HYDROELECTRICITY: AQUAMAN’S POWER
-Hiranya Bose
In this research document, we shall cover the basics of hydroelectricity, where it can be implemented, its pros, and its cons. This piece explores the fundamental physics behind hydel power, it’s sources and variations – and of course, how it would benefit the environment. When the topic of renewable energy comes up, hydroelectricity is mentioned but never studied or understood in detail. This document will discuss the hydroelectricity everyone’s learnt in geography, through the physics lying behind it. There is massive science and architecture behind dams but when it comes to generating power without one, several factors, including the tiny charges of molecules come into play.
What is hydropower?
Hydropower is the electricity or power generated through fast falling water whose kinetic energy is converted into electrical energy.
What are the methods used for generating hydroelectricity?
There are mainly 3 methods to generate hydropower/hydroelectricity. These methods are:
Impoundment
Diversion
Pumped Storage
How does the “Impoundment” facility work?
Impoundment facilities are the most used ones out of the three methods. These facilities use dams which store river water in a reservoir on one side of the structure. When water is released from the reservoir, it flows downward through a pipe in the dam called the penstock. The falling water reaches a turbine in the powerhouse and circles around it until it is let out via a draft tube. This turbine is spun by the movement of the water. The water then gets released into a river on the other side of the dam after spinning the turbines in the tube (the system of powerhouse is used by all types of hydropower plants). When the turbine spins, it rotates a metal shaft above it which is connected to an electrical generator. The rotation of the shaft causes the generator to rotate, and the kinetic energy is then converted to electrical energy. This electrical energy is transported to a transformer after which the current is transported from one circuit to more (in the city). This transformer system applies to most power plants out there, from nuclear to thermal and hydro.
IMPOUNDMENT FACILITY
What is a dam?
A dam is a structure built across a stream or river to control the flow of water. Hence, preventing overflow leading to floods and aiding in generating electricity.
What is a reservoir?
A reservoir is simply a large man-made lake behind a dam, used to store fresh water and generate electricity.
What is the ‘fishway’ in the dam’s diagram?
The ‘fishway’ or ‘fish ladder’ is a type of slide in the dam connected to the water bodies. This slide is meant to provide for the migration of fish, rather than having man-made structures disrupt them. Although this may sound like a good idea, studies show that these fishways don’t really perform up to expectation.
How does the “Diversion” facility work?
Diversion facilities resort to collecting water from rivers and returning that same water back into the stream during electricity production, they use the natural decline of the river for this. Here, a manmade canal offshoot from the main river stream forms a diversion. The point from where the water from the river enters the canal is called the intake which may be controlled by a door. The water flows into a tank called the forebay. From there, the water flows downhill, almost parallel to the descending river, in a penstock. The water travelling in the penstock reaches the powerhouse from where the turbine-generator system is used to convert kinetic energy into electricity. As this happens, water is released from the powerhouse into the river via the tailgate.
DIVERSION FACILITY
What is the need for the forebay?
The forebay which is located at the end of the channel, plays a crucial role. It acts as a temporary water storage to regulate flow and avoid turbulence as water enters the penstock.
What is the “Sediment Exclusion Chamber” in the diagram?
Sediment exclusion chambers contain basins/tanks in diversion facilities and even in some dams where impurities and sediments in the river water are filtered out.
What is the need for such a chamber?
Sediments present in water can accumulate in the infrastructure and installations of the hydropower facility. It can tamper with the machinery and the blades of the turbines in the powerhouse which can decrease efficiency in the process and hinder the work being done.
How do these chambers work?
A sediment exclusion chamber functions by directing water containing sediments like sand and silt into a tank or basin. The design of the chamber slows down the velocity of water coming from the intake/reservoir. As the water slows, the process of sedimentation takes place where the heavy particles and impurities settle at the bottom of the chamber due to gravity. With a reduced sediment load, the cleaner water is released from the chamber, and it follows its path to the powerhouse. Meanwhile, the accumulated particles at the bottom of the chamber are removed through processes such as hydraulic flushing and mechanical dredging to ensure zero blockage in the chamber.
What is hydraulic flushing?
Hydraulic flushing is a method used to expel sediments through tanks by releasing large amounts of water into the chamber through valves or gates. This sudden release of water leads to high velocity which disturbs the accumulated sediments, hence, mobilizing them. Next, the water is released from the chamber and is then discharged through designated valves or openings downstream into the river. This works differently in dams as some sediments accumulate at the bottom of the reservoir which are then expelled through an outflow.
What is mechanical dredging?
Mechanical dredging is a method used to remove sediments from the chamber by using excavator or other machinery to scrape off the sediments from the bottom of the chamber. In dams, these machines scrape the reservoir bed to remove accumulated sediments.
Why did the diagram state the exclusion chamber as “optional”?
This is because the presence and need for an exclusion chamber may vary from place to place and several factors such as:
Load of water
Design and purpose of facility
Environment and climate
How does the “Pumped Storage” facility work?
Pumped storage facilities function similarly to dams and diversions. Here, two reservoirs are built with one being higher than the other. During times of high demand, fast falling water is released by the higher reservoir through penstocks. Due to gravity, the water travels downwards where it reaches the powerhouse just before it gushes into the lower reservoir. As the blades spin and the kinetic energy is converted to electricity by the generator, water falls into the lower reservoir. After this stage, the process varies – Open loop & close loop.
What is an ‘open loop’ pumped storage system?
Once the water reaches the lower reservoir it flows to a river or any water body which is artificially connected to the reservoir. This system is, hence, open.
What is a ‘closed loop’ pump storage system?
When demand is high, water flows into the lower reservoir and generates electricity as it crosses a specific turbine called a Francis turbine. Due to water’s head, Francis turbines are used. Once demands lower down, all the water in the lower reservoir comes back up to the higher reservoir through the penstocks. This ‘gravity defying’ event takes place with the help of the Francis turbine which rotates the same way it did while generating electricity, but its direction is reversed, and this acts somewhat like a suction.
CLOSED PUMP STORAGE FACILITY
What is water’s head?
Water’s head is simply the vertical distance between the water in the upper reservoir and the water in the lower reservoir. In a hilly region, the head will be high due to the distance between both the reservoirs.
How does water’s head determine the turbine to be used?
Water’s head dictates the choice of the turbine due to factors like speed, pressure, and rate of flow. Most pumped storage plants have medium to high heads, which is best for a Francis turbine.
How does a Francis turbine work?
It works in a very simple manner. Water passes through a spiral tube from the inlet connecting the penstock. The water flows around the main part of the turbine called the runner, which rotates and along with it, rotates the metal shaft and generator. Hence, the generator’s movement will create electricity.
FRANCIS TURBINE
What are the advantages of hydroelectricity?
It is renewable.
It can pair well with other renewable sources of energy.
It controls water flow.
Building of lakes and reservoirs can open space for recreational activities like fishing, boating, swimming etc.
What are the disadvantages of hydroelectricity?
Has an adverse effect of aquatic life.
Expensive up front, that is, requires high cost to run an entire region alone.
Lack of area for building these structures.
Impacted by droughts due to lower water flow.
What are new methods and solutions through which hydroelectricity can become a ‘zero energy wastage’ dream come true?
New and upcoming implementations include:
Whirlpool electricity generation – This was implemented and continues to be implemented in rural areas by a Belgian company called Turbulent. Here, water flow offshoots via a gate from a canal into a circular basin with a turbine in the center. The movement of water in this basin forms a vortex in which the turbine spins.
Wave power electricity generation – Several methods are under development to harness the power of ocean waves for electricity. These methods include floatable devices on the surface of the water which convert the movement of waves into electricity, as how Portugal is experimenting. Other methods include devices on the ocean floor, converting the swiftness of the channels into power, and tapered canals connected to reservoirs which capture waves to drive turbines. Coastal countries such as the US, Japan, and New Zealand are trying out such methods to ensure full efficiency from the sea.
WHIRLPOOL VORTEX
Can rain be converted in electricity?
Yes, it can. Rain energy can be used to power homes when the lights go out as it pours down, it can also be used in conjunction with other sources of energy like solar and grid (electricity supply) energy when the weather is clear. This energy would prove fruitful in areas where it rains a lot. Two ways can be used to implement such a method:
Electricity generation through a triboelectric nanogenerator or TENG. It uses liquid-solid contact electrification. Here, the frictional charges between the water droplets and solid are captured by water-based triboelectricity nanogenerators, which converts the mechanical energy into electrical energy.
The next method is theoretical but utilizes piezoelectricity, which envisages vibrations of the rain drops to patter onto a thin metal sheet connected to a resonator. As the sounds are amplified, transducer mechanisms can convert the energy from the vibrations to electric energy using an electromagnetic generator. A magnet is attached to a sensitive and flexible membrane with a coil kept separated. As vibrations pass through the membrane, it moves and so does the attached magnet. The distance between the coil and the magnet keeps on changing due to the movement of the membrane. These magnetic fluctuations produce electricity through electromagnetism as the change in the magnetic field pushes electrons in a circuit. This method may be done by another generator which is piezoelectric, that is, a piezoelectric crystal reacts to soft vibrations and is put under strain, hence, generating a current.
What is a ‘triboelectric nanogenerator’?
It is a type of energy-harvesting generator which converts mechanical energy (the energy acquired by objects upon which work is done) into electrical energy using the triboelectric effect.
TENG STRUCTURE
What is the ‘triboelectric effect’?
This effect describes the electric interactions of charges (electrical nature) between objects which contact or slide against each other.
What is a transducer?
A transducer is an electronic device which converts energy from one form to the other. In this case, vibrations to electricity.
What is the meaning of ‘piezoelectric’?
Piezoelectric is the property describing certain objects which undergo the Piezoelectric effect, that is, their ability to produce electrical energy under any mechanical stress or pressure.
What is the future of hydroelectricity?
The disadvantages of hydroelectricity can be fixed as time moves on. We may develop more eco-friendly ways to tap the power of water, but in this world, demand comes first. Time moves ahead and so does the population, leading to a rising global demand of electricity. This demand will overtake electricity generated by rivers and lakes, but will require infinite efficiency, which can only be harnessed if we find an economically viable, safe, and sustainable way to use the great oceans to our advantage.