What Makes Hydroelectricity More Flexible Than Other Forms Of Renewable Energy?

Hydroelectricity is electricity generated from flowing water, often from dams constructed on rivers. Hydroelectric dams capture the energy of falling water to turn turbines and generate electricity. Hydroelectric power provides around 16% of the world’s electricity and is one of the most common renewable energy sources, along with wind and solar power.

While most renewables like solar and wind are intermittent, meaning their power output varies based on weather conditions, hydroelectricity is more flexible and controllable. Hydroelectric dams with reservoirs can store water and rapidly increase or decrease power output as needed. This makes hydroelectricity uniquely valuable for grid stability and meeting demand.

This article will examine the advantages hydroelectric dams provide in flexibility compared to other renewables. Key factors enabling hydroelectricity’s flexibility include dam design, storage capabilities, fast startup and shutdown, load following abilities, ancillary grid services, transmission support, and geographic diversity.

Hydroelectric Dam Design

Hydroelectric dams utilize reservoirs to store water, which allows output to be adjusted as needed. Water can be held back or released through turbines to increase or decrease electricity generation [1]. Many dams are designed with “pumped storage,” where water is pumped back into the reservoir during periods of low energy demand. This stores energy for later high-demand periods when electricity prices are higher [2].

The volume of water flowing through the turbines determines the amount of power generated. Operators can open or close turbine gates to rapidly scale power output up or down. Large hydroelectric plants are capable of going from zero to full power generation within minutes [1]. This ability to quickly adjust electricity generation makes hydroelectric dams highly flexible.

Quick Startup and Shutdown

One of the key advantages of hydroelectric plants is their ability to start up and shut down much more quickly than most other power generation technologies. According to a Hydro Review article, most hydroelectric turbines in the U.S. can go from a cold start to full operations in less than 10 minutes. This rapid startup capability allows hydro plants to respond quickly to changes in electricity demand.

In comparison, coal plants can take over 8 hours to startup, while nuclear plants take even longer at up to 2 days. Renewables like wind and solar have no control over startup and shutdown – they can only generate when the resource is available. The quick start-stop ability of hydro gives grid operators much more flexibility to ramp production up or down to match demand.

Hydroelectric facilities are also able to shut down their generators very quickly if needed. Within minutes, water flow can be stopped and turbines brought offline. This rapid shutdown time allows hydro plants to instantly reduce grid supply during periods of overgeneration or excess capacity.

Storage Capabilities

One of the key advantages of hydroelectric power is the ability to store energy in the form of water held behind dams. The reservoirs act like large batteries, storing power that can be dispatched on demand. Pumped storage hydropower builds on this capability by pumping water uphill into a reservoir when electricity supply exceeds demand. This water can then be released to generate power at times of peak demand (Pumped storage hydropower: Water batteries for solar and wind).

The storage capacity of pumped hydro allows the grid to balance variations in supply and demand. For example, excess solar or wind generation during the day can be used to pump water uphill. Then when the sun sets or wind dies down, that stored water can be released to generate hydroelectricity (How Pumped Storage Hydropower Works). This makes hydroelectricity an ideal complement to intermittent renewable sources.

Globally, pumped hydro stations provide over 127 gigawatts of storage capacity. In the United States alone, pumped storage represents 97% of utility-scale energy storage (Pumped-storage hydroelectricity). The storage capabilities of hydroelectric dams and pumped storage give the technology unmatched flexibility compared to other renewables.

Load Following Abilities

Load following refers to the capability of a power plant to adjust its power output to match fluctuations in electricity demand throughout the day. Traditional baseload generation sources such as coal and nuclear are not designed to flexibly ramp production up and down. Renewables such as solar and wind also face intermittency challenges in matching grid demand.

In contrast, hydropower is uniquely able to provide load following services. The generating units at a hydroelectric facility can quickly increase or decrease power output through starting up, shutting down, or adjusting their turbines and generators. As the OECD report states, hydroelectricity offers “sub-minute to seconds” ramp rates to smoothly follow intraday load variations. Pumped storage hydro takes this a step further by pumping water uphill during low demand so it can be released to generate extra electricity during peak hours. This makes hydroelectricity exceptionally flexible to match real-time shifts in grid load.

Ancillary Services

Ancillary services refer to functions that help grid operators maintain a reliable electricity system. These services help manage grid operations through frequency control, voltage control, operating reserves, and system support in the event of outages. Hydroelectric dams are uniquely suited to provide key ancillary services that support grid reliability.

Hydroelectric generators can respond very quickly to changes in electricity supply and demand to provide frequency control. The generating units can rapidly adjust output to help maintain the desired system frequency. Hydro dams also offer operating reserves that can come online within 10 minutes in case of a generator or transmission outage elsewhere on the grid. In addition, hydro generators can provide reactive power to control grid voltage and ensure system stability.

According to Creating an Ancillary Services Matrix, hydro plants supply “frequency control (primary, secondary, dynamic), fast start and load following capabilities” as well as “black start capabilities” to restore power after an outage. The quick ramping abilities and storage capacity make hydropower an ideal provider of essential ancillary services.

Transmission Support

Hydroelectric power provides critical support for grid stability and helps match electricity supply with demand. The generating units can start up quickly and adjust output to prevent frequency fluctuations across the transmission system (https://www.pnnl.gov/hydropower-and-electric-grid).

Hydropower’s storage capabilities and fast ramping abilities allow it to dispatch power to the grid immediately when needed to meet surges in demand. This helps avoid grid instability and prevents blackouts that could occur when supply and demand are mismatched (https://www.energy.gov/eere/articles/4-reasons-why-hydropower-guardian-grid).

The agility and flexibility of hydropower offers increasingly important support for energy grid resilience. Hydroelectric facilities provide essential grid services such as frequency regulation, spinning reserves, and voltage control (https://www.asce.org/publications-and-news/civil-engineering-source/civil-engineering-magazine/article/2022/03/hydropower-helps-ensure-energy-grid-resilience-report-says).

Geographic Flexibility

One of the main advantages of hydroelectric power is its geographic flexibility compared to other renewable energy sources like wind and solar. Hydroelectric dams can be built in a wide range of locations, as long as there is flowing water available. This makes hydroelectricity much less dependent on specific geographic factors than wind or solar power.

Wind power requires locations with consistently strong winds, which limits viable sites to certain coastal areas, mountaintops, and plains. Solar power depends heavily on regions with abundant sunshine and minimal cloud cover. But hydroelectric dams only need access to flowing water, which exists across diverse geographies and climates.

According to a 2021 review, “hydroelectricity has a distinct advantage in geographic flexibility over other renewables like wind and solar” (Zhao et al., 2023). This geographic diversity makes hydroelectricity a more reliable renewable energy source.

Low Environmental Impact

Hydroelectric power has several environmental benefits compared to fossil fuel power plants. Unlike coal, natural gas, and oil plants, hydroelectric dams do not burn fuel to generate electricity. This means they produce no greenhouse gas emissions and no air pollution. According to the U.S. Energy Information Administration, hydroelectricity is one of the lowest-cost and lowest-emitting sources of electricity.

While fossil fuel plants release pollutants like nitrogen oxides, sulfur dioxide, particulate matter, mercury, and other heavy metals into the air, hydroelectric plants emit none of these harmful substances. The EPA estimates that in 2017, hydroelectric generation avoided over 200 million metric tons of carbon dioxide emissions compared to fossil fuel generation. This makes hydroelectricity an attractive renewable energy source to combat climate change and improve public health.

Additionally, hydroelectric reservoirs provide recreational opportunities like boating, swimming, and fishing. The reservoirs can also help control flooding, provide irrigation for agriculture, and supply drinking water. Overall, hydroelectricity delivers renewable power with substantial environmental advantages over conventional fossil fuel generators.

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Conclusion

In summary, hydroelectric power has unique advantages in flexibility compared to other renewable energy sources. Hydroelectric dams can start up and shut down generation quickly to meet shifts in electricity demand. Their storage capabilities allow them to hold water to generate power when it is most needed. Hydropower facilities can also provide vital grid services like frequency regulation, spinning reserves, and voltage control. The geographic diversity of dams gives the overall hydroelectric system more flexibility. Additionally, the flexibility of hydroelectricity comes with a low environmental impact compared to fossil fuels. With their quick ramping abilities and storage capacity, hydroelectric dams play an indispensable role in integrating variable renewable sources like wind and solar onto the grid.