How it works
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HP schemes, considered as those with installed capacity of up to 10 MW *, generate electricity or mechanical power by converting the power available in fl owing water of rivers, canals and streams. The objective of a hydropower scheme is to convert the potential energy of a mass of water, flowing in a stream with a certain fall (termed the «head»), into electric energy at the lower end of the scheme, where the powerhouse is located. The power of the scheme is proportional to the flow and to the head. 1 GWh supplies electricity for about 220 European households One small hydropower plant of 1 MW produces on average 5 GWh/ year in Austria, supplying electricity to 1100 households 5 GWh/year supplies electricity to 2200 households in a developing country.
Hydropower produces high-quality electricity Hydropower has the ability to generate electricity instantly to supply both, base-load and peak - load generation. Hydropower electrify is easy to predict and to manage, it can be easily adapted to unexpected increases in electricity demand.
* the defined upper power limit varies from country to country from 1.5 to 12 MW, but 10MW is becoming the generally accepted limit for SHP and has been adopted by ESHA and the European Commission.
Supported by
SMALL HYDROPOWER
HYDROPOWER TECHNOLOGY
Beginning of the water right
Desablor Water chamber
How do SHP plants produce electricity?
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The turbine
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he purpose of a hydraulic turbine is to transform the water potential and kinetic energy to mechanical rotational energy. Various types of turbines exist to cope with different levels of head and flow. The two broad categories are: Impulse turbines – notably the Pelton, Turgo or the Banki-Michell (cross-flow) - in which water impinges or enters the runner, which is designed to change the water’s direction and thereby extract the momentum from it with scarce change of pressure energy.
Reaction turbines – notably Francis and Kaplan – which run full of water and in effect generate hydrodynamic “lift” forces to propel the runner blades, extracting thus the pressure energy of inflowing water.
Electrical grid
Penstock
he basic principle of hydropower is to transform the potential energy of water into mechanical energy available at a turbine shaft and afterwards into electricity through a generator. Water can be piped from a certain level to a lower level. Then the resulting water pressure and/or kinetic energy can be used to do some useable work. If the water is allowed to move a mechanical component then that movement involves conversion of the mechanical energy of the water into mechanical energy of this component. Hydro turbines convert water pressure and kinetic energy into mechanical energy, which can be used to drive an electricity generator. The main requirement is to have a ‘head’ so that water, diverted through an intake channel or a pipe (the penstock) into a turbine, discharges back into the river downstream. Sometimes the river has a suitable drop in level and the head is geologically given and available. In other cases it is necessary to create an artificial head. The head is the difference in altitude between the water intake and the lower water level. It is normal to achieve optimum energy conversion efficiencies with all types of hydraulic turbines in the range of 80 up to over 90%.
Water intake: dam with fish ladder
Power station
Command Control Residus flow
Turbine and generator (c) OFCL
The generator
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enerators transform mechanical energy into electrical energy. An electric generator is made up of a stationary part (stator) and a moving part (rotor). The electric current is generated by the rotation of the magnetic field of the rotor through the coil of the conducting wiring of the stator. Once set in motion, the turbine drives the electric generator (either directly or through a multiplier), which then transforms the mechanical energy from the shaft into electrical energy. There are two categories of generators: the synchronous generators, and the asynchronous (induction) generators. Asynchronous motors in generating mode are commonly used as generators in micro power plants.
Speed increasers and control systems
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he optimal rotation speed of the turbine depends at the same time on the type of turbine, on the head and on the flow. In order to synchronise the work of the different equipments it is necessary to situate the speed increaser in between the turbine and the generator. Since small hydro schemes are nowadays unattended, control systems that increase the efficiency of the plants, based on personal computers are commonly used.
Planning a small hydropower scheme The final implementation of a SHP plant is the result of a complex and interactive process, where consideration is given to both environmental impacts and different technological options as assessed from the economic point of view.
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Main types of Turbines
Features
Pelton
Impulse turbine suitable for high heads (from 100 to 1 000 meters and more) and small discharges
Banki-Michell
Impulse turbine suitable for medium head typically from 4 to 200 meters
Francis
Radial-flow reaction turbines suitable for medium head from 10 to 100 –500 meters
Kaplan
Axial or radial flow reaction turbine, generally used for low heads from 1,5 to 10-50 meters.
List of the studies that should be undertaken
Topography and geomorphology of the site. Evaluation of the water resource and its generating potential Site selection and basic layout Hydraulic turbines and generators and their control Environmental impact assessment and mitigation measures Economic evaluation of the project and financing potential Institutional framework and administrative procedures to attain the authorizations
1. Flow calculation
2. Head Calculation
The calculation of the flow is essential for the project. The flow will influence the power of the SHP and its profitability. In order to understand the availability of flow in a river section, it is very useful to plot that stream flow records through the flow duration curve (FDC). This curves shows the portion of time in which the discharge equals or exceeds certain values. In this way it is possible to estimate the medium number of days in a year in which a certain flow is available and to program the water use of the plant. In parallel necessary information on measuring the flow of the river is needed, and the catchments area should be evaluated. Information drawn from the stream flow records, statistical information on the weather forecasts and on-spot measurements are needed. In Europe, these can be obtained from national hydrological institutes.
The gross head may be rapidly estimated, either by field surveying or by orthophotographic techniques. The gross head is the vertical distance that the water falls through when generating useable power, i.e. the difference between the upper and lower water surface levels. Having established the gross head available, it is necessary to take into account the losses arising from trash racks, pipe friction, bends, valves and unutilized kinetic energy at the turbine outlet. The net head will be determined after having estimated the various head losses.
3. Approximated annual energy production Knowing the flow and the net head, the estimated annual energy production of the site can be calculated.
The output of a hydropower plant is given in terms of power [kW] and electricity production [kWh]. The result can be calculated as follows: P (kW) = Q (m3/s) x H (m) x tot x 9,81 and approximately Q x H x 7,8 tot = total efficiency (turbine x generator x speed increaser x trafo) P = electrical power output Q = rated discharge H = net head Electricity production - the thing we pay for - is electrical power supply during a certain time period. The annual electricity production of a hydropower (HP) station is approximately calculated as E (kWh) = P (kW) x 4500 (h)
How the electricity is distributed? Energy Transformer
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he transformer allows electricity to be efficiently transmitted over long distances. This makes it possible to supply electricity to homes and businesses located far from the electric generating plant. The transformer is a device, which through electromagnetic induction transforms alternating electric energy in one circuit into energy of a similar type in another circuit, commonly Off grid with altered values of voltage and current. The transformer situated SHP systems can also be alone stand-alon installations, inside the powerhouse takes the alternating electric current from i.e not connected to the grid. Stand-alone micro-hydro the generator terminals and converts it to the current of lower does not need to have a battery bank. The frequency value while increasing the voltage in the same ratio. of the electricity is controlled using a load controller.
The Grid
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ower travels from the power plant to the end user through the power distribution grid. Because of the European effort for the development of renewable energy sources, utilities have received a large increase in demand for the connection of decentralised plants. The European policy framework supports easy access to the grid for renewable energy producers.
But, a stand-alone scheme can be used to charge a battery bank, if this energy service is required. Off grid small hydropower schemes are a suitable solution for electricity supply in developing countries and in mountainous areas in developed ones. Increasing automation State of the art industrial automation components and excellent communication features ensure that an operator can identify the status of the plant at any time and anywhere, using computers, PDAs, cell phones or just a simple telephone and allows to respond remotely on problems, where applicable.
SMALL HYDROPOWER
In order to use the electricity produced by the SHP plant it should be transmitted to the final user.
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n investment in a small hydropower scheme entails a certain number of expenses, extended over the project lifetime, and produces at the same time revenues also distributed over the same period. The expenses include a fixed component - the capital cost, insurance, taxes, etc- and a variable component -operation and maintenance costs-. Feasibility studies They include hydrological and environmental assessment, preliminary designs, permits and approvals (for water, land use and construction), land rights, interconnection studies, power purchase agreements (PPA), project management and financing fees. The cost of required permits varies from country to country with an average from 10 000 to 30 000 euros for a request of authorisation. This amount is lost if the authorisation is denied. Grid interconnection studies as well as the relevant contracts for interconnection, transmission of energy through the power grid, and power sales themselves (PPA) are of course fundamental for the success of a grid-connected plant. Operation and Maintenance These are regular costs that occur on a yearly basis and include transmission line maintenance, general administration, repairs etc. The constructions The amount to invest varies from project to project. On average the range of investment costs varies in the range of 1000-3000 €/kW. In other term the financial investment is recovered in 10-20 years, without public financial assistance.
Investment and production costs of SHP plants in some Members States of the EU (2003) Country
Average SHP production costs Ecents/kWh
Range Investment costs E/kW
Spain
3.5 - 7
1500
Austria
3.6 – 14.5
2500
Sweden
4–5
1800-2200
Czech Republic 2-3
600-2000
Lithuania
2.5-3
2200-2500
Slovenia
4-7.9
1500-2200
Poland
3
700-2500
The Revenues
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evenues come from specific purchase contracts signed with the electric utilities. Depending on the legislation, electric utilities are usually obliged to buy the electricity generated from renewable energy resources on a priority basis. In some countries there are specific incentives given to investment in electricity production using RES. According to these special schemes, renewable energy projects can apply for special loans with low or even zero interest rates, or receive other types of investment subsidies. Prices paid to SHP producers vary considerably among European countries. In the tariff structure different components can be found, according to the country: a market price, an avoided carbon price, a green certificate price. The different support schemes can affect greatly the development of SHP. Whereas a fixed feed-in tariff reduces uncertainty and guarantees cash flow for a determined duration, market-based schemes can sometimes reveal themselves too uncertain and therefore unattractive to developers. Germany
Average feed-in tariff is 6.65 €cents/kWh (66,5 EUR/ MWh). It depends on the capacity of the plant. Maximum can reach up to 8 €cents/kWh (80 EUR/MWh). Scheme valid for 20 years.
Italy
Average 75 €/MWh (for selling electricity) + 125,2 € /MWh (Green certificates) The grid authority fixes a cap (upper) price for green certificates every year. Certificates are issued only for the first 12 years of operation.
Slovenia
Feed-in (61,45 €/MWh; 2003), premium (28,12 €/ MWh; 2003) included. SHP>1 MW: Feed-in=59,29 €/MWh (premium=25,96 € /MWh - included).
EUROPEAN SMALL HYDROPOWER ASSOCIATION Renewable Energy House 63-67 Rue d’Arlon - B-1040 Brussels • Belgium T: +32 2 546 1945 • F: +32 2 546 1947 E: info@esha.be • I: www.esha.be ESHA is founding member of EREC, the European Renewable Energy Council
Illustration sources: Ageneer, Universidad de Jaen, Kö, IED, BOKU, MHyLab, VATECH, Elmotech, Ingegneri Maggia SA, Commune de Savièse (CH), ISET, Studio Frosio, SERO, EPFL-LCH, Walcher, Sasso s.r.l. Design : ACG Brussels The sole responsibility for the content of this publication lies with the authors. It does not necessarily reflect the opinion of the European Communities. The European Commission is not responsible for any use that may be made of the information contained therein.
How much does a SHP project cost?