Generating Electricity: Hydroelectric Power

In Canada, we often use moving water to generate electricity. This is called hydroelectric power﹘often shortened to hydropower. Almost two thirds of electricity in Canada is produced using hydropower. Hydropower is a renewable source of energy. This is because we can use water over and over again to generate electricity.

Did you know?

Hydroelectricity generates about 16% of the world’s electricity.

Types of Hydroelectric Generation

There are four main ways to generate electricity using moving water.

These are:

1. Storage and Pumped Storage
2. Run-of-river
3. Tidal Hydropower
4. Wave Hydropower

The first two ways happen in rivers. The second two ways happen near or in oceans.

Storage Hydropower

Storage is one of the most common ways of producing hydropower. This usually starts with building a structure called a dam across a river. The dam blocks the flow of the river, storing water above it. This storage area is called a reservoir.

Image - Text Version

Shown is a colour photograph of a huge cement wall holding back a large body of water. The camera looks down at the dam from above. The dam is built across a narrow river gorge. The water behind the dam is high and deep blue. A much lower body of water is just visible in front of the dam, in the foreground of the image. The dam itself is tall and made of grey concrete. Six objects that look like long pipes project out the front. Roads and other concrete structures surround it.

The water in the reservoir is at a higher elevation than the water in the river on the other side of the dam. This means the water in the reservoir has gravitational potential energy. When the water flows down through the dam, this is converted into kinetic energy.

Inside the dam structure is a turbine. A turbine is a device that converts kinetic energy into mechanical energy. The turbine is attached to a rotor in the generator. The generator converts mechanical energy into electrical energy. It does this by spinning a wire within a powerful magnet. When more electricity is needed, workers can let more water flow through the dam.

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Storage hydroelectricity has some advantages. People can use the water in reservoirs for drinking water. They can also use the water for irrigation. They can even use it for recreation, like sailing.

Image - Text Version

Shown is a colour photograph of a dam at the end of a lake. Most of the photograph is taken up with a rippling, greyish blue lake. On the right are two small sailboats. In the distance is a wide, low concrete wall. It is flat on top, with pillars visible near the water below. In the centre is a taller structure that looks like a gate, with vertical metal girders down to the wall below.

This method also has some downsides. Storage hydroelectric systems affect natural water systems. They change where and how water flows and often affect the plants and animals that live in the water. This means people in local communities can lose the fish and wildlife they depend on for food.

Building reservoirs also often involves flooding land. If land is flooded, people cannot use it for farming, hunting or homes. Flooding can also damage the ecosystems along riverbanks by covering them with water. 

Sometimes dams fail. This can cause a lot of damage to nearby human and natural environments.

The lands of Indigenous communities in Canada have often been flooded without their consent. Communities have lost the land they depend on for hunting, fishing, foraging, and cultural needs. Scientists have also found that rotting plants and soil under the water can release toxins. These accumulate in the fish and birds people eat, causing health consequences. Many Indigenous people and their supporters protest the construction of hydroelectric projects near their communities.

Pumped Storage Hydropower

Pumped storage is a variation of the traditional storage method. Here, there are two reservoirs of water. One is at a higher elevation and one is at a lower elevation.

When more electricity is needed, water is allowed to flow from the upper reservoir down to the lower reservoir. Electricity generation happens in the same way as standard storage hydropower.

Image - Text Version

Shown is a colour illustration of a cross section of a pump storage dam in the daytime. The dam is built into the side of a green hill. On the left, at the top of the hill, is a body of bright blue water labelled “Upper Reservoir.” An arrow labelled “Flow of water,” shows that water moves into an opening in the dam. The water then flows down a pipe, through a chamber containing a turbine, and out into a body of water in the lower right corner of the image, labelled “Lower Reservoir.” In the middle of the dam, above the turbine, is an illustration of a generator. A yellow arrow labelled “Flow of electricity” points away from here. It leads along power lines, across the landscape, to a city in the distance.

When less electricity is needed, such as at night, a pump moves water from the lower reservoir up to the higher one. These pumps are powered by other forms of renewable energy.

Image - Text Version

Shown is a colour illustration of the same dam as above, with water being pumped uphill at night. The illustration shows the same landscape, but darker and moonlit. Here, arrows show that the water flows from the lower reservoir, through the pipes in the dam, to the upper reservoir. Yellow arrows show the flow of electricity is coming from the city, along the power lines, to the generator.

The advantage of pumped storage systems is that they do not need to be on a river. All they need are two bodies of water at different elevations.

These systems do have a disadvantage. They use more electricity than they generate. So why do we use them? The electricity they generate when people need it most, can be sold at a high price. And the electricity they buy to pump water uphill has a lower price. This is because the pump runs at night, when fewer people need electricity. So, pumped storage systems can make a profit.

Run-of-river Hydropower

Run-of-river hydropower gets its kinetic energy from the natural flow of a river. These systems usually don’t use reservoirs. This means run-of-river systems can’t store much energy.

Sometimes the river flows through a turbine system. You can see this in the picture below. To the left is the hydropower station. To the right is the natural flow of the river.

Other times, some water is diverted away from a river through the turbine system. Then, this water is returned to the river, downstream.

The advantage of run-of-river systems is that they are less disruptive to rivers. They have smaller effects on water flow. And land does not need to be flooded for reservoirs.

There are disadvantages to run-of-river systems. They usually can’t generate as much electricity as storage hydropower systems. And they can’t operate without flowing water. If the flow of the river decreases, so does electricity generation. This is a problem because climate change is causing less rainfall in some areas. Finally, run-of-river systems need specific river conditions. The water in the river must be flowing fast enough, and at a high enough volume for electricity to be generated.

Tidal Hydropower

Tidal hydropower uses the natural rise and fall of oceans, called tides. Tidal hydropower can be found along coastlines of the world. For these systems to work, the water level must change by at least 5 metres. That’s quite a lot!

Tidal Power 101 (2015) by Student Energy (2:14 min.).

Tidal power uses similar structures to hydropower systems on land. For example, a tidal barrage is like a run-of-river system. And tidal turbines are like wind turbines.

An advantage of tidal hydropower is that tides are very predictable. This makes them a reliable energy source.

There are disadvantages to tidal hydropower. First, most places do not get high enough tides for it to work. Tidal hydropower can also affect sea life. Finally, salty ocean water can be hard on mechanical parts. All these factors mean tidal hydropower has not yet been used a lot.

Wave Hydropower

Waves in the ocean also have lots of energy. People are working to harness this energy in different ways. Engineers have tried using different types of objects that move with the waves. This movement is used to do different things. Some systems use the movement to push air or other fluids through a turbine connected to a generator. Other systems use the up and down motion of waves to move a magnet inside a generator, which can generate electricity.

Did you know?

The first commercial wave hydropower system was built on the Isle of Islay, Scotland in 2000. It was closed in 2011. But engineers learned enough from it to build another, larger plant in Spain.

Although wave hydropower has a lot of potential, it also has a lot of challenges. As with tidal power, ocean water is hard on mechanical devices. And unlike tides, the size and speed of waves are unpredictable. This means they are challenging to design for. Finally, objects on, or in the ocean can affect sea life. They can also be a danger to ships.

Despite the challenges, people are eager to design innovative ways to harness the power of waves.