Ocean waves contain energy both through water motion (kinetic energy) and due to the elevation of water as the waves crest (potential energy). On average, the potential and kinetic energies in a wave are equal, while the energy fluctuation is a function of the square of the wave height, the distance between waves, and the wave period. Wave energy fluctuates daily and seasonally, depending on when and where storms occur to generate deep-water ocean waves. Monthly averages can be used to estimate seasonal variations in wave energy, which are maximum in winter. Wave forecast models can approximately predict wave energy from one to three days in advance. Both the kinetic and potential energy of waves are utilized in the range of ocean wave energy conversion devices being developed or deployed. These devices either transfer water motion into mechanical action or use the wave height to create a potential energy head across a generator.
Ocean Wave Technology in Alaska
To put together an ocean wave energy project, exact conditions of the site need to be determined. This information includes daily and monthly wave heights and periods, extreme wave events, ice conditions, wind and ocean currents, depths, fish data, and commercial and navigational uses. Some of this data can be obtained from public sources. Information about Alaska coastal ocean basin conditions and characteristics can be obtained from the Alaska Ocean Observing System (ak.aoos.org), NOAA, and Coast Guard buoys among other sources.
Advanced ocean power technologies fall into three general categories: ocean thermal energy conversion (OTEC), tidal energy, and wave energy. OTEC technology requires warm waters and therefore is not suitable for development in Alaska. However, tidal and wave energy may prove useful in expanding Alaska’s energy diversity and providing stably priced power to Alaskan residents.
Most tidal energy systems work very similarly to the technology used in traditional dams. Tidal energy systems, however, have several notable differences. They are often much larger, stretching across entire inlets or estuaries rather than rivers. Tidal systems generally use turbine systems: short, strong blades that are turned by the incoming and outgoing tides and create energy through a generator system. For this system to work, the difference between high and low tide must be at least 5 meters, or about 15 feet. In Alaska, tides of this magnitude occur on a regular basis, particular in the south central region.
The challenges of producing ocean based energy via tides are many. In many areas of Alaska where the tides are large enough to produce sufficient energy, the ocean bottom is very silty and dangerous to build on. Building materials have the potential to sink, and installing infrastructure can prove to be extremely hazardous to workers. The capital costs of installing tidal energy systems are extremely high, particularly in areas with challenging geography and extreme tides. Sea ice also presents a huge challenge in that it can destroy an energy system in just one tide cycle. Thus, all tidal energy systems must be installed in ice-free areas. With all of these challenges, Alaska is a difficult place to use tidal energy systems year round. However, southeast Alaska has great potential for tidal energy development.
Generating electricity from waves is a new technology, and right now there are many different devices that are being produced that can harness the energy. Total wave power flux on Alaska’s southern cost is estimated at 1,250 TWh per year. Much of this energy is in places where there is no demand for it - unpopulated coast. The first successful commercial wave energy was developed far off the coast of Portugal. Opened in 2008 with 3 Pelamis Wave Energy Converters producing 2.5 MW, there are plans to install 28 more wave energy converters for a total capacity of 22.5 MW.
Other ideas for generating electricity via wave motion include anchoring buoys to the ocean floor and using resistance to generate electricity as they ride over the surfaces of incoming waves. This idea is still brand new and in need of development, but it demonstrates the many ways in which the ocean could provide a renewable energy source.