Is Hydro The Same As Tidal?

Both hydro power and tidal power utilize the natural movement of water to generate electricity, but there are some key differences between these two renewable energy sources. Hydro power harnesses the energy from flowing rivers or waterfalls by directing water through turbines, while tidal power captures energy from the rise and fall of ocean tides to turn turbines. In broad terms, hydro power relies on inland water flows, while tidal power taps into coastal ocean movements.

This article will provide an overview of how hydro power and tidal power work, compare their locations, scales, and environmental considerations, and highlight the main differences between these two forms of renewable energy.

Hydro Power Overview

Hydroelectric power plants generate electricity by harnessing the power of flowing water. A dam is constructed to form a reservoir, which controls the flow of water. The reservoir water flows through an intake and pushes against blades in a turbine, causing them to turn. The turbine spins a generator to produce electricity. Gravity causes the water to flow downward, while the dam controls the flow to produce dependable electricity.

As explained by the Tennessee Valley Authority, “A conventional dam holds water in a man-made lake, or reservoir, behind it. When electricity is needed, reservoir gates are opened so water can flow down through a large pipe called a penstock. At the bottom of the penstock, the fast-moving water spins the blades of a turbine generator to make electricity” (

Tidal Power Overview

tidal energy turbine underwater
Tidal power is a form of hydro power that uses the energy from the natural movements of ocean tides and currents to generate electricity. There are two main types of tidal power – tidal stream and tidal barrage.

Tidal stream systems use turbines placed in channels or open areas with strong tidal currents to capture energy. The movement of the water spins the turbine blades which then turn an electrical generator (

Tidal barrage systems build barriers like dams across tidal bays or estuaries. Sluice gates in the barriers allow water to flow into the bay or estuary during high tide, and during low tide the water is released back to the ocean to power turbines ( The difference in water height, also known as tidal range, determines the amount of power that can be generated.

Key Differences

While hydro and tidal power share some similarities in harnessing the power of water to produce electricity, there are several key differences between these two renewable energy sources:


Hydro power relies on rain and snowfall over land to continuously fill reservoirs, while tidal power relies on the gravitational forces of the moon, sun, and Earth to produce regular tidal cycles. Both are considered renewable sources, but tidal power offers more predictable renewability since it is driven by predictable astronomical forces (StackExchange, 2016).


The ebb and flow of tides follow well-understood cycles, allowing tidal power generation to be predicted precisely and electricity output scheduled accordingly. In contrast, hydro power relies on seasonal precipitation patterns that can vary substantially year-to-year.


Hydro power requires rivers or reservoirs with substantial water flow, limiting feasible locations mainly to mountainous regions. Tidal power systems can be built in coastal areas with sufficient tidal ranges. While there may be geographic overlap in some locations, tidal power offers more site options along seacoasts.

Environmental Impacts

Hydro power dams and reservoirs substantially alter natural water flows and ecosystems. Tidal power systems, while not without impacts, are considered more environmentally friendly with fewer disruptions to marine habitats (Population Education, 2015).

Hydro Power Locations

Hydro power plants are typically located on rivers, lakes, and waterfalls where there is flowing water that can be used to spin turbines to generate electricity. Some of the key locations for hydro power include:

  • Rivers – Many hydro facilities are located along major rivers like the Columbia River in the Pacific Northwest, the Colorado River in the Southwest, and the Mississippi River. Rivers provide both the elevation drop and flow rate needed for hydro power.
  • Lakes – Reservoirs created by damming lakes and rivers are used for pumped storage hydro plants. These facilities pump water uphill into the reservoir when electricity demand is low and then release it to generate power when demand is high.
  • Waterfalls – The immense power of waterfalls has been harnessed for hydro electricity at places like Niagara Falls on the U.S.-Canada border. The height of waterfalls provides the elevation drop to spin hydro turbines.

According to the U.S. Energy Information Administration, the majority of U.S. hydro capacity east of the Mississippi River is located along the Alabama and Tombigbee rivers. Out west, major facilities harness the power of the Columbia and Colorado rivers.

Tidal Power Locations

Tidal power stations are located in coastal areas with high tidal ranges. According to, some of the leading countries utilizing tidal power include France, Russia, and Canada.

Tidal power plants are often built in bays, estuaries, and inlets where there is a significant difference between high and low tides. The Bay of Fundy in Canada has one of the highest tidal ranges in the world, making it an ideal location for tidal power. Other prominent tidal power plant locations include the Rance tidal power station in France, located on the estuary of the Rance River, and the Kislaya Guba Tidal Power Station in Russia, situated in the Barents Sea.

In general, coastal areas along ocean shorelines with sufficiently high tidal ranges are the prime locations for tidal power stations. The oscillating flow of the tides can be harnessed to generate renewable electricity.

Hydro Power Scale

Hydroelectric power plants come in a wide range of sizes and scales. On the large end are massive hydroelectric dams and reservoirs that can generate hundreds or thousands of megawatts of power. The Three Gorges Dam in China, for example, has a capacity of 22,500 megawatts, making it the largest hydroelectric power station in the world (Large Scale Hydro — 350Vermont). Large-scale hydro projects like Three Gorges require enormous civil engineering works, with costs often reaching into the billions of dollars. Despite the high upfront costs, large hydro often has lower overall costs per megawatt compared to smaller projects (Hydropower Special Market Report).

On the smaller end, micro-hydro systems can generate just a few kilowatts to serve isolated homes, villages or small communities. Small-scale hydro projects have much lower civil engineering costs compared to massive dams and reservoirs. A 5 megawatt hydro station may cost $10-25 million, while a large 500 megawatt dam could cost over $1 billion (Watch out for these 20 Power Generation Projects in Africa). Smaller hydro stations are often situated on existing weirs or dams, or make use of natural features like small waterfalls.

Tidal Power Scale

Tidal power projects generally fall into two categories – small scale and large scale. Small scale tidal projects utilize tidal energy converters like turbines that can be installed in arrays. These small scale tidal farms typically generate up to 10 MW of electricity.

In contrast, large scale tidal projects harness the power of tidal barrages and lagoons. Barrages span across tidal estuaries and lagoons are created by building impoundment structures. The UK’s proposed Swansea Bay tidal lagoon project is an example of a large scale tidal development expected to generate 320 MW. The world’s largest tidal power station is the Sihwa Lake Tidal Power Station in South Korea, which has a capacity of 254 MW. While small scale tidal farms have become more common, few large scale tidal projects have been built globally.

Environmental Considerations

Both hydro power and tidal power can impact the surrounding environment and ecosystems. Hydro power dams and reservoirs may change or destroy natural habitats both upstream and downstream, affecting fish migration and breeding. Building dams floods areas upstream and changes the natural water flow downstream, which impacts plants and animals that rely on certain water levels and river systems.

Tidal power also affects marine ecosystems and aquatic life. The underwater turbines used can injure or kill fish and marine mammals that get too close. The structures themselves create artificial reefs that alter marine habitats. Tidal currents and sediment transportation patterns also get changed by tidal power facilities, impacting where nutrients, sediments, and organisms flow.

Proper siting, design, and environmental impact monitoring are important for both hydro and tidal power to minimize ecosystem damage. Fish ladders, turbine grates, lower turbine speeds, wildlife corridors, and compensatory habitat restoration can help mitigate environmental impacts. Overall, the effects on natural habitats and biodiversity must be carefully weighed against the clean energy benefits.


In summary, while hydro power and tidal power share some similarities in utilizing water resources for renewable energy generation, they have key differences. Hydro power relies on the potential energy of river water captured behind dams, while tidal power harnesses the kinetic energy of coastal tidal movements. Both provide clean energy alternatives to fossil fuels, but tidal power offers more predictability and less environmental impact on ecosystems and wildlife. However, hydro power facilities are more numerous and generate electricity on a much larger scale globally. Ultimately, both hydro and tidal power can play important roles in transitioning away from coal, oil, and natural gas, but regionally must be evaluated based on feasibility and local environmental considerations.

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