Hydropower Plant: How Does it Work?

Hydropower is electricity that generates through a generator that drives by the movement of water. Hydropower plant generally consists of dams that built to block water of the rivers, form reservoirs, or to collect water pushed into the dam. When the water drains, the pressure following the block sends drainpipes to the turbine. This turns the turbine, which in turn, turns the generator that generates the hydroelectricity. The hydroelectric power plant has many types that we will later. 

While dependence on conventional and some other sources like coal, oil, natural gas, etc., has put a strain on the planet, we live by damaging the environment and polluting the air. To retrieve energy from these fossil fuels, they must be burned. When burned, they release greenhouse gases such as N2O, CH4, CO2, and H2O. Greenhouse gases emit and absorb radiation.

Amongst the greenhouse gases mentioned, CO2 is the most prevalent. It makes up over 80% of total greenhouse gases. The problem with an increased amount of C02 is that it absorbs and emits infrared radiation. This causes the Earth’s surface and the atmosphere closest to the surface to increase in temperature, leading to many potential problems.

As the temperature increases on Earth, the ice caps begin to melt and release huge amounts of water into the oceans leading to rising sea levels. The consequence of this is the displacement of millions of people living in areas at sea level. In the current environmental landscape, the need for renewable energy sources is beginning to grow. Energy is considered renewable if it derives from a limitless source.

Explanation:

Hydropower accounts for 16.6% of global electricity and 70% of all renewable energies in 2015. It expects to grow annually by around 3.1% over the next twenty-five years.

The relatively low expenses of hydropower make it a cheap resource of renewable electricity. In contrast to coal or gas power plants, hydropower plant does not expend water. Typical energy costs for a hydropower plant over 10MW are 3-5 cents per kWh. With the help of dams and reservoirs, this is also an elastic source. The energy generated by the hydropower plant rises and falls very quickly (only a few seconds) to adapt to the fluctuating energy requirements. The project does not generate any direct waste when building a hydropower plant.

hydropower plant

Historically hydropower has been used for crop irrigation, milling, and pumping. But in the 19th century, its use extended to producing electricity on a smaller scale at the time.

Since the hydroelectric power plant only requires the vertical movement of water. The reason for choosing hydroelectricity over the other renewable energy types is due to the shear amount of it used per year compared to the rest. Different statistics show that in 2017 hydroelectric energy consumption was 4065TWh (terawatt-hours), whereas the other renewable energy sources’ cumulative energy consumption was roughly 2200TWh. Also, if we compare the usage of hydropower to that of traditional biofuels (fossil fuels), we can find that hydropower alone has the possibility to replace the entirety of biofuels as a renewable energy source.

Hydropower Plant Turbine Types


There are three principal kinds of hydraulic turbines: reaction turbines, gravity turbines, and impulse turbines. The type of turbine for a hydropower plant selects according to the requirements of head and flow rates—some other factors such as cost, efficiency, and turbine depth are involved in selecting turbines.

1) IMPULSE TURBINE

Impulse turbines usually use water speed to cross the flow path and release it at atmospheric pressure. Water hits every bucket in the corridor. The underside of the turbine is not sucked in. The water hits the rotor and then flows from the turbine housing base. Impulse turbines generally suitable for applications with low flow and high head.

Impulse turbine has three major types: The Crossflow turbine, the Turgo, and the Pelton wheel turbine.

i) Cross-Flow Turbine

The cross-flow turbines are cylindrical-shaped and use an elongated nozzle with a rectangular cross-section, pointing to the curved blades of a cylindrical runner. Cross-flow turbines resemble a “cage blower.” Cross-flow turbines push water throughout the blades two times. The first step is when the water flows in from the outside and the second step from the inside to out. Turbine inlet guide vanes direct the flow directly to a limited part of the corridor. Cross-flow turbines have high flow rates and lower heads than Pelton wheel turbines.

ii) Pelton Turbines

Pelton wheel turbines have one or more free nozzles that drain water into the expanded space and hit the runner’s hub. These turbines do not require an intake manifold. So, the flow path in these turbines must lie above the extreme tailwater to enable operation at atmospheric pressure.

Parts of the Pelton wheel turbine are given below.

  1. Runner
  2. Buckets
  3. Braking Jet
  4. Nozzle and Flow Regulating Arrangement
  5. Casing
iii) Turgo Turbines

Turgo turbines are similar to Pelton turbines, but the nozzles meet the runner level at an angle (typically 20 ° to 25 °). In these turbines, one side of the water enters the corridor, and the other side flows off. Therefore, the flow is not limited by the wastewater liquid that disturbs the inward water jet (the Pelton wheel turbine has the same function).

CHARACTERISTICS OF TURGO TURBINES

  • It has a compact design.
  • Healthy design as well as assembly
  • Designed for nominal safeguarding
  • Available in single, double, or triple spray configurations
  • Fixed, variable manual or fully automatic flow setting
  • It can be made with different materials to meet customer requirements.
  • Each turbine has a 10 MegaWatt output.

2) REACTION TURBINE

Reaction turbine is the most famous type of hydroelectric powerplant turbines. Reaction turbines generate electricity through the mutual action of running water and pressure. Place the flow path directly into the water running through the vanes instead of hitting once at a time. In comparison to impulse turbines, reaction turbines typically use in high-pressure heads and high-flow locations. All types of reaction turbines have a diffuser below the flow path, referred to as a “draft pipe (or draft tube)” through which the water discharges. As the flow dividing pipe slows down the draft’s flow rate, the suction force is generated below the flow path, increasing the effective height.

Relative Efficiencies

A turbine that runs at a particular speed produces a certain flow. If the river flow is insufficient to meet this need, the turbine will begin to drain, and its performance will quickly decrease. Then you have to close it or change its inner shape. This process is called regulation. A regulated turbine can move its inlet influence blades or impeller vanes to increase or decrease its intake flow. Different turbines absorb less flow, which inevitably leads to lower efficiency. Therefore, a key factor when comparing different turbine types is their relative efficiency at the design point and the efficiency in reducing the flow. For example, the Kaplan and Pelton turbines remain highly efficient even if they operate below the design flow in the hydroelectric power plant. In contrast, cross-flow turbines and Francis turbines are less efficient when operating beneath half the normal flow.

Advantages of Hydroelectricity


1) Flexibility:

This type of energy is a flexible source of electricity. It can raise and lower through a hydropower plant very rapidly to meet the changing energy needs. In the hydroelectric power plant, the turbine has only a few minutes to start. It takes 60-90 seconds from cold start to full charge. This is much shorter than a steam power plant or a gas turbine. Even if there is excess electricity generation, it can quickly reduce the amount of electricity generation. Therefore, in addition to emptying the basin or covering downstream needs, the limited capacity of the hydropower plant is generally not used to generate basic electricity.

2) Low Cost:

The main benefit of a conventional hydraulic dam with a reservoir is storing water as high-quality clean energy for later shipping at a low cost. The average electricity price for hydropower plants over 10 MW is 3-5 cents per kWh. If hydroelectricity is used as a current peak to encounter requirements, it has more valuable than basic electricity than intermittent electricity.

The economic lifespan of a hydropower plant is very long, and some plants can be used after 50 to 100 years. It has low labor cost for operation because the system is automated, and there are only a few people on-site during normal operation.

If the dam uses multiple times, adding a hydroelectric power plant at relatively low construction costs can be a useful income source to offset the dam’s operating costs. However, some data show that without adequate risk management measures in most countries, the construction costs for large dams are too high and the construction time too long, which leads to an adjustment of the risk. It shows that you cannot make a profit later.

3) Suitability for Industrial Applications:

While many hydropower projects supply electricity to public networks, some projects serve certain industrial companies. For example, a special hydropower project is generally being built to supply the large amount of electricity needed for an aluminum electrolysis plant. Support for World War II aircraft to support Alcoa in Bellingham, WA, after the war before the Great Curry Dam was allowed to provide irrigation and energy (in addition to aluminum power) to American citizens. I decided to do it. In Suriname, the construction of the Broco Pond reservoir is intended to promote Alcoa Industries. The New Zealand Manapouri power plant is designed to power the aluminum foundries at Tiwai Point.

4) Reduced CO2 Emissions:

Hydroelectric power plants do not consume fuel and therefore do not produce carbon dioxide. Carbon dioxide generates for the first-time during project construction. The reservoir emits some methane every year, but the life cycle of greenhouse gas emissions from hydropower is usually the lowest. In 2011, hydropower replaced 3 billion tons of carbon dioxide than fossil fuels from the same production. Wind energy is the second. Nuclear energy is the third, and solar energy is the fourth. Hydropower has little impact on greenhouse gases, especially in temperate climates. The effects of greenhouse gas emissions can observe in tropical regions since power plants and reservoirs produce more methane in tropical regions than in tropical regions.

These powerplants have low greenhouse gas emissions than solar power plants and other power plants that have to be operated with fossil fuels.  Like other non-fossil fuels, hydropower plant does not emit nitrogen oxides, sulfur dioxide or other particles.

5) Safe:

Hydropower is safer than other fossil fuels and nuclear power. Does not contain fuel (other than water).

Disadvantages of Hydroelectricity


1) Ecosystem damage and loss of land

Large reservoirs connected to traditional hydropower plant can flood large areas upstream from dams and destroy biologically costly and useful lowland and grasslands, swamps, and valley forests. The construction of large dams generally involves the movement of people and wildlife. But dams can hinder river flow and damage local ecosystems. The fragmentation of the surrounding habitats caused by reservoirs often makes worse the loss of land.

Hydropower projects can damage aquatic ecosystems before and after the plant. Hydroelectric has changed the environment of the downstream river. The water flowing out of the turbines is generally free of suspended sediments that can cause better erosion and bank loss. The turbine doors often open temporarily and observe rapidly.

2) Water loss by Evaporation:

A 2011 survey by the National Institute of Renewable Energy found that U.S. hydropower plants produced 5.39 to 68.14 cubic meters of hydroelectricity per megawatt-hour (megawatt-hours (1,425 to 18,000 US gallons)). The average was 17.00 m3 / MWh (4,491 US gallons / MWh). Thus, over the loss of power generation technology uses cooling towers, including solar energy at 3.27 m3 / MWh (865 US gallons / MWh) at 2.98 cubic meters / CSP tank megawatt-hours (786 Gallons/megawatt-hour). If the reservoir uses several times (water supply, recreation, flood protection, etc.), the evaporation of all reservoirs is due to hydroelectricity.

3) Siltation and flow shortage:

When water flows, it can transport heavier particles downstream than itself. This has a detrimental effect on the dam and subsequent power plants, especially rivers and silo basins. The silt fills the reservoir, reduces its ability to control floods. It exerts horizontal pressure on the upriver part of the dam. During a flood, some deposits can fill with sand, become unusable, or become flat.

Changes in river flow are related to the energy generated by the dam. A low river flow reduces the amount of living water in the reservoir and the amount of water available for hydropower. Due to the reduced river flow, areas heavily dependent on hydropower may experience a lack of energy.

Climate change can increase the risk of traffic congestion. A study of the Colorado River in the USA showed that moderate climate change could reduce the river’s drainage by up to 40%. For example, a temperature rises of 2 degrees Celsius could reduce precipitation by 10%). Brazil particular is vulnerable due to its high dependence on hydropower. At the turn of the century, rising temperatures, reduced water flow, and changing rain conditions could reduce total energy production by 7% a year.

4) Methane Emissions:

A lower positive impact was found in the tropics as it observed that deposits from tropical power plants produce large amounts of methane. This is because the plant material in the flooded area decomposes in the anaerobic environment and forms methane (greenhouse gas). The World Dam Commission reports that the reservoir is larger than the power generation capacity. In the reservoir, the surrounding forests were not cleared until the greenhouse had stored water. Gas emissions from reservoirs can be higher than from conventional reservoirs.

In Canada and northern European reservoirs, greenhouse gas generally discharges only two percent to eight percent of conventional electricity generation from fossil fuels. A new way of underwater deforestation in underwater forests can alleviate the results of forest decay.

5) Relocation:

For a hydropower plant, dams need a place, and the people relocate who live in planned reservoirs area. In 2000, the World Commission for Dams estimated that 400 to 80 million people worldwide were evacuated from the dam.

Types of Hydropower Plant


Several renewable energy types are in function at present, such as hydroelectricity, solar thermal, solar electricity, wind power, wave, heat pump, to name a few. Though there are such a vast number of renewable energy sources, choosing which type of energy to use is as big of a topic as using renewable energy. When choosing the type of renewable energy, several factors must be considered, including the environmental effect, cost, efficiency, and energy source.

In reality, hydropower and coal plant produce electricity in the same way. In mutual situations, an energy source consumes to revolve a propeller-shaped component, called a turbine. The turbine rotates the electrical axis of a generator. A coal-fired hydroelectric power plant uses steam to rotates the turbine vanes. The hydroelectric power plant uses wastewater to drive turbines.

Hydroelectricity is a method of renewable energies accounts for about a sixth of the world’s electrical energy. Less contamination than with a steam engine. In some countries like Quebec and Norway get the maximum amount of electricity through this way.

A dam stocks a lot of water in a water tank. The water intake is near the bottom side of the dam. Gravity pushes the water into the dam through pressure pipes. At the end of the pressure line, the propeller of the turbine turns and releases water. The turbine shaft turns, and the generator produces electrical energy. The power cord links to a generator that provides your and my home with power. The water continues to run over the engines, through the propellor, and into the river next to the dam.

For a complete understanding of hydroelectricity operations, the transfer of several energy types must be considered. There are three main types of hydroelectric power plants; impoundment pumped storage and run-of-river.

Hydroelectric power generation

1) Impoundment Hydroelectric Power Plant

Among the three hydropower plant types, the most common type used to gather hydroelectricity is the impoundment. The system uses a dam to store water from a river in a reservoir. During the working of this hydroelectric power plant, the water releases from the reservoir into the penstock. The water strikes with the turbine forcing it to spin. The turbine connects to a generator. The generator operates due to the movement of the turbine shaft. From the generator (located in the powerhouse), the produced electricity is then transferred to local communities via powerlines and grids. The famous example of impoundment hydroelectric power plants includes the Hoover Dam (Colorado River, USA) and the Three Gorges Dam (Yangtze River, China).

The turbines don’t just place in the middle of the river or a dam. So, that the turbine can rotate easily. The reason is that the river water flow doesn’t have enough energy (both kinetic and potential) to spin the turbines fast enough, so there isn’t enough energy transmitted to the generator as a result. Therefore, in an impoundment system, a hydraulic head which has the vertical height difference between the water level at the high reservoir and the water level at the lower reservoir. This gives the water flowing down into the turbine much larger kinetic and potential energy. Due to the change in height and an increase in the velocity of the turbine spinning. This increased energy input then provides a larger energy output to the generator. Due to that, higher output hydroelectricity produces.

2) Pumped Storage Hydroelectric Power Plant

The pumped storage dam is an extension of both the impoundment and run-of-river hydropower systems. They are generally much smaller in terms of energy generation as compared to other hydropower plant types.

hydroelectricity production

Pumped storage is simply adding a method of pumping. In this, the discharged water from the lower reservoir backs up to the upper reservoir for re-use at a time of higher electricity demand. During off-peak periods, the plant switches the direction of the turbines so that the discharged water from the lower reservoir can be pumped back up the penstock into the upper reservoir for re-use when electricity demand is higher.

3) Run-of-River (Diversion) Hydropower Plant

A run-of-river hydroelectric power plant system is a famous method of production of hydroelectricity. It is a system where the natural water flow rate uses to turn the turbines. These turbines connect with generators that produce hydroelectricity. They lack the potential energy that conventional plants have due to the absence of a major drop in height. For a diversion plant to be constructed, a constant flow rate requires. Without the reservoirs, the water is channeled down sometimes through a decrease in the head. The channeled water through a penstock flows through a generator house where the water flow turns a turbine identical to that of the impoundment plant. This turbine delivered mechanical energy to the generator, which converts it into electrical energy. Like before, this energy transmits to locations where it’s required via powerlines.

Efficiency of Hydropower Plant


To date, hydroelectricity is the most effective method of generating electricity on a large scale. The energy flow can be converged and keep under control. The transformation process absorbs K.E and transforms it directly into electrical energy. There are no ineffective thermodynamic intermediate processes or heat losses, or chemicals. To extract 100% of the kinetic energy from the flowing water, the flow must be stopped so that the overall efficiency is never 100%.

Hydropower uses P.E from rivers and currently provides 17.5% of global electricity (Norway 99%, Sweden 40%, Switzerland 55%, Canada 57%, and USA 7%). Except for some countries, hydropower is often used for peak load requirements because it is easy to stop and start. In industrialized countries, this is not the main option for the future. Most of these countries have developed because they have important locations that could use gravity or are not available for other reasons (e.g., environmental factors). For 2030 growth is imagined mostly in China and Latin America.

Future of Hydropower

  • (No stored water- no reservoir) (run of river)
  • Expansion of many more irrigation-based points to power plants.

Conclusion:

Hydroelectricity is the cheapest form of electricity. It is increasing day by day all over the world. The conversion efficiency of a hydropower plant mainly varies on the type of turbine used. For large mechanisms, the conversion efficiency can reach 95%. Small power plants’ efficiency with an output of less than 5 MW is between 80% and 85%. However, it is hard to obtain energy from low flow rates.

 

 

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