The waves breaking against the shoreline contains vast amounts of energy. The International Energy Agency (IEA-OES) estimates that up to 80.000 TWh of energy can be harvested worldwide from waves per year.
Waves – energy transport caused by wind
The waves you see on the sea surface is really energy transport. Frequently transport of large amounts of energy.
Waves are formed by the wind blowing along a water surface. These starts out as small ripples, but if the wind continues the waves gradually grow in size. When strong winds blows across long stretches of the ocean, the result is large swells that can travel very far, and continues to propagate long after the wind has died down.
Interest through the ages
The idea of extracting energy from the waves is not new. The first patent related to the use of wave energy was granted in 1799! Since then, a multitude of inventors have seen the potential of the waves, and have conceived of ideas to harness this power.
There exists hundreds, perhaps thousands of principles and patents related to harvesting energy from the waves. A common classification of the main principles is:
-Oscillating water column
Within these categories resides a range of subcategories and different implementations from different providers.
Many Norwegian companies are developing, or have developed, wave energy concepts. Some of them have given up after their plants was wrecked by the force of the ocean or other problems, while some are still active with prototyping or in different stages of concept development.
The Norwegian developers have predominantly have predominantly focused on plants of the following types: oscillating water column, overtopping devices and heaving devices. Langlee is the only company to develop a plant with “flaps” to utilize wave generated currents (surging device). Intentium have developed an interesting variant of a heaving device, with an elongated pontoon aligned perpendicular to the wave propagation direction in order to harvest more energy.
Pontoon Power is developing a similar concept, but instead use many cylindrical buoys in a line. In these implementations the generator is afloat, submerged in the sea, rather than fixed on the bottom. It is hoped that this implementation will avoid excessive peak forces on the system, due to inbuilt flexibility.
Known plants from Norwegian companies are:
Oscillating water column plant at Sotra 1984-1988. Wrecked in 1988, but a new initiative might be in the pipeline.
Oscillating water column plant developed by Ola Stornes, Tingvoll. Now owned by Runde Environmental Centre.
Overtopping devise at Sotra 1985. Wrecked in 1991.
Overtopping device for inclusion in breakwaters or as floating devices.
Floating overtopping device, with foundation for wind mills.
Fred. Olsen Energy:
“Buldra”. Platform with heaving devices. Continued as “Bolt”, and under development.
E-Co Energi “Seahorse”:
Simple heaving device with bottom-mounted generator. Prototype deployed at Runde. Wrecked in 2011.
Floating platform utilizing wave generated currents.
Floating platform with a line of heaving devices.
Heaving devise with submerged generator. Under development.
Most people looking out at the sea on a day with big waves have probably philosophized about the immense forces at play, and considered ways to harness some of that energy. Wave power is a subject that attracts many inventers and developers, and it is hard to keep track of them all. If you know about some Norwegian wave plants or developments that should be added to the list, do not hesitate to contact us.
About harnessing waves
A successful wave energy plant must be able to extract the energy from the waves. A good way to tell the amount of energy extracted by the plant, is to compare the size of waves before and after they pass the plant. A reduction in size is an indication of absorbed energy. (Unless the waves and energy is merely reflected). But how to absorb a wave?
Paradoxically, what characterizes a good wave absorber is the ability to generate waves itself! By generating waves with the right phase in relation to incoming waves, it is possible to generate destructive interference in a way that leaves incoming waves intact, but absorbs all the waves behind the plant.
This applies for all installations designed to absorb the wave energy directly through induced motion. For overtopping devices the energy absorption mechanism is different – these devises use the energy in the waves to lift volumes of water instead of moving the installation.
Although much thought, research and development have gone into wave energy over the last 200 years, we are still waiting to see operational large scale commercial plants. From an academic perspective, the theory behind wave energy plants is relatively well developed. This is to a large extent due to substantial research effort during the seventies and eighties, both in Norway and internationally, as well as because a lot of knowledge from ship design developments can be transferred directly. The needed technical components (hydraulics, power electronics, control systems, maritime operations..) are also well developed, in particular due to the massive technological development caused by offshore oil exploration.
Still, the ocean, particularly in rough weather and big waves, is a hostile environment for mechanical and electrical components, and the challenges are plentiful:
- Excessive strain from large waves and high winds
- Too low efficiency from small waves in calm weather
- High development costs
- High material- or construction costs
- Need for expensive cables to shore (to transfer electricity)
- Difficult and expensive operations for deployments and maintenance
- Strong competition from other kinds of renewable energy (hydro power, wind energy, solar energy..)
- Low visibility in politics and in the public opinion (compared with offshore wind, oil & gas, carbon capture..)
- And not least: Too many wrecked plants have given wave energy a bad reputation
In spite of all these challenges, we believe there is hope for wave energy. At some point in the future technology transfer, shared infrastructure with offshore wind, and general development will make wave energy profitable. If Norwegian technology companies take part, we could look at a very large new market for maritime technology and expertise