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Ocean Power

Ocean Waves Could Provide Up to 2 Terawatts of Electricity
 
Renewable energy analysts believe that ocean waves could provide up to 2 terawatts of electricity. That's enough to power rougly 200 million homes with average electricity usage for one year!

What is Ocean Energy?

The ocean covers 71% of the Earth’s surface and more than 95% of our oceans remain unexplored. Even though we still have much more to learn and discover with our oceans, there are some things we do know, like the currents, tides, and the fact that ocean currents carry a significant amount of energy. Through developments in Tidal Energy, Wave Energy, and Ocean Thermal Energy Conversion we can apply our knowledge of the ocean and use its strength to generate power.

Ocean Energy (also referred to as “Marine and Hydrokinetics”) is the term used to describe different forms of renewable energy harnessed from the ocean. Hydropower refers to electricity generated using the energy of moving water. While mechanical Ocean Energy technologies (tidal and wave) generate electricity using the energy of moving water, hydropower typically refers to energy generated from bodies of water other than the ocean. Hydropower is most commonly associated with the use of dams to generate electricity. Ocean Energy and Hydropower have been separated into two different renewable energy sections to organize the renewable energy sources available through the ocean, from renewable energy sources available through other water sources.

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History of Tidal, Wave, and Ocean Thermal

The earliest traces of tidal power date back to about 900 A.D. when a barrage would be built across the opening of a naturally occurring tidal basin. Wave power started to make its debut around the late 1700s, with the first known patent that used energy from ocean waves dating back to 1799. Even ocean thermal energy conversion has been around for over 100 years, appearing in 1881 when a French physicist, Jacques-Arsène d'Arsonval, proposed extracting the ocean’s thermal energy. The three different types have been attempted throughout the years, but the biggest breakthroughs, at least for wave and OTEC, did not come about until a few years into the 1970s gaining motivation from the 1973 oil crisis.

Ocean Energy Technologies

Tidal Energy
In order for tidal energy to be successful, the chosen location must have a difference of at least 16 feet between high and low tides. There are only about 40 sites on Earth with suitable tide ranges. Although there currently aren’t any tidal plants in the United States, there are locations in the Pacific Northwest and the Atlantic Northeast regions that meet the necessary conditions.

There are three main types of tidal energy technologies used today: barrages or dams, tidal fences, and tidal turbines.

Barrages or dams force water through turbines which activate a generator to make electricity. A barrage is built across a long narrow area of water and has metal barriers, commonly referred to as sluice gates that control the water levels and flow rates. There is a tidal basin that the gates allow to fill on incoming high tides. The basins empty through the turbine system on the outgoing tide. Tidal energy is converted into electricity through this process on both the incoming and outgoing tides.

Tidal barrage diagram

*Energy generated travels through underground cables.

If you’ve ever tried to use the NYC subway system, then you’re familiar with turnstiles- those horizontal bars that rotate around, forbidding you to pass until you successfully swipe your metro ticket. You push the bar and enter through while a different bar moves in to block the path forbidding the next person from entering. Maybe you’ve seen them at an amusement park or any place of a “screened” entry. If you can picture giant turnstiles reaching across channels between small islands or spanning across the strait between the mainland and an island, then you have a good idea of what a tidal fence looks like. Tidal currents typical of coastal waters spin the turnstiles which generates electricity.

Tidal turbines are very similar to wind turbines, except are located underwater. They are arranged in rows and work well where coastal currents are between 3.6 - 4.9 knots or 4 -5.5 miles per hour. Tidal turbines are much heavier than wind turbines as they must be built much sturdier to withstand the pressure and strong forces of the sea, but they are able to catch more energy.

Tidal Turbine

More information on tidal energy technologies can be found at Tidal Energy Basics - Department of Energy.

Wave Energy
OPT Power Buoy

Everyone is familiar with waves in the ocean- whether from going to the beach or through the media, we are no strangers to the pounding of waves against the shore, but just how much energy is really in those waves? Is it really possible to harvest this energy?

Waves come in all different sizes, but looking at ocean waves overall, renewable energy analysts believe that there is enough energy to provide up to 2 terawatts of electricity- that’s 2 trillion watts! The main types of wave energy converters are terminators, attenuators, point absorbers, and overlapping devices. These technologies extract energy directly from surface waves or from pressure fluctuations below the surface. Just like with tidal power, location of wave power technology is key; it cannot just be setup anywhere there are waves. Suitable locations include the northeastern and northwestern coasts of the United States, western coasts of Scotland, northern Canada, southern Africa, and Australia.

More information on wave energy and wave energy converters can be found at BOEM: Ocean Wave Energy and DOE: Wave Energy Basics.

Ocean Thermal Energy Conversion (OTEC)
OTEC Plant in HawaiiLarge bodies of water that are exposed to the sun can be very deceiving with their temperatures. There is a good chance that you have experienced dipping your feet into a pool while thinking, “Oh wow, this is great!” Upon gaining the courage to finally go down the ladder into the pool, you have second thoughts since the water is much colder at the bottom. The same principle applies to the ocean, but on a much larger scale. The sun heats up the surface of the water, but the farther below the surface you go (where the sun’s rays cannot reach) the colder the water gets. In tropical regions, the difference in water temperature can vary greatly and this large difference can be used to produce electricity.

Ocean Thermal Energy Conversion Technologies use fluids with a low boiling point (in closed-cycle) or warm surface water (in open cycle) to rotate a turbine which then generates electricity.  Besides from generating electricity, OTEC technology can produce fresh water from seawater, support aquaculture, and make it possible to grow temperate plants in the subtropics. OTEC power plants come with a steep front end cost which does not make OTEC technologies a strong competitor from an economic stand point. If you would like to learn more about OTEC, please visit DOE: Ocean Thermal Energy Conversion Basics for a more in-depth look at how the technologies work along with more information about byproducts formed.

More information on Ocean Energy in general can also be found at EIA - Hydropower and CT Clean Energy - Wave/Tidal.

Ocean Power in Connecticut

Opportunities in CT exist for wave and tidal technologies. If you are interested in developing a new technology or seek financial assistance with any sort of ocean power project, please visit the Clean Energy Finance and Investment Authority.

Ocean thermal power is listed as a Class I renewable energy source as defined in the Connecticut General Statutes (CGS) Section 16-1(a)(26)(vii). Wave or tidal power is also listed as a Class I renewable energy source as defined in the CGS Section 16-1(a)(26)(viii).

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