Small Hydro Technologies

Small hydropower is a well established renewable energy technology that allows to produce electricity at competitive prices. Water wheels are among the oldest hydro-power devices and consist of large spinning wheels with attached paddles or buckets which are turned by the force of moving water. Historically, hydropower was developed on a small scale to serve localities in the vicinity of the power plants.

Hydro-electric power is derived by harnessing the power released when water passes trough a vertical distance usually referred to as the ‘head’. The idea is build around the principle that gravity gives water above sea level potential energy. This potential energy is transformed into kinetic energy when water is set in motion. This causes the rotation of a turbine which causes the rotation of a generator to produce electricity.

There is no universal definition of a small hydro power plant. In general, the term Micro hydro is used for hydroelectric power installations of less than 100kW, and the term of Mini hydro for installations with a production beyond (100kW to 1MW). However, according to local definitions, the term of Micro hydro is also used for projects up to 200 kW or even 500 kW.

1. Key Characteristics of a Small Hydro Installation

Key physical parameters for a Small Hydro Project (SHP) are the head, the civil works and the electro-mechanical equipment. The main civil works are the powerhouse, the dam, the spillway or diversion weir, and the water passages to the powerhouse.

These works are carried out before installing the turbine, generators and transmission equipment. The Central (powerhouse) houses hydromechanical components, ie the turbine and its components of regulation, generators and most of the electrical control, processing and regulation. The plant is usually built of concrete and other local materials.

2. Basic Principles of Operation of the Technology

Small hydro power plants generally use water from a spring, a stream river or a lake. Water is directed to the central either by a flume, a penstock, a dam or a floodway. The water turns the turbines and the energy generated is used to rotate a generator and produce electricity.

Necessary Pre-conditions and Context

• Sufficient quantity of falling water must be available (for instance a river head)
• Water must be available throughout the year, which usually, but not always, means that hilly or mountainous sites are best.

Other Important Considerations

Before constructing a small scale hydro power plant, it is necessary to conduct topographic and geomorphological studies on the site, to evaluate the water resources and potential of production, and to assess the environmental impact.

If it is determined that the site is feasible for a small hydro power system, the next obvious step consist in an economical and financial evaluation to determine whether it makes sense economically to undertake building a small hydro power system.

Whereas large scale hydro power plants with large dams are very capital intensive, investment costs are less for small scale systems with small derivation dams or run-of-river-installations that are more suitable for small projects in rural zones.

3. Benefits and Best Practices

Small-hydro power, unlike some sources of energy, has the great advantage of multiple uses, namely; electricity generation, irrigation, water supply, and providing mechanical shaft power. In addition, small-hydro is a very reliable technology that has a solid proven performance track record. The relatively high capital investment is amortized by long service life and low (but also not neglectable!) maintenance requirements (SHP, 1994). These costs can also be reduced when the work partly done by oneself.

Small-hydro power development mainly targets the rural areas which usually are not connected to the grid and thus promotes rural industrial growth and improvement in the general welfare of the people (Ranganathan, 1992). An assessment of the pre- and post-electrification energy expenditure patterns in Kenya demonstrates that the small-hydro power-based electrification led to a reduction in energy expenditure.

Other benefits of small hydro are:

• Small hydropower is a cheap, clean, domestic and renewable source of energy.
• Unlike other energy sources such as fossil fuels, water is not destroyed during the production of electricity—it can be reused for other purposes.
• Impact on environment is minimal if sufficient precautions are taken: The dams built for some run-of-the-river small hydropower projects are very small and impound little water - many projects do not require a dam at all. Negative side effects associated with dams such as oxygen depletion, increased temperature, decreased flow, and interference with upstream migration like fish are not problems for many run-of-the-river projects.

Uses of Small Hydro Power

• Renewable electricity generation
• Irrigation and water supply
• Mechanical shaft power

4. Often Encountered Problems and Possible Solutions

• The ideal location of small-hydro power plants is where there exists a constant water supply throughout the year. A period of drought risks to reduce or even stop the energy production. This considerably limits the choice of appropriate sites. In addition, people living in areas without such water supplies cannot benefit from the technology. small hydro power plant.
• Another significant limitation of small-hydro power is that it is almost always obtained from run-off-the-river plants with limited reservoir capacity to store water. Consequently, severe seasonal variations in power output may occur.
• Some small hydro power technologies have been developed to counter the above drawbacks. For instance, the Rainbow micro hydro, developed in Australia, is consistently efficient over a wide range of sites. It is, therefore, suitable for areas where water supply is low (Hydronet, 1994).
• Spare parts availability is a potential challenge of small-hydro especially in cases where some components were imported specifically for a particular project.
• For this reasons, a stock of spare parts should be set up to be used quickly and effectively when needed and prevent a break in production. This stock should include at least one set of seals, valves, sealed bearings and blades.
• Regulatory requirements may become an obstacle for small-hydro especially in cases where entrepreneurs may wish to install this technology for electricity sale to the public.
• Another challenge facing small-hydro installations aimed at low-income rural populations, is that it may be difficult for the target group to raise the required capital.
• Finally, the availability of information on installations and their performance is rather limited.

The main reasons for unsuccessful small hydropower projects are:

• Studies conducted before the set up of the plant have been insufficient.
• Failure of locally made equipment due to use of substandard material.
• Over-estimation of the amount of the stream flow and its consistency throughout the year.
• Penstocks or flumes that are too small to allow the plant to operate at full capacity i.e. undersizing of power system.
• Failure to anticipate the expense of keeping trash racks clear and machinery in good repair.
• Oversizing of the power system.

What to Consider When Installing these Technologies

• Collect extensive field data to choose the best site and design a safe dam, if required. The construction of a dam is a highly technical undertaking that needs sound preparation. Often the costs of civil work, especially for constructing a dam, are underestimated
• The project developer/owner must obtain reliable cost estimates for the construction and maintenance of a small hydropower.
• Take account of laws that govern construction of small hydropower vary from country to country - some are lenient; some are very stringent. It is imperative that the project developer finds out what permits are required for small hydropower development.
• Possession of land rights for the area on which the hydropower system will reside is imperative.
• In the event of dam failure, the project owner/developer will be responsible for all downstream damage. A competent insurance underwriter would advise appropriately availability of liability insurance.
• The project developer/owner must respect the rights of others to use the stream outside the small hydropower facility.

Case Study

Background

A project aimed at demonstrating that small hydro technology is a sustainable and affordable technology for community electrification was developed through the collaboration between the Nottingham Trent University (NTU) and ITDG-EA Energy Programme.

The objectives of the project were twofold:

• To demonstrate that small hydro (up to 5 kW) is a sustainable and affordable technology for community electrification projects in rural Sub-Saharan Africa.
• To establish infrastructure to encourage manufacture, sales and productive use of small hydro systems.

Location/Sites

The project is comprised of two sites located along Mukengeria and Rutui Rivers in Kirinyaga District with the Central Province of Kenya – about 130 km from Nairobi.

Technical skills in the local manufacture/fabrication of some small hydro components were transferred into the country from Nepal and the UK. Local skills in scheme maintenance and operation were also developed as a result of the project. Nevertheless, one of the lessons learnt from the project was the need to develop standards for community-managed electricity distribution schemes.

Environmental benefits of the project included reduced indoor air pollution – as a result of substituting kerosene lighting with electricity. In addition, there was little impact on the local environment as a result of damming the rivers on which the project was developed.

The key characteristics of the project are given below, as of the year 2000: 

Source: Adapted from Maher, 2002a; 2002b; Balla, 2003

Funding

The following organizations provided support for the project:

• European Union (EU) funded a significant part of the project.
• Nottingham Trent University (NTU) - Contribution was in kind, mainly in the form of technical assistance.
• Ministry of Energy (MoE)- Renewable Energy Department - Contribution was in kind, mainly in the form of technical assistance.
• Local community - Contribution was in kind, through manual labour and provision of distribution poles and cables and payment of connection fee, to the tune of Euros 4,724 for the two schemes.
• ITDG-EA - Contribution was in kind, mainly in the form of technical assistance and community mobilization.

by AFREPREN

References and Links

http://www.ieahydro.org/reports/AnnexII_Objectives_for_SH_Tech.pdf

http://commons.wikimedia.org/wiki/File:Hydroelectric_dam-letters.svg

http://www.green-trust.org/hydro.htm

http://www.wvu.edu/~exten/infores/pubs/ageng/epp13.pdf

http://www.nrel.gov/docs/fy01osti/29065.pdf

http://www.alternative-energy-news.info/micro-hydro-power-pros-and-cons/

Gitonga S. and Balla P. 2002. Poverty Impacts of Pico Hydro Power Schemes in Kenya Intermediate Technology Development Group-East Africa.

Balla P. 2003. Development of Community Electrification in Kenya. A Case of Small Scale Hydropower for rural energy Masters Thesis presented at Lund University, 2003, Sweden. 12

Maher, P., 2002a. Community Pico Hydro in Sub-Saharan Africa: Case Study 1. The Nottingham Trent University.

Maher, P., 2002b. Community Pico Hydro in Sub-Saharan Africa: Case Study 2. The Nottingham Trent University.

Karekezi, S. and Ranja, T. 1997. Renewable Energy Technologies in Africa. African Energy Policy Research Network, Nairobi and ZED Books, London.

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