Ocean Enregy
Wave Energy
Introduction to Wave Energy
Wave power is the transport of energy by ocean surface waves, and the capture of that energy to do useful work — for example for electricity generation, desalination, or the pumping of water (into reservoirs).
Wave energy is different from tidal energy, which is energy captured from tides. Tides are the result of gravitational forces that the sun and moon exert on the earth. Waves are the result of wind blowing over the sea.
Compared to renewable energy industries such as wind, solar and biofuels however, the wave energy industry is relatively new and some even consider it to be in its infancy
Wave Energy Potential
Research reveals that wave energy is a suitable renewable energy resource for certain coastlines in Australia, the United States, the United Kingdom, the Pacific Islands, Japan, China, Western Europe, South America and Africa. The International Energy Agency (IEA) estimates the worldwide potential for electricity production from wave energy technology to be 10 percent to 50 percent of the world’s yearly electricity demand of 15,000 TWh, depending on the expected load factor and wave regime.
The most intense wave energy locations are found between 30o and 70o latitude in the northern and southern hemispheres. The UK, Portugal, Spain and Norway in particular harbour excellent resource. According to the Carbon Trust report Future Marine Energy (2006), the UK’s exploitable wave resource has been estimated at 50 TWh/year – enough to meet around 14% of UK electricity demand. An estimated 30% of Portugal’s electricity demand can be met from wave power. The Atlantic and Pacific coastlines of North and South America also offer excellent resource and commercial opportunities.
The potential market for wave energy is worth about $1 trillion worldwide, according to the World Energy Council, a nonprofit research organization. In the United States alone, wave technology could supply 6.5 percent of the nation's energy.
Wave energy technologies are the most heavily researched and funded sector in the ocean
power industry. The potential to bring renewable electricity to a significant percent of the world’s population living within 60 miles of a coastal area is a key factor driving the outsized development of wave energy technologies.
A Global Wave Energy Resource Assessment
Source- Andrew M. Cornett
Canadian Hydraulics Centre, National Research Council
Ottawa, Ontario, Canada
Technology
For wave energy conversion, there are three basic systems
- Channel systems that funnel the waves into reservoirs
- Float systems that drive hydraulic pumps
- Oscillating water column systems that use the waves to compress air within a container.
The mechanical power created from these systems either directly activates a generator or transfers to a working fluid, water, or air, which then drives a turbine/generator.
Among the above, float systems are the most popular.
The majority of companies developing wave energy technologies are working on devices called point absorbers. Point absorbers resemble offshore floats / buoys used for marking channels and collecting environmental and meteorological data. These devices are preferred over other types of wave energy devices because of their ability to absorb energy from oncoming waves in all directions. These devices bob in reaction to multi-directional ripples. Other wave energy devices are designed to absorb oncoming energy from only one direction or dimension in space.
Such multidirectional absorption, however, poses some problems. For instance, unless the wave energy is tuned to the wave climate in which it is submerged, energy will not flow smoothly through the power-take off system. Companies in the wave energy field are developing advanced tuning systems to tackle this issue.
It should be noted that different companies are experimenting with a variety of float systems, each having different designs and shapes.
Here’s a description of how the Pelamis Wave Energy Converter (WEC) works (The WEC is a snake-like float): WEC is a concept for extracting energy from ocean waves and converting it into electricity, direct hydraulic pressure or potable water. The system is a semi-submerged, articulated structure composed of cylindrical sections linked by hinged joints. The wave-induced motion of these joints is resisted by hydraulic rams that pump high-pressure oil through hydraulic motors via smoothing accumulators. The hydraulic motors drive electrical generators to produce electricity.
Regional Scenario for Wave Energy
The United Kingdom has led the development of the wave energy industry. As easrly as the 1970s, the U.K. Wave Energy Program provided £60 million in funding for wave energy research. A professort from the University of Edinburgh (Prof. Stephen Salter) spearheaded most of the research, developing a prototype that laid the foundation for many of the current technologies. His device, called the Duck, reportedly absorbed 90% of the energy incident on the device, and achieved conversion efficiencies of close to 90% at costs that were comparable to grid electricity costs. The country’s wave energy program was disbanded later, but the design and engineering advancements introduced by Prof. Salter provided the groundwork for future wave power research.
As a result of its geographical advantages, the potential for small wave projects seems highest in the UK, where wave power density is high and much of the wave energy research is centered. Other major countries with a direct interest in wave energy are Japan, Norway, Portugal, Denmark and USA. Some estimates suggest that these countries could derive a significant percentage (10-30%) of their total electric energy requirements from wave energy.
Wave Energy – Status and Trends
Current contribution of wave energy
Currently, wave energy contributes insignificant amount to the world’s electricity generation.
An independent market assessment estimated the potential world-wide wave energy economic contribution in the electricity market to be on the order of 2,000 TWh/year. That is about 12% of world electricity consumption (based on 2009 data) and is comparable to the amount of electricity currently produced world-wide by large scale hydroelectric projects. The potential world-wide wave energy contribution to the production of electricity is estimated by IEA (International Energy Agency) to be between 10 and 50% of the world’s yearly electricity demand of about 16,000 TWh.
The future of wave energy will depend on the efficiencies of the technologies under development. Capital cost will be a primary determinant in the success of wave energy. Other cost variables also play a significant role. Unplanned O&M costs, especially in the event of system failure related to ocean storms can increase the cost of energy significantly. Thus, investing the development of robust devices able to withstand heavy seas and high winds will likely continue to be a primary investment driver in this industry.
There have been estimates that investments of over £500 billion would be necessary for wave energy to contribute 2000 TWh per year worldwide.
Wave Energy References
Wave Energy Organizations
The European Commission - The aim of the commission is to strengthen the development of the markets and technology for ocean energy in the European Union. It has promoted cooperation between leading organisations and institutes, via the formation of a Thematic Network (www.waveenergy.net ) and a Coordinated Action (www.ca-oe.net). It has made direct contributions towards developing particular technologies, including: shoreline OWCs at Pico in the Azores, the Wave Dragon (www.wavedragon.com), the Wave SSG (www.waveenergy.no) and the SEEWEC (a multinational project to build a device containing an array of wave energy floats, www.seewec.org/)
The International Energy Agency - In 2001, the International Energy Agency (IEA) formed an Implementing Agreement on Ocean Energy (www.iea-oceans.org), which is the IEA’s mechanism for providing a framework for international collaboration in energy technology R&D, demonstration and information exchange.
The European Marine Energy Centre - It provides four test sites in 50 m water depth for wave energy devices, each with its own subsea cable, as well as a monitoring station and other facilities (www.emec.org.uk). The Centre has hosted a number of wave energy devices (as well as tidal current devices at a nearby site) and is proving pivotal in establishing wave energy as a reliable energy source (e.g. allowing developers to demonstrate their technologies in real sea conditions, coordinating activities around performance measurement and design standards).
Useful Web Resources on Wave Energy
- Wave energy efforts worldwide - http://cesenet.org/documents/wave_country_notes.pdf
- Ocean wave energy - http://ocsenergy.anl.gov/guide/wave/index.cfm
- Wave Energy Today - http://waveenergytoday.com/
- WaveEnergy Centre - http://www.wavec.org/
Tidal Energy
Introduction to Tidal Energy
Tides are the result of gravitational forces that the sun and moon exert on the earth.
Tidal energy is generated by the relative motion of the earth, sun and the moon, which interact via gravitational forces. Periodic changes of water levels, and associated tidal currents, are due to the gravitational attraction by the sun and moon. The magnitude of the tide at a location is the result of the changing positions of the moon and sun relative to the earth, the effects of earth rotation, and the local shape of the sea floor and coastlines.
Because the earth's tides are caused by the tidal forces that are present due to gravitational interaction with the moon and sun, and the earth's rotation, tidal power is practically inexhaustible and classified as a renewable energy source.
A tidal energy generator uses this phenomenon to generate energy. The stronger the tide, either in water level height or tidal current velocities, the greater the potential for tidal energy generation.
Tidal Barrages – The concept of tidal barrage is quite old, and there are a few tidal barrages that have been in existence for decades. Tidal barrages make use of the potential energy in the difference in height between high and low tides. Tidal barrages are essentially dams built across a tidal estuary, and the technology used is similar to that used in hydroelectric plants. Owing to the large amount of construction required, tidal barrages suffer from very high infrastructure costs. Another bottleneck for tidal barrages is the shortage of viable sites worldwide; tidal barrages also pose serious environmental issues.
Tidal Stream Systems - Tidal stream systems make use of the kinetic energy of moving water to operate turbines. Unlike tidal barrages that require water to be stored, this method relies only on the moving water, and hence method is gaining in popularity because of the lower cost and lower ecological impact compared to barrages.
Tidal Lagoons - Offshore tidal lagoon power generation resolves the environmental and economic problems of the barrage system and puts tidal power generation back amongst the choices for commercial-scale renewable power generation. Rather than blocking an estuary with a barrage, offshore tidal power generators use an impoundment structure, making it completely self-contained and independent of the shoreline. It is similar to having a circular dam, built on the seabed. Tidal lagoons eliminate the environmental problems associated with blocking off and changing the shoreline. Likewise, the concept of a tidal lagoon is not a recent proposition. As of 2009, No tidal lagoon has ever been built anywhere in the world, and although the technologies used would themselves be classed as mature, the concept itself is currently unproven due to a number of remaining uncertainties over design, construction methods and physical impacts.
Tidal Energy Potential
A miniscule portion (less than 0.01%) of the world’s electricity requirements is currently being generated from tidal sources. Tidal constitutes about 0.02% of the total electricity generated from all renewable energy sources.
As of 2009, all electricity from tidal energy is obtained from tidal barrages. Tidal streams and tidal lagoons are yet to have any completed projects that generate electricity.
Top Ten Potential Locations for Tidal Energy
Country | Locations |
France | La Rance |
Canada | Bay of Fundy – Cumberland Basin,shepody,cobequid |
Russia | Mezan Bay and Tugur,penzhisnk |
Korea | Siwha & Garolim,,cheonsu |
India | Kambhat,kutch |
Australia | Secure Bay & Cape Keraudren,Walcott inlet |
Argentina | San Jose / Nuevo,rio Gallegos,santa cruz |
UK | Severn & Mersey Yy |
Mexico | Rio Colorado |
USA | Pasamaquoddy,knik arm,turnagain arm |
Source: WEC, 2001
Existing Large Tidal Power Plants
Country | Site | Installed Power (MW) | Basin Area (km2) | Mean Tide (m) |
France | La Rance | 240 | 22 | 8.55 |
Russia | Kislaya Guba | 0.4 | 1.1 | 2.3 |
Canada | Annapolis | 18 | 15 | 6.4 |
China | Jiangxia | 3.9 | 1.4 | 5.08 |
Source: www.gcktechnology.com
Tidal Stream Resources
Location | Total(TWh/Year) | Extractable (TWh/Year) | Economic(TWh/Year) |
UK | 90 | 18 | ~12 |
EUROPE(excluding UK) | 90 | 17 | ? |
Others Worldwide | 600 | 120? | ? |
Source: Black & Veitch-for Carbon Trust -2004-5
Tidal Barrage Projects and Proposals
Country | Location | Power MW | Energy TWh/yr |
France | La Rance | 240 | 0.5 |
Canada | Bay of Fundy – Cumberland Basin | 1400 | 3.3 |
China | Various | 1000 | 2.5 |
Russia | Mezan Bay and Tugur | 28000 | 31.0 |
Korea | Siwha & Garolim | 740 | 1.4 |
India | Kambhat | 1800 | 3.9 |
Australia | Secure Bay & Cape Keraudren | 600 | 1.1 |
Argentina | San Jose / Nuevo | 600 | 1.8 |
UK | Severn & Mersey | 9300 | 18.5 |
Source: http://www.raeng.org.uk/policy/reports/pdf/energy_2100/David_Lindley.pdf
Types of Tidal Energy Technology
Tidal Turbines
In many ways tidal turbines used for energy from tidal streams are analogous to wind turbines, in terms of the general shape, mounting and fixing technology, and power take-off system designs. The one critical difference between wind turbines and wave energy turbines is the size. For instance, tidal turbines generating 1 MW of power have sizes that are only about a third the size of a wind turbine with a similar generating capacity.
Tidal turbines are arrayed underwater in rows, as in some wind farms. Ideal locations for tidal turbine farms are close to shore in water depths of 20–30 meters (65.5–98.5 feet). The turbines function best where coastal currents run at between 3.6 and 4.9 knots (4 and 5.5 mph). In currents of that speed, a 15-meter (49.2-feet) diameter tidal turbine can generate as much energy as a 60-meter (197-feet) diameter wind turbine.
The majority of tidal energy companies are developing horizontal axis turbines that are similar to wind turbines. Other types of tidal turbines being experimented are:
· Reciprocating Tidal Stream Devices - These have hydrofoils which move back and forth in a plane normal to the tidal stream, instead of rotating blades. One design uses hydraulic pistons to feed a hydraulic circuit, which turns a hydraulic motor and generator to produce power.· Venturi Effect Tidal Stream Devices - In these, the tidal flow is directed through a duct, which concentrates the flow and produces a pressure difference. This causes a secondary fluid to flow through a turbine and generate electricity.Tidal Barrages
Tidal barrages are essentially dams. In this method, a barrage or dam is typically used to convert tidal energy into electricity by forcing the water through turbines, activating a generator. Gates and turbines are installed along the dam. When the tides produce an adequate difference in the level of the water on opposite sides of the dam, the gates are opened. The water then flows through the turbines. The turbines turn an electric generator to produce electricity.
Tidal Industry - Status and Trends
Current Contribution of Tidal Energy
As of 2009, of the total electricity production from renewables, less than 0.03% is obatained from tidal sources.
Electricity generation from tidal energy could be much higher in future, with some estimates suggesting a potential generation in the range 1000 TWh to 3500 TWh. (For comparison, the total electricity generation worldwide was about 17000 TWh in 2008)
The United Kingdom is a leading country both in terms of activity and in terms of support to the sector. According to estimates, 20% of UK's total electricity requirement can be harnessed from ocean energy, comprising primarily tidal and wave energy sources. The Carbon Trust has also predicted that marine energy could contribute up to one sixth of the UK's '20% renewable energy by 2020' target. Scotland with its rich ocean energy resources plays an important role. In fact, 25% of Europe's tidal resources and 10% of Europe's wave energy resources are found in Scotland.
It has been estimated that if ocean energy technologies continue to be supported and achieve their predicted potential, approximately 3 gigawatts (GW) of installed capacity could be available in the EU by 2020.
Ocean Thermal EnergyThe main objective of ocean thermal energy or Ocean Thermal Energy Conversion (OTEC) is to turn the solar energy trapped by the ocean into useable energy. OTEC systems use the ocean's natural thermal gradient—the fact that the ocean's layers of water have different temperatures—to drive a power-producing cycle. As long as the temperature between the warm surface water and the cold deep water differs by about 20°C (36°F), an OTEC system can produce a significant amount of power.
Get more information from the following pages
See also
An article specific to British tidal energy use
The Energy Story: Ocean Energy
Here is an article on “Ocean Energy – A Certain Kind of Hydropower”
