As international developers of renewable energy projects, we often field questions about the classification of legacy technologies. The query "is hydroelectric energy renewable or nonrenewable" is a primary example, as this is one of the oldest and most established forms of large-scale renewable generation.
The definitive technical answer is: Yes, hydroelectric energy is classified as a renewable resource.
However, the reason this question is asked so frequently is due to the significant, and in many cases severe, environmental and social impacts associated with its most common form: large-scale dams. From our expert perspective, it is critical to separate the renewable nature of the fuel (water) from the sustainability of the infrastructure.
What Technically Makes Hydroelectric Energy "Renewable"?
The classification of any energy source as "renewable" hinges on whether its fuel is replenished by natural processes on a human timescale.
Hydroelectric power is a function of the global water cycle. This cycle is driven by solar energy, which causes evaporation from oceans and lakes. This moisture precipitates as rain or snow, gathers in rivers, and flows back to the sea. Hydroelectric power plants simply intercept the kinetic energy of this "fuel" (flowing water) and use it to turn a turbine, generating electricity.
Because the water cycle is a constant, solar-driven process, the "fuel" for hydropower is inexhaustible and is not depleted upon use. Therefore, it is unequivocally a renewable resource, in the same category as solar and wind (which are also driven by the sun).
The public's hesitation to classify hydro as renewable stems from the environmental and social consequences of its most visible form: massive impoundment dams. These impacts are severe and long-lasting, feeling "nonrenewable" in their finality.
A dam creates a wall that fundamentally alters a river's entire ecosystem. It blocks fish migration (such as salmon), which can destroy entire fisheries and species. It also stops the flow of sediment, starving downstream deltas of nutrient-rich silt, while also changing water temperature and oxygen levels, harming all aquatic life.
This is the most critical technical point. Hydro is not a zero-emission source. When a dam floods a vast area, all the trees, plants, and soil underneath are submerged. This organic matter decomposes anaerobically (without oxygen) at the bottom of the reservoir, a process that releases vast quantities of methane (CH4). Methane is a greenhouse gas over 25 times more potent than CO2 over a 100-year period. In some (especially tropical) cases, a large hydro plant can have a larger carbon footprint per kilowatt-hour than a fossil fuel plant.
The creation of a large reservoir often requires the flooding of enormous tracts of land, displacing thousands of people and destroying communities, farmland, and forests.
As project developers, we must differentiate between hydro technologies, as their impacts vary wildly.
This is the classic model: a large dam creates a massive reservoir. It provides baseload power and water storage but has all the environmental impacts listed above.
This is a more sustainable, lower-impact alternative. ROR systems divert a portion of the river's flow through a channel or pipe to a powerhouse. It does not require a large reservoir. This drastically reduces the environmental footprint, prevents methane emissions, and allows the river to flow more naturally. However, its power output is more variable as it fluctuates with the river's natural flow.
As we note in our own expertise, this is a storage technology, not a generator. It functions as a large-scale battery, using excess electricity to pump water to an upper reservoir and releasing it to generate power when needed.
Our Expert Conclusion
To answer the query "is hydroelectric energy renewable or nonrenewable," the technical classification is clear: It is renewable. The solar-driven water cycle is inexhaustible and self-replenishing.
However, we must differentiate this classification from "clean" or "sustainable." The most common form of hydro (large-scale dams) carries devastating environmental consequences, including habitat loss and significant methane emissions.
This is why the global energy transition, which we are actively developing projects for, is now focused on newer, low-impact renewables like photovoltaics (solar), wind, and enabling technologies like battery storage and green hydrogen. These technologies offer a path to decarbonization without the severe ecological trade-offs of large-scale hydro.
Resources
U.S. Energy Information Administration (EIA) - Hydropower Explained: https://www.eia.gov/energyexplained/hydropower/U.S. Department of Energy (DOE) - Water Power Technologies Office: https://www.energy.gov/eere/water/water-power-technologies-officeInternational Renewable Energy Agency (IRENA) - Hydropower: https://www.irena.org/Energy-Transition/Technology/Hydropower