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.
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
- Power house
Main concepts (Working Principle)
Head and flow results in potential energy
P = H.Q.p.g.ƞ.10-6
- 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)
- Hn – Net Head
Potential Energy for Hydro with Losses
Different Hydro Systems and their Advantages and Disadvantages
|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|
- 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
- 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
|Broad range of head/flow||
|Broad efficiency range||
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