Hydroelectric Power:
What is Hydropower Energy

Learn everything about hydroelectric power and what hydropower energy is in this full breakdown article.

Hydroelectric Power - What is Hydropower Energy

It’s no secret that water is powerful. The sound of huge waves pounding the shore; the sight of a massive waterfall tumbling through the air; even the knowledge that a small, consistent trickle of water can wear down solid stone is enough to leave you feeling small and insignificant when compared to the majesty and tenacity of .

Very early in our history, mankind learned to harness the power of water. We built boats that could drift down a river to facilitate trade. We diverted and stored water to help farms grow. We built large waterwheels that could use a running river to grind corn and grain into flour. And humanity’s latest trick? Converting the motion of water into the electrical energy we use to power our homes and businesses.

While water is one of the oldest renewable energy sources on the planet, it still offers plenty of potential. After all, 70% of the earth’s surface is covered in water. If we can find a way to tap into all of that waiting energy, humanity could be powered well into the future.

Some Facts About Water

Before we dive (pun intended) into the nitty-gritty of hydroelectric power, it might help to learn a bit more about the source of that power. Water is everywhere, but just because you see it everyday doesn’t mean you know all of its secrets. Here are just a few:

A single water molecule is made up of two Hydrogen atoms and a single Oxygen atom (hence the abbreviation,).

Earth’s water supply is endlessly conserved, which means there is the same amount of water on Earth as there was when the planet initially formed.

While 70% of Earth’s surface is covered in water, almost 97% of that water is undrinkable, and 2% of it is frozen into ice caps, which leaves only 1% of Earth’s water available for human use.

Water is an excellent temperature regulator. It helps keep Earth’s temperature stable, and is even used to cool down nuclear power plants!

In the United States, the average person uses nearly 50 gallons of water each day.

(Very) Early Hydro Power

As was mentioned, water is one of the oldest renewable energy sources on the planet. Humans have made excellent use of water to power everything from transportation to wheat mills. While it’s difficult to know the very first-time mankind used water for power, some clues have emerged in ancient Greece:


Nearly 2,000 years ago, the ancient Greeks used water wheels to grind wheat into flour. The earliest version of a water wheels was called the Perachora wheel, which was first mentioned by the Greek engineer Philo of Byzantium, around 200 BC. Early water wheels were primarily used as grain mills, but later uses of the water mill expanded to include sawmills, textile mills, and other types of manufacturing.

France (Bernard Forest de Bélidor)

While the early Greek water wheels were adopted throughout much of the world, the next innovation of water power didn’t come until thousands of years later. Up through the 1700’s, water wheels were primarily mechanical: they turned the rushing of water into mechanical energy, which was then used to grind flour or saw wood.

In the mid-1700’s, a French engineer named Bernard Forest de Bélidor wrote a treatise titled Architecture Hydraulique. In his book, Bélidor detailed the intricate mechanics of watermills, and discussed the possible use of water to run a motor. At this point in time, steam engines were emerging as a world-changing invention, and Bélidor believed that liquid water could prove to be just as powerful as steam. Bélidor also developed equations modeling fluid dynamics, which would prove useful to later engineers tackling both the motion of water, and aerodynamics.

Enter Electricity: Hydroelectric Power

Though Bélidor’s thoughts and equations were interesting, they were too theoretical to apply on a broad scale. Watermills continued to be used primarily for grinding grain, just as they had been for the past several thousand years. But less than 100 years after the publication of Architecture Hydraulique, a new type of energy burst onto the scene; a type of energy uniquely suited to work hand-in-hand with water: Electricity.

Faraday’s Law of Induction

In 1831, an English scientist named Michael Faraday made a discovery that changed the world. After years of experimentation, Faraday was able to produce an electrical current by simply moving a magnet through a coil of wire. ‘Faraday’s Law of Induction’ was born, and it formed the basis of the new scientific field known as Electromagnetism: the study of magnets and electricity.

After discovering electrical induction, Faraday quickly invented the first electrical generator; a device he called a dynamo. While electrical energy generation wasn’t yet widespread, Faraday’s Law of Induction and original dynamo design would have far-reaching effects on the world of water power.

Grand Rapids, Michigan – 1880

Less than 50 years after Michael Faraday first created a dynamo, his invention was put to commercial use in the town of Grand Rapids, Michigan. A dynamo driven by a water turbine was used to provide lighting to a theatre and storefront in the city, sparking the possibility that water-powered dynamos might actually be commercially viable.

In 1881, less than one year after the first water-powered dynamo, a dynamo connected to a flour mill turbine was able to light the streets of Niagara Falls, New York. Both of the first water-powered dynamos provided direct current energy, which was the primary type of electrical energy for the time.

Enter the Alternating Current

As electrical energy became more commonplace, a disconnect emerged between the two types of electrical energy: AC (alternating current) and DC (direct current). The war between currents involved several prominent scientists of the time, including Thomas Edison and Nikola Tesla. These two famous scientists were both pioneers in the field of electrical energy, but both were convinced that different types of electrical current were better.

Edison believed that direct current was preferable, as it ran continuously in a single direction. Direct current is produced in batteries or fuel cells, and it was the early electricity standard in the United States. The problem with early forms of direct current was that it didn’t easily convert to different voltages; if you were using DC, you were pretty much stuck at the same voltage.

Because of this difficulty, Tesla believed that an alternating electrical current would work better. AC reverses its direction multiple times per second (60 times/second in the United States). Although an alternating current may sound more complicated, it is much easier to convert to different voltages using a device known as a transformer.

The debate between Tesla and Edison became heated, with both parties convinced that their type of electricity was best. The matter was complicated by the fact that both scientists had serious money to gain if their preferred type of electricity was embraced by the world. At the Chicago World’s Fair of 1893, the question was put to the test: which was cheaper, and thus the winner? Edison lost the contract to provide electricity to the event; the honor going instead to a businessman named George Westinghouse, who used Tesla’s alternating current to provide electrical power for the fair – for $150,000 cheaper than Edison’s direct current designs.

AC grew rapidly in popularity after the 1893 World Fair. The same year, the Niagara Falls Power Company gave Westinghouse a contract allowing him to generate AC electricity using Niagara Falls as the energy source. The alternating current electricity derived from the Falls was so effective, it could power the entire city of Buffalo, New York, and convinced General Electric to invest in AC technology.

The 20th Century and Beyond

After the unprecedented success of alternating current generation in the late 1800’s, AC spread across the United States, becoming the main type of electricity generated and used throughout the nation. Hydroelectric power became commonplace; currently, every single state in the U.S. obtains some of their electricity through hydropower, with over 70% of Washington State’s electricity generated through water. Half of all renewable energy in the United States is generated via hydroelectric plants across the nation.

Famous Hydropower Locations

While many people don’t know the location of hydroelectric plants right off the top of their heads, there are a couple of famous landmarks that also happen to generate electricity:

Hoover Dam

One of the largest dams in the United States, Hoover Dam is particularly famous. It’s shown up in movies (Transformers), books (Percy Jackson, anyone?), and other pop culture arenas such as music, video games, and television. While it’s plenty stunning on its own, Hoover Dam is also a phenomenal hydroelectric plant, producing about 4 billion kilowatt-hours of power every year. That’s enough electricity to serve 1.3 million people. In the early 1900’s, Hoover Powerplant was the largest hydroelectric plant in the world. While it’s since been passed by other water-powered installations around the globe, Hoover Dam is still one of the United States’ largest hydroelectric plants.

Niagara Falls

While many people think of Niagara Falls mostly as a tourist attraction, the massive series of waterfalls powered one of the first hydroelectric plants in the United States. Niagara currently has several hydroelectric plants located along the river, with some of the plants falling on the Canadian border, and others located in the U.S. The Niagara power stations provide 25% of all the electricity used in the state of New York and Ontario, Canada. Since their first foray into hydroelectric power in 1893, the power plants located around Niagara have overgone several updates and restructurings to help maximize the efficiency of the plants. The New York-based power plants are still increasing in efficiency, while the Ontario Power Generation is at its maximum capacity for power generation.

How Does a Hydroelectric Generator Work?

Hydroelectric generators work on Faraday’s Basic Principles of Electromagnetic Induction: as with all electric generators, you just need to find a way to rotate a coil of wire next to a magnet in order to induce an electrical current.

The Mechanics

It’s important to remember that one of the first uses of water power came in the form of watermills. The basic design of a watermill was simple: put little paddles in a moving river, and the motion of the water would push against the paddles, spinning a turbine which could then grind flour, work a saw, or accomplish any number of mechanical tasks.

Hydroelectric generators work on the same principle: use the motion of water to spin a turbine. The only difference is that the turbine is hooked up to an electrical generator, which uses the spinning motion of the turbine to rotate a magnet through a coil of wire. The electrical generator that sits inside a hydroelectric plant is nearly the same as the first dynamo invented by Michael Faraday. As the magnet rotates through a coil of wire, an electrical current is induced, which can then be stored in batteries or transferred through the electrical grid to waiting households across the country.

One key piece of engineering in hydroelectric plants involves the movement of water. Unlike wind turbines, water turbines need an ‘outflow’ or escape route for the water that’s gone through the turbine. That’s why many hydroelectric plants are built into dams: the structure of the dam allows operators to control the flow of the water and process only the optimal amount. Any extra water can be held back in the dam, or let loose through the spillway that empties into the river below. Dams are especially useful vehicles for hydroelectric power, as they also introduce the extra power of gravity. The steep drop of the water as it moves through the plant increases the speed at which the turbines spin, which then generates more electricity.

While dams can be hazardous for wildlife, many newer hydropower facilities are also equipped with what’s known as a ‘fish ladder;’ a special section of the dam that lets migrating fish hop up the river and over the dam. Fish ladders let fish traverse the entire river freely, without dams blocking access to migratory patterns and important breeding grounds.

The Numbers

Every state in the U.S. currently generates at least some of their electricity through hydroelectric power. Washington state has the most hydroelectric capacity, at 27% of the nation’s total. California, Oregon, New York, and Alabama can each produce over 3,000 megawatts of electrical energy each year.

While many dams in the U.S. can effectively generate hydroelectric power, most of the dams in the United States don’t produce any electricity at all. These dams have been built for irrigation or flood control purposes, and haven’t been equipped with hydroelectric generators. It’s estimated if these dams were converted to hydropower, they would be able to generate an additional 12,000 megawatts of capacity: enough to power nearly 8 million homes!

The Cycle

Water cycle, that is! You may remember learning about the water cycle at some point in elementary school (my teacher even taught us a song about it: evaporation, condensation, precipitation on my mind; it is just the water cycle, and it happens all the time… the song was incredibly catchy; it still pops into my head randomly, sometimes). And while the idea of the water cycle may feel very basic, the principle of the water cycle is actually very important for the future of hydroelectricity.

The basic idea of the water cycle is as follows: water on earth evaporates into the air, where it then condenses and falls make to earth as precipitation (snow, rain, etc.) This constant movement of water in our little earth-terrarium is what gives us weather – and the flowing of rivers, rising of lakes, and filling of reservoirs. Without the constant motion of water through the water cycle, hydroelectric power would be unsustainable. Rivers would run dry, lakes would empty, and the moving water spinning our electrical generators would stop. The water cycle is what makes hydroelectricity a source of renewable energy. The water cycle keeps on repeating, the rivers keep flowing, and our electrical generators continue to induce energy.

Types of Hydroelectricity

While all hydroelectric plants use water as the source of their power, there are actually four main categories of hydropower: Run-of-river, storage, pumped storage, and offshore hydropower plants.


Run-of-river hydroelectric plants operate very similarly to their waterwheel counterparts. These facilities channel flowing water through a canal to spin a turbine, which then spins an electric generator.


One big advantage of run-of-river hydroelectricity is that the generators can be easily scaled down for smaller systems. A small system won’t cost much to produce: all you need is an electrical generator and turbine, and you can generate immediate energy from even the smallest of streams. Smaller systems also mean less environmental disruption; run-of-river plants work in tandem with the natural flow of the river, and are usually considered to be much better for the environment. Run-of-river systems also provide a continuous supply of electricity, and you can even work in some flexibility by regulating water flow through a bit of engineering.


While run-of-river systems provide continuous energy, they usually don’t have the ability to store any of that energy. You’re limited to the flow of the river: you don’t hold water back or store it at all. If it’s rained heavily, you may generate a lot of electricity; if you’re in the middle of a dry spell, the river level might be low, and you may not generate any electricity at all.

Storage hydropower

These are some of the most common types of hydroelectric systems, and involve using a dam to store water in a reservoir. As the dam operators release the water from the reservoir, it moves through a series of pipes to the turbine, which then spin to power the generator.


Storage hydroelectric systems are convenient because they are extremely controllable. Operators have a nearly unlimited store of potential energy, and they can tap into it according to current energy needs. It’s easy to start up and shut down a dam-based hydroelectric system on relatively short notice, and even if the area goes through a dry spell, the reservoir of water provides the potential for consistent power for several weeks or months. Beyond its uses for providing energy, hydroelectric dams create reservoirs that are popular for recreational use: swimming, fishing, boating, and more.


Not every aspect of dams is positive, however. Large, man-made dams can be devastating to their environment and surrounding habitats. Some dams have caused massive problems for native animal populations, including for fish that are no longer able to migrate upriver to spawn. Some dam projects have also caused problems for human settlements. New dams can force people to move from their homes, which are then submerged beneath the new reservoir.

The famous Aswan dam in Egypt provided an excellent source of renewable energy and stored water for the region, but was built at a huge environmental cost. Over 90,000 Egyptian citizens, as well as thousands of Sudanese Nubian nomads, were forced to resettle; their homes were flooded by the new Lake Nasser formed by the dam. And thousands of years of Egyptian archeological history was lost beneath the rising waters, in spite of the massive rush to salvage dig sites that were affected in the region. The fish populations in the Nile have plummeted, and the fertility of the Nile delta has decreased in subsequent years.

Pumped storage hydropower

Pumped storage hydroelectric systems use a pump and gravity cycle to circle water through a series of pipes. The pumps don’t require much energy to run, so operators can cycle the same water through the system for a net gain of energy.


Pumped storage hydroelectricity is very similar to the operations of a regular hydro powered dam, with the additional benefit that it reuses some of the water. The normal ebb and flow of the water is harnessed so that water is pumped up to the top of the system when the energy is least expensive to produce, and then dropped back down when the system is pricy to run. This model is more efficient and less wasteful, and can be combined with solar energy to make it a financially-viable option for electrical companies.


Because pumped storage hydropower involves a dam, it also comes with all the disadvantages of regular storage hydropower. Dams can be environmentally destructive, not to mention loud, large, and sometimes dangerous. Pumped storage hydroelectricity can also be pricier for companies to run, especially if the timing of the pumps isn’t executed correctly.

Offshore hydropower

Offshore hydropower is a newcomer on the scene of water-based electricity. But there is plenty of energy to be found in the tides, waves, and heat of the ocean.

Tidal Power

If you’ve ever watched the tide come in or go out, you know how strong of a force it can be. Ship captains time their launches around the tide in order to harness the powerful energy lurking in the water, and modern updates have found a way to convert that energy into electricity. Ocean levels normally rise once each day, and then fall each day along with the tide. Placing a turbine near the moving waterline allows the system to catch water when the tide comes in, and then release the water as the tide goes back out. It’s a very similar system to a pumped storage dam, but in this case the pump is the motion of the tide.

Wave Power

While wave power isn’t quite as reliable as tide power, there’s plenty of energy to be found in this sector of offshore electrical generation. As waves rise and fall, the moving water causes turbines to spin, generating electricity.

Ocean Thermal Energy Conversion (OTEC)

If you’ve read or studied anything about thermodynamics, you probably know that hot fluids rise, and cold fluids sink. The ocean is variable in temperature, with some parts of it warmer or colder than others. As these different temperatures of water interact, the warmer pockets rise while the cooler pockets of oceanwater sink. This temperature-balancing-act is what creates ocean currents (much like the different temperatures of air create wind and weather systems in the atmosphere). Because the contrast in water temperature causes movement, that motion can be tapped by a turbine to generate electrical energy. OTEC is still in early phases, although its early results have been promising.


One of the clearest advantages of offshore hydropower is that 70% of Earth’s surface is covered with ocean. Tapping into the power of the sea can provide us with substantial amounts of energy that are extremely reliable and definitely renewable. After all, the tides are constant and predictable. Offshore hydropower is also useful in that it doesn’t take up space mankind would normally be using. People won’t have to relocate in order to construct a dam, and offshore hydropower won’t damage land fertility or archeological sites.


There is the worry that offshore hydropower might disrupt sea life habitats in unforeseen ways. Spinning turbines under the water can cause injuries to large and small creatures of the oceans, and any oil spills associated with maintaining offshore hydroelectric plants could be disastrous to wildlife.

Can You Harness Your Own Hydroelectric Energy?

While it’s not as common as wind or solar energy, homeowners with water on their property may want to try their hand at harnessing their own hydroelectric energy.

Things to Consider

Before you decide to implement hydroelectric energy, there are a few things to think about:

Power Output

What will you be using your system to power? Personal hydroelectric generators almost always have to be small, so they won’t produce much electricity. Hydropower may not be the best way to power your entire home, for example, but it may act as a nice supplement to additional sources of electricity.


Luckily, small hydroelectric generators can be very cheap to make! All you need is some sort of spinning turbine that you can attach to an electric generator. Small systems also come prefabricated online, and sell for less than $50, ready to install. The cost to operate your generator should be nonexistent, although you may need to repair or replace parts of the system as they wear down.


This one is a must: you need water before you can set up a hydroelectric system. Locations with running water are preferable, as they don’t require nearly as much maintenance or upfront work as calmer lakes or ponds. The more natural motion to the water, the more electricity you’ll be able to generate.


Check to make sure you’re allowed to build a hydroelectric generator if you have water on your property. There are specific laws and regulations when it comes to water rights, and even if you have a river running across your land, you may not actually have access to use the water in it. You’ll want to be especially careful if your plans impact the flow rate of the water, because that can cause problems for people and installations downstream.


It’s best to not disturb the natural environment surrounding water. If you’re installing an electrical generator, make sure it doesn’t mess with any of the wildlife in the area. Avoid blocking off rivers completely, as that can make it difficult or impossible for fish to migrate upstream. You’ll also want to make sure your equipment isn’t leaking oil or other dangerous chemicals into the water or riverbed, as those can travel downstream and pollute everything in their path.

The Pros of Hydroelectric Energy

There’s a reason hydropower has been a favorite source of electrical energy for so long. In fact, there are several reasons:

Renewable Resource

One of biggest perks of hydroelectricity is that it’s renewable. Because the path of water is cyclical, mankind can count on the flow of rivers and the movement of the tides to provide us with unlimited electricity.

Clean Energy

Water power is a remarkably clean source of energy. Most hydroelectric plants require no additional fuel to operate, and many only need minimal maintenance to continue running. Not to mention that sending water through a hydroelectric plant doesn’t pollute the water at all, keeping it safe for wildlife and humans alike.

Historically Accepted

Water power has been around for literally thousands of years. It’s natural and accepted, unlike some newer forms of energy production (such as nuclear) that communities tend to fear and distrust.

Excellent Domestic Energy Option

There’s a reason every state in the U.S. gets at least a little bit of its electricity from hydropower: it’s a great local energy resource. Even the driest states have at least one river or coastline that can be tapped for hydroelectric energy. And the energy is available immediately at the source; you don’t have to ship or pipe it in like you have to do with oil.


Hydropower is actually the cheapest source of energy when compared to all major fossil fuels and renewable energy sources. Because many hydroelectric plants are capable of producing electricity for a long time with minimal upkeep, the overall cost of the plant is greatly reduced. And because hydropower is dependable and consistent, it’s not subject to changes in fuel costs caused by fluctuating oil prices.

Immediate Power Option

Once you have a hydroelectric plant up and running, you have the benefit of immediate electricity generation. You don’t have to mine or process resources like you have to do with fossil fuels; instead, the water converts directly into electricity that is ready for use.


One of the biggest perks of hydroelectric energy is its consistency. While river levels may vary, newer forms of hydropower are incredibly reliable. Tides are remarkably consistent, and tapping into their motion can provide dependable energy.

The Cons of Hydroelectric Energy

Just like with any energy source, however, hydropower isn’t perfect. Harnessing electricity from water comes with plenty of cons that must be addressed:


The biggest downside to hydroelectric plants is the dams that often appear alongside them. Dams can cause massive environmental impacts, not to mention disrupt the lives of nearby human populations. Any sort of dam failure can also be deadly to those living downstream of the manmade barrier.

Location Limitations

Even though most areas have some sort of water that can be harnessed for energy, in some locations, it may just not be feasible. In order for a hydroelectric plant to be efficient, you’ll need a substantial body of moving water to tap into. Areas that are prone to droughts might not be ideal for the development of a hydroelectric plant.


While hydropower plants tend to be low-emission in their operations, plants in the flooded areas beneath reservoirs can rot and decompose, releasing methane gases into the atmosphere.

So, Is Hydroelectric Energy Worth It?

As an energy source, hydropower is indeed worth it. The positive aspects of hydroelectric power make it a phenomenal resource for mankind, especially with new tweaks and updates meant to tackle some of the negative aspects of this technology.

Future hydroelectric projects promise to tap into the potential of the oceans and tides, providing the world with a renewable energy source that is consistent, cost-effective, and safe. We’ve come a long way from the humble watermills once used to grind wheat, but the respect mankind has held for the power contained within water hasn’t changed.

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