View source for Micro hydro

{{Short description|Hydroelectric power generation of 5 to 100 kW of electricity}}
{{Use dmy dates|date=January 2017}}
[[Image:Nw vietnam hydro.jpg|thumb|300px|Micro hydro in northwest Vietnam]]

'''Micro hydro''' is a type of [[hydroelectric power]] that typically produces from 5&nbsp;kW to 100&nbsp;kW of [[electricity]] using the natural flow of water. Installations below 5&nbsp;kW are called [[pico hydro]].<ref name="irena">{{cite report|date=June 2012|title=RENEWABLE ENERGY TECHNOLOGIES: COST ANALYSIS <:SERIES|url=https://www.irena.org/DocumentDownloads/Publications/RE_Technologies_Cost_Analysis-HYDROPOWER.pdf|publisher=[[International Renewable Energy Agency]] |page=11|access-date=14 January 2017}}</ref> These installations can provide power to an isolated home or small community, or are sometimes connected to electric power networks, particularly where [[net metering]] is offered.
There are many of these installations around the world, particularly in developing nations as they can provide an economical source of energy without the purchase of fuel.<ref name="tve">{{cite web|url=http://www.tve.org/ho/doc.cfm?aid=1636&lang=English|title=Micro Hydro in the fight against poverty|author=<!--Staff writer(s); no by-line.-->|date=November 2004|website=tve.org|publisher=TVE/ITDG |access-date=14 January 2017|archive-url=https://web.archive.org/web/20070730205707/http://www.tve.org/ho/doc.cfm?aid=1636&amp;lang=English|archive-date=30 July 2007|url-status=dead}}</ref> Micro hydro systems complement [[solar PV power system]]s because in many areas water flow, and thus available hydro power, is highest in the winter when solar energy is at a minimum. Micro hydro is frequently accomplished with a [[pelton wheel]] for high [[Hydraulic head|head]], low flow water supply. The installation is often{{when|date=July 2023}}{{where|date=July 2023}} just a small [[dam]]med pool, at the top of a waterfall, with several hundred feet of pipe leading to a small generator housing. In low head sites,{{examples|date=July 2023}} generally [[Water wheel|water wheels]] and [[Archimedes' screw|Archimedes' screws]] are used.{{citation needed|date=July 2023}}

==Construction==
[[File:Microhydro System.svg|thumb|right|Typical microhydro setup.]]

Construction details of a microhydro plant are site-specific. Sometimes an existing mill-pond or other artificial reservoir is available and can be adapted for power production. In general, microhydro systems are made up of a number of components.<ref name="Energy Savers: Components">{{cite web|title=How a Microhydro System Works|url=http://www.energysavers.gov/your_home/electricity/index.cfm/mytopic=11060|publisher=U.S. DOE|access-date=28 November 2010}}</ref> The most important include the intake where water is diverted from the natural stream, river, or perhaps a waterfall. An intake structure such as a catch box is required to screen out floating debris and fish, using a screen or array of bars to keep out large objects. In temperate climates, this structure must resist ice as well. The intake may have a gate to allow the system to be dewatered for inspection and maintenance.

The intake is then brought through a canal and then forebay. The forebay is used for sediment holding. At the bottom of the system the water is tunneled through a pipeline ([[penstock]]) to the powerhouse building containing a [[water turbine|turbine]]. The penstock builds up pressure from the water that has traveled downwards. In mountainous areas, access to the route of the penstock may provide considerable challenges. If the water source and turbine are far apart, the construction of the penstock may be the largest part of the costs of construction. At the turbine, a controlling valve is installed to regulate the flow and the speed of the turbine. The turbine converts the flow and pressure of the water to mechanical energy; the water emerging from the turbine returns to the natural watercourse along a tailrace channel. The turbine turns a [[electrical generator|generator]], which is then connected to [[electrical load]]s; this might be directly connected to the power system of a single building in very small installations, or may be connected to a community distribution system for several homes or buildings.<ref name="Energy Savers: Components"/>

Usually, microhydro installations do not have a dam and reservoir, like large [[hydroelectricity|hydroelectric plants]] have, relying on a minimal flow of water to be available year-round.

==Head and flow characteristics==
Microhydro systems are typically set up in areas capable of producing up to 100 [[Watt|kilowatts]] of electricity.<ref name="Energy Savers: Main">{{cite web|title=Microhydropower Systems|url=http://www.energysavers.gov/your_home/electricity/index.cfm/mytopic=11050|publisher=U.S. DOE|access-date=28 November 2010}}</ref> This can power a home or small business facility. This production range is calculated in terms of "head" and "flow". The higher each of these are, the more power available. [[Hydraulic head]] is the pressure measurement of water falling in a pipe expressed as a function of the vertical distance the water falls.<ref name = "Energy Savers: Main"/> This change in elevation is usually measured in feet or meters. A drop of at least 2 feet is required or the system may not be feasible.<ref name="Oregon.gov">{{cite web|title=Micro Hydroelectric Systems|url=http://www.oregon.gov/ENERGY/RENEW/Hydro/Hydro_index.shtml|publisher=Oregon DOE|access-date=1 December 2010|url-status=dead|archive-url=https://web.archive.org/web/20101129052257/http://www.oregon.gov/ENERGY/RENEW/Hydro/Hydro_index.shtml|archive-date=29 November 2010|df=dmy-all}}</ref> When quantifying head, both gross and net head must be considered.<ref name = "Oregon.gov"/> Gross head approximates power accessibility through the vertical distance measurement alone whereas net head subtracts pressure lost due to friction in piping from the gross head.<ref name = "Oregon.gov"/> "Flow" is the actual quantity of water falling from a site and is usually measured in gallons per minute, cubic feet per second, or liters per second.<ref>{{cite web|title=Determining a Potential Microhydropower Site's Flow|url=http://www.energysavers.gov/your_home/electricity/index.cfm/mytopic=11090|publisher=U.S. DOE|access-date=28 November 2010}}</ref> Low flow/high head installations in steep terrain have significant pipe costs. A long penstock starts with low pressure pipe at the top and progressively higher pressure pipe closer to the turbine in order to reduce pipe costs.

The available power, in kilowatts, from such a system can be calculated by the equation P=Q*H/k, where Q is the flow rate in gallons per minute, H is the static head, and k is a constant of 5,310 gal*ft/min*kW.<ref name="motherearthnews">{{cite web|url=http://www.motherearthnews.com/renewable-energy/preparing-hydroelectric-power-zmaz86jfzglo|title=Preparing Your Land for Hydroelectric Power - Renewable Energy|publisher=[[Mother Earth News]]|date=February 1986|website=motherearthnews.com|access-date=14 January 2017}}</ref> For instance, for a system with a flow of 500 gallons per minute and a static head of 60 feet, the theoretical maximum power output is 5.65&nbsp;kW. The system is prevented from 100% efficiency (from obtaining all 5.65&nbsp;kW) due to the real world, such as: turbine efficiency, friction in pipe, and conversion from potential to kinetic energy. Turbine efficiency is generally between 50-80%, and pipe friction is accounted for using the [[Hazen–Williams equation]].<ref name="rpitt">{{cite web|url=http://rpitt.eng.ua.edu/Class/Water%20Resources%20Engineering/M3e%20Comparison%20of%20methods.pdf|title=Module 3e: Comparison of Pipe Flow Equations and Head Losses in Fittings|first=Robert|last=Pitt|first2=Shirley|last2=Clark|date=n.d.|website=eng.ua.edu|publisher=University of Alabama College of Engineering|access-date=14 January 2017}}</ref>

==Regulation and operation==
Typically, an automatic controller operates the turbine inlet valve to maintain constant speed (and frequency) when the load changes on the generator. In a system connected to a grid with multiple sources, the turbine control ensures that power always flows out from the generator to the system. The frequency of the [[alternating current]] generated needs to match the local standard [[utility frequency]]. In some systems, if the useful load on the generator is not high enough, a [[load bank]] may be automatically connected to the generator to dissipate energy not required by the load; while this wastes energy, it may be required if it's not possible to control the water flow through the turbine.

An [[induction generator]] always operates at the grid frequency irrespective of its rotation speed; all that is necessary is to ensure that it is driven by the turbine faster than the synchronous speed so that it generates power rather than consuming it. Other types of generator can use a speed control systems for frequency matching.

With the availability of modern power electronics it is often easier to operate the generator at an arbitrary frequency and feed its output through an [[inverter (electrical)|inverter]] which produces output at grid frequency. Power electronics now allow the use of permanent magnet alternators that produce wild AC to be stabilised. This approach allows low speed / low head water turbines to be competitive; they can run at the best speed for extraction of energy, and the power frequency is controlled by the electronics instead of the generator.

Very small installations ([[pico hydro]]), a few kilowatts or smaller, may generate direct current and charge batteries for peak use times.{{citation needed|reason=Need RS|date=March 2016}}

==Turbine types==
Several types of [[water turbine]]s can be used in micro hydro installations, selection depending on the head of water, the volume of flow, and such factors as availability of local maintenance and transport of equipment to the site. For hilly regions where a waterfall of 50 meters or more may be available, a [[Pelton wheel]] can be used. For low head installations, [[Francis turbine|Francis]] or [[Kaplan turbine|propeller-type]] turbines are used. Very low head installations of only a few meters may use propeller-type turbines in a pit, or water wheels and Archimedes screws. Small micro hydro installations may successfully use industrial centrifugal pumps, run in reverse as prime movers; while the efficiency may not be as high as a purpose-built runner, the relatively low cost makes the projects economically feasible.

In low-head installations, maintenance and mechanism costs can be relatively high. A low-head system moves larger amounts of water, and is more likely to encounter surface debris. For this reason a [[Banki turbine]] also called [[Ossberger turbine]], a pressurized self-cleaning crossflow waterwheel, is often preferred for low-head micro hydro systems. Though less efficient, its simpler structure is less expensive than other low-head turbines of the same capacity. Since the water flows in, then out of it, it cleans itself and is less prone to jam with debris.

*[[Screw turbine]] (Reverse Archimedes' screw): two low-head schemes in England, [[Settle Hydro]] and [[Torrs Hydro, New Mills|Torrs Hydro]] use an Archimedes' screw which is another debris-tolerant design. Efficiency 85%.
*[[Gorlov helical turbine|Gorlov]]: the Gorlov helical turbine free stream or constrained flow with or without a dam,<ref name="GorlovReport1998">''Gorlov A.M.'', [http://www.osti.gov/bridge/servlets/purl/666280-D6NWM1/webviewable/666280.pdf Development of the helical reaction hydraulic turbine]. Final Technical Report, The US Department of Energy, August 1998, The Department of Energy's (DOE) [http://www.osti.gov/bridge/ Information Bridge: DOE Scientific and Technical Information].</ref>
*Francis and propeller turbines.<ref>{{cite web |url=http://www.ashdenawards.org/micro-hydro |title=Micro-hydro |author=Ashden Awards |access-date=29 June 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090426012345/http://www.ashdenawards.org/micro-hydro |archive-date=26 April 2009 |df=dmy-all }}</ref>
*[[Kaplan turbine]] : Is a high flow, low head, propeller-type turbine. An alternative to the traditional kaplan turbine is a large diameter, slow turning, permanent magnet, sloped open flow VLH turbine with efficiencies of 90%.<ref name="vlh">{{cite web|url=http://www.vlh-turbine.com/EN/html/History.htm|title=Hydrovision 2015|author=<!--Staff writer(s); no by-line.-->|date=n.d.|website=vlh-turbine.com|publisher=MJ2 Technologies|access-date=14 January 2017|archive-url=https://web.archive.org/web/20170116173648/http://www.vlh-turbine.com/EN/html/History.htm|archive-date=16 January 2017|url-status=dead|df=dmy-all}}</ref>
*[[Water wheel]] : advanced hydraulic water wheels and hydraulic wheel-part reaction turbine can have hydraulic efficiencies of 67% and 85% respectively. Overshot water wheel maximum efficiency (hydraulic efficiency) is 85%.<ref>{{cite journal|last1=Quaranta and Revelli|title=Output power and power losses estimation for an overshot water wheel|journal=Renewable Energy|date=2015|volume=83|pages=979–987|doi=10.1016/j.renene.2015.05.018}}</ref><ref>{{cite journal|last1=Quaranta and Muller|title=Sagebien and Zuppinger water wheels for very low head hydropower applications|journal=Hydraulic Research|date=2017}}</ref> Undershot water wheels can operate with very low head, but also have  efficiencies below 30%.<ref>{{Cite web |url=http://www.british-hydro.org/downloads/TypesofHydro/Web%20page%20suggested%20update%2010Dec2017.pdf |title=Archived copy |access-date=25 December 2017 |archive-url=https://web.archive.org/web/20171226130450/http://www.british-hydro.org/downloads/TypesofHydro/Web%20page%20suggested%20update%2010Dec2017.pdf |archive-date=26 December 2017 |url-status=dead |df=dmy-all }}</ref> 
*[[Gravitation water vortex power plant]] : part of the river flow at a weir or natural water fall is diverted into a round basin with a central bottom exit that creates a vortex. A simple rotor (and connected generator) is moved by the kinetic energy. Efficiencies of 83% down to 64% at 1/3 part flow.{{Citation needed|reason=ref for 83%|date=December 2017}}

==Use==
Microhydro systems are very flexible and can be deployed in a number of different environments. They are dependent on how much water flow the source (creek, river, stream) has and the velocity of the flow of water. Energy can be stored in battery banks at sites that are far from a facility or used in addition to a system that is directly connected so that in times of high demand there is additional reserve energy available. These systems can be designed to minimize community and environmental impact regularly caused by large dams or other mass hydroelectric generation sites.<ref name="RISE">{{cite web|title=Microhydro|url=http://www.rise.org.au/info/Tech/hydro/small.html|publisher=Research Institute for Sustainable Energy|access-date=9 December 2010}}</ref>

===Potential for rural development===
In relation to [[rural development]], the simplicity and low relative cost of micro hydro systems open up new opportunities for some isolated communities in need of electricity. With only a small stream needed, remote areas can access lighting and communications for homes, medical clinics, schools, and other facilities.<ref name="Ashden Awards">{{cite web|title=Micro-hydro|url=http://www.ashdenawards.org/micro-hydro|publisher=The Ashden Awards for Sustainable Energy|access-date=20 November 2010|url-status=dead|archive-url=https://web.archive.org/web/20101101184402/http://www.ashdenawards.org/micro-hydro|archive-date=1 November 2010|df=dmy-all}}</ref> Microhydro can even run a certain level of machinery supporting small businesses. Regions along the [[Andes]] mountains and in Sri Lanka and China already have similar, active programs.<ref name = "Ashden Awards"/> One seemingly unexpected use of such systems in some areas is to keep young community members from moving into more urban regions in order to spur economic growth.<ref name = "Ashden Awards"/> Also, as the possibility of financial incentives for less [[emission intensity|carbon-intensive]] processes grows, the future of microhydro systems may become more appealing.

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{{spaced ndash}} alongside standard electrification{{spaced ndash}} into the project design.

==Cost==
The cost of a micro hydro plant can be between 1,000 and 5000 U.S. dollars per kW installed {{citation needed|date=March 2020}}

==Advantages and disadvantages==

===Advantages===
Microhydro power is generated through a process that utilizes the natural flow of water.<ref name="Wind and Hydro">{{cite web|title=Microhydropower|url=http://www1.eere.energy.gov/windandhydro/pdfs/doewater-10107-vol.1-pt1.pdf|publisher=U.S. DOE|access-date=20 November 2010}}</ref> This power is most commonly converted into electricity. With no direct [[Pollution|emission]]s resulting from this conversion process, there are little to no harmful effects on the environment, if planned well, thus supplying power from a [[Renewable resource|renewable]] source and in a [[Sustainable energy|sustainable]] manner. Microhydro is considered a "[[Run-of-the-river hydroelectricity|run-of-river]]" system meaning that water diverted from the stream or river is redirected back into the same watercourse.<ref name="Microhydro Pros and Cons">{{cite web|title=Micro Hydro Power - Pros and Cons|url=http://www.alternative-energy-news.info/micro-hydro-power-pros-and-cons/|publisher=Alternative Energy News Network|access-date=24 November 2010}}</ref> Adding to the potential economic benefits of microhydro is efficiency, reliability, and cost effectiveness.<ref name = "Microhydro Pros and Cons"/>

===Disadvantages===
Microhydro systems are limited mainly by the characteristics of the site. The most direct limitation comes from small sources with the minuscule flow. Likewise, flow can fluctuate seasonally in some areas. Lastly, though perhaps the foremost disadvantage is the distance from the power source to the site in need of energy. This distributional issue as well as the others are key when considering using a micro-hydro system.

== See also ==
{{Portal|Renewable energy|Energy|Water}}
*[[Small hydro]] up to 10,000&nbsp;kW
*[[Pico hydro]] up to 5&nbsp;kW
*[[Hydro power]]
*[[Renewable Energy]]
*[[Sustainable energy]]
*[[Water wheels]]
*[[Vortex power]]
*[[Gravitation water vortex power plant|Gravitation water vortex power]]

==References==
{{Reflist}}

==External links==
{{Commons category|Micro-hydroelectric power plants}}
*[http://microhydropower.net Portal on microhydro power]
*[https://web.archive.org/web/20181121075109/http://www.smarthydro.eu/ SMART - Strategies to promote small scale hydro electricity production in Europe] (project financed by the European Commission, involves Italy, Croatia, Norway, Greece and Austria)
*[http://www.doradovista.com/DVPower2.html Micro Hydro information], Dorado Vista ranch application
*[https://web.archive.org/web/20110501225851/http://www.esha.be/ European Small Hydropower Association]
*[http://www.microhydroassociation.org Micro Hydro Association UK]
*[https://web.archive.org/web/20070205093845/http://hydro2.inel.gov/prospector/ Hydropower Prospector], Idaho National Engineering Laboratory
*[https://web.archive.org/web/20080926190919/http://www.ashdenawards.org/case_studies?filter0=22&filter1= Ashden Awards hydro power winners]
*[https://sites.google.com/site/sandaigknoydart2/sandaig-cottage-knoydart/the-micro-hydro-system Example of a new Scottish Highland micro hydro system]
*[http://www.homebrewhydro.com/ Home built micro hydro project]
*[http://www.remotehydrolight.com/ Microhydro in Afghanistan with drawings of equipment]

{{Hydropower}}
{{Authority control}}

{{DEFAULTSORT:Micro Hydro}}
[[Category:Appropriate technology]]
[[Category:Power station technology]]
[[Category:Hydroelectricity]]
[[Category:Distributed generation]]