Technology Description and Status

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Ocean (marine) energy technologies for electricity generation are at a relatively early stage of development. Approaches to using ocean energy fall into several categories (Table 5.5): converting potential and kinetic energy associated with ocean waves into electricity; harnessing kinetic energy associated with marine (tidal) currents; converting potential energy associated with tides to electricity by building tidal barrage plants and by using mature hydro-electric turbine/generator technologies; extracting power from temperature differences between the surface and the seabed in deep oceans (ocean thermal energy conversion); using salinity gradients such as the latent heat of dilution at river mouths; and making use of marine biomass.

Wave energy and tidal current energy are the two main areas under development. The IEA Ocean Energy Systems Implementing Agreement is developing programs expected to be operational in 2007.

The technology required to convert tidal energy into electricity is very similar to that used in hydroelectric power plants. Gates and turbines are installed along a dam or "barrage" that goes across a tidal bay or estuary. Electricity can be generated

10 See: CSP Global Market Initiative (GMI; www.solarpaces.org/gmi.htm).

Table 5.5 Status of ocean renewable energy technologies Sub-sector Status

Wave Several demonstration projects up to a capacity of

1 MW and a few large-scale projects are under development. The industry aims to have the first commercial technology by about 2007. Tidal and marine currents Three demonstration projects up to a capacity of 300 kW

and a few large-scale projects are under development. Industry is aiming for 2007 for the first commercial technology.

Tidal barrage (rise and fall of Plants in operation include the 240 MW unit at La Rance the tides) in France (built in the 1960s), the 20 MW unit at

Annopolis Royal in Canada (built in the 1980s) and a unit in Russia. Tidal barrage projects can be more intrusive to the area surrounding the catch basins than wave or marine current projects. Ocean thermal energy conversion There are a few demonstration plants, up to 1 MW, but (OTEC) there is still uncertainly surrounding the commercial viability of OTEC.

Salinity gradient/osmotic energy A few preliminary laboratory-scale experiments, but limited R&D support. Marine biomass Negligible developmental activity or interest.

Note: In addition to the grid-connected electricity generation opportunities, there are potential synergies from the use of ocean renewable energy resources, for example: off-grid electrification in remote coastal areas; aqua-culture; production of compressed air for industrial applications; desalination; integration with other renewables, such as offshore wind and solar PV, for hybrid offshore renewable energy plants; and hydrogen production by water flowing into and out of a bay (a difference of at least 5 m between high and low tides is required). As there are two high and two low tides each day, electrical generation from tidal power plants is characterized by periods of maximum generation every 6 h. Alternatively, the turbines can be used to pump extra water into the basin behind the barrage during periods of low electricity demand. This water can then be released when demand on the system increases. This allows the tidal plant to function with some of the characteristics of a pumped-storage hydroelectric facility.

Ocean thermal-energy conversion (OTEC) may become important in the long term, after 2030, for certain countries, but it is considered uneconomic in the short or medium term. Salinity gradient and marine biomass systems are currently the object of very limited research activities. Neither seems likely to play a significant role in the short or medium term.

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