MRES.B.02.07 Small Hydroelectric Power Plant (MRES.B.02.07)
Georgios TSEKOURAS
Overview of Small Hydroelectric Power Plant course module:
- General introduction to hydroelectric power plant (Basic operation principles, categorization, differences between small and large hydro-electric power plant, definition of small hydropower, site configurations (Run-of-river, at the base of a dam, within an irrigation canal, in a water abstraction system), planning)
- Fundamental of Hydraulic Engineering (introduction, water flow in pipes (head losses due to friction, local head losses, transient flow, hydraulic hammer), water flow in open channels (Classification of open channel flows, uniform flow, efficient cross-section & principles of energy in open channel flows))
- Evaluating stream flow (introduction, stream flow records, evaluating stream flows by discharge measurements (with velocity-area, weir, slope-area methods), stream flow characteristics (hydrograph, flow duration curves, standardised flow duration curves, water pressure)), residual, reserved or compensation flow, estimation of plant capacity and energy output (influence of flow variation and head variation on the turbine capacity, peaking operation, firm energy, floods (flood control design, statistical analysis of flood data, hydrological modelling of the catchment area))
- Site evaluating methodologies (cartography, geochemical studies, practical cases, learning from failures)
- Hydraulic structures (dams (types: embankment, concrete, other; loads and stability, dam safety), weirs and spillways (gated, ungated), energy dissipating structures, intake structures (types, head losses, trashracks, vorticity), sediment traps (efficiency, design), gates and valves, open channels (design and dimensioning, excavation and stability), forebay tanks, penstocks, tailraces)
- Electromechanical structures (powerhouse, hydraulic turbines ( types and configuration, specific speed and similitude, preliminary design, selection criteria, efficiency), speed increasers (types, design, maintenance), generators (configurations, synchronous- asynchronous –dc generators, exciters, voltage regulation and synchronization, special specifications), turbine control, switchgear equipment, automatic control (governor – automatic voltage regulator – case of autonomous operation), ancillary electrical equipment (plant service transformer, DC control power supply, headwater and tailwater recorders, outdoor substation))
- Connection of hydro-power plant with grid through transmission / distribution lines: steady state and transient state current analysis for different operation modes, faults, power quality issues, power stability
- Environmental impact and its mitigation ((introduction, burdens and impacts identification, impacts in the construction phase (reservoirs, water intakes, open canals, penstocks, tailraces), impacts arising from the operation of the scheme (sonic, landscape, biological impacts), impacts from transmission lines (visual, health)))
- Economic analysis (basic considerations, time value of money, methods of economic evaluation (payback time period, net present value, benefit-cost ratio, internal rate of return), tariffs and incentives)
- Administrative procedures (types of procedures (energy regulation – water rights, environmental procedures, public inquiry, construction requirements, connection to the grid, others), examples)
- Special issues: Small hydropower plant in the modern electricity market, possibility for pump hydropower plants, etc.
Overview of Small Hydroelectric Power Plant course module:
- General introduction to hydroelectric power plant (Basic operation principles, categorization, differences between small and large hydro-electric power plant, definition of small hydropower, site configurations (Run-of-river, at the base of a dam, within an irrigation canal, in a water abstraction system), planning)
- Fundamental of Hydraulic Engineering (introduction, water flow in pipes (head losses due to friction, local head losses, transient flow, hydraulic hammer), water flow in open channels (Classification of open channel flows, uniform flow, efficient cross-section & principles of energy in open channel flows))
- Evaluating stream flow (introduction, stream flow records, evaluating stream flows by discharge measurements (with velocity-area, weir, slope-area methods), stream flow characteristics (hydrograph, flow duration curves, standardised flow duration curves, water pressure)), residual, reserved or compensation flow,
Overview of Small Hydroelectric Power Plant course module:
- General introduction to hydroelectric power plant (Basic operation principles, categorization, differences between small and large hydro-electric power plant, definition of small hydropower, site configurations (Run-of-river, at the base of a dam, within an irrigation canal, in a water abstraction system), planning)
- Fundamental of Hydraulic Engineering (introduction, water flow in pipes (head losses due to friction, local head losses, transient flow, hydraulic hammer), water flow in open channels (Classification of open channel flows, uniform flow, efficient cross-section & principles of energy in open channel flows))
- Evaluating stream flow (introduction, stream flow records, evaluating stream flows by discharge measurements (with velocity-area, weir, slope-area methods), stream flow characteristics (hydrograph, flow duration curves, standardised flow duration curves, water pressure)), residual, reserved or compensation flow,
Syllabus
Course Objectives/Goals
Upon successful completion of the course, students are expected to be able to:
- Describe and explain the basics of a small hydro-electric power plant
- List by name, describe and classify major problems that are typically addressed through different technologies of small hydro-electric power plants (especially dam, intakes, turbines, generators)
- Collaborate with civil engineers and hydrologists to carry out the design of civil structures such as dam and spillway
- Carry out the design of hydraulic structures such as pipe, open channel, intake, sediment traps for nominal flow supply
- Carry out the selection of electro-mechanical structures such as hydro-turbine, generator, step-up transformer for nominal flow supply and estimation of power capacity and energy output
- Carry out the technical-economic viability study of a small hydro-electric power plant in a preliminary design stage
- Explain and interpret results from the aforementioned stage; comment on their validity; make decisions on the basis of these results
- Collaborate with others in a team in order to address a realistic (but not real) situation/problem
- Transfer the skills acquired in this field in order to address real situations/problems.
Prerequisites/Prior Knowledge
Mandatory:
- A course/ two courses on electric circuits (dc, ac, multi-phase ac)
- A course / two courses on electric machines (electromechanical transformation principles, three-phase transformers, three-phase synchronous generators (cylindrical, salient pole), three-phase induction machines (squirrel, double-fed), dc machines, steady state and transient analysis)
- A course / two courses on power systems (power system elements, p.u. power system representation, steady state and transient analysis of power systems with emphasis on short circuits, stability and power quality issues)
- A course / two courses on automatic control systems (concept of feedback, Laplace transformation, system description-block diagrams, dynamic response of first and second order systems, steady state errors, controllers (P,PI, PD, PID), stability issues and criteria (Routh-Hurwitz, root locus, Bode plots, Nyquist plots), state space representation & analysis, controllability, observability, Lypapunov stability, state feedback techniques, transient response analysis, optimal control principles)
- A course on mechanics (static & kinematic equations, isostatic and hyper-static formations, Elasticity theory, Hooke’s law, uniaxial and biaxial stress, strain, tension, compression, shearing, bending torsion and combined loading, buckling, creep, impact etc.)
Desirable:
- A course on automatic control electric power systems (stability criteria, governor and automatic voltage control)
- A course on fluid mechanics (on pipes, open channels, turbines and pumps)
Assessment Methods
Student evaluation comes from
- Class participation, mini-tests and contribution in the discussions held in class and online x 10%
- Grade of Homework Assignment x 40%
- Final written exam x 50%
Bibliography
- European Small Hydropower Association (2004). Guide on How to develop a Small Hydropower plant (1st Edition), p. 296.
- Hydro-power – V. Schnitzer (2009). Micro Hydro scout guide. gtz publishing, Germany (1st edition), p. 118.
- Celso Penche (1998). Layman’s guidebook on how to develop a small hydropower plant. European Small Hydropower Association (1st Edition), p. 266.
- SWECO Norge AS (2012). Cost base for small scale hydropower plants (With a generating capacity of up to 10 000 kW). Norwegian Water Resources and Energy Directorate (NVE), editor Jan Slapgård, (1st edition), p. 91.
- PPA-SEIAPI (2020). Micro Hydropower System Design The Pacific Power Association (PPA) and the Sustainable Energy Industry Association of the Pacific Islands (SEIAPI), (1st edition), p. 72.
- SWECO Norge AS (2012). Cost base for small scale hydropower plants (With a generating capacity of up to 10 000 kW). Norwegian Water Resources and Energy Directorate (NVE), editor Jan Slapgård, (1st edition), p. 91.
- Bureau of Reclamation (1987). Design of small dams. United States Department of Interior, Bureau of Reclamation, A Water Resources Technical Publication, (3rd edition), p. 904.
- J. Peterka (1984). Hydraulic Design of Stilling Basins and Energy Basins. United States Department of Interior, Bureau of Reclamation, Engineering Monograph No.25, (8th printing), p. 240.
- E. Krueger (1976). Selecting Hydraulic Reaction Turbines. United States Department of Interior, Bureau of Reclamation, Engineering Monograph No.20, (4th edition), p. 54.
- N. Goncharov (1972). Hydropower stations Generating equipment and its installation. Energiya, Moskva, translated in English by Th. Peltz, Keter Publishing, Israel (1st edition), p. 367.
Additional info
RESEARCH ARTICLES
- S. Roy. Optimal planning of generating units over micro-hydro resources within a catchment area. IEEE Transactions on Energy Conversion, vol. 20, no. 1, March 2005, 231-236,
- J.S.Anagnostopoulos, D.E.Papantonis. Optimal sizing of a run-of-river small hydropower plant. Energy Conversion and Management, Vol. 48, no. 10, October 2007, 2663-2670.
- A.D.Karlis, D.P.Papadopoulos. A systematic assessment of the technical feasibility and economic viability of small hydroelectric system installations. Renewable Energy. Vol. 20, no. 2, June 2000, 253-262.
- V. Yildiz, J.A.Vrugt. A toolbox for the optimal design of run-of-river hydropower plants. Environmental Modelling & Software, vol. 111, January 2019, 134-152.
- R. Peña, A. Medina, O. Anaya-Lara, James R.McDonald. Capacity estimation of a minihydro plant based on time series forecasting. Renewable Energy, Vol. 34, no. 5, May 2009, 1204-1209.
- X. Liu, Y. Luo, B.W.Karney, W. Wang. A selected literature review of efficiency improvements in hydraulic turbines. Renewable and Sustainable Energy Reviews. Vol. 51, November 2015, 18-28.
- A.H. Elbatran, M.W. Abdel-Hamed, O.B. Yaakob, Y.M. Ahmed, I. M. Arif. Hydro power and turbine systems reviews. Jurnal Teknologi, Vol. 74, no. 5, 2015, 83 - 90.
- K.X.Soulis, D.Manolakos, J. Anagnostopoulos, D. Papantonis. Development of a geo-information system embedding a spatially distributed hydrological model for the preliminary assessment of the hydropower potential of historical hydro sites in poorly gauged areas. Renewable Energy. Vol. 92, July 2016, 222-232.
- S. Basso, G. Botter. Streamflow variability and optimal capacity of run-of-river hydropower plants. Water Resources Research, Vol. 48, no.10, W10527, 13.
- G.-K. Sakki, I. Tsoukalas, A. Efstratiadis. A reserve engineering approach across small hydropower plants: a hidden treasure of hydrological data? Hydrological Sciences Journal, vol. 67, no.1, 2022, 94-106.
- I.A. Niadas, P.G. Mentzelopoulos. Probabilistic Flow Duration Curves for Small Hydro Plant Design and Performance Evaluation. Water Resources Management 2008, Vol. 22, 509–523.
- C. Monteiro, I.J. Ramirez-Rosado, L.A. Fernandez-Jimenez, “Short-term forecasting model for electric power production of small-hydro power plants,” Renewable Energy, Vol. 50, February 2013, 387-394.
- K.K. Drakaki, G.K. Sakki, I. Tsoukalas, P. Kossieris, A. Efstratiadis, “Day-ahead energy production in small hydropower plants: uncertainty-aware forecasts through effective coupling of knowledge and data,” Adv. Geosci., Vol. 56, 2022, 155–162.
- Angelos P. Moschoudis, George J. Tsekouras, Fotios D. Kanellos, Antonios G. Kladas. Generator and Transformer Efficiency Study for the Design of a Run-of-River Small Hydropower Plant with One Hydro-Turbine. 7th International Conference on Mathematics and Computers in Sciences and Industry, Marathon Beach, Athens, Greece, August 22-24, 2022, p. 9.
- Vasiliki-Eleftheria K. Sarantopoulou, Korina Konstantina Em. Drakaki, George J. Tsekouras, Anastasios D. Salis, Georgia-Konstantina Sakki, Andreas Efstratiadis, Dimitrios E. Papantonis, Vasilis Riziotis, George Caralis, Konstantinos Χ. Soulis. Optimal Operation of a Run-of-River Small Hydropower Plant with Two Hydro-Turbines. 7th International Conference on Mathematics and Computers in Sciences and Industry, Marathon Beach, Athens, Greece, August 22-24, 2022, p. 9.
TOOLS
- Geographical data for renewable energy sources: https://geo.rae.gr/
- MATLAB: https://www.mathworks.com/products/matlab.html
- Meteorological data for Greece: https://meteo.gr
- Topographical data: https://en-gb.topographic-map.com
WEBSITES
- https://rae.gr/
- https://ich.no/
- https://www.alpiq.com/power-generation/new-renewable-energy-sources/small-scale-hydropower-plants
- https://www.gilkes.com/small-hydropower-solutions/gilkes-turbines
- https://www.global.toshiba/ww/products-solutions/renewable-energy/products-technical-services/hydro-power.html
- https://www.andritz.com/hydro-en/about-andritz-hydro
- http://voith.com/en/products-services/hydro-power/small-hydro-power-plants-552.html
- https://www.irem.it/en/hydro-power/pelton-turbines/
- https://www.sulzer.com/en/applications/power-generation/renewables/hydro-power-generation
- https://www.spaansbabcock.com/hydropower/hydro-power/
- https://www.akersolutions.com/what-we-do/renewable-energy-solutions/hydropower
Upon successful completion of the course, students are expected to be able to:
- Describe and explain the basics of a small hydro-electric power plant
- List by name, describe and classify major problems that are typically addressed through different technologies of small hydro-electric power plants (especially dam, intakes, turbines, generators)
- Collaborate with civil engineers and hydrologists to carry out the design of civil structures such as dam and spillway
- Carry out the design of hydraulic structures such as pipe, open channel, intake, sediment traps for nominal flow supply
- Carry out the selection of electro-mechanical structures such as hydro-turbine, generator, step-up transformer for nominal flow supply and estimation of power capacity and energy output
- Carry out the technical-economic viability study of a small hydro-electric power plant in a preliminary design stage
- Explain and interpret results from the aforementioned stage; comment on their validity; make decisions on the basis of these results
- Collaborate with others in a team in order to address a realistic (but not real) situation/problem
- Transfer the skills acquired in this field in order to address real situations/problems.
Mandatory:
- A course/ two courses on electric circuits (dc, ac, multi-phase ac)
- A course / two courses on electric machines (electromechanical transformation principles, three-phase transformers, three-phase synchronous generators (cylindrical, salient pole), three-phase induction machines (squirrel, double-fed), dc machines, steady state and transient analysis)
- A course / two courses on power systems (power system elements, p.u. power system representation, steady state and transient analysis of power systems with emphasis on short circuits, stability and power quality issues)
- A course / two courses on automatic control systems (concept of feedback, Laplace transformation, system description-block diagrams, dynamic response of first and second order systems, steady state errors, controllers (P,PI, PD, PID), stability issues and criteria (Routh-Hurwitz, root locus, Bode plots, Nyquist plots), state space representation & analysis, controllability, observability, Lypapunov stability, state feedback techniques, transient response analysis, optimal control principles)
- A course on mechanics (static & kinematic equations, isostatic and hyper-static formations, Elasticity theory, Hooke’s law, uniaxial and biaxial stress, strain, tension, compression, shearing, bending torsion and combined loading, buckling, creep, impact etc.)
Desirable:
- A course on automatic control electric power systems (stability criteria, governor and automatic voltage control)
- A course on fluid mechanics (on pipes, open channels, turbines and pumps)
Student evaluation comes from
- Class participation, mini-tests and contribution in the discussions held in class and online x 10%
- Grade of Homework Assignment x 40%
- Final written exam x 50%
- European Small Hydropower Association (2004). Guide on How to develop a Small Hydropower plant (1st Edition), p. 296.
- Hydro-power – V. Schnitzer (2009). Micro Hydro scout guide. gtz publishing, Germany (1st edition), p. 118.
- Celso Penche (1998). Layman’s guidebook on how to develop a small hydropower plant. European Small Hydropower Association (1st Edition), p. 266.
- SWECO Norge AS (2012). Cost base for small scale hydropower plants (With a generating capacity of up to 10 000 kW). Norwegian Water Resources and Energy Directorate (NVE), editor Jan Slapgård, (1st edition), p. 91.
- PPA-SEIAPI (2020). Micro Hydropower System Design The Pacific Power Association (PPA) and the Sustainable Energy Industry Association of the Pacific Islands (SEIAPI), (1st edition), p. 72.
- SWECO Norge AS (2012). Cost base for small scale hydropower plants (With a generating capacity of up to 10 000 kW). Norwegian Water Resources and Energy Directorate (NVE), editor Jan Slapgård, (1st edition), p. 91.
- Bureau of Reclamation (1987). Design of small dams. United States Department of Interior, Bureau of Reclamation, A Water Resources Technical Publication, (3rd edition), p. 904.
- J. Peterka (1984). Hydraulic Design of Stilling Basins and Energy Basins. United States Department of Interior, Bureau of Reclamation, Engineering Monograph No.25, (8th printing), p. 240.
- E. Krueger (1976). Selecting Hydraulic Reaction Turbines. United States Department of Interior, Bureau of Reclamation, Engineering Monograph No.20, (4th edition), p. 54.
- N. Goncharov (1972). Hydropower stations Generating equipment and its installation. Energiya, Moskva, translated in English by Th. Peltz, Keter Publishing, Israel (1st edition), p. 367.
RESEARCH ARTICLES
- S. Roy. Optimal planning of generating units over micro-hydro resources within a catchment area. IEEE Transactions on Energy Conversion, vol. 20, no. 1, March 2005, 231-236,
- J.S.Anagnostopoulos, D.E.Papantonis. Optimal sizing of a run-of-river small hydropower plant. Energy Conversion and Management, Vol. 48, no. 10, October 2007, 2663-2670.
- A.D.Karlis, D.P.Papadopoulos. A systematic assessment of the technical feasibility and economic viability of small hydroelectric system installations. Renewable Energy. Vol. 20, no. 2, June 2000, 253-262.
- V. Yildiz, J.A.Vrugt. A toolbox for the optimal design of run-of-river hydropower plants. Environmental Modelling & Software, vol. 111, January 2019, 134-152.
- R. Peña, A. Medina, O. Anaya-Lara, James R.McDonald. Capacity estimation of a minihydro plant based on time series forecasting. Renewable Energy, Vol. 34, no. 5, May 2009, 1204-1209.
- X. Liu, Y. Luo, B.W.Karney, W. Wang. A selected literature review of efficiency improvements in hydraulic turbines. Renewable and Sustainable Energy Reviews. Vol. 51, November 2015, 18-28.
- A.H. Elbatran, M.W. Abdel-Hamed, O.B. Yaakob, Y.M. Ahmed, I. M. Arif. Hydro power and turbine systems reviews. Jurnal Teknologi, Vol. 74, no. 5, 2015, 83 - 90.
- K.X.Soulis, D.Manolakos, J. Anagnostopoulos, D. Papantonis. Development of a geo-information system embedding a spatially distributed hydrological model for the preliminary assessment of the hydropower potential of historical hydro sites in poorly gauged areas. Renewable Energy. Vol. 92, July 2016, 222-232.
- S. Basso, G. Botter. Streamflow variability and optimal capacity of run-of-river hydropower plants. Water Resources Research, Vol. 48, no.10, W10527, 13.
- G.-K. Sakki, I. Tsoukalas, A. Efstratiadis. A reserve engineering approach across small hydropower plants: a hidden treasure of hydrological data? Hydrological Sciences Journal, vol. 67, no.1, 2022, 94-106.
- I.A. Niadas, P.G. Mentzelopoulos. Probabilistic Flow Duration Curves for Small Hydro Plant Design and Performance Evaluation. Water Resources Management 2008, Vol. 22, 509–523.
- C. Monteiro, I.J. Ramirez-Rosado, L.A. Fernandez-Jimenez, “Short-term forecasting model for electric power production of small-hydro power plants,” Renewable Energy, Vol. 50, February 2013, 387-394.
- K.K. Drakaki, G.K. Sakki, I. Tsoukalas, P. Kossieris, A. Efstratiadis, “Day-ahead energy production in small hydropower plants: uncertainty-aware forecasts through effective coupling of knowledge and data,” Adv. Geosci., Vol. 56, 2022, 155–162.
- Angelos P. Moschoudis, George J. Tsekouras, Fotios D. Kanellos, Antonios G. Kladas. Generator and Transformer Efficiency Study for the Design of a Run-of-River Small Hydropower Plant with One Hydro-Turbine. 7th International Conference on Mathematics and Computers in Sciences and Industry, Marathon Beach, Athens, Greece, August 22-24, 2022, p. 9.
- Vasiliki-Eleftheria K. Sarantopoulou, Korina Konstantina Em. Drakaki, George J. Tsekouras, Anastasios D. Salis, Georgia-Konstantina Sakki, Andreas Efstratiadis, Dimitrios E. Papantonis, Vasilis Riziotis, George Caralis, Konstantinos Χ. Soulis. Optimal Operation of a Run-of-River Small Hydropower Plant with Two Hydro-Turbines. 7th International Conference on Mathematics and Computers in Sciences and Industry, Marathon Beach, Athens, Greece, August 22-24, 2022, p. 9.
TOOLS
- Geographical data for renewable energy sources: https://geo.rae.gr/
- MATLAB: https://www.mathworks.com/products/matlab.html
- Meteorological data for Greece: https://meteo.gr
- Topographical data: https://en-gb.topographic-map.com
WEBSITES
- https://rae.gr/
- https://ich.no/
- https://www.alpiq.com/power-generation/new-renewable-energy-sources/small-scale-hydropower-plants
- https://www.gilkes.com/small-hydropower-solutions/gilkes-turbines
- https://www.global.toshiba/ww/products-solutions/renewable-energy/products-technical-services/hydro-power.html
- https://www.andritz.com/hydro-en/about-andritz-hydro
- http://voith.com/en/products-services/hydro-power/small-hydro-power-plants-552.html
- https://www.irem.it/en/hydro-power/pelton-turbines/
- https://www.sulzer.com/en/applications/power-generation/renewables/hydro-power-generation
- https://www.spaansbabcock.com/hydropower/hydro-power/
- https://www.akersolutions.com/what-we-do/renewable-energy-solutions/hydropower
Students can find sample evaluation material for this course module under the "DOCUMENTS" in the left frame menu.
Basic operation principles, categorization, differences between small and large hydroelectric power plant, definition of small hydropower, site configurations, planning
Fundamental of Hydraulic Engineering: introduction, Bernoulli equation, water flow in pipes (head losses due to friction, local head losses, transient flow, hydraulic hammer), water flow in open channels (Classification of open channel flows, uniform flow, efficient cross-section & principles of energy in open channel flows)
Evaluating stream flow: introduction, stream flow records, evaluating stream flows by discharge measurements (with velocity-area, weir, slope-area methods), stream flow characteristics (hydrograph, flow duration curves, standardised flow duration curves, water pressure)), residual, reserved or compensation flow, estimation of plant capacity and energy output (influence of flow variation and head variation on the turbine capacity, peaking operation, firm energy, floods (flood control design, statistical analysis of flood data, hydrological modelling of the catchment area)
Site evaluating methodologies: cartography, geochemical studies, practical cases, learning from failures
Hydraulic structures: dams (types: embankment, concrete, other; loads and stability, dam safety), weirs and spillways (gated, ungated), energy dissipating structures, intake structures (types, head losses, trashracks, vorticity), sediment traps (efficiency, design), gates and valves, open channels (design and dimensioning, excavation and stability), forebay tanks, penstocks, tailraces
Electromechanical structures: powerhouse, hydraulic turbines ( types and configuration, specific speed and similitude, preliminary design, selection criteria, efficiency), speed increasers (types, design, maintenance), generators (configurations, synchronous- asynchronous –dc generators, exciters, voltage regulation and synchronization, special specifications), turbine control, switchgear equipment, automatic control (governor – automatic voltage regulator – case of autonomous operation), ancillary electrical equipment (plant service transformer, DC control power supply, headwater and tailwater recorders, outdoor substation)
Connection of hydro-power plant with grid through transmission / distribution lines: steady state and transient state current analysis for different operation modes, faults, power quality issues, power stability
Economic analysis: basic considerations, time value of money, methods of economic evaluation (payback time period, net present value, benefit-cost ratio, internal rate of return), tariffs and incentives
Environmental impact and its mitigation: introduction, burdens and impacts identification, impacts in the construction phase (reservoirs, water intakes, open canals, penstocks, tailraces), impacts arising from the operation of the scheme (sonic, landscape, biological impacts), impacts from transmission lines (visual, health)
Administrative procedures: types of procedures (energy regulation – water rights, environmental procedures, public inquiry, construction requirements, connection to the grid, others), examples
Special issues: Small hydropower plant in the modern electricity market, possibility for pump hydropower plants, etc.
Arithmetic examples
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