How Do We Get Water Power?

Water power refers to the various ways in which the energy from water movement, such as flowing rivers or ocean waves and tides, can be harnessed and converted into useful forms of power like electricity. Unlike fossil fuels which are finite resources, the energy potential from Earth’s water cycles is constantly being renewed from solar energy and the gravitational pull of the moon. There are many established and emerging technologies that allow us to tap into the tremendous power inherent in moving water.

Water power is considered a renewable energy source since it originates from ongoing natural processes driven by the sun and moon. The main methods for capturing energy from water movement rely on hydropower from dams, tidal power from coastal inlets, wave power from ocean surfaces, and emerging technologies like hydrokinetic turbines placed directly in streams and rivers.

Globally, hydropower from dams is by far the most widely used form of water power generation, providing around 16% of the world’s electricity. Other technologies like tidal, wave, and hydrokinetic power currently play a smaller role but have great potential for growth in the future. Overall, water power offers a sustainable way to produce electricity without carbon emissions or resource depletion, as long as it’s implemented responsibly.

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Hydropower

Hydropower is one of the most common sources of renewable energy and accounts for around 16% of the world’s total electricity production. It utilizes the natural water cycle to generate electricity through the force of flowing or falling water.

The most common type of hydropower plant uses a dam on a river to store water in a reservoir. The water flows through a turbine to generate electricity. The amount of electricity that can be generated depends on the volume of water flow and the height from which it falls. Large hydropower plants can generate hundreds of megawatts of power.

Hydropower is a renewable source of energy as the water cycle is continuously replenished by rainfall and snowmelt. However, the availability of hydropower depends on precipitation patterns which can vary from year to year. Climate change is also affecting patterns of precipitation and evaporation which can impact hydropower generation.

While hydropower is renewable and carbon-free, large hydropower dams and reservoirs can negatively impact the local environment and ecosystems. Careful planning is required to weigh the tradeoffs between clean energy generation and potential environmental impacts.

Tidal Power

Tidal power harnesses the energy from the natural rise and fall of tides to generate electricity. There are two main types of tidal power systems:

Tidal Stream Generators

Tidal stream generators, also known as tidal turbines, are underwater turbines that take advantage of tidal currents to produce electricity in a similar way to wind turbines capturing the energy from wind. The blades of tidal stream turbines spin as the currents move past them, powering a generator that converts the rotational energy into electrical energy. These generators can be placed individually or in clusters in areas with consistently strong tidal currents.

Tidal Barrages

Tidal barrages are essentially dams built across estuaries or inlets that capture water during the high tide. Then during low tide, the water flows back through the dam, powering hydro turbines that generate electricity. Tidal barrages require suitable geographies where there is a large vertical difference between the high and low tides. The 22-mile long La Rance tidal barrage in France built in 1966 was the first major tidal power station.

Tidal stream generators have less environmental impact than tidal barrages since they do not require building dams. However, both technologies can disrupt marine ecosystems and shipping routes when not implemented carefully.

Wave Power

Wave power utilizes the energy from ocean surface waves to generate electricity. Two main technologies are used to harness this energy:

Wave energy converters: These floating or submerged devices convert the up-and-down and side-to-side motions of waves into mechanical energy that powers a generator.
Oscillating water columns: Partially submerged structures use the rise and fall of waves to compress air that powers a turbine.

Wave power has several key advantages compared to other renewable energy sources:

High energy density: Waves contain a significant amount of energy in a relatively small area.
Predictability: Wave patterns can be forecast accurately several days in advance.

Minimal visual impact: Wave devices can be located far offshore.

However, wave energy technology is less mature than other renewables. Challenges include surviving harsh ocean conditions and transmitting power to shore. But with continued development, wave power has immense potential for climate-friendly electricity generation.

Ocean Thermal Energy

Ocean thermal energy conversion (OTEC) utilizes the temperature differences between warm surface ocean waters and cold deep ocean waters to generate electricity. OTEC systems involve using the warm surface water to boil an ammonia working fluid which then turns a turbine. The cold deep ocean water is used to condense the vapor back into a liquid and complete the cycle.

OTEC systems are able to be implemented at tropical locations where surface water temperatures exceed 25°C. At these locations, cold water intakes can be placed around 1000 meters deep to utilize the dramatic temperature difference between surface and deep waters. The larger the temperature difference, the more power can be generated.

OTEC systems come in three main types: closed-cycle, open-cycle, and hybrid. Closed-cycle systems are the most common and enclose the working fluid in a closed loop, while open-cycle systems allow the evaporated seawater to expand and spin the turbine directly before being re-condensed. Hybrid systems combine aspects of both open and closed-cycle designs.

OTEC generation does not emit any CO2 or pollutants, provides constant base-load power unaffected by weather, and has minimal environmental impacts. However, the systems require very cold deep water intakes, have low thermal efficiencies, and can be expensive to implement on a large scale.

Salinity Gradients

Salinity gradient energy, also known as osmotic power, utilizes the energy from the difference in salt concentration between fresh water and salt water. As salt water and fresh water come into contact in an enclosed system, the fresh water will pass through a membrane to equalize the salinity, generating pressure that can be converted into electricity via a turbine.

This method has several benefits:

It is completely renewable and does not require any fuel.

It is emission free and environmentally friendly.
The power generation process itself does not impact the environment.
The membrane technology used continues to improve.

There is an immense amount of osmotic energy available where rivers meet the ocean.

However, there are also some challenges:

The membrane technology needs further development to become more efficient and cost effective.

Finding optimal locations to implement salinity gradient plants can be difficult.
Output levels are still quite low compared to other renewable sources.

Overall, salinity gradient power represents an extremely promising carbon-free energy source if further technological advances can be achieved. With ample potential capacity available globally, it may play a significant role in renewable energy production in the coming decades.

Hydrokinetic Turbines

Hydrokinetic turbines are a technology used to harness the kinetic energy from river and ocean currents and turn it into electricity. They work in a similar way to wind turbines, except they are placed underwater where flowing water turns the turbine blades. The rotational motion of the turbine is converted into electrical energy through a generator.

Hydrokinetic turbines have some key advantages over other renewable energy technologies:

Rivers and oceans provide a predictable, steady source of kinetic energy from currents.

They produce renewable energy without dams or diversions that can impact wildlife.
Turbines can be placed directly in channels, tidal areas, or ocean currents with minimal environment impact.
Energy production can be scaled up by adding more turbines.

There are some technical challenges to overcome with hydrokinetic turbines. The equipment must withstand corrosive saltwater, debris strikes, and powerful currents. Turbine designs are focused on maximizing efficiency and durability. However, hydrokinetic power has major potential as a carbon-free energy source worthy of continued research and development.

Pumped Storage

One way to store energy from water is through pumped storage hydropower. This involves pumping water from a lower reservoir to an upper reservoir when energy demand is low. The water is then released from the upper reservoir to the lower reservoir to generate electricity when demand is high.

The process works like a battery, storing energy by using excess electricity to pump water uphill. When electricity is needed, the water flows back downhill through turbines to generate power. Pumped storage allows energy from intermittent renewable sources like wind and solar to be stored for later use.

Pumped storage hydropower is currently the largest-capacity form of grid energy storage. Facilities are located across the United States, providing over 20 gigawatts of storage capacity. This allows the grid to stay balanced during peak times of electricity usage.

Pros and Cons

Water power offers several benefits as an energy source, but also has some limitations to consider.

Benefits

Water power is renewable and sustainable. Unlike fossil fuels, water will not run out. Building hydropower plants creates clean electricity without emitting greenhouse gases or other pollutants.

Facilities like pumped storage provide energy storage, which helps balance electricity supply and demand. Hydropower can also quickly go from zero power to maximum output, making it useful to fill gaps when solar or wind power is unavailable.

Water power is affordable and cost-effective. Once a hydropower plant is built, the fuel source is free. Operating and maintenance costs are low compared to other energy sources.

Dams provide reservoirs that can be used for recreation, flood control, irrigation, and drinking water supplies. They can help make shipping routes navigable.

Limitations

Building large dams and reservoirs can negatively impact the natural environment and ecosystems. They alter water flows and can obstruct fish migration routes.

Suitable sites with the proper landscape and water flow may be limited in some regions. Projects can be impacted by droughts or seasonal precipitation changes.

Dams require significant upfront investments and can take many years to build. Permitting and regulations may also slow development. However, long lifespans make up for high initial costs.

Water power options like tidal require technology still in early stages. Wave and ocean thermal energy have not yet reached commercial scale.

Future Outlook

The future looks bright for harnessing the power of water. As climate change leads to rising sea levels and increased precipitation in some areas, there will likely be more opportunities to utilize ocean and river energy. At the same time, improvements in turbine technology, materials science, and energy storage will allow us to harvest energy from water more efficiently and cost-effectively.

One exciting area of development is tidal lagoons and barrages. By building structures to capture tidal flows, we can generate electricity in a more consistent and predictable manner. The first major tidal lagoon project is underway in Swansea Bay, UK, with plans for larger lagoons around the UK coastline. Scientists are also looking at using tidal barrages to protect coastal cities from storm surges and flooding.

New hydrokinetic turbine designs, like flexible fluttering blades inspired by fish fins, can extract more energy from rivers and ocean currents. And adding sensors and artificial intelligence to turbines allows them to automatically adjust for changing water conditions. Floating offshore wind turbines that can be paired with wave energy converters are also being tested.

However, expanding water power will require overcoming some persistent challenges. Projects like tidal lagoons and barrages can be enormously capital intensive. There are also environmental concerns over their impact on wildlife and habitat disruption. Careful study and mitigation strategies will be needed. Finding suitable rivers and coastlines with the right conditions is also difficult. But with more investment and research, water power could grow to provide a sizeable share of renewable energy worldwide.