Is Water A Good Renewable Energy Source?

Renewable energy comes from natural sources that are constantly replenished, such as sunlight, wind, rain, tides, waves, and geothermal heat. Renewable energy is crucial for building a sustainable future, as it produces much less pollution and greenhouse gas emissions compared to fossil fuels. Unlike coal, natural gas, and oil, renewable sources will not be depleted if we continue using them responsibly.

One renewable source is hydropower, which captures the energy of flowing water to generate electricity. Hydropower is a clean, domestic energy source that currently provides 6.5% of U.S. electricity and over 16% of the world’s electricity. Advocates argue hydropower is renewable, reliable, and does not emit greenhouse gases. However, critics point out hydropower dams can disrupt ecosystems and wildlife habitats. There are important tradeoffs to consider regarding hydropower’s role in our energy future.

The Science Behind Hydropower

Hydropower plants generate electricity by harnessing the power of moving water. A dam is typically built to create a large reservoir, allowing control over the water flow. The water in the reservoir has potential energy because of its elevation above the turbines. Gates open to allow water to flow through penstocks, which are pipes that channel the water downhill towards the turbines at high velocity.

The fast-moving water strikes turbine blades attached to a shaft, making them spin. The spinning shaft rotates electromagnets inside a generator, creating an electric current via electromagnetic induction. The electricity is then fed into transmission lines to bring the power to homes, businesses and industries.

Hydropower facilities can vary greatly in size and generation capacity. Small hydropower plants may produce enough electricity for a home or small community, generating less than 100 kilowatts. Large-scale hydroelectric dams can produce over 4,000 megawatts, enough to power millions of homes. The Three Gorges Dam in China, currently the world’s largest hydroelectric power station, has a 22,500 megawatt capacity.

The Benefits of Hydropower

Hydropower offers several key benefits that make it an attractive renewable energy source. First and foremost, hydropower is a sustainable and renewable source of energy. The fuel for hydropower is water, which is continuously replenished through the natural water cycle
¹. As long as there is flowing water, hydropower can produce electricity.

Hydropower plants also provide reliable base load power that can be dispatched on demand. The storage capability of reservoirs means hydropower can rapidly ramp up or down to meet fluctuations in electricity demand
². This makes hydropower a stable and consistent energy source.

Once hydropower plants are constructed, they have relatively low operating and maintenance costs compared to other types of power plants
³. The lifetime of a hydroelectric power plant can span over 50 years. This makes the levelized cost of hydropower energy competitive.

Finally, hydropower does not burn fuel, so it has minimal direct waste products or emissions. This makes it one of the cleanest sources of renewable energy available today.

The Drawbacks of Hydropower

While hydropower offers many advantages, it also comes with some significant drawbacks that must be considered. One major disadvantage is the high upfront infrastructure costs required to construct hydropower facilities and dams. Building a large-scale hydropower plant requires substantial capital investment, with costs frequently running into the billions of dollars (https://www.energysage.com/about-clean-energy/hydropower/pros-cons-hydropower/).

Another drawback is that suitable hydropower sites are geographically constrained by the need for flowing water. Areas with inadequate river flow or other water resources are not viable options. Building hydropower and dam projects is also limited by topography, as steep elevation drops are required to generate electricity (https://www.envirothonpa.org/documents/19bHydropowerAdvantagesandDisadvantages.pdf).

There can be major environmental impacts on rivers and wildlife habitats from hydropower facilities. Damming rivers alters natural water flows, which can negatively affect fish migration and spawning. Flooding land areas behind dams can also destroy natural ecosystems. Other ecological concerns include reduced river flows downstream and lower water quality (https://www.energysage.com/about-clean-energy/hydropower/pros-cons-hydropower/).

Lastly, hydropower output relies on adequate water flow, making it vulnerable to droughts. During dry periods and seasons with low precipitation, less electricity can be generated by hydropower plants. This intermittency can make hydropower an unreliable source compared to fossil fuels or other renewables (https://www.envirothonpa.org/documents/19bHydropowerAdvantagesandDisadvantages.pdf).

Small Scale and Run-of-River Hydropower

Traditional large-scale hydroelectric dams often require flooding large areas of land to create reservoirs for water storage. However, there are smaller and less environmentally invasive hydroelectric projects that harness the energy from rivers and waterways without the need for large dams and reservoirs.

Run-of-river hydroelectric systems divert a portion of a river’s water flow into a canal or penstock and through turbines to generate electricity. These systems do not require large dams or water storage reservoirs. As the International Hydropower Association explains, “Typically a run-of-river project channels a portion of a river’s water through a pipe or canal to spin turbines and generate electricity” (Source). The water is then discharged back into the river downstream.

Run-of-river systems take advantage of a river’s natural flow and elevation drop to generate power. They have a minimal impact on the surrounding environment compared to large dam projects. Run-of-river systems allow rivers to continue to flow largely unaffected, maintaining natural water levels and wildlife habitat.

Other Forms of Hydrokinetic Power

In addition to conventional hydropower from dams, there are other emerging technologies that harness the energy from water flows like ocean waves, tides, and currents. These novel hydrokinetic technologies have great potential as renewable energy sources.

Tidal power utilizes the rise and fall of ocean tides to generate electricity through tidal barrages or underwater turbines. Tidal barrages act like dams, using the difference in height between high and low tides to drive turbine generators. In-stream tidal turbines function more like underwater wind turbines, spinning as the tide flows past them. Studies estimate over 1,200 TWh of potential global tidal energy capacity, with high tidal ranges especially suitable along western Europe and northeastern North America coasts (An Overview of Ocean Renewable Energy, 2006).

Wave power devices convert the mechanical energy of ocean surface waves into electricity. Technologies like oscillating water columns, hinged contour devices, and buoys can generate up to 2,640 TWh per year globally according to estimates. Areas with consistently large wave activity like western Europe, South Africa, Australia, and the U.S. northwest coast have abundant wave energy resources (Ocean Renewable Energy Potential, Technology, and Challenges, 2019).

Ocean currents are another potential energy source. As bodies of water circulate, they contain kinetic energy that can be tapped by placing underwater turbines in high flow areas. Though small in scale presently, utilizing major ocean currents like the Gulf Stream has potential to generate gigawatts of clean, renewable power (The ocean as a source of renewable energy in sub-Saharan Africa, 2023).

The Role of Hydropower Globally

Hydropower plays an important role in electricity generation worldwide. According to the International Energy Agency (IEA), in 2020, hydroelectricity accounted for around 17% of total global electricity production. This makes it the third largest electricity source globally after coal and natural gas.

Some major hydropower producing countries include China, Brazil, Canada, the United States, and Russia. China generates the most hydroelectricity globally, meeting around 18% of its electricity demand from hydro facilities. Large growth regions for new hydro development include Southeast Asia, Africa, and South America.

Major international hydroelectric projects currently under development or recently completed include the Grand Ethiopian Renaissance Dam in Ethiopia, the Belo Monte Dam in Brazil, and the Bui Dam in Ghana. Large scale hydro projects like these can provide much needed electricity access, but also raise environmental and social concerns that must be addressed.

The Role of Hydropower Nationally

Hydroelectric power accounted for around 6.5% of total U.S. utility-scale electricity generation and 38% of all renewable electricity generation in 2021. The top producing states for hydroelectricity are Washington, Oregon, and California. In comparison to other renewable energy sources in the U.S., hydropower contributes a larger share of total electricity generation than solar and wind power combined. However, growth in hydroelectricity has stagnated while other renewables like wind and solar have expanded rapidly in recent years.

Environmental Impacts and Mitigation

Hydropower dams and reservoirs can have significant environmental impacts on rivers and surrounding habitats and wildlife. Some of the main concerns include:

• Altered river flows – Dams disrupt the natural flow regimes of rivers, which can impact sediment transport, floodplain connectivity, and cues for fish migration.
• Habitat loss – Reservoirs flood upstream areas, inundating natural habitats like wetlands and forests. Downstream areas can also be deprived of water, altering habitats.
• Wildlife impacts – Riverine and terrestrial species can lose habitat and migratory routes. Wildlife like fish can be injured or killed passing through dams.
• Ecosystem and water quality changes – Slow moving reservoir water accumulates sediments and can change oxygen levels compared to free flowing rivers.

However, there are ways to mitigate some of these effects. Fish ladders provide passage around dams for migratory fish like salmon. Bypassing river flows through the dam or controlling water releases can help maintain downstream habitat conditions and natural flow variability. Setting minimum environmental flows helps ensure enough water for river ecological health. Sediment management through flushing and sluicing can maintain downstream transport. While impacts can’t be fully prevented, careful dam siting and operations can reduce environmental effects. For more information, see this overview of strategies for minimizing hydropower impacts.

Conclusion

Hydropower provides many benefits as a renewable energy source, but also has some drawbacks that must be considered. The main advantages are its low operating costs once facilities are built, the lack of greenhouse gas emissions, and its ability to quickly adjust output to meet demand. The consistent baseload power from hydroelectric dams provides an important foundation for integrating other renewable sources like wind and solar. However, hydropower projects require substantial upfront investments and can have significant environmental impacts like habitat destruction, disrupted fish migration, and reduced downstream water flows. Small scale and run-of-river projects can help mitigate some of these downsides.

Looking forward, global hydropower capacity is expected to continue growing, especially in developing countries. More growth in North America and Europe will likely come from retrofitting existing dams and low-impact hydrokinetic projects that harness tides and waves. Overall, hydropower will remain an important piece of the renewable energy portfolio, but a balanced approach is needed considering all economic, social, and environmental tradeoffs. With proper siting and management, hydropower can be considered a good renewable energy source in many situations.