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As one of the oldest energy sources, hydropower dates back over 2000 years. Ancient Greek farmers leveraged water to help them grind wheat into flour. Today, it has evolved to become an important part of the renewable energy landscape in the United States, providing 6% of the country’s power.

However, concerns about stability and environmental impact in the face of a rapidly changing climate have called into question the long-term future of hydroelectricity in our energy mix. Breaking down hydropower’s evolution through the centuries, we’re exploring the pros and cons of this widely-used energy source today.

The historical evolution of hydropower

Modern hydropower has roots in the mid-nineteenth century, when in 1849 British-American engineer James Francis developed the first modern water turbine. It remains the most widely-used water turbine around the world today, spawning some of the first hydropower installations in places like Grand Rapids, Michigan and Niagara Falls, New York.

By the early 1900s, hundreds of small hydropower plants were in operation, playing a significant role in the industrialization of America. As rapid innovations in technology and design continued to improve hydropower’s efficacy, the technology spread across the world.

By 1940, legislative policies like President Franklin Roosevelt’s New Deal enabled new innovative facility designs, which helped hydropower generate up to 40% of the electricity in the U.S. To meet growing energy demands, hydropower continued to expand across the world throughout the 20th century. But, as the reliance on the water cycle to generate essential energy grew, so did concerns around its value in the context of renewable energy efforts.

Hydropower: How does it really work?

Hydropower is considered a renewable energy source, because it is reliant on a natural water cycle driven by gravity. The kinetic energy of flowing or falling water is harnessed to move giant turbines, which spin electric generators in turn. These activated generators produce electricity, which can now be sent across the grid — powering millions of homes and businesses across the country.

There are many different types of hydroelectric installations, and range from small “micro-hydros” to expansive hydroelectric plants like the Hoover Dam. According to the U.S. Department of Interior’s Bureau of Reclamation, the Hoover Dam actually generates about 4 billion kilowatt-hours of hydroelectric power each year, which serves about 1.3 million homes in Nevada, Arizona, and California.

Is hydropower good?

Hydropower is usually counted in the category of renewable energy sources. It isn’t always without a notable environmental impact. As countries and communities set course towards a 100% clean energy future, they’ll have to weigh their options and impacts appropriately.

Pros of hydropower

  • Hydropower is generally free of greenhouse gas emissions, air pollution, and toxic byproducts.
  • It is a low-cost, domestic energy source that is not subject to market fluctuations.
  • Hydropower is more flexible, meaning production of electricity can be easily conserved or increased based on demand.
  • It is one of the most efficient methods of generating electricity because, according to Green Garage, nearly 90% of the energy captured through hydro-powered means is converted into electrical power.

While hydropower does not produce greenhouse gas emissions, air pollution, or toxic byproducts directly, it does comes with some important disadvantages:

Cons of hydropower

  • Hydropower relies on the use of reservoirs which are costly and time-consuming to build.
  • Unstable and inconsistent precipitation levels may negatively impact the productivity of hydroelectric plants in certain geographic areas.
  • Water quality may be affected by operating a hydroelectric plant which also may harm nearby plants and animals.
  • In 2016, BioScience reported that the reservoirs created by hydroelectric dams may contribute exceptionally higher greenhouse gas emissions than natural lakes.

Hydropower has a rich history in powering the U.S. and ensuring states like Washington and California can keep energy bills low through a renewable, domestic energy source. But efforts to understand the full environmental impact of hydropower will be critically necessary as the world continues towards a cleaner energy future. With new technologies and conscientious design, environmental impacts can be minimized, and hydropower may still expand its role in a 100% clean energy future.

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