Understanding how wave energy operates is essential for tapping into the immense power of ocean waves.

"This should be easy," you tell yourself when you first try surfing. But after a few wipeouts, bruises appear, and you quickly realize how wild and forceful the waves truly are. Tragically, surfing accidents remind us of just how dangerous these waves can be. Yet, this formidable wave power is exactly what some researchers believe could help reduce humanity's reliance on fossil fuels.

If you look at a world map, it's clear that land is the exception, with water covering about 70 percent of Earth's surface. The idea of harnessing the energy from the forces of nature acting on water’s surface is a promising one.

Wave energy is the process of harnessing the tremendous power contained within ocean waves. These waves carry an enormous amount of untapped potential energy, some of which could be used to power a significant portion of global electricity needs. Although estimates vary, some suggest that wave energy could contribute around 10 percent of the world's energy consumption [source: OEC].

In theory, the energy contained in ocean waves could supply far more than just a fraction of the planet’s power needs. In fact, only about 0.2 percent of wave energy could potentially power the entire world [source: Drollette]. Given this, one might ask why there isn't more focus on and investment in wave energy development.

The real challenge lies in figuring out how to convert this immense wave power into usable energy. This article will explore the various techniques engineers have devised to capture wave energy. But before that, it’s important to understand where and how waves acquire this energy.

Wave Energy Basics: How Waves Are Created Waves begin when wind blows across the water’s surface, creating small ripples. As the wind strengthens, it pulls these ripples along, allowing them to grow into larger waves.

In one way, wave energy can be seen as a form of solar energy. While this might seem strange, think about it: waves originate from wind, which is caused by the sun heating the Earth.

The sun never heats the Earth evenly. Due to the Earth's terrain and its position relative to the sun, some areas receive more heat than others. When air gets heated, it becomes lighter and less dense, causing it to rise. This creates space for cooler, denser air to rush in, which is what produces the refreshing breeze we feel on a sunny day.

Wind is also the driving force behind powerful waves. As wind moves along the surface of the water, its friction creates ripples. The wind then continues to push against these ripples, amplifying them in a snowball effect until they become large waves. This process is essentially energy being transferred from the sun to the wind and finally to the waves.

Several factors determine the strength of an individual wave. These include:

Interestingly, waves transmit energy, not water, over vast distances. Water serves as the medium through which kinetic energy, or energy in motion, is transferred. While the water moves, it only does so in a circular motion. Think of water particles like rollers on a conveyor belt — they rotate to move the belt, but they don’t move forward themselves. This explains why buoys bob up and down in a vertical motion with the waves.

­

If we already have wind turbines to capture wind energy, why should we bother with ocean waves? Despite seeming like an unnecessary intermediary, waves offer some distinct advantages over wind when it comes to harvesting usable energy. For one, ocean waves are packed with energy. In contrast to wind, which requires a vast area to hold a small amount of energy, waves can concentrate a great deal of energy in a compact space.

Another benefit of ocean waves is their reliability. We can more accurately predict wave movement than wind direction. Moreover, wind can initiate a wave, and that wave can travel long distances on its own. Waves that travel far from their point of origin are known as swell waves. This means the entire ocean surface can gather energy, and without any intervention, waves can reach us, even from distant locations.

Now that we understand how waves gain their energy, let's explore how we can harness that energy.

Methods for Harnessing Wave Energy

The concept of harnessing energy from ocean waves has been considered for centuries. However, it wasn't until the oil crisis of the 1970s that the idea gained significant traction [source: CRES]. This notion tends to resurface every time oil prices climb.

So far, engineers have devised and put into practice several methods for capturing wave energy. These techniques can be employed along the shoreline, near the shore, or offshore. Most of the devices located near or offshore are anchored to the sea floor. Below is a list of the main types of wave energy converters (WECs), devices designed to convert wave energy into usable electricity.

Terminator: Wave energy devices positioned at right angles to the wave direction are referred to as terminators. These terminators consist of a stationary part and a movable part that reacts to the wave motion. The stationary component may be anchored to the sea floor or the shore, remaining fixed, while the moving part behaves like a piston in a car -- moving up and down. This motion compresses air or oil to power a turbine.

An oscillating water column (OWC), illustrated in the image above, is an example of a terminator. OWCs feature two openings -- one at the bottom that allows water to flow into the column and another narrow passage at the top to let air pass in and out. As waves enter and fill the column with water, the air inside becomes pressurized, forcing it through the top opening. This rush of air spins a turbine. Then, when the waves recede, water flows out, drawing more air back in through the top, driving the turbine once more.

Another type of terminator is the overtopping device, which has a wall designed to collect water from rising waves into a reservoir. The water can escape through an opening, but as it passes through, it drives a turbine. The most iconic terminator, however, is undoubtedly the Schwarzenegger of WECs. Salter's Duck features a bobbing, cam-shaped (tear-shaped) head that drives a turbine. Though not fully developed, this device is theoretically the most efficient WEC.

Attenuator: These devices are aligned parallel to the direction of the waves. One of the most famous examples is the Pelamis, a series of long cylindrical floating devices connected by hinges and anchored to the sea floor. The cylindrical sections activate hydraulic rams in the connecting parts, which then drive an electric generator. The generated electricity is transmitted through cables to the seabed and further carried to shore via an underwater cable.

Point absorber: These devices aren't fixed in a specific direction toward the waves, but are designed to "absorb" energy from waves coming from all directions. One example is the Aquabuoy, created by Finavera. In this device, a vertical tube submerged underwater allows waves to rush in and move a piston, which is attached to a buoyant disk connected to hose pumps. As the piston moves up and down, it pressurizes seawater inside the tube. The pressurized water is then used to power a turbine, which drives an electrical generator [source: Finavera]. Multiple Aquabuoys can collectively send electricity to a central point, from where it travels to the seafloor and onward to shore via cables.

­­

A collection of WECs, such as Pelamis or Aquabuoy devices linked together, forms a wave farm.

On the following page, we'll delve into some of the challenges that come with trying to establish wave energy in today's economic landscape.

Challenges of Wave Energy

Whenever oil prices climb, the global demand for renewable energy alternatives surges. Though there is widespread support for this shift, several obstacles hinder wave energy from fully satisfying this growing demand.

Earlier, we mentioned that some estimates suggest current wave energy technology could potentially supply up to 10% of the world's energy needs. In theory, if the technology evolves significantly, it could do much more. As observed on the previous page, engineers are exploring various methods, yet no single technique has achieved high-efficiency energy conversion. One challenge with wave energy is the low frequency of waves, which makes it difficult to operate turbines efficiently [source: Chauhan].

Moreover, these devices must be affordable enough to justify their development and usage. If wave energy can never be as cheap as fossil fuels like coal and oil (even as their costs rise) or nuclear energy, it will struggle to become a major player in the energy sector. In fact, during the oil crisis of the 1970s in Europe, wave energy advocates vied for funding against nuclear energy supporters and lost, which led to the termination of some wave energy research programs. The belief that nuclear energy was a more promising investment led to this outcome.

However, even this 10% potential is significant when considering that only specific regions of the world are naturally suited for capturing wave energy. Since consistent and powerful waves are required to power the WECs, the most ideal locations for wave power are those between 30 and 60 degrees latitude [source: EUOEA]. For the U.S., the Oregon coast is the most viable option. Scotland, which experiences strong waves, has become a testing ground for wave energy solutions. Portugal is pioneering the world's first wave farm, utilizing Pelamis devices.

Although waves are often more predictable than wind, we can't always rely on consistent wave action, which means we need reliable energy storage solutions. On the flip side, at times waves and weather conditions can be so extreme that wave energy devices can't endure. Therefore, not only do we need more efficient WECs, but they must also be exceptionally durable, which can drive up their costs.