The "Forgotten Giant" of Clean Energy

Hydropower–or hydroelectric power–is the world’s cheapest and most popular renewable energy source. But if you’re wondering why you’ve never heard of hydropower, you’re not alone. While wind and solar power have been getting more press, hydropowet accounts for 60 percent of global renewable energy generation, beating out the 13 percent and 23 percent accounted for by solar power and wind power respectively. Still, these impressive statistics come with considerable drawbacks.

Hydroelectric power generation begins with a river that feeds into a reservoir, where water is stored as gravitational potential energy. When the dam is opened, the water flows out of the reservoir and through a channel. The flowing water spins a turbine, powering a generator.

One of hydroelectric power’s biggest strengths is its ability to generate electricity at any time; when more power is needed, operators can merely open the gate in a dam. This stands in contrast with variable renewables like wind and solar, both of which can only generate electricity when the sun is shining or the wind is blowing.

Another crucial trait of hydroelectric power is its ability to store the intermittent energy generated by renewables. Hydropower plants used for storage are called pumped-storage hydropower (PSH). These plants, which work slightly differently than those described earlier, contain an upper and a lower reservoir. When variable generation is high, this electricity is used to pump water from the lower to the upper reservoir. When the generation falls, a dam in the upper reservoir is opened. This causes water to flow through a turbine and power a generator, before settling back into the lower reservoir. Energy storage will likely be crucial to the switch to clean energy, and while the buzz surrounding large-scale energy storage tends to focus on batteries, hydropower accounted for 99 percent of the world’s energy storage as of 2021.

In a June 2021 report, the International Energy Agency referred to hydropower as the “forgotten giant” of clean energy and reported that current investment in hydropower was far below what would be necessary to limit global temperatures to 2°C. Indeed, while global hydropower capacity is set to increase between 2021 to 2030, its projected growth is nearly 25 percent slower than the previous decade.

Leading in hydropower is China, which accounts for 40 percent of global hydropower expansion. With global coal and liquified natural gas (LNG) prices soaring sky-high amidst Western sanctions on Russia, hydropower is helping China cut down on coal and LNG, though climate-caused droughts may jeopardize this power. Next up is India, where the World Bank is financing dozens of hydroelectric projects along India’s Himalayan states.

In the United States, however, hydropower has remained largely stagnant. The United States has already built reservoirs in most viable rivers, and aside from that, new hydropower plants must go through a permitting process that takes years of effort and millions of dollars. Since the average U.S. plant is over 60 years old, many plants will need to be relicensed, which, combined with the decreased output seen by hydropower plants due to climate-caused droughts, will likely cause a flood of license surrenders.

Hydroelectricity is also the cheapest source of electricity worldwide, including fossil fuels. However, while the low operating costs and long lifespan of hydroelectric power plants keep prices low, hydroelectric plants have much higher initial costs per kilowatt than most other power sources. These costs are more than monetary, as hydropower has negative environmental effects. The land flooded to make way for hydropower plant construction emits the greenhouse gasses stored. Worse yet, the emissions persist throughout a dam’s lifetime as the sediment flowing downstream gets trapped by dams and as plants continue to regenerate in the reservoir. Emissions from hydropower plants are almost always lower than those from fossil fuel plants, though there are a few exceptions. Hydropower plants also harm the river ecosystems in which they’re built. As reservoir water remains stagnant, cold, deoxygenated water sinks to its bottom. When the dam is opened, this water flows into the river below and harms downstream ecosystems. Ecosystems can benefit from fish ladders, which allow fish to hop upstream to warmer waters, while emissions can be reduced by building dams in steeper valleys or in areas with fewer microbes. Yet, hydropower is considered a mature technology, so further improvements are limited.

Additionally, hydropower plants can only be built around rivers and waterfalls. The drawback makes it unideal for countries with limited water resources and difficult to incorporate into the grid. This location dependency is shared amongst solar, wind, geothermal, and many more power sources.

Hydropower plants are occasionally constructed in rivers that communities have already settled around, which has displaced millions throughout history. The Souapiti Dam in Guinea, which went online in 2020, has forcibly removed over 16,000 residents of 100 villages from their ancestral homelands, along with flooding 253 square kilometers of land. In 1982, 400 were killed and 3,500 were displaced by the former military dictatorship in Guatemala when communities in the Chixoy River refused to relocate for the Chixoy Dam. Construction for both of these dams was funded by international powers, including the World Bank, in the name of “sustainable development”.

Many argue that hydropower’s drawbacks must be weighed against fossil fuels. After all, hydropower is far from the only renewable with its downsides, from the storage of nuclear waste to a lack of recycling systems in place for solar panels. Others worry that hydropower may create more problems than it solves, especially given that hydropower is a mature technology. Regardless of the world’s trajectory, in the fight for clean energy, this “forgotten giant” cannot be ignored.