Hydropower

Hydropower

Energy in water can be harnessed and used. Since water is about 800 times denser than air, even a slow flowing stream of water, or moderate sea swell, can yield considerable amounts of energy. Forms of water energy:

  • Hydroelectric energy is a term usually reserved for large-scale hydroelectric dams. E.g. Three Gorges Dam, China (22,500 MW)
  • Micro hydro systems are hydroelectric power installations that typically produce up to 100 kW of power. They are often used in water rich areas as a remote-area power supply (RAPS).
  • Run-of-the-river hydroelectricity systems derive kinetic energy from rivers and oceans without using a dam.

5.1 Inside a hydropower plant

Hydro Power History 

Up to 1700 – Water wheels

1750 – Turbine theory developed

1800 – First turbines built

1850 – Francis runner invented

1900 – Pelton runner invented

– Kaplan runner invented

1950 – Turbines begin to drive electric generators

2000 – Computer assisted design methods

Main components

  • Intake
  • Penstock
  • Power house

Main concepts (Working Principle)

Head and flow results in potential energy

P  = H.Q.p.g.ƞ.10-6

Where

  • P  = Power (MW)
  • Q = Water flow (m3/s)
  • P  = Pressure head (m)
  • p = Density of Water (kg/m3)
  • g = gravity (9.8 m/s2)
  • ƞ = Conversion efficiency (%)
  • H consists of two parts
    • Hn – Net Head
      • Head pond levels drops, tail race levels rises with flow and friction losses in penstock and valves
    • Hg – Gross Head
      • Difference between head pond and tail race water levels with no water flow (shut down)
 4.2 Head losses and Net Head

Potential Energy for Hydro with Losses

Different Hydro Systems and their Advantages and Disadvantages

Advantage  Disadvantage 
 
  • Resource is not consumed
  • Multiple uses (irrigation, flood control, water sports)
  • Clean operation
  • Technology well understood
  • Efficient, Safe,
  • Long asset life
  • Efficient storage
  • Footprint
  • Small scale and run-off-river (no dam) garnering increasing interest
  • Mature technology
  • Easy and fast to start/stop
  • Ability to follow moving load
  • High Availability
  • Very low operating cost
  • Provide flood protection
  • Improve shipping upstream
  • Avoid CO2 emissions
  • Requires specific site characteristics
  • Dependent on resource availability
  • Flooding of natural environment (storage systems)
  • Carbon release from dams (storage systems)
  • Every unit is custom designed
  • Alter stream flows
  • Increased landslifes, shifts in sedimentation patterns
  • Hinder/prevent passage of migratory fish
  • Depending on the site, could displace people
  • Flood land with value from agriculture, forestry, transport and inhabitance
  • Difficulty with instantaneous response (< 6s)
  • Capacity is limited by resource
Run of the RiverNo water storagePower generated from water in the river at the timeE.g. Chacayes, run-of-river, Chile Minimal environmental impactLower cost Water is not always available when energy is required
Storage Water is stored for later releaseRequires suitable site for a damE.g. Ord Hydro, storage station, WA Flexible generationMatch hydrology with demand profiles Flooding of natural environmentCost (if no dam existing)Emission abatement is less in later years due to vegetation decomposition
Cascade SystemWater discharged from power station is re-used in the next Very flexible generation Efficient use of the resource Complex optimisation
Pumped StorageTurbine can also act as a pumpE.g. Dinwarg pump storage station, Wales Store water when power price is lowGenerate power when price is highPractical storage of renewable power Less efficient than dedicated unit

Turbine Designs

4.3 Main types of hydro

Turbine Design

Pelton:

  • Can have a number of nozzles
  • Water jet directed onto turbine
  • Velocity of water jet is proportional to head
  • Maximum efficiency when the peripheral bucket speed is half the water velocity.
  • Rotational speed affected by generator design and system frequency.
  • Need high head to have practical runner diameter
  • Pelton’s paddle geometry was designed so that when the rim runs at ½ the speed of the water jet, the water leaves the wheel with very little speed, extracting almost all of its energy, and allowing for a very efficient turbine
  • The largest units can be up to 200 MW
  • Power curve is the flattest but lower peak

Francis Turbines (most commonly used)

  • Spiral case diverts water into the turbine runner
  • Inward-flow reaction turbine that combines radial and axial flow concepts
  • Narrows along the length to keep the water pressure even all the way around
  • The main valve isolates the turbine from the penstock when stopped
    • Operate in a head range of 10 to 650 meters (33 to 2,133 feet) and are primarily used for electrical power production
    • Power output generally ranges from 10 to 750 megawatts, though mini-hydro installations may be lower
    • Runner diameters are between 1 and 10 meters (3 and 33 feet).
    • Speed range of the turbine is from 83 to 1000 rpm.
    • Turbines are almost always mounted with the shaft vertical to keep water away from the generator and also to facilitate access to it.
  • Power curve has best peak efficiency

Kaplan Turbines

  • Propeller-type water turbine which has adjustable blades.
  • Developed in 1913 as an evolution of the Francis turbine by combing automatically adjusted propeller blades with automatically adjusted wicket gates to achieve efficiency over a wide range of flow and water level
  • Allows efficient power production in low-head (measure of liquid pressure) that was not possible with Francis turbines.
    • The head ranges from 10–70 meters and the output from 5 to 120 MW
    • Runner diameters are between 2 and 8 meters
    • The range of the turbine is from 79 to 429 rpm
    • Power output from 5 to 120 MW.
    • Kaplan turbines are now widely used throughout the world in high-flow, low-head power production
  • Power curve is very broad with high peaks

Choice of turbine

Pelton

Francis

Kaplan

Broad range of head/flow

Best

Peak efficiency

3

Best

2

Broad efficiency range

Best

3

3

Mechanical simplicity

Best

Best

3

Three Gorges Dam

Three Gorges Dam – China 2009

  • Located in  Hubei, China
  • Became fully operational in July 2012 at 22.5 GW (32 x 700 MW and 2 x 50 MW Francis type generators)
  • Began construction in 1993 at a cost of $US23B
  • Stores 6 billion m3 of water with a hydraulic head of 80m
  • Annual generation 80 TWh

Snowy Hydro Scheme

  • Largest engineering project ever in Australia

Snowy Mountain Hydro

  • Construction commenced in 1947 and completed in 1973
  • The Snowy Mountains Scheme consists of:
    • sixteen major dams
    • seven power stations (total of 3.8 GW capacity)
    • a pumping station (300 MW pumping capacity)
    • 225 kilometres of tunnels, pipelines and aqueducts

Sources: Wikipedia

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