2. Goals of This 15-Minute Module
Know what small hydro is.
Understand major features,
components, and selection criteria
Understand technical and financial
considerations when assessing a
site
3. Fundamentals of Small Hydro
SH 101:
Overview and
Background
SH 102:
Fundamentals
SH 103:
Review and
Quiz
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4. What is Small Hydro
Small Hydro (also called small hydroelectric or small hydro) refers to the generation of
electrical power by using diverted water to rotate a turbine.
The major components include:
• An intake
• A penstock
• A turbine & generator
• A switchyard for connection to the power pole
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5. What is Small Hydro
The most commonly used form in intake structure design is the “Discharge Equation.”
Different forms are used for flow over the spillway, Coanda accelerator, measurement
weirs, and various secondary spills.
Generally the value of C, the discharge coefficient, will adjust based on some empirical
test.
The basic discharge equation is Q=Clh^3/2
Where:
Q=Flow
C=Discharge coefficient
l=Length of the weir
h=head above the crest
The most important thing when selecting and implementing a discharge equation is
ensuring it matches in all respects the condition it was intended for.
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6. Calculating Power Potential
Power is given as:
P=HQkG
Where:
P=Power in watts
H=Head (the difference in elevation between the intake and the powerhouse
Q=Flow in m^3/s
G=Gravity (9.8 m/s^2)
k=Turbine efficiency
A quick estimate is to take 7 * Q* H
Head (m)
Flow (m3/s)
Power in kW
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7 x Head x Flow
7. What is Small Hydro
What counts as small hydro?
Typical Power
Micro
Mini
100 to 1,000 kW
Small
7
< 100 kW
1 to 50 MW
8. What is Small Hydro
Type of grid
– Central-grid: Generated power is sold back
to a power grid such as a utility.
– Isolated-grid or off-grid: Generated power is
used locally near the point of generation.
Type of civil works
– Run-of-river
• No water storage
• Power varies with flow available from river:
lower firm capacity
– Reservoir
• Higher firm capacity year-round
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• Significant damming usually required
10. Process for Sizing Site
• Estimate flow duration curve based on
Measurements of flow over time
Size of drainage above site, specific run-off, and shape of flow
duration curve
The easiest way to mess up a high head site is to overestimate the
flow (as this is the only variable)
Flow-Duration Curve
Flow (m³/s)
50.0
40.0
30.0
20.0
10.0
0.0
0
10 20 30 40 50 60 70 80 90 100
Percent Time Flow Equalled or Exceeded (% )
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11. Process for Sizing Site
Picking the Turbine
at various points on the FDC
Flow-Duration Curve
40.0
• Estimate the cost of
equipment cost associated
with those. This includes
questions such as the size of
the equipment and how many
nozzles will be used.
• Integrate the area under the
curve with various scenarios
and pick the best payback.
Sometimes this can be
approximated by simply slicing
the FDC into a few scenarios.
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Flow (m³/s)
• Estimate the installed capacity
50.0
30.0
20.0
10.0
0.0
0 10 20 30 40 50 60 70 80 90 100
Percent Time Flow Equalled or Exceeded (% )
For example:
The green line has high
capacity to “catch” high flow
events, but may not run
enough to be worth the cost.
The blue line will be cheaper,
but may leave power on the
table. The red line may be the
best return.
12. Small Hydro Major Components
The most expensive cost component for a small hydro plant is the Civil Cost.
Much of our approach is in lowering the civil cap-ex.
Small Hydro Cost Estimate
Other
10%
Electrical
10%
Mechanical & Controls
25%
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Civil Cost
55%
13. Small Hydro Major Components
The major components for the site are:
• Intake structure
• Penstock
• Powerhouse – the primary components of the powerhouse are:
o Turbine-generator
o Switchyard
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14. Intake Structure
The intake structure needs to deliver clean water to the penstock
Traditional intakes include a coarse screen
with secondary screening and settling
basins to remove sand.
Coanda screens eliminate secondary
screening need & use overflowing water to
stay clean.
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16. Pelton Turbine Details
As Coanda Screens are most suitable for medium and high head sites they
are commonly paired with Pelton Machines
Peltons have a series of nozzles controlled by actuated needle valves, that
spray water onto the runners.
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21. Other Powerhouse Components
The generator is connected to the turbine.
A generator can be either synchronous (i.e. designed to work with an existing
load) or asynchronous.
For very small sites an induction motor can be used in place of the generator.
Additional components are the plant controls and basic facility requirements
like lighting, fire protection, personnel protection, and monitoring equipment.
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26. Design Considerations
Social
Fisheries
• Build projects good for
people
• Don’t screw landowners.
Be fair.
• Improve diversion
• Improve survival
Environmental
Land Use
• Intake
• T&D
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Proper O&M
27. Review Questions
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What are the components of calculating
power capacity?
What are the balance of plant benefits of a
Coanda intake
