Let's Talk About Renewable Energy #1: Hydropower

The topic for today is renewable energy with the aim to provide a better understanding about these so-called ‘green’ sources of energy, to learn how they are harnessed and most importantly how they are affecting our daily lives and the environment in which we live in.

For starters let us define first what renewable energy sources are. Renewable energy sources are basically energy sources that regenerate or replenish on a human timescale. It includes sunlight(solar), wind, hydropower, geothermal and biomass. When we were in high school and even today we usually use the terms ‘renewable’ source and ‘alternative’ source interchangeably. There is a subtle difference between a renewable energy source and an alternative energy source. The term ‘alternative’ is used to refer energy sources that are non-traditional. It is defined as an energy source that has a low environmental impact. We can consider renewable sources as alternatives, but it doesn’t necessary mean that all alternatives are renewables.
(Note: An example of a traditional source are fossil fuels.)

This time we are going to discuss one type of renewable energy source which is hydropower. And our main objective is to explain/answer the following before the end of this article:

1. What is hydropower?
2. How does a hydropower plant operate?
3. How does harnessing hydropower affects us?

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What is hydropower?

𝖢𝗋𝖾𝖽𝗂𝗍𝗌: 𝖯𝗂𝗑𝖺𝖻𝖺𝗒
The definition of hydropower is plain simple. The greek word 'hydro' translates to water. The full meaning obviously translates to water power or power of water. It's not really something new as most us are familiar with this kind of renewable energy. We've read it in our science books and even watched documentaries about it. Hydropower or which is also referred today as hydroelectric power is harnessed from moving water. Flowing, falling or any type of water movement contains a certain amount of free energy. And because human beings are rather smart we established means on how to harness this free energy and turn it to something beneficial to us, like electricity. But before we dive too deep, do you know that hydropower was not first used as a source of electricity? Even before the industrial revolution and the discovery of electricity, hydropower has always been there.

Some History...

In ancient times, hydropower had played a relevant role in agriculture, woodworking and mining. People harnessed this energy to turn their grains into flour which would later be turned to bread. Of course it was not only limited to grains. It was also used to process lumber, textile, metals and even stone products.[1]

How did they do it? They used watermills, one of the earliest known device to harness hydropower. There are different kinds of watermills but the most common is the one with a large wheel (water wheel) attached to a building like structure, like the one on the right. And just to make things much clearer let us clarify that the water wheel is a part of the watermill. It is considered as most iconic part of the mill as most watermills' age and type can be determined just by looking at it's wheel.

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Mills and their Wheels

There are two characteristics that make a watermill unique from others, these are the wheel's driving surfaces (blades or buckets) and it's rotational axis. Generally, the more ancient mill models have flatter blades and the latest models have buckets as their driving surfaces. From a modified channel known as mill race water would flow or fall hitting these driving surfaces that would turn the wheel. The image on our left is known as a tub or Norse Mill. This is one of the earliest type of mills with horizontal wheels and also one of the most inefficient. This inefficiency means that the work output of the mill is very much less compared to the work input by the driving force, in this case it's the water which hits the blades. In their book, Major Historical Developments in the Design of Water Wheels and Francis Hydroturbines, Lewis, Cimbala and Wouden described the efficiency of norse mills as very poor. There is no specific percentage but base on the other wheel models it is certain that the efficiency is less than 20% . Actually watermills only acquired decent efficiency(50-60%) in the early 19th century which is also the start of the industrial revolution.[2] During and after the industrial revolution the water mills' efficiency were improved to 80-90% but the use of mills became obsolete due to the development of a more efficient and cheaper technology, the hydroturbines.

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Hydropower Now...

Although water mills are still present most of them are not used and this is due to the industrial revolution which sped up development at an exponential rate. With many great minds at that time the first electrical generator was also developed. Fusing these two technologies they arrived of what we know today as hydroelectricity.

In 1878 the first house was lit by hydroelectricity. It was the house of the Sir William Armstrong. This guy is so awesome here's his brief description from wiki in case you're being lazy to click the link. XD

Armstrong was knighted in 1859 after giving his gun patents to the government. In 1887, in Queen Victoria's golden jubilee year, he was raised to the peerage as Baron Armstrong of Cragside, becoming the first engineer – and, indeed, the first scientist – to join the House of Lords.

Sorry for being a little off topic there. After the incident of lighting the first household harnessing hydroelectricity for power generation have spread like a wildfire. Just before the end of the 20th century there are already hundreds of hydroelectric power stations in North America alone which powered up thousands of households at that time. And the trend didn't end as many more power stations were built with higher power output and capacity.

At present, these are the four dams with the highest power capacities exceeding 10,000 MW:

Dam	Capacity
Three Gorges Dam	22,500 MW
Itaipu Dam Brazil	14,000 MW
Xiluodu Dam	13,860 MW
Guri Dam	10,200 MW

𝖲𝗈𝗎𝗋𝖼𝖾: 𝖶𝗈𝗋𝗅𝖽 𝖶𝖺𝗍𝖼𝗁 𝖨𝗇𝗌𝗍𝗂𝗍𝗎𝗍𝖾

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Power Generation and Energy Conversions

There are four main methods of harnessing and generating power and these are the conventional dams, pump-storage systems, run-of-the-river and tide. But we will focus this discussion on the conventional dams as this generation method is the one we are most familiar with. It is also the method which produces the highest power output among the four.

How does a Hydroelectric Dam Operate?

Before anything else we need to know that most dams were not built for power generation but for irrigation and flood control. Only hydroelectric dams are built for such purposes.

Hydroelectric Dams are built on river systems that have large elevation gaps and the reason for this is to utilize the force of gravity. The larger the drop elevation the more potential energy it will build up. The formula for potential energy is m x g x h (mass x gravity x height). It means that as height increases the potential energy value also increases.

A hydroelectric dam became a mainstream power generation device because it has an excellent control over the water flow. A reservoir is built behind as a water storage. The intake below the dam acts as a floodgate which regulates the water flow; it is opened if it's time to generate power and is usually closed when there is insufficient water in the reservoir to propel the turbine.

When the floodgates are opened the water flows through the penstock. In this process the previous potential energy is converted to kinetic energy (KE). Just an example let us assume that we are in an equilibrium and PE = KE. The formula for KE is 1/2mv^2. If the converted potential energy value is high it means that the speed value(v) is also high. The faster the speed of the water flow the faster the turbine spins. From KE it is converted to mechanical energy by the hydraulic turbine's rotational motion.

On our left is a hydroelectric generator connected by a shaft to a turbine. Moving water hits the turbine and the rotor spins with it generating electricity. The rotor is the part of the generator attached to the shaft while the stator is the stationary part. But what happens inside the generator? How is electricity produced? The answer lies in Faraday's Law of Electromagnetic Induction. Rotors are made up of wire loops stacked around magnetic steel laminations when it is fed by a direct current from a source an electromagnet is formed. The rotation causes the magnetic field to move cutting the flux constantly as the electromagnet passed through the conductors mounted in the stator. This process produces current and develop voltage at the output terminals of the generator.[3] The voltage and current values produced by hydroelectric dams are very high for the normal household so it still needed to pass through several substations and transformers to be fully usable.

Summary of Energy Conversions

Potential Energy(Flood Gate Closed) -->> Kinetic Energy (Water Flows through the penstock) -->> Mechanical Energy(Turbine Spins) -->> Electrical Energy(Rotor Spins Producing Electricity)

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Pros and Cons of Harnessing Hydropower

Pros

1. It's Cheap!
The energy source is FREE making the operations cost very low. The bulk of expenditure will go to dam and plant construction. And because this kind of power is produced at lower costs it is expected the selling price to the consumers is also cheaper.

Depending on a power plant's size the budget needed for construction is in several millions to billions. But a well-maintained plants lasts very long. According to wikipedia and it's sources some plants last even 50-100 years! Take the Three Gorges Dam in China for example. It is estimated that the the construction cost will be covered after 5-8 years of full generation. So after the 8th year the plant's only liability is the annual maintenance cost and taxes(of course), aside from that everything is pure profit.

2. It's Clean!
Hydoelectric plants don't burn anything so they do not release of CO2.

While carbon dioxide is initially produced during construction of the project, and some methane is given off annually by reservoirs, hydro normally has the lowest lifecycle greenhouse gas emissions for power generation. Compared to fossil fuels generating an equivalent amount of electricity, hydro displaced three billion tonnes of CO2 emissions in 2011.

3. It's flexible in many ways!
a. It is very easy and quick to control
Power adjustments can easily be implemented because hydraulic turbines have a fast start up time. It is also the same for decreasing the power generation. This made the efficiency of the plant operation very high.

b. Storage Facility
Another good thing with hydroelectric power plants is the dam. Having a resevoir is an assurance of having spare power supply in cases when the demand is high. Some reservoirs can also be used for recreational activities like swimming and boating.

c. The outflow is still usable
After the water passed through the turbine it would flow to the river below. The flowing water is commonly used to irrigate farm fields.

Cons

1. Water Cycle Dependency
The amount of precipitation determines the amount of water available for hydropower production. Droughts are always accompanied by fast evaporation rates which greatly diminishes the stored water, sometimes it even render the unavailability of power plant operations.

2. Environmental Impacts
a. Ecology

Dams can affect the river ecology in some serious ways. A good example is the salmon migration. Salmon is an anandromous fish which means that they spend their life cycles in both fresh and salt waters. They spent their youth in rivers and go to the ocean to mature and breed. They later come back to the rivers to lay their eggs. Most of the spawning sites are upstream so building a dam is literally blocking their way. This problem is somehow mitigated by using fish ladders. Although the mortality due to blockage of adult salmons are lessened it is still a different story for the young salmons(smolts). Their first journey to the ocean becomes several times longer as compared to the time before the dams were built. They become an easier prey to predators and it also affects their breeding patterns.[4]

b. Atmosphere
There are more methane emissions from reservoirs of power plants in the tropics because it is more humid. Environmental conditions promotes the decay of plant material in flooded areas which produces methane.

3. Failure Risks
Have you watched the movie Evan Almighty? The materials used in the dam were sub-standard and at the later part of the movie the dam broke. This is one example of failure risks(minus the fiction). There are three main reasons why is there failure risks and these are poor construction, natural disasters and sabotage. Large dams hold more water making them more susceptible to these risks.

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Final Thoughts

We learned many things today about hydropower. From the cool water mills, when they became obsolete and were replaced by hydraulic turbines up to the process of harnessing electricity from a hydroelectric power plant. We also learned about the effects of hydropower to our environment. Personally if I weigh the pros and cons of hydropower I think it has a more positive impact in our society and environment as a whole. The flowing water is free and if we can develop better electrical storage facilities we can take the opportunity of harnessing power especially when there is low demand. Of course we also have to improve the mitigation process of the damages the dams would bring like the case of the salmons. What do you think?

It's 1 A.M. here. I'll write the credits and it's time to sleep. Haha. I hope you learned something. Good night. XD

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Credits:

[1] - [2] - [3] - [4]
https://en.wikipedia.org/wiki/Hydropower
https://en.wikipedia.org/wiki/Watermill
https://en.wikipedia.org/wiki/Water_wheel
https://en.wikipedia.org/wiki/Hydroelectricity
https://www.eia.gov/energyexplained/index.cfm?page=hydropower_home
https://water.usgs.gov/edu/hyhowworks.html
https://www.nationalgeographic.com/environment/global-warming/hydropower/
https://www.internationalrivers.org/dams-and-migratory-fish