ERC: Lesson - Hydroelectric Power (Topic 6.9) 📖

⏳ Estimated Reading Time: 10 - 13 minutes

Describe the use of and effects of the use of hydroelectricity in power generation on the environment.

Hydroelectric Power

Hydropower (also known as “water power”) was one of the first sources of natural energy to be harnessed to produce electricity. Humans have been using the power of moving water as a source of energy for centuries. The moving water in rivers and streams provided a means of power to grind grain, irrigate crops, and for mining assistance.

Today, hydroelectric power provides over 7% of the electricity used in the United States and over 19% of the electricity used worldwide. The states in the Northwest are the largest producers of hydroelectric power.

Hydroelectric power works off of the principles of kinetic and potential energy. To gain potential energy in water, it depends on the hydrologic (water) cycle to “lift” water into a position where it can move downhill with gravity flow. Evaporation moves water into the atmosphere and precipitation places the water in high altitudes to begin its journey towards sea level.

The amount of energy available is also determined by the flow of the water. The more flow, the more energy available. The reservoir is at a higher altitude than the river below it. This represents a significant amount of stored, potential energy.

Water in the reservoir behind the hydropower dam flows through an intake screen, which filters out large debris, but allows fish to pass through. The water flows through a large pipe, known as a penstock. The force of the water then spins a turbine at low speed, allowing fish to pass through unharmed. The stored water can then be allowed to move downhill through the penstock of the dam.

a detailed, annotated diagram of the hydroelectric process from water intake to electricity generation. — **A diagram of the hydroelectric dam at Cornell University in the United States.**

The kinetic energy of the moving water is converted into mechanical energy and then into electrical energy by passing through turbine blades which turn a generator. Inside the generator, the shaft spins coils of copper wire inside a ring of magnets, creating an electric field, producing electricity. The electricity is then sent to a switchyard, where it can travel to the electric grid and end users. The water in the dam flows out of the penstock into the downstream river.

During its downhill journey, the water’s potential energy is converted into kinetic energy. To retain the remaining potential energy in the water, dams are built which capture the water in a reservoir.

Essential Knowledge

Hydroelectric power can be generated in several ways. Dams built across rivers collect water in reservoirs. The moving water can be used to spin a turbine. Turbines can also be places in small rivers, where the flowing water spins the turbine.

Ocean Power

Ocean tides, ocean waves, and ocean currents contain a tremendous amount of energy. The tides are caused by the gravitational pull of the moon, waves are caused by wind, and currents are caused by differentials in temperature and salinity in the oceans.

The energy in these sources, though, is fairly difficult to access in a reliable fashion. Let’s take a look at several promising methods of using the ocean for power.

Tidal Barrage

a tidal turbine used to generate renewable energy from ocean currents, illustrating how tidal energy is harnessed by the turbine’s rotation driven by the natural movement of water. — **Tidal currents turn underwater turbines, capturing kinetic energy.**

What is it?

A tidal barrage is a dam built across the mouth of a bay and turbines are mounted in the structure. Water is held in the bay or out of the bay until there is a significant enough difference in water level that will force water in and out of the running turbines. Incoming tides flowing through the turbines generate power.

Benefits:

✅ reliable due to the predictability of tides

✅ long operational life

✅ does not cause air pollution

✅ sustainable and renewable energy

Drawbacks:

❌ only feasible in about 30 locations worldwide

❌ expensive to construct

❌ often negatively affects bay environments

❌ changes the hydrology of the bay

❌ restricts the passage of fish and changes habitats for birds and other organisms

Tidal Turbine

What is it?

Tidal turbines are similar to land-based wind turbines. Instead of the wind causing the turbine blades to turn, however, the moving water of tides, currents, and even rivers cause the blades to move.

Benefits:

✅ more energy can be captured per turbine, compared to wind turbines

✅ does not cause air pollution

✅ reliable due to the predictability of tides

✅ sustainable and renewable energy

✅ minimal visual impact

✅ can be deployed in various sizes

Drawbacks:

❌ expensive to construct

❌ operating and maintaining underwater turbines can be complex

❌ only suitable for areas with strong tidal currents

Tidal Fence

This conceptual illustration presents an underwater view of tidal energy turbines. — **Tidal fences use a turnstile-like layout.**

What is it?

Tidal fences use vertical axis turbines mounted in rows or “fences” placed on the bed of the ocean. They operate similar to tidal turbines in that water passing through them generates electricity. This is one of the least explored forms of tidal power.

Benefits:

✅ efficient energy conversion

✅ does not cause air pollution

✅ can be adjusted to optimize energy production based on tidal conditions

✅ reliable due to the predictability of tides

✅ sustainable and renewable energy

Drawbacks:

❌ expensive to construct

❌ requires specialized engineering and construction

❌ often negatively affects bay environments

❌ changes the hydrology of the bay

❌ restricts the passage of fish and changes habitats for birds and other organisms

Wave Power

a maritime scene featuring a large, yellow mechanical structure installed in the ocean. This structure is connected to pipes and anchored to a floating brown base. — **Azura wave energy converter installation at U.S. Navy test site in Hawaii.**

What is it?

Since more than 50% of the United States human population living within 50 miles of a coastline, wave power deserves a closer look.

Wave power devices capture the kinetic energy found in ocean waves. Some of these devices are located along coastlines while others can be anchored offshore.

The “Azura” device shown in the image above is located in the Hawaiian Islands and can capture wave energy in a 360-degree pattern. Whether the waves move the device up, down, or sideways, the Azura turns that kinetic energy into electrical energy and is already providing power to Hawaii.

This diagram illustrates the oscillating water column design for wave power generation. — **An “oscillating water column” wave power device.**

Other wave energy devices are located closer to the coastline. The device to the right is an oscillating water column wave power device, designed to be installed in hollow areas of rocky coastlines. As waves enter device (#1, #2), air is compressed up and into a hollow chamber (#3). The compressed air is forced through turbine blade chamber (#4) and moves back and forth as the water from waves comes and goes. The turbine blades cause a generator to produce electricity.

There are a number of wave energy capture devices being developed and tested. It is hoped that some of the designs will be effective at capturing the energy found in ocean waves but, again, location is everything and challenges remain.

Benefits:

✅ does not cause air pollution

✅ waves are consistent and abundant

✅ low operating costs once infrastructure is in place

✅ sustainable and renewable energy

Drawbacks:

❌ waves are not always the same size or intensity

❌ salt water can rust metal and electrical systems

❌ wave power is influenced by weather patterns

❌ efficient wave energy converters are in its infancy

Ocean Thermal Energy Conversion (OTEC)

What is it?

Ocean-thermal energy conversion (OTEC) uses temperature differences between shallow and deep ocean water. It uses a low-boiling point liquid, like ammonia, to vaporize and turn the turbine and spin the generator to make the electricity. Cold ocean water is pumped up from the deep ocean and re-condenses the ammonia vapors.

Benefits:

✅ does not cause air pollution

✅ low operating costs once infrastructure is in place

✅ sustainable and renewable energy

Drawbacks:

❌ this technology is only experimental

❌ OTEC systems are expensive to build

❌ technology can be complex

❌ limited geographic applicability, as they work best in areas with consistent temperature differences between the surface and deep ocean.

The oceans contain vast amounts of potential and kinetic energy and as our population continues to grow, the use of this energy will continue to get more and more attention.

Essential Knowledge

Tidal energy uses the energy produced by tidal flows to turn a turbine.

Environmental Effects of Hydroelectricity

Like every energy source, there are pros and cons to hydroelectric power. Humans have created over 45,000 large dams worldwide. These dams have enormous ecological impacts, especially for estuaries that occur at the mouths of rivers.

Let's explore a few of these below. After reading through the pros and cons, what do you think? Are the disadvantages worth the benefits?

✅ Little to No Air Pollution (click to reveal)

Hydroelectric power eliminates the environmental costs of fossil fuels and nuclear power.

✅ Increases Reliability of Local Water Resources (click to reveal)

Dams and their associated reservoirs can provide flood control, drinking water, and irrigation water.

✅ Renewable Energy Source (click to reveal)

Hydroelectric power is a clean, renewable energy source that can help reduce reliance on fossil fuels.

✅ Recreational Opportunities (click to reveal)

Reservoirs are often used as recreational/tourist locations.

✅ Cheap to Maintain (click to reveal)

After the initial investment, hydropower is relatively cheap to maintain and operate.

❌ Reservoirs Drown Land and Displace Residents (click to reveal)

The area upstream from the dam is flooded with water that is prevented by the dam from flowing downstream. Creating this reservoir behind the dam drowns farmland and wildlife habitats and can displace rural populations.

The average forest area submerged per dam works out to approximately 4,879 ha. Therefore, the 1,877 dams built between 1980 and 2000 would have submerged 9,157,883 ha. (roughly 9.1 million ha.) of forests.

Reservoirs also submerge productive agricultural land in the valley. This not only has a social and economic cost but also adversely affects cultivated biodiversity and a host of birds, insects, mammals, and reptiles that have adapted to agricultural ecosystems. In many cases, traditional crop varieties and methods of cultivation disappear because of dams.

The Three Gorges Dam (shown in the image below) built in China in 2003 displaced over one million people.

an aerial view of the Three Gorges dam, showcasing its massive concrete construction with multiple red cranes positioned along the top. — **The Three Gorges Dam built in China in 2003 displaced over one million people.**

❌ Susceptible to Droughts (click to reveal)

Reservoirs are also highly susceptible to droughts. If water is not available, they cannot produce electricity. The effectiveness of hydropower is dependent on local water flow, which can be affected by droughts and climate change.

We are already seeing impacts on lakes such as Lake Mead, a reservoir on the Colorado River that provides electricity for people in Nevada, Arizona, and California.

When water in the reservoir is used for irrigation, a significant amount of water is diverted from the river and transported out by canals. This results in significant shortfalls in the natural flow and in the net flow of water in the river.

Meanwhile, the soil downstream from the dam tends to become drier and less nutrient-laden because the dam prevents flooding that used to replenish nutrients to the bottomland near the river.

❌ Aquatic Ecosystem Disruption (click to reveal)

One major consequence of dam construction is the inhibition of the ecosystem's ability to regenerate itself. By blocking the natural flow of the river, dams disrupt the processes that support the health and biodiversity of the ecosystem. Additionally, heavy monsoon flows that typically act as a cleanse for the riverbed and mouth are impeded by dams, leading to the accumulation of silt, garbage, and stagnant water that would otherwise be cleared away.

Besides, by interrupting the flow of water, dams disrupt ecological continuity. For example, some species of fish are unable to access their breeding grounds due to the dam.

The nutrient cycle of the river ecosystem is also disrupted. A significant amount of essential nutrients are trapped behind the dam, depriving the ecosystem downstream of vital nutrients. This starvation effect further hinders the ecosystem's ability to sustain itself and thrive.

In addition to altering the flow of nutrients, dams also impact the water temperature of the river. As water is released from the reservoir at the base of the dam, it tends to be colder than the water entering the reservoir. This variance in water temperature below and above the dam can disrupt the preferred habitat conditions for different aquatic species, influencing the overall biodiversity of the aquatic ecosystem.

❌ Expensive to Construct (click to reveal)

The construction of hydroelectric dams requires a substantial initial financial investment.

❌ Limited Locations (click to reveal)

There are only so many places where hydroelectric plants can be feasibly built.

Because of environmental concerns along with the many dams that have already been built, new hydroelectric projects do not usually involve building dams. Cities are exploring the use of water moving through their drinking and sewage systems to provide power. Others are looking towards ocean currents, submerged turbines in rivers, and tidal power as possibilities for electricity production. In short, the days of building major dams on rivers—especially in developed countries—may have seen their better days but scientists continue to explore other ways to generate hydroelectric power due to its many advantages.

Essential Knowledge

Hydroelectric power does not generate air pollution or waste, but construction of the power plants can be expensive, and there may be a loss of or change in habitats following the construction of dams.

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