Hydropower
Is Hydropower a Sustainable Source of Energy?
Hydropower is the largest source of renewable energy worldwide. In 2019, hydropower made up 6.4 percent of global energy consumption, and as countries continue to look for alternatives to fossil fuels, hydropower has the potential to play a much larger role in the global energy mix.
There are two main types of hydropower generating facilities. Conventional hydropower facilities use a dam to store water in a reservoir. Diversion facilities, on the other hand, divert a portion of water through a separate channel. In both cases, water is passed through a large turbine to harness gravitational energy and generate electricity.
This article is part of a series on alternative energy sources and the advantages and disadvantages of each. It will focus primarily on conventional hydropower facilities, though many of the main points can be applied to both. Because hydropower facilities are unique and tailormade to fit their location, generalizations made here may not apply to every facility in every scenario.
How is Hydropower Used Today?
There are nearly 50,000 large dams located around the world. China leads the world with 23,841, followed by the U.S. with 9,263, India at 4,407, and Japan at 3,130.
Canada is the world’s fourth-largest producer of hydropower. It has a total installed capacity of 81,000 megawatts (MW) across more than 1,100 dams.
Hydropower accounts for 24 percent of total power consumption in Canada, 63.2 percent in Norway, and 54.6 percent in Iceland. Some countries, mostly in desert regions with large repositories of oil and gas, produce no hydropower at all.
The Advantages of Hydropower
Flexibility and Responsiveness
Power is not produced or consumed at a constant rate. Consider the changes in energy usage on a hot summer’s day compared to a cool autumn night. Flexibility ensures that a power station can reliably and cost-effectively manage variability without disrupting supply.
Unlike solar, wind, or nuclear, hydropower can be turned on or off to meet the needs of the grid. The reservoir created by dams acts as an energy storage system, almost like a large battery. In response to changes in demand, facilities can quickly and easily increase or decrease the flow of water.
The responsiveness of hydropower will allow it to play a key role in the transition to low greenhouse gas emitting energy. It can serve as a reliable and flexible source of power in addition to more variable sources such as wind and solar, accelerating the adoption of these technologies and reducing the need for other flexible sources such as natural gas.
Efficiency and Low Generating Cost
Very little energy is wasted in the production of hydropower, especially when compared to traditional fossil fuels. Generating stations harness the gravitational energy of falling water to directly spin a turbine. Fossil fuel plants, on the other hand, burn fuel to boil water and then harness the pressurized steam. This extra step results in heat and other waste and reduces the overall efficiency.
According to Natural Resources Canada, hydropower converts more than 90 percent of available energy into electricity, making it the most efficient source. In contrast, the best fossil fuel facilities operate at 60 percent.
Better efficiency directly translates into lower generating costs. A report by the International Renewable Energy Agency found that the global weighted cost of newly commissioned hydropower projects was just $0.047/kilowatt-hour (kWh). More than 90 percent of all hydropower capacity commissioned in 2019 produced electricity for less than the cheapest new fossil fuel-fired project.
Renewable Capacity
There is a massive amount of potential hydro energy. A 2017 study estimated that the theoretical hydropower potential is 52 petawatt-hours/year (PWh), or about one-third of total global energy requirements. Not all of this is accessible due to technological, geographical, and other barriers, but it shows that we have only scratched the surface of total generating capacity.
High capacity is especially important in emerging economies that are in the process of electrifying. In sub-Saharan Africa, for example, less than 10 percent of possible hydropower has been developed, leaving an estimated 400 gigawatts (GW) of potential energy, or more than quadruple the power currently generated in all of Africa.
Hydropower is renewable since water is not consumed to generate electricity. The natural water cycle should replenish the reservoir and ensure a constant flow of energy. One important caveat to this, however, is that changes in climate, rainfall, or weather patterns can reduce the flow of water. A recent study suggests that 86 percent of hydropower facilities could see cuts due to variability in rainfall caused by climate change.
This can have serious implications for countries that rely on hydropower for most of their electricity. Zambia, which gets 95 percent of its electricity from dams, suffered a severe drought in 2015 which led to a 50 percent decline in generation and crippling power shortages across the country.
The Disadvantages of Hydropower
High Construction Costs
While hydropower is low-cost and efficient at the point of production, the infrastructure required is often prohibitively expensive. The U.S. Energy Information Administration showed that a conventional hydropower facility costs $2,769/kilowatt (kW) of generating capacity, far more than solar photovoltaic ($1,248/kW) and wind ($1,846/kW).
Further research has found that construction projects are often rife with corruption and end up exceeding projected costs by more than 90 percent. Large dams can take decades to build at a cost of billions of dollars, and this does not include the ongoing maintenance and operating costs as the dam deteriorates over time. Many then fail to generate as much power as anticipated.
A 2014 report by Oxford analyzed 245 dams in 65 countries and concluded that, in the vast majority of cases, dams were not economically viable. Not only did they not recoup the cost of construction, but they also resulted in massive amounts of debt, especially in emerging economies, which crippled the government’s finances.
Long-Term Environmental Damage
As one Slovenian biologist succinctly put it, “When you build a dam, you destroy the single most important thing about a river: the flow. You kill the whole ecosystem.”
The reservoirs created by hydropower dams have a severe impact on surrounding ecosystems. The physical barrier itself intercepts the migration and spawning routes of fish and other animals. It also disrupts the flow of sediment, increasing sediment levels above the reservoir and decreasing them below. High sediment content can result in low-oxygen dead zones that essentially wipe out the habitat of local species, while the fast-flowing “hungry water” below the dam increases erosion.
Further, evaporation from reservoirs increases the amount of moisture in the air to the point that it can affect local rainfall patterns and increase the risk of floods. One study found that 170 cubic kilometers of water evaporate from reservoirs each year, nearly 7 percent of all fresh water consumed by humans.
Beyond damage to wildlife, flooding from dams displaces entire communities. The Internal Displacement Monitoring Centre claims that dams displace around 80 million people, many of whom are already the most vulnerable and impoverished.
Hidden Greenhouse Gas Emissions
Hydropower is considered a low greenhouse gas emitting energy source. This is especially true at the point of production, as water passing through the turbine does not produce carbon dioxide (CO2) or other emissions.
However, some studies are starting to suggest that the reservoirs created by dams can emit high amounts of methane, CO2, and other greenhouse gases due to the breakdown and decomposition of organic materials.
One such study in Bioscience found that reservoirs may produce as much as one billion tons of CO2 equivalents each year, mostly in the form of methane, which is more than the total emissions of Canada. A Brazilian facility was found to emit 3.6 times more greenhouse gases than an oil plant generating the same amount of electricity.
It is important to note that the amount of greenhouse gases released by reservoirs is highly dependent on the location of the dam, the amount of organic material that is flooded, and the technologies and types of facilities used. To reduce the risk, dams should be built in areas with thin soil and low levels of organic materials. They should also be placed away from natural carbon stores such as wetlands, bogs, or marches.
Hydropower Will Undoubtedly Play a Role in Future Energy Production
Hydropower is one of the world’s oldest sources of energy, and it is one that we will continue to use for the foreseeable future. The efficiency, flexibility, and potential capacity of hydropower make it an attractive option that allows for more variable sources of energy to be brought online without compromising on reliability.
However, the high construction costs create a significant barrier to new projects, especially as delays, cost overruns, and corruption result in economically unviable dams in some of the world’s poorest countries.
Additionally, environmental concerns need to be considered. New generating facilities must be placed in areas where they have the lowest impact on surrounding ecosystems, wildlife, and communities. And as research begins to understand more about the potential emissions caused by decomposing organic matter in areas flooded by dams, we must make better decisions about how, where, and when to build dams.
Hydropower has the potential to reshape the way we produce energy. And as we continue to transition away from fossil fuels, it will play an increasingly important role in the global energy mix.
