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Small Hydro Power (SHP) Preliminary Study and Hydro Resource Assessment Roberto Suffredini

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Small Hydro Power (SHP) Preliminary Study and Hydro Resource Assessment Roberto Suffredini Enel – Generation and Energy Management Renewable Energies. Hydro Power Convert potential and kinetic energy of water flow into electrical energy:

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Small Hydro Power (SHP)

Preliminary Study and Hydro Resource Assessment

Roberto Suffredini

Enel – Generation and Energy Management

Renewable Energies

Hydro Power
  • Convert potential and kinetic energy of water flow into electrical energy:

Power (kW) = Head (m) x Flow (m3/s) x 9.81 x Plant Efficiency

  • Hydro Power system are primarily classificated such as:
    • RUN-OF-RIVER (Run-off dependent, without reservoir, grid base load)
    • STORAGE (Renewable Energy may be storage, power modulation and grid frequency regulation, high power)
    • PUMPED STORAGE (High energy storage capacity, high power)
Hydro Power
  • Secondary classification for HPP is for:
    • LOW HEAD

Above definitions are not univocal, but power-related

  • Hydro Power providing more than 19% of world’s electricity
  • Mature (more than 100 years old) and high reliable technology
  • High efficiency convertion from primary energy, up to 90%
  • Very large power size in single station, up to 14.000 MW
  • Impact on environment is size dependent and may be very large
  • Very long lifetime of plant
  • Low O&M costs
Hydro Power
  • An Hydro Power facility consist of:
    • Diversion structure and reservoir (river run-off capture; storage and transport of water)
    • Powerhouse (hydraulic to electric energy conversion)
    • Transformers, Substation and Powerlines (voltage convertion; switching and energy trasmission)
    • Access roads
Hydro Power

Plant typical scheme

Hydropower Plant



Hydro Power Plant general layout
  • Diversion & storage
    • Dam or weir
    • Intake
    • Open surface or pressure canal
    • Forebay or surge tank
    • Penstock and valves
    • Tailrace
  • Powerhouse (outdoor or underground)
    • Turbines and valves (hydraulic to mechanical power)
    • Generators (mechanical to electric power)
    • Substation with transformers and switchyard (generator to line connection)
    • Control & Protection system
    • Ancillary (e.g.: cooling & lubricating system, governing, crane)
Hydro Power Plant
  • Very large size Storage HPP



Paranà River

World’s Largest HPP

Reservoir: 29 x 109 m3

Units: 20 x 800 MVA

Capacity: 14.000 MW

Energy: 90 TWh/yr




Hydro Power Plant
  • Underground Pumped Storage Plant Scheme



Lower Reservoir


Hydro Power Plant
  • Power spectrum of Pumped Storage Power Plant
Small Hydro Power (SHP)
  • Hydro Power Plant having power up to 10 MW
    • Other classification limit is in max discharge for Low-Head SHP
  • Small-scale Hydropower is one of the most cost-effective and reliable energy technology
  • More detailed power-classification:
    • SMALL HYDRO: from 1 to 10 MW
    • MINI HYDRO: from 100 kW to 1 MW
    • MICRO HYDRO: < 100kW
  • Generally, SHP are run-of-river system
  • Environmental impact is minimal if sufficient precaution are taken
  • Grid connection:
    • Usually on central grid in developed country
    • On insulated grid or off-grid are typical in developing country
Small Hydro Power (SHP)
  • An example of Run-of-River SHP


North Italy

Cervo River

Head: 75 m

Units: 1 x 1.4 MVA

Cross-Flow Turbine

Capacity: 1 MW

Energy: 5 GWh/yr




Planning Run-of-River Small Hydro Project
  • Preliminary Site Investigation
    • Land reconnaissance and maps research
    • Hydrology and flow duration curve assessment
    • Head measurement
    • Preliminary geological and climatological land survey
    • Gross hydropower potential estimation
    • Residual flow determination
    • Electric grid distance survey (if grid connected)
    • Access way evaluation
    • Regional laws assessment
    • Energy price
Planning Run-of-River SHP

Land reconnaissance and Maps research

  • Topographic maps are essential for any step of project development
  • Maps scale (Italy)
    • From 1:100.000 to 1:25.000 usable prefereably only for hydrology and general land survey, electric grid distance, access way
    • From 1:10.000 usable for geodetic and gross head estimation in High and Medium Head SHP
    • Low Head SHP assessment require most detailed maps (1:2.000, 1:1.000 or less scale) and customized topographic survey
  • Land survey and detailed photographic relief are required
  • Images from aerial and satellite survey may be very useful
Planning Run-of-River SHP

Hydrological study

  • Need for river flow statistics assessment



Water cycle


Planning Run-of-River SHP

Hydrology for SHP evaluation – Main problems

  • Hydrology and river flow statistics assessement often represent a great difficulty step for SHP feasibility study
  • For a correct SHP planning is required run-off database based on a reliable long-term record, ideally 10 years
  • Unfortunately, when long-term run-off records exist, not always the recorded river site is the same or near to the projected SHP water diversion
Planning Run-of-River SHP

Hydrology – Statistics at ungauged river site

  • If streamflow statistics are missing or incomplete, catchment must be characterizated from thematic and topographic maps, meterological and geographical database
    • Catchment area and their boundary perimeter, hypsographic curve and mean altitude
    • Side and riverbed talweg slope, main river and tributary lenght, catchment form
    • Soil permeability classification and groundwater presence
    • Mean rainfall heigh and isohyet curves
    • Vegetation kindes and their surfaces
    • Snow presence, air temperature, wind intensity and other meteorological data
    • Other (e.g. time constants)
  • Above methodology may be adopted by an expert hydrologist for to work out an accurate, complete, but many expensive and long duration hydrologic study. This is typically unacceptable for an SHP, particularly for the preliminary feasibility assessment
Planning Run-of-River SHP

Hydrology – Methods for to obtain statistics at ungauged river site

  • Alternative ways for streamflow statistics estimation:
    • Regionalization methods (dimensionless FDC)
    • Catchments similitude method (trasposition of hydrometric data from nearest gauged catchment)
    • Hydrological software tools (if relevant meteorological and topographical data are available then it may be used for a quick flow statistics assessment)
    • Recording streamflow at continous gauged station for relevant time (almost one year)
    • Flow measurement only at significant run-off conditions
    • Measurement ofQ95% (or Q90%) low flow indicator. It could help the user in estimation of flow statistic curves, of natural yearly mean flow and also for the study of SHP environmental impact mitigation
Planning Run-of-River SHP

Hydrology – Final data outputs

  • Hydrological study on the catchment has the following goals:
    • Flow Duration Curve (FDC)
    • Simulated (or analiysed) Streamflow
      • Streamflow analysis has like output an hourly (daily) time series of streamflow at an indicated river site.
    • Flood peak intensity and frequency analysis, necessary for to assess the hydraulic risk in engineering of weir, intake, powerhouse, tailrace canal and access road

Daily simulated streamflow

Planning Run-of-River SHP

Hydrology – Flow Duration Curve (FDC) analysis

  • The Flow Duration Curve is the graph showing the percent time (e.g. of year or month) that the streamflow at a site is equal or exceed to an assigned value
Planning Run-of-River SHP

Hydrology – Main parameters related to water flow

  • Run-off statistics at an analysed site:
    • Flow Duration Curve
    • Average yearly natural flow Qnat
    • Flood peak flow (for assigned return time)
    • Q95% (or Q90%) like low-flow indicator
Planning SHP resources in large area region
  • Requirement of Topographical Maps for Large Area
  • Geographic Information System (GIS) for topographic and thematic maps. GIS tools for hydrology
  • Remote Sensing Technology (aerial & satellite)
  • Hydrological Assessment Software Tools

GIS and Remote Sensing used for potential SHP assessment in Uganda region – 2005, Lund University/Sweden

Planning Run-of-River SHP

Head estimation

  • Measurement of geodethical heads
    • From topographic site survey
    • From maps
    • Other (GPS, water level instrument on Very Low Head site)
  • Net Head
    • Gross Head Hg is the indicator of potential hydro power available at the site, in accord with the adopted SHP scheme
    • Gross head may be variable with flow discharge
    • Net Head Hn = Hg – Head Loss
    • Head losses are analysed as:
      • Friction Loss-> quadratic function of flow: DH = k x Q2
      • Local Loss->quadratic function of velocity: DH = k x V2
Planning Run-of-River SHP

(Related with Qnat)

(Related with Qdiv)

Planning Run-of-River SHP

SHP-related flow definitions

  • Main flow parameters in SHP facility are:
    • Maximum diverted flow Qmax
    • Minimum usable flow Qmin(from hydraulic turbine lower operation limit)
    • Average diverted flow Qdiv(related to net mean water volume used for energy production)
    • Residual flow Qres (released at the intake for enviromental impact mitigation purposes)
Planning Run-of-River SHP

Turbine selection


  • Turbinetype and number of units choice are depending by:
    • Net Head (Hn) and Design Flow (Qmax)
    • FDC trend, by means of energy production estimation (interactive analysis)
    • Suction head Hs on Low Head SHP





Planning Run-of-River SHP

Plant Global Efficiency and Power Duration Curve

  • Efficiency items:
    • hH Hydraulic, from all water conduit loss
    • hT Turbine
    • hG Generator (and gearbox if present)
    • hTR Trasformer
    • hA Ancillary system
    • Above efficiency parameter may be defined for every value of flow discharge
  • Punctual SHP Global Efficiency hi
    • hi=hHi x hTi x hGi x hTRi x hAi
    • To abtain net power on the grid connection, the punctual global efficiency hi will be applied to gross hydraulic power available for each flow related to every 5% of duration in FDC
Planning Run-of-River SHP

Energy items summary

  • From SHP preliminary study we can obtain the following main energy parameters:
    • Average annual energy delivered Em(MWh/year)
    • Peak powerPmax (kW)[Plant capacity]
    • Minimum powerPmin(Firm capacity for a related time period)
    • Plant capacity factor = Em/Hydraulic energy available
  • Energy Em is the main economic item
  • Peak power is related, e.g., to the possibility of connection to main grid
  • Minimum power is important parameters for energy production on insulated grid or off grid
Planning Run-of-River SHP

Geology and Land survey

  • Geological preliminary study is essential for to perform at first step an accettable layout for new SHP plant and to supply at hydrologist the necessary information about catchment
  • Soil geological information at a studied site may be obtained by geologic maps (if exist) or from a land survey, performed by an expert geologist
  • Clearly, all parts of land interested by SHP layout may be critical and must be examined mainly in sense of soil stability evaluation
  • In the main component site, e.g. weir and powerhouse, is important to evaluate necessity of core boring investigation (e.g. for water filtration and stability of weir and for good engineering of concrete foundation of powerhouse). Usually this important step on SHP design will be performed after preliminary study. The cost must be considered now
  • Access road may be an important part of plant cost. In a correct preliminary land survey must be added reconnaissance for plant access evaluation . The same is valid for grid connection.
Planning Run-of-River SHP

Potential environmental impact of SHP plant

  • Main effect of new SHP plant on preexistent environment condition are:
    • River streamflow reduction on subtended lenght
    • Fish migration obstacle
    • Fish damage on turbine crossing
    • Modify of river section at weir and powerhouse sites resulting on flood risk increase
    • Landscape alteration
  • Another important environmental impact may be during the construction stage of the project
Planning Run-of-River SHP

Environmental impact mitigation of SHP plant

  • The essential environmental conditions for new SHP project acceptance are generally as follow:
    • Release of certain residual flow at weir section (e.g. 10% of annual natural mean flow)
    • Installation of fish ladder across the weir section to restore fish migration
    • When is technically possible, use of low width space between screen bars for to prevent fish passage through the turbine
    • Remowable gates may be installed on weir barrage for to prevent flood damage (e.g. inflatable rubber weir)
    • Careful design for to prevent flood damage at powerhouse and tailrace
    • Careful architectural design (mainly for powerhouse) respectful of site landscape
    • Plant construction engineering and yard planning can reduce the environmental impact in construction step
Planning Run-of-River SHP

SHP plant authorization

  • There are two main step for to obtain the necessary authorization for the construction and operation of new SHP plant:
    • Water diversion licence
    • Plant construction authorization
  • Another important permit to obtain is for to deliver energy on central grid and for relative interconnection
  • Inside to above steps is the environmental impact evaluation
  • Preliminary request must be do for to obtain Green Energy benefits (e.g. Green Certificate or other grant)
Planning Run-of-River SHP

SHP costs analysis – Investment cost

  • Each SHP plant has so particulary character so isn’t possible to define reliable power-related global cost index
  • For every parts of SHP are available methods based on algorithms for to evaluate their preliminary cost, but:
    • Preliminary cost estimation is regional dependent
    • Preliminary tun-up is required
    • Valid only for “standard” layout
  • More reliable process is to evaluate investment costs with detailed methods
  • Usually the investment cost are so detailed:
    • Civil works (all civil and hydraulic works, access road)
    • Electromechanical & Electrical (from turbine-generator, up to line)
    • Electric line and grid connection
    • Engineering cost
    • Contingency (usually 10%)
  • Feasibility study and development may be not investment cost
Planning Run-of-River SHP

SHP costs analysis – O&M costs

  • Operation
    • Water rental
    • Land rental (if present)
    • Central grid connection cost
    • Metering cost
    • Insurance cost
    • Surveillance and Operation labour cost
    • General and administrative cost
  • Maintenance
    • Spare parts and other consumable materials
    • Labuor cost for ordinary maintenance
    • Fault repair
    • Extraordinary maintenance (only for some scheduled year)
Planning Run-of-River SHP

SHP benefits

  • Environmental benefits
    • Clean energy production
    • Land control
    • Other uses of water
      • Irrigation system for agriculture
      • Municipal water system, industrial acqueduct
      • Recreation use of intake’s basin)
  • Economical benefits
    • Energy selling
      • Energy base price
      • Energy incentived price (regional regulation, e.g. Green Certificate)
    • Other green energy incentives
      • Partial grant on investment cost
Planning Run-of-River SHP

Economics - Generality

  • Current SHP economic analysis model based on Discounted Cash Flow (DCF) analysis
  • Series of annual renevues (or benefits) and costs over an assumed investment time horizon
  • Economic indicators such as IRR, NPV, SP, available for Decision Makers
  • DCF is a flexible tools, adaptable for any stage of SHP project development
Planning Run-of-River SHP

Economics - Discounted cash flow (DCF) analysis

Input Data

  • DCF input data are connected to:


    • (investment cost, construction period, O&M cost, energy production, energy destination, technical lifetime, etc.)


    • (capital cost, internal discount rate, equity, etc. )


    • (energy price, tax, asset depreciation, water licence cost, land rental, incentives, etc.)
Planning Run-of-River SHP

Economics - Discounted cash flow (DCF) analysis – Output

  • DCF output main indicators:

Net Present Value NPV

    • Sum of all discounted annual cash flow over the assigned lifetime. Must be > 0. Size dependent

Internal Rate of Return IRR

    • The discount rate that brings NPV=0. Must be > investor’s internal discount rate. Size independent

Payback Period or Simple Payback SP

    • Total investment cost divided by first year benefits.

Energy production cost (currency/kWh)

    • Avoided cost of energy that brings the NPV=0
Planning Run-of-River SHP

Economics - Sensitivity and Risk Analysis

  • Particularly necessary for SHP development in:
    • Ungauged river (cash flow risk)
    • Uncertain geological terrain (investment cost risk)
    • Uncertain energy price market (cash flow risk)
Table of Contents
  • Hydropower
  • Planning Run-of-River Small Hydro Project
    • Land reconnaissance and maps research
    • Hydrology and streamflow assessment
    • Planning SHP resource in large area region
    • SHP typical scheme
    • Head definition
    • Head estimation
    • Using Flow duration curve
    • SHP turbine selection
    • Efficiency
    • Power duration curve and energy evaluation
    • Geology and land survey
    • Environmental impact / mitigation
    • SHP plant authorization
    • Cost analysys
    • Benefits
    • Economics