Category Action on Deployment

Tidal and Marine Current Energy

Marine currents are mainly driven by the rise and fall of the tides, but also by differences in seawater composition and by oceanic circulation. The mechanisms for exploiting this kinetic energy resource are similar to those for wind energy. An advantage of the marine energy resource is that it is generally predictable since the drivers tend to be gravitational rather than meteorological.

In most places, the movement of seawater is too slow and the energy available is too diffuse to permit practical energy exploitation. However there are locations where water velocity is speeded up by a reduction in cross section of the flow area, such as straits between islands and the main­land, around the ends of headlands, in estuaries, and so forth...

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OCEAN ENERGIES

The oceans cover more than two-thirds of the surface of our planet and represent a potential, chemical, and kinetic energy resource, which the­oretically is far larger than the entire human race could possibly use. The huge size of the marine energy resource is to some extent academic, as most of the energy available is either too diffuse for economic exploitation or located too far from the end-use sites. However, there are places where the different types of marine energy tend to be concentrated that may be located a “feasible” distance from prospective markets. In such cases, pros­pects for future exploitation are good.

There are six quite different marine energy resources that could be developed, as follows:

• Tidal and marine currents

• Wave energy

• Ocean thermal energy con...

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Trends in Technologies

Generally speaking, the most attractive sites in all countries have already been developed. Although large hydro is still being built, there is growing interest in small-scale and lower head sites, and in retrofitting and upgrading existing sites. Lower head sites are statistically much more common as there are many thousands of kilometers of rivers with low gradients. Reflecting this situation, in recent years considerable research effort has gone into the development of more efficient and economic technologies to exploit low – head hydro.

Furthermore, there is a growing international interest in the develop­ment of small-scale hydropower (SHP) because it does not have the same kind of adverse effects on the local environment as large hydro...

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Technologies

Hydropower schemes are usually divided into two categories: large-scale (above 10MW) and small-scale (below 10 MW, including mini – and micro­power schemes).

Most of the effort in developing hydropower has focused on the exploita­tion of “heads” (elevation) of 5 meter or more (often much more). Locations with such large falls of water represent the most highly concentrated form of renewable energy resource. If such a head is not available naturally, it may be created artificially by cutting streams and building a reservoir. This involves substantial modification of the local environment and high cost for the civil works.

A great deal of the hydroelectric resources in the world are used as energy storage devices...

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HYDROPOWER

Hydropower—the conversion of potential energy of water into sec­ondary energy carriers by means of hydraulic systems—throughout history has played an important role in providing first mechanical, then electrical power. Of the various forms of renewable energy, hydropower is the single

largest contributor, representing almost 75% of total global renewable elec­tricity production. However, (large) hydro has a rather poor image with governments and agencies, is often excluded from (voluntary) green energy schemes, and is therefore not enjoying the boom in increased deployment like some other renewable sources have enjoyed in the last decade. The main reasons for this are the sometimes large environmental effects and social impacts of large hydro...

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Trends in Technologies

Mass-produced solar cells are traditionally semiconductor devices made of silicon, which is the most abundant element in the earth’s crust. R&D focuses on scaling up the mass production technologies for multi – and sin­gle-crystalline solar modules (the majority of the market) and on improv­ing thin film silicon cells and production technology (amorphous silicon, CdTe and CIS). The focus is also on the development of next-generation solar cells, such as dye-sensitized and organic solar cells. While these promise to be a lot less expensive, they are still some years away from commercial production.

In CSP, parabolic trough plants are the main technology, using parabolic mirrors to reflect the radiation to linear receivers. There is also a growing interest in other CSP technologies...

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Technologies

Direct use of solar heat is the predominant form of solar energy use, like in heat­ing of houses. This energy use can be “passive” direct heating (through walls and windows), but also active, with the use of devices like solar boilers or storage systems. Most of this heat is used at the point of demand. See also Section B.8.

CSP is expected to become an important energy source in sunny, arid countries, for example, in the Mediterranean region in Europe and North Africa. In this technology solar radiation is used to heat water or other fluids to high temperatures (e. g., >100°C), where the heated steam or fluids can drive power generators. Concentration of solar radiation with mirrors is the common basic technology here.

PV conversion of sunlight still provides a tiny share of global ...

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Trends in Technologies

One promising conversion technology for power plants is the cocombustion of biomass in coal-fired power generation. Its benefits are self-evident, such as economies of scale, due to the huge amounts of biomass that can be used. Cogasification is another opportunity, with the same economies of scale bene­fits. In addition, stand-alone biomass plants are more and more becoming viable.

The introduction of CO2 emission standards for power plants (e. g., on the level of natural gas power plants) is believed to be a stimulating measure for cocombustion or cogasification, because of their ability to decrease CO2 emissions from coal power plants substantially.

As for biofuels, woody fuels and algae (“second-” or “third-”generation biomass) warrant a lot of attention...

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