energy production capacity, small-scale hydropower production is broken into four size categories of pico- (<5 kilowatts), micro- (5-100 kW), mini- 100 kW-1 MW), and small (1-10 MW).
However, classifications vary from country to country as there is currently no common consensus among countries and hydropower associations regarding the upper limit of small-scale hydropower plant capacity. For instance, some European Union countries like Portugal, Spain, Ireland, Greece and Belgium accept 10 MW as the upper limit for small-scale hydropower installed capacity, while others place the maximum capacity from 3 to 1.5 MW. Outside the EU, this limit can be much higher, as in the USA (30 MW) and India (25 MW).
> 100 MW
Large urban population centres
10 – 100 MW
Medium urban population centres
1 – 10MW
Small communities with possibility to supply electricity to regional grid.
100 kW – 1MW
Small factory or isolated communities.
5 – 100kW
Small isolated communities.
1 – 2 houses.
Types of Small Hydropower Schemes
Because hydropower generation depends on only two factors (water flow and head) to produce energy, small-scale hydropower can be implemented in any system where these factors are met. This can include natural systems such as streams or rivers, but can also include any water network where pipes provide water flow over a decline (head). Hydropower can therefore also be integrated into many stages of the drinking water or wastewater network (KUCUKALI 2011). Most small hydropower schemes fit into two main categories: run-of-river systems, or integrated in existing water infrastructure.
Adapted from SINGH (2009)
In run-of-river systems, river water is diverted by a weir through an opening in the river side (the ‘intake’) into a channel. A settling basin is built in to the channel to remove sand and silt from the water. The channel follows the contour of the area so as to preserve the elevation of the diverted water. The channel directs the water into a small reservoir/tank known as the ‘forebay’ from where it is directed on to the turbines through a closed pipe known as the ‘penstock’. The penstock essentially directs the water in a uniform stream to the turbine at a lower level. The turning shaft of the turbine can be used to rotate a mechanical device (such as a grinding mill, oil expeller, or wood lathe), or to operate an electricity generator. When electricity is generated, the ‘power house’ where the generator is located, transfers the electricity to a step-up ‘transformer’ which is then transmitted to the grid sub-station or to the village/area where this electricity is to be used. Once electricity is produced, the water flow is returned back to the river. For this reason, small hydropower plants are considered a renewable, non-polluting and environmentally source of energy.
Most small hydropower plants are “run-of-river” schemes. The power is generated only when enough water is available from the river/stream. When the stream/river flow reduces below the design flow value, the generation ceases, as the water does not flow through the intake structure into the turbines.
Integrated in Existing Water Infrastructure
Small-scale hydropower plants within existing water infrastructure have four main advantages compared to those which utilise rivers and streams (KUCUKALI 2011):
- All civil works are already present, which can reduce the investment cost for new infrastructure by about 50%.
- Facilities have no significant environmental impacts, and will have a guaranteed discharge (and production rate) throughout the year.
- The generated electricity can be used in the water supply system, with excess electricity sold to the government.
- There will be no land acquisition or significant operating costs.
Small-scale hydropower can be implemented in the following ways within existing drinking water or wastewater infrastructure (SAN BRUNO et al. 2010):
- Within a drinking water network: Excess pressure in pipes is used to generate hydropower by replacing pressure breakers with turbines.
- Within an irrigation network: Implementation is similar to within a water supply network, but special considerations need to be taken to produce energy outside the irrigation season.
- Before wastewater treatment: Wastewater is diverted through a turbine before it enters a wastewater treatment plant. A trash rack should be installed to remove solids before wastewater passes through the turbine.
- After wastewater treatment: Before being discharged to the environment, wastewater is passed through a turbine to generate electricity.
- Within a runoff collection system: Implementation is similar to within a water supply network, but consideration needs to be taken to remove particles that may be suspended in stormwater before it passes through the turbine.
- On a reserved flow or compensation discharge: In large hydropower schemes or in water works, water is often discharged according to national laws. A turbine can be installed to generate hydropower from this discharge.
- On a fish pass system: In order for fish to migrate past obstacles such as dams, a fish pass systems are often installed. To allow fish to find the pass, an “attraction discharge” is necessary. A turbine placed at this discharge can make use of the difference in water level between the upstream basin and fish pass entrance to generate hydropower.
- In a navigation lock or dam: Locks and dams regulate water levels. Turbines can be installed that utilise fluctuating water levels for hydropower generation during the filling and emptying of the locks.
- In a desalination plant: The process of reverse osmosis to separate water from dissolved salts through semi-permeable membranes necessitates high pressures (from 40 to 80 bars). The high-pressure residue of liquid water containing salt can be passed through a turbine in order to recover part of the energy used for the initial compression.
- In a cooling or heating system: Cooling or heating systems can produce excess pressure that can be recovered by hydro-turbines to produce energy.
How to Optimise?
Hydropower is a non-consumptive water use. Therefore, there are possibilities to link hydropower to other uses, such as irrigation in agriculture. This can reduce the investment costs for individual users, thus expanding the possibilities for income generation and development.
Water for Energy and the Millennium Development Goals
Adapted from UN-HABITAT (2012)
Because of their geographical versatility and relatively low investment costs, the development of small hydropower could be key in spreading access to electricity in rural and developing areas. Access to electricity can have many positive development impacts, which can be regarded for each of the Millennium Development Goals.
Goal 1: Eradication extreme poverty and hunger
Energy inputs such as electricity and fuels are essential to generate jobs, industrial activities, transportation, commerce and micro-enterprises.
Goal 2: Achieve universal primary education
To attract teachers, electricity is needed for homes and schools. After dark study requires illumination. Many children, especially girls, do not attend school in order to carry wood and water to wood and other energy sources to meet the family’s energy needs.
Goal 3: Promote gender equality and empower women
Adult women are responsible for the majority of household cooking and water boiling activities. This takes time away form other productive activities. With modern fuels, stoves and mechanical power for food processing and transportation, women’s time would be freed up for more productive uses.
Goal 4: Reduce child mortality
Diseases caused by lack of clean boiled water and respiratory illness caused by the effects of indoor air pollution from traditional fuels and stoves, directly contribute to infant and child disease and mortality.
Goal 5: Improve maternal health
Lack of electricity in health clinics, illumination for night-time deliveries and the physical burden of fuel collection and transport by pregnant women all contribute to poor maternal health conditions.
Goal 6: Combat HIV/AIDS, malaria, and other diseases
Electricity for communication of radio and television can foster the delivery of proper public health information to combat disease. Health care facilities require electricity for illumination, refrigeration and sterilisation to deliver effective health services.
Goal 7: Ensure environmental sustainability
Energy production, distribution and consumption has many adverse environmental effects at the local, regional and global levels including indoor air pollution in slum communities, land degradation and global warming. Cleaner energy systems are needed to address all of these for environmental sustainability.
Goal 8: Develop a Global Partnership for Development
The World Summit for Sustainable Development (WSSD) called for partnerships between public entities, development agencies, civil society and the private sector to support sustainable development including the delivery of affordable, reliable and environmentally sustainable energy services.
Cost, Operation and Maintenance
The construction of small-scale hydropower systems depends on a number of variables such as site characteristics, power plant size, and location, with cost generally ranging from $1,000 - $20,000 USD/kW. Maintenance costs are relatively small in comparison to other technologies. Given a reasonable head, small-scale hydropower is a concentrated energy source. It is a long-lasting and robust technology, and the life of systems can be as long as 50 years or more without major new investments (SINGH 2009).
Assessments of the feasibility of small hydropower in rural areas have shown that even if population density is sparse, micro- and pico- hydropower may be cost-effective solutions due to the low cost of distribution and minimal effects on the environment (WILLIAMS & PORTER 2006). Integrating small-scale hydropower scheme as part of an existing water or sanitation infrastructure can reduce the investment costs while simultaneously producing valuable electricity that can be used by the facility or by an electricity grid.
Environmental and Social Aspects
- As most small hydropower schemes are run-of-river or integrated within an already existing water infrastructure, the effect on the local environment is minimal. Run-of-river systems return water to streams, thus minimising the impact on stream ecosystems, while systems integrated into existing infrastructure merely make use of existing water flows.
- Small hydropower is a non-polluting, renewable energy source. Unlike large hydropower schemes, small hydropower does not necessitate a reservoir, and therefore does not lead to methane production, a potent greenhouse gas.
- Small hydropower schemes take up little space. Because no reservoir is created, there is minimal impact on nearby communities with respect to displacement.
Adapted from SINGH 2009
Small hydropower can provide clean, renewable, and relatively inexpensive energy. They can be constructed in any location where there is enough water flow and head to make energy generation viable, even in rural or undeveloped locations. This can include natural water sources such as streams and rivers, or existing manmade infrastructure such as water distribution networks, wastewater collection and treatment systems, and dams. In this way, small-scale hydropower can take advantage of current infrastructure to produce power and reduce the environmental impact (KUCUKALI 2011).
This UN-Energy paper on the importance of energy for achieving the Millennium Development Goals (MDGs)1 was drafted collectively by the UN agencies, programmes and organisations working in the area of energy, reflecting their insights and expertise. Currently, the available energy services fail to meet the needs of the poor. This situation entrenches poverty, constrains the delivery of social services, limits opportunities for women, and erodes environmental sustainability at the local, national and global levels. Much greater access to energy services is essential to address this situation and to support the achievement of the MDGs.UN-HABITAT (2005): The Energy Challenge for Achieving the Millennium Development Goals. Nairobi, Kenya: UN-HABITAT URL [Accessed: 09.05.2019]
Comparison of hydropower options for developing countries with regard to the environmental, social and economic aspects
Micro-Hydropower: A Promising Decentralized Renewable Technology and its Impact on Rural Livelihoods
The present research paper discusses the health, environment and agriculture benefits of micro hydropower to final users in Nepal.ANUP, G. ; BRYCESON, I. ; SANG-EUN, O. (2011): Micro-Hydropower: A Promising Decentralized Renewable Technology and its Impact on Rural Livelihoods. In: Scientific Research and Essays : Volume 6 , 1240-1248. URL [Accessed: 09.05.2019]
This presentation shows all the elements for developing small hydropower in rural areas from fundamentals to financing models in Africa.AFREPREN (2007): Fundamentals of Small Hydro Power Technologies. Nairobi: Energy, Environment and Development Network for Africa (AFREPREN). [Accessed: 02.10.2012] PDF
Mini and small hydropower is a renewable, clean and efficient resource for the production of mechanical and electrical power. This paper aims to identify and develop policy shaping institutional mechanisms (including spatial planning) to facilitate mini and small hydropower.CRETTENEND, N. HEMUND, C. (2010): The Facilitation of Mini and Small Hydropower through Institutional Mechanisms for Development. (= International Scientific Conference on Technologies for Development 8-10 February 2010 ). Lausanne: Ecole polytechnique federale de Lausanne (EPFL) URL [Accessed: 02.02.2012]
This guide brings together all the aspects related to developing of small hydropower ranging from business, engineering, financial, legal and administration. The document is presented in a step-by-step approach and is very helpful tool for practitioners and potential local developers of small hydropower scheme.ESHA (2004): Guide on How to Develop a Small Hydropower Plant. Brussels, Belgium: European Small Hydropower Association (ESHA) URL [Accessed: 09.05.2019]
This report describes the development of local capacities in planning, design, implementation and operation of Small-scale hydropower systems at local and sub-regional scale in Burundi, Ethiopia, Kenya, Rwanda, Tanzania and Uganda.KASSANA, L. MASHAURI, D. CHAMBEGA, D.G. MKILAHA, I.S.N. MHILU, C.F. NGELEJA, J. NGELEJA, J. MAKHANU, S. CASIMIR, M. KIZZA, M. MUNIIMA, K. MTALO, F. PETRY, B. (2005): Small Scale Hydropower for Rural Development. Cairo, Egypt: Nile Basin Capacity Building Network (NBCBN) URL [Accessed: 09.05.2019]
This report synthesises the experience of micro hydro developments in Sri Lanka, Peru, Nepal, Zimbabwe and Mozambique. It attempts to draw out the Best Practice from this experience. The report provides a rigorous comparative micro economic analysis of the cost and financial returns of a sample of plants across the five countries.KHENNAS, S. BARNETT, A. (2000): Best Practices for Sustainable Development of Micro Hydro Power in Developing Countries. London: Department For International Development (DFID), UK. URL [Accessed: 02.02.2012]
This is a field study on micro hydropower in a rural society context that investigates the importance of micro hydropower for rural electrification in the northern part of Lao. The second part of the work is to evaluate the micro hydropower plants already existing in the country and find new sites in the rivers for new hydropower plants construction.SUNDQVIST, E. WARLIND, D. (2006): The Importance of Micro Hydropower for Rural Electrification in LAO PDR. Lund, Sweden: Lund University URL [Accessed: 02.02.2012]
This case study provides technical information regarding the use of biogas produced in municipal wastewater treatment plants for generating electricity. Moreover, it provides information on the use of hydraulic potential of potable water in water supply structure for electricity production with help of small hydropower station.GONO, M. KYNCL, M. GONO, R. (2009): Practical Experience with Electricity Production from Unused Energy at the Water Management Company. (= International Conference on Renewable Energies and Power Quality, 15-17 April, 2009 ). Valencia, Spain: European Association for the Development of Renewable Energy, Environment and Power Equality (EA4EPQ), University of Vigo, University of the Basque Country URL [Accessed: 02.02.2012]
This paper determines the cost-effectiveness of developing small-scale hydropower sites in the USA aiming to contribute to the renewable energy mix of the country and thus reduced the current carbon emissions.KOSNIK, L. (2010): The Potential for Small Scale Hydropower Development in the United States of America. In: Energy Policy : Volume 38 , 5512 – 5519. URL [Accessed: 02.02.2012]
This document provides information on hydropower project, under the clean development mechanism scheme, located in a western region in Honduras, where it generates renewable energy with no waste and minimum environmental impact.SOUTH POLE CARBON ASSET MANAGEMENT (2010): Small Scale Hydropower Projects, Honduras. Zurich, Switzerland: South Pole Carbon Asset Management Ltd
This document presents the general overview of small hydropower development and how it can contribute to meet the electricity needs of the national grid as well as the isolated rural areas. It presents a case study from Nepal that shows how a country that relied on external assistance for its hydropower development has now developed its local capability and utilised the internal resources available to develop it hydropower resources, especially the small hydro projects.BASNYAT, D. (2006): Fundamentals of Small Hydro Power Technologies. Nairobi. Kenya: African Development Bank FINESSE training course on Renewable Energy and Energy Efficiency for Poverty Reduction URL [Accessed: 09.05.2019]
This presentation gives information on micro hydro projects, which includes definitions, power calculations and some technical aspects to civil works.EERE (2011): Types of Hydro Power Facilities. Washington, D.C.: U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy (EERE) URL [Accessed: 09.05.2019]
This factsheet provides information five small-scale hydropower stations on the municipal water system in the city of Boulder Colorado.CADDET RENEWABLE ENERGY (2000): Small-scale Hydro within a Municipal Water Supply System. Oxfordshire, U.K.: Caddet Centre for Renewable Energy. [Accessed: 05.02.2012] PDF
This short factsheet provides a condense overview on small scale hydro power, including different types of systems, components, energy production and maintenance.CALON TEIFI (2011): What is Small Scale Hydro Power. West Wales, U.K.: Calon Teifi. [Accessed: 05.02.2012] PDF
This factsheet information covers various facts on the subject of water, energy and hydropower focusing on Switzerland but also covering the international perspective. MC CARTHY, P. (2006): Small Scale Hydroelectricity. Carlow, Ireland: Teagasc Mellows Development CentreEAWAG (2010): Factsheet: Water and Energy. Duebendorf: Swiss Federal Institute of Aquatic Science and Technology (EAWAG) URL [Accessed: 05.02.2012]
This document presents general specifications on low head and small-scale hydroelectric power plants.TOSHIBA (2011): Hydro-eKids Micro Hydro Power Generating Equipment. Tokyo: Toshiba Corporation URL [Accessed: 09.05.2019]