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Small hydropower stations are usually run off schemes. The most known example in central Europe would probably be a traditional mill. In most countries where water power is used mills have been the firs usage. Originally the water wheel drove the millstones directly. Modern micro-hydro power (MHP) plants use Turbines instead of water wheels and mostly power a generator to produce electricity. But in cases where machinery can be used and installed near the turbine direct driven systems have some advantages . Such systems are purely mechanical and therefore extremely robust. Actually there is no comprehensive technology to drive machinery without combustion engines.
Categories on small hydropower are mostly taken by size of output power. Nevertheless is the upper limit of a locations power determined by the local conditions like amount of flowing water and height difference.
Table 1: Classification of small hydropower by size [ kW (Kilowatt) = 1000 Watts; MW (Megawatt) = 1,000,000 Watts or 1000 kW]
1 - 15 MW - usually feeding into a grid
from ~ 100 kW up to 1 MW; either stand alone schemes or more often feeding into the grid
from few kW up to 100 kW; usually provided power for a small community or rural industry in remote areas away from the grid.
from a few hundred watts up to 5kW
Figure 1 shows the main components of a run-of-the-river micro-hydro scheme. This type of scheme requires no water storage but instead diverts some of the water from the river which is channelled along the side of a valley before being 'dropped' into the turbine via a penstock. In figure 1, the turbine drives a generator that provides electricity for a workshop. The transmission line can be extended to a local village to supply domestic power for lighting and other uses.
Figure 1: Layout of a typical micro hydro scheme
There are various other configurations which can be used depending on the topographical and hydrological conditions, but all adopt the same general principle.
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Water into Watts
To determine the power potential of the water flowing in a river or stream it is necessary to determine both the flow rate of the water and the head through which the water can be made to fall. The flow rate is the quantity of water flowing past a point in a given time. Typical flow rate units are litres per second or cubic meters per second. The head is the vertical height, in meters, from the turbine up to the point where the water enters the intake pipe or penstock.
The potential power can be calculated as: P = g * Q * H * feff
Example:A location with a head of 10 metres, flow of 300 liter / sec (= 0.3 m3/s) will have a potential power of 15 kW electricity:
10m/s2 * 0.3m3/s * 10m * 0.5 = 15m5/s3
= 15m5/s3 * 1000 kg/m3 (density of water)
= 15000 J/s
= 15000 W
Power in kW (P); Flow rate in m3 /s (Q); Head in m (H); Gravity constant = 9.81 m/s2 (g); Efficiency factor (feff) => 0.4 - 0.7 *
*Small water turbines rarely have efficiency better than 80%. Generators' efficiency of ~ 90% and power will also be lost in the pipe carrying the water to the turbine, due to frictional losses. A rough guide used for small systems of a few kW rating is to take the overall efficiency as approximately 50%. Thus, the theoretical power must be multiplied by 0.50 for a more realistic figure
If a machine is operated under conditions other than full-load or full-flow then other significant inefficiencies must be considered. Part flow and part load characteristics of the equipment needs to be known to assess the performance under these conditions. It is always preferable to run all equipment at the rated design flow and load conditions, but it is not always practical or possible where river flow fluctuates throughout the year or where daily load patterns vary considerably.
Depending on the end use requirements of the generated power, the output from the turbine shaft can be used directly as mechanical power or the turbine can be connected to an electrical generator to produce electricity. For many rural industrial applications shaft power is suitable
(for food processing such as milling or oil extraction, sawmill, carpentry workshop, small scale mining equipment, etc.), but many applications require conversion to electrical power. For domestic applications electricity is preferred.
This can be provided either:
- directly to the home via a small electrical distribution system or,
- can be supplied by means of batteries which are returned periodically to the power house for recharging - this system is common where the cost of direct electrification is prohibitive due to scattered housing (and hence an expensive distribution system),
Where a generator is used alternating current (a.c.) electricity is normally produced. Singlephase power is satisfactory on small installations up to 20kW, but beyond this, 3-phase power is used to reduce transmission losses and to be suitable for larger electric motors. An a.c. power supply must be maintained at a constant 50 or 60 cycles/second for the reliable operation of any electrical equipment using the supply. This frequency is determined by the speed of the turbine which must be very accurately governed.
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Suitable Conditions for Micro-Hydro Power
The best geographical areas for exploiting small-scale hydro power are those where there are steep rivers flowing all year round, for example, the hill areas of countries with high year-round rainfall, or the great mountain ranges and their foothills, like the Andes and the Himalayas. Islands with moist marine climates, such as the Caribbean Islands, the Philippines and Indonesia are also suitable. Low-head turbines have been developed for small-scale exploitation of rivers where there is a small head but sufficient flow to provide adequate power.
To assess the suitability of a potential site, the hydrology of the site needs to be known and a site survey carried out, to determine actual flow and head data. Hydrological information can be obtained from the meteorology or irrigation department usually run by the national government. This data gives a good overall picture of annual rain patterns and likely fluctuations in precipitation and, therefore, flow patterns. The site survey gives more detailed information of the site conditions to allow power calculation to be done and design work to begin. Flow data should be gathered over a period of at least one full year where possible, so as to ascertain the fluctuation in river flow over the various seasons. There are many methods for carrying out flow and head measurements and these can be found in the relevant texts.
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A turbine converts the energy in falling water into shaft power. There are various types of turbine which can be categorised in one of several ways. The choice of turbine will depend mainly on the pressure head available and the design flow for the proposed hydropower installation. As shown in table 2 below, turbines are broadly divided into three groups; high, medium and low head, and into two categories: impulse and reaction.
Table 2: Classification of turbine types:
- Multi-jet Pelton
- Multi-jet Pelton
- Pump-as-turbine (PAT)
The difference between impulse and reaction can be explained simply by stating that the impulse turbines convert the kinetic energy of a jet of water in air into movement by striking turbine buckets or blades - there is no pressure reduction as the water pressure is atmospheric on both sides of the impeller. The blades of a reaction turbine, on the other hand, are totally immersed in the flow of water, and the angular as well as linear momentum of the water is converted into shaft power - the pressure of water leaving the runner is reduced to atmospheric or lower.
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The load factor is the amount of power used divided by the amount of power that is available if the turbine were to be used continuously. Unlike technologies relying on costly fuel sources, the 'fuel' for hydropower generation is free and therefore the plant becomes more cost effective if run for a high percentage of the time. If the turbine is only used for domestic lighting in the evenings then the plant factor will be very low. If the turbine provides power for rural industry during the day, meets domestic demand during the evening, and maybe pumps water for irrigation in the evening, then the plant factor will be high.
It is very important to ensure a high plant factor if the scheme is to be cost effective and this should be taken into account during the planning stage. Many schemes use a 'dump' load (in conjunction with an electronic load controller - see below), which is effectively a low priority energy demand that can accept surplus energy when an excess is produced e.g. water heating, storage heaters or storage cookers.
Load control governors
Water turbines, like petrol or diesel engines, will vary in speed as load is applied or relieved. Although not such a great problem with machinery which uses direct shaft power, this speed variation will seriously affect both frequency and voltage output from a generator. Traditionally, complex hydraulic or mechanical speed governors altered flow as the load varied, but more recently an electronic load controller (ELC) has been developed which has increased the simplicity and reliability of modern micro-hydro sets. The ELC prevents speed variations by continuously adding or subtracting an artificial load, so that in effect, the turbine is working permanently under full load. A further benefit is that the ELC has no moving parts, is very reliable and virtually maintenance free. The advent of electronic load control has allowed the introduction of simple and efficient, multi-jet turbines, no longer burdened by expensive hydraulic governors.
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The Economics - Cost Reduction
Normally, small-scale hydro installations in rural areas of developing countries can offer considerable financial benefits to the communities served, particularly where careful planning identifies income-generating uses for the power.
The major cost of a scheme is for site preparation and the capital cost of equipment. In general, unit cost decreases with a larger plant and with high heads of water. It could be argued that small-scale hydro technology does not bring with it the advantages of 'economy of scale', but many costs normally associated with larger hydro schemes have been 'designed out' or 'planned out' of micro hydro systems to bring the unit cost in line with bigger schemes.
This includes such innovations as:
- using run-of-the-river schemes where possible - this does away with the cost of an expensive dam for water storage
- locally manufactured equipment where possible and appropriate
- use of HDPE (plastic) penstocks where appropriate
- electronic load controller - allows the power plant to be left unattended, thereby reducing labour costs, and introduce useful by-products such as battery charging or water heating as dump loads for surplus power; also does away with bulky and expensive mechanical control gear
- using existing infrastructure, for example, a canal which serves an irrigation scheme
- siting of power close to village to avoid expensive high voltage distribution equipment such as transformers
- using pumps as turbines (PAT) - in some circumstances standard pumps can be used 'in reverse' as turbines; this reduces costs, delivery time, and makes for simple installation and maintenance
- using motors as generators - as with the PAT idea, motors can be run 'in reverse' and used as generators; pumps are usually purchased with a motor fitted and the whole unit can be used as a turbine/generator set
- use of local materials for the civil works
- use of community labour
- good planning for a high plant factor (see above) and well balanced load pattern (energy demand fluctuation throughout the day)
- low-cost connections for domestic users (see following chapter on this topic)
- self-cleaning intake screens - this is a recent innovation which is fitted to the intake weir and prevents stones and silt from entering the headrace canal; this does away with the need for overspill and desilting structures along the headrace canal and also means that, in many cases, the canal can be replaced by a low-pressure conduit buried beneath the ground - this technology is, at present, still in its early stages of dissemination
Maintenance costs (insurance and water abstraction charges, where they apply) are a comparatively minor component of the total - although they may be an important consideration in marginal economic cases.
For further details of the economics of micro-hydro power see the case study on the Micro-hydro Scheme in Zimbabwe
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Programmes promoting the use of micro-hydro power in developing countries have concentrated on the social, as well as the technical and economic aspects of this energy source. Technology transfer and capacity building programmes have enabled local design and manufacture to be adopted. Local management, ownership and community participation has meant that many schemes are under the control of local people who own, run and maintain them. Operation and maintenance is usually carried out by trained local craftspeople.
Low-cost Grid Connection
Where the power from a micro-hydro scheme is used to provide domestic electricity, one method of making it an affordable option for low-income groups is to keep the connection costs and subsequent bills to a minimum. Often, rural domestic consumers will require only small quantity of power to light there houses and run a radio or television. There are a number of solutions that can specifically help low-income households to obtain an electricity connection and help utilities meet their required return on investment.
- Load limited supply.
- Load limiters work by limiting the current supplied to the consumer to a prescribed value. If the current exceeds that value then the device automatically disconnects the power supply. The consumer is charged a fixed monthly fee irrespective of the total amount of energy consumed. The device is simple and cheap and does away with the need for an expensive metre and subsequent meter reading.
- Reduced service connection costs. Limiting load supply can also help reduce costs on cable, as the maximum power drawn is low and so smaller cable sizes can be used. Also, alternative cable poles can sometimes be found to help reduce costs.
- Pre-fabricated wiring systems. Wiring looms can be manufactured 'ready to install' which will not only reduce costs but also guarantee safety standards.
- Credit. Credit schemes can allow householders to overcome the barrier imposed by the initial entry costs of grid connection. Once connected, energy savings on other fuels can enable repayments to be made. Using electricity for lighting, for example, is a fraction of the cost of using kerosene.
- Community involvement. Formation of community committees and co-operatives who are pro-active in all stages of the electrification process can help reduce costs as well as provide a better service. For example, community revenue collection can help reduce the cost of collection for the utility and hence the consumer.
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Complexity of Micro-Hydropower (MHP) - Barriers to Success
A wide range of topics needs to be address to implement MHP projects successfully. The Thumbnail Diagramm ( click to enlarge) below provides an overview of ascpects to be considered when planning or implementing a MHP scheme. There is another article which provides an insight into Complexity of MHP and the barriers to success.
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Appropriate Scale Hydro-power
In recent years there has been much debate over the appropriate scale of hydro power. Many argue that large hydro is not only environmentally damaging (as large areas of land are flooded) but that there is also a negative social impact where large imported technologies are used.
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The information below provides a short summary for constructing a small hydro power.
Equip a Certain Place with Hydropower (A)
1. Check the sites feasibility.
This means, gather the following Data:
head, flow, number of consumers, location data (distance from grid...).
► Go there and fill out this form => a two page condensed site assessment
► If you need further quick information go to Hydropower Basics
2. Calculate the sites hydropower potential:
Multiply the (minimal) flow in liter/second with the available height difference. The result times 5 gives you an estimation on how many Watts can be produced.
► see also Hydropower Basics
3. Estimate the required power at the site.
Separate consumer power and productive use power. Keep in mind that transmission cables are costly.
Consumers basics are light and TV. Light requires min. 5 -20 Watt per bulb (5 W = energy saving lamp, if available). A TV requires 40 - 150 W (depending on size and type). Machinery needs much more power. Motors may require from 1000 Watt (1kW = small) upward. Heating needs also a lot power (min. 500 W for a small water heater).
4. Compare the local hydropower potential with the de'mand of electric power.
If the potential is to be gained, check if the Data from point 1. is really valid.
Is the measured flow available all year round?
Is the head available on a short horizontal distance - means "how long have canal and penstock to be?"
5. Cost estimation:
There is no general cost estimation possible as any site differs from the other. Biggest cost blocks are usually:
Civil structure: Ask a company to find out the local cost for building (material).
mansion cost per m3 weir - 1.5 m height x width of river; cost per m canal - size depends on water volume; cost per m2 powerhouse ~ 10 - 25 m 2
Penstock: ask the local prices for pipes - size depends on water volume
Turbine, Generator, Controller: Ask a turbine manufacturer for an offer for your power range and site conditions (flow and head). The final price will range between the offer from a German producer and some Chinese products.
Transmission line: Check required local standards. Ask the cable cost/meter for your potential power. Cable length goes from powerhouse towards the load center (village center)
Transformer: Power > 10 kW and long transmission lines > 2 km require transformer stations.
House connections: Depending on distance towards house and power line (cable length), number of appliances (just lights?), safety standards (mcb) and metering devices/ load limiters.
-> please feel free to extend and sharpen this cost section <-
With the above knowledge you should be able to discuss a projects realisation seriously. First step is usually a professional feasibility study.
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Implementing a mhp Scheme in an Area / Region / Country (B)
- for business, demonstration or informative reasons -
1. Set preferences for the potential mhp project
If you not fixed to a certain location to implement a mhp scheme you start chose a range of preferences. These define a potential sites features.
| Site features ( + sufficient hydro potential)
| Difficulties (possible) / interference with|
| stable management, solid equipment
| social issues are difficult to predict|
| long term operation
| good social setup, stable management
| social issues are difficult to plan
| high social impacts
| intensive social setup, high level of participation
| time intensive, depending on social developments|
| poverty reduction
| poor clients, opportunities for productive use
| low financial resources, support often leads to dependencies, requires high efforts in social setup|
| high financial revenues
| rehabilitation of existing sites, feed in tariffs, grid connection, financial potent customers
| including financial entities (Banks, Governmental bodies)|
| productive usage
| demand for machinery, potential for marketable products, local entrepreneurship available.
| high effort to identify strengths within a society;|
tightrope walk between support and incapacitation
Feasibility, planning, social setup and installation requires regular trips to the site. Traveling efforts can be reduced if accessibility is adequate.
'2. Find suitable lo'cation(s)
Check, how far a mhp power potential suits the preferences set by the project / clients. (=> see A)
3. Integrate the potentially affected communities as soon as possible in the process.
If supplying a local or isolated grid the local community plays a key role for the sites later success.Do not ever promise anything before you sure that a project will be implemented at a certain location.
Concentrate on cooperation and integration of participants. Use local resources where ever possible. Social issues are usually much more complicated than technical issues. They are time consuming, may vary during the process and are different on each location. Nevertheless a working social network is usually the biggest factor towards success.
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Standard Procedure - Typical Questions
- Interest on a potential hydropower location
- Idea for energy usage: direct drive of machinery, electricity production for local use or feed into grid for revenue
- Difficulty: financial coverage, remote location, specific conditions, uncertain outcome
- Price range: depends on size of potential site, ranges from 2000 - 5000 USD/kW
- Material needed: Turbine, generator, controller come from a specialist
- Suitable geographic area: usual hilly and all year round water flow, also irrigation canals can have good hydropower potential
- Required competencies: Experience in mhp feasibility for pre-study and planning, patience in cooperation with the local entities
- Supply for how many people: Available share per household (hh) depends on local hydro potential and type of use (lighting, TV, machinery, ...)
- How Long does it take: Ideally flow measurements should be taken over several years to ensure safe data. A must is the measurement of the minimal flow during dry season. From there on a mhp plant can be installed within one year. Accessibility of remote location, delivery times for turbine and generator and social setup usually take longer than estimated.
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- ↑ Micro-hydro Design Manual, IT Publications, 1993
- Micro-hydro Design Manual, A Harvey & A Brown, ITDG Publishing, 1992.
- Micro-hydro power: A guide for development workers, P Fraenkel, O Paish, V Bokalders, A Harvey & A Brown, ITDG Publishing, IT Power, Stockholm Environment Institute, 1991.
- Small hydro Power in China, ITDG Publishing, 1985.
- Motors as Generators for Micro-Hydro Power, Nigel Smith, IT Publications, 1994.
- Pumps as Turbines - A users guide, Arthur Williams, ITDG Publishing, 1995.
- Rural Energy in Peru - Power for Living, ITDG, 1996.
- Low-cost Electrification - Affordable Electricity Installation for Low-Income Households in Developing Countries, IT Consultants/ODA, 1995.
- The Micro-hydro Pelton Turbine Manual: Design, Manufacture and Installation for Small-scale Hydropower, Jeremy Thake, ITDG Publishing, 2000.Going with the Flow: Small-scale Water Power, Dan Curtis, CAT 1999 Small Hydro as an Energy Option for Rural Areas of Perú by Teodoro Sanches ITDG Latin America
- The Role of the Private Sector in the Small-scale Hydropower Field, K. Goldsmith, SKAT, 1995