Tidal Kites: A New Kind of Renewable Energy

Elle
Jul 9
5 min read

Imagine a kite that flies underwater instead of in the sky, gracefully gliding through ocean currents to generate clean electricity. This isn't science fiction—it's the cutting-edge technology of tidal kites, one of the most promising new forms of renewable energy. These innovative devices are opening up vast new possibilities for powering our world with the predictable, powerful forces of the ocean.

What Are Tidal Kites?

Tidal kites are underwater energy-harvesting devices that work remarkably like the kites you might fly on a windy day, except they "fly" through moving water instead of air. These systems generate electricity from tidal streams and ocean currents by a unique and patented principle similar to a kite flying in the wind.

The most advanced tidal kites currently in operation are developed by Minesto, a Swedish company that has pioneered this technology. Their fully operational Dragon 12 looks like some sort of futuristic military drone, but it behaves remarkably like a kite underwater, using lift generated by tidal flows to fly patterns faster than the currents, harvesting renewable energy.

How Do Tidal Kites Work?

The physics behind tidal kites is fascinating and relies on several key principles:

The Kite Principle

"We use the same principle as kite flying, but we do it submerged in the water," explains Minesto's technology. Just like an aerial kite uses wind to generate lift and pull on its string, tidal kites use water currents to create lift and generate energy.

The Figure-8 Flight Pattern

The Dragon 12, being 12 meters wide and 28 tons heavy, is anchored with a tether to the seabed and steered in an 8-shaped flight trajectory powered by the tidal flow. The device resembles a plane, with a wing and control surfaces to steer the device through the water in a figure-of-eight shape.

Speed Enhancement

Here's where the technology gets really clever: The subsea kite is designed to fly across the main flow direction, achieving a relative speed many times the current speed. This speed enhancement reduces the size of the kite and rotor required to collect the energy compared with a fixed turbine.

Think of it this way: when you move a kite sideways through the wind, it travels much faster than the wind itself. The same principle applies underwater, allowing tidal kites to move through water at speeds up to 10 times faster than the actual current speed.

Energy Generation

The kite carries a turbine that spins as it moves through the water. It is tethered to the seabed by a cable that also carries power and communication signals. The spinning turbine generates electricity, which is transmitted through the tether cable to the onshore electrical grid.

The Power of Water

Why is tidal energy so promising? The answer lies in the fundamental properties of water versus air. Water is hundreds of times denser than air, which makes tidal energy more powerful than wind. It is more efficient than wind or solar energy due to its relative density and produces no greenhouse gases or other waste.

This density difference means that even slow-moving water can generate substantial amounts of energy. A 5-knot ocean current has the same energy potential as a 350 mph wind!

Real-World Performance

The technology has moved from concept to reality with impressive results. With a wingspan of 12 metres, the so-called 'Dragon' is expected to generate 1.2MW of clean electricity once operational. To put this in perspective, 1.2 megawatts is enough to power approximately 1,000 homes.

Minesto's tidal kites have been generating electricity to the grid for three months, with test data showing that the technology is ready for commercial production. This represents a major milestone in making tidal energy a practical reality.

Environmental Benefits

Tidal kites offer several environmental advantages over traditional energy sources:

Clean Energy Production

Tidal energy is a growing renewable, clean, and environmentally friendly energy source that produces far fewer greenhouse gases than fossil fuels such as coal and oil.

Predictability

Unlike wind and solar energy, which depend on weather conditions, tidal energy is incredibly predictable. Producing energy using tidal power is predictable because it relies on tidal currents. Although tides change regularly depending on the time of day, we can calculate exactly when and how strong they'll be for centuries into the future.

Lower Environmental Impact

Compared to traditional tidal energy systems that require large dams (called barrages), tidal kites have a much smaller environmental footprint. Researchers are trying to figure out how to harness tidal currents with much less environmental impact than older technologies.

The Future of Tidal Energy

While tidal kites represent an exciting breakthrough, the technology is still in its early stages. Set against other renewables, such as wind and solar, it is clear that the global potential of tidal is smaller. But it can make regionally and nationally significant contributions.

The key to success will be scaling up the technology and bringing down costs. Currently, achieving the full potential of tidal energy will depend on continued government support, private investment, and successful demonstrations of both energy and environmental performance.

Challenges and Opportunities

Technical Challenges

Operating in the harsh marine environment presents unique engineering challenges. Saltwater is corrosive, and underwater equipment must withstand strong currents, marine life, and extreme pressures. The tether system must be robust enough to handle the forces generated by a 28-ton kite moving at high speeds underwater.

Economic Considerations

Like all emerging technologies, tidal kites face the challenge of competing with more established energy sources. However, as the technology matures and production scales up, costs are expected to decrease significantly.

Global Potential

The energy itself is kinetic, harvested from the intensity of water flow, and Minesto's tidal technology can collect energy from low-flow tides as well as higher, more powerful currents. This versatility means tidal kites could potentially operate in many coastal locations around the world.

Riding the Wave of Innovation

Tidal kites represent a remarkable fusion of simple physics and advanced engineering. By applying the age-old principle of kite flying to the underwater world, engineers have created a technology that could help power our future with clean, predictable energy from the ocean.

While we're still in the early days of this technology, the successful operation of systems like Minesto's Dragon 12 proves that tidal kites are more than just a promising concept—they're a working reality that could play an important role in our transition to renewable energy.

As we continue to search for ways to reduce our dependence on fossil fuels and combat climate change, innovations like tidal kites remind us that sometimes the most powerful solutions come from looking at familiar problems in entirely new ways. The ocean's endless dance of tides, which has shaped coastlines for millions of years, may now help shape a cleaner, more sustainable future for humanity.