Small hydro is the development of hydroelectric power on a scale serving a small community or industrial plant. The definition of a small hydro project varies, but a generating capacity of up to 10 megawatts (MW) is generally accepted as the upper limit, which aligns to the concept of distributed generation. The liimit may be stretched up to 30 MW in the United States, and 50 MW in Canada. In contrast many hydroelectric projects are of enormous size, such as the generating plant at the Hoover Dam of 2,074 MW or the vast multiple projects of the Tennessee Valley Authority.
Small hydro can be further subdivided into mini hydro, usually defined as less than 1,000 kilowatts (kW), and micro hydro which is less than 100 kW. Micro hydro is usually the application of hydroelectric power sized for smaller communities, single families or small enterprise.
Small hydro plants may be connected to conventional electrical distribution networks as a source of low-cost renewable energy. Alternatively, small hydro projects may be built in isolated areas that would be uneconomic to serve from a network, or in areas where there is no national electrical distribution network. Since small hydro projects usually have minimal reservoirs and civil construction work, they are seen as having a relatively low environmental impact compared to large hydro. This decreased environmental impact depends strongly on the balance between stream flow and power production. One tool that helps evaluate this issue is the Flow Duration Curve or FDC. The FDC is a Pareto curve of a stream's daily flow rate vs. frequency. Reductions of diversion help the river's ecosystem, but reduce the hydro system's Return on Investment (ROI). The hydro system designer and site developer must strike a balance to maintain both the health of the stream and the economics.
Plants with reservoir, i.e. small storage and small pumped-storage hydropower plants, can contribute to distributed energy storage and decentralized peak and balancing electricity. Such plants can be built to integrate at the regional level intermittent renewable energy sources.
During 2008 small hydro installations grew by 28% over year 2005 to raise the total world small hydro capacity to 85 gigawatts (GW). Over 70% of this was in China (with 65 GW), followed by Japan (3.5 GW), the United States (3 GW) and India (2 GW). China plans to electrify a further 10,000 villages by 2010 under their China Village Electrification Program using renewable energy, including further investments in small hydro and photovoltaics.
Hydroelectric power is the generation of electric power from the movement of water. A hydroelectric facility requires a dependable flow of water and a reasonable height of fall of water, called the head. In a typical installation, water is fed from a reservoir through a channel or pipe into a turbine. The pressure of the flowing water on the turbine blades causes the shaft to rotate. The rotating shaft is connected to an electrical generator which converts the motion of the shaft into electrical energy.
Small hydro is often developed using existing dams or through development of new dams whose primary purpose is river and lake water-level control, or irrigation. Occasionally old, abandoned hydro sites may be purchased and re-developed, sometimes salvaging substantial parts of the installation such as penstocks and turbines, or sometimes just re-using the water rights associated with an abandoned site. Either of these cost saving advantages can make the ROI for a small hydro site well worth the use of existing site infrastructure & water rights.
Many companies offer standardized turbine generator packages in the approximate size range of 200 kW to 10 MW. These "water to wire" packages simplify the planning and development of the site since one vendor looks after most of the equipment supply. Since non-recurring engineering costs are minimized and development cost is spread over multiple units, the cost of such systems is improved. While synchronous generators capable of isolated plant operation are often used, small hydro plants connected to an electrical grid system can use economical induction generators to further reduce installation cost and simplify control and operation.
Micro-hydro plants may use purpose-designed turbines or use industrial centrifugal pumps, connected in reverse to act as turbines. While these machines rarely have optimum hydraulic characteristics when operated as turbines, their low purchase cost makes them attractive for micro-hydro class installations.
Regulation of small hydro generating units may require diversion of water around the turbine, since the project may have no reservoir to store unused water. For micro-hydro schemes feeding only a few loads, a resistor bank may be used to dissipate electrical energy as heat during periods of low demand. In a sense this energy is wasted but the incremental fuel cost is negligible so there is little economic loss.
Other small hydro schemes may use tidal energy or propeller-type turbines immersed in flowing water to extract energy. Tidal schemes may require water storage or electrical energy storage to level out the intermittent (although exactly predictable) flow of power.
Since small hydro projects usually have minimal environmental and licensing procedures, and since the equipment is usually in serial production, standardized and simplified, and since the civil works construction is also small, small hydro projects may be developed very rapidly. The physically small size of equipment makes it easier to transport to remote areas without good road or rail access.
Micro-hydro installations can also provide multiple uses. For instance, micro-hydro projects in rural Asia have incorporated agro-processing facilities such as rice mills – alongside standard electrification – into the project design.
Small-scale DIY hydroplants
With a growing DIY-community and an increasing interest in environmentally friendly "green energy", some hobbyists have endeavored to build their own hydroelectric plants from old water mills, or from kits or from scratch. Usually, the DIY-community uses decayed/abandoned water mills to mount a waterwheel and other electrical components. This approach has also been popularised in the TV-series It's Not Easy Being Green. These are usually smaller turbines of ~5 kW or less. Through the internet, the community is now able to obtain plans to construct DIY-water turbines, and there is a growing trend toward building them for domestic requirements. The DIY-hydroelectric plants are now being used both in developed countries and in developing countries, to power residences and small businesses.
Sample list of small installations worldwide
- Bario Asal & Arur Layun Micro-Hydro Community Project, Kelabit Highlands, Sarawak, Malaysia.
- Pakpattan Hydro Power Project, a 2.82MW plant on Pakpattan Cannal in Pakpattan District, Pakistan
- Green Valleys Project, Brecon Beacons National Park, Wales, United Kingdom. Joint winner of £300K in Big Green Challenge 2009.
- St Catherine's, a National Trust site near Windermere, Westmorland, United Kingdom.
- Ames Hydroelectric Generating Plant, Colorado, United States. On the List of IEEE Milestones
- Buckeye, Arizona, United States.
- Childs-Irving Hydroelectric Facilities, Arizona, United States.
- Snoqualmie Falls, Washington, United States.
- Malibu Hydro, British Columbia, Canada.
- Electricity generation
- Hydro power
- Low head hydro power
- Micro hydro
- Pico hydro
- Small pumped-storage hydropower
- "Small hydro in Canada". Canmetenergy-canmetenergie.nrcan-rncan.gc.ca. 2009-03-23. Retrieved 2013-10-16.
- Crettenand, N. (2012). "The facilitation of mini and small hydropower in Switzerland: shaping the institutional framework. With a particular focus on storage and pumped-storage schemes". Ecole Polytechnique Fédérale de Lausanne (EPFL). PhD Thesis N° 5356. Infoscience.epfl.ch.
- Renewables Global Status Report 2006 Update, REN21, published 2006, accessed 2007-05-16
- PACOS Trust Projects in Malaysian Borneo
- Old water mills idea for `green' electricity[dead link]
- It's not easy being green featuring diy converted water mills to hydropower plants
- "Watermills poweramounts depending on streams/rivers" (PDF). Retrieved 2013-10-16.
- "15kwh sometimes acquired, (yet not frequently) as a power output with converted watermills". De.green-acres.com. Retrieved 2013-10-16.
- "Navitron's hydroelectric plants information page". Navitron.org.uk. Retrieved 2013-10-16.
- "Hydroelectric plants DIY plans". Green-trust.org. Retrieved 2013-10-16.
- Cunningham, Ian; Woofenden. "Simplified overview of diy hydroplants installation". Homepower.com. Retrieved 2013-10-16.
- VillageEarth AT SourceBook: Microgeneration DIY information[dead link]
- "Bario Asal & Arur Layun Micro-Hydro Project A community project www.kelabit.net/bariohydro". Kelabit.net. Retrieved 2013-10-16.
- "The Green Valleys —". Thegreenvalleys.org. 2013-04-07. Retrieved 2013-10-16.
- "UK | Wales | Mid Wales | Beacons green project scoops £20k". BBC News. 2008-10-17. Retrieved 2013-10-16.
- "biggreenchallenge.org.uk". biggreenchallenge.org.uk. Retrieved 2013-10-16.
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- Images of construction of a DIY undershot wheel