Tuesday, June 11, 2013

Wind and sun

Wind and sun:

Renewable energy sources
5.39 Renewable energy can be utilized directly on board ships (by using solar, wave and wind energy) or energy can be generated on-land and converted and stored in an energy carrier to produce energy, such as electricity from batteries.

Wind power, onboard use
5.40 Wind power can be harnessed in many ways and used as the motive power for ships, for example by:
.1 Conventional sails;
.2 Solid wing sails;
.3 Kites; and
.4 Flettner-type rotors.
5.41 These systems have varying properties. Wind conditions vary depending on location; hence, certain regions have greater potential for wind power use and as routes than others. This study showed that the potential for wind energy was better in the North Atlantic and North Pacific than in the South Pacific. Fuel reductions were slightly higher at faster speeds.
However, in terms of percentages, the fuel savings were higher at lower speeds, due to the reduced total demand for propulsion power. In percentage terms, savings were typically about 5% at 15 knots, increasing to about 20% at 10 knots.
5.42 Present-day exposure to these technologies on board large vessels is limited, and modelling data are, therefore, hard to confirm. However, wind-assisted energy appears to have good prospects for saving fuel in the short and long run.
5.4 Solar and wind energy could also add to reduced CO2 emissions; but as a auxiliary source of energy rather than a single source. Propulsion using nuclear energy has been effectively operated in navy ships.

Solar power, onboard use
5.43 Present solar-cell technology is enough to address a mere portion of the auxiliary energy needs of a tanker, even though the whole deck space were installed with photovoltaic cells.

Obviously, during certain periods and in certain places, solar energy will be more than sufficient and the auxiliary power requirements could be supplied. Furthermore, since solar energy is not continuously available (e.g., at night), backup supply would be required. Hence, solar power seems to be of interest generally as a supplementary source of energy. With available technology, only a small percentage of savings on the total energy requirements can be realized, even with wide use of solar energy.

Moreover, currents price levels and efficiency put solar energy within the bottom end of the cost-effectiveness list [9].

Wave power, onboard use

5.44 This involves concepts for harnessing wave energy and/or vessel motion. For instance, gyro-based internal systems and wavefoils for external systems, stern flaps or relative motion between multiple hulled-vessels (such as trimarans) can augment a vessel’s power needs. These systems are highly complex and technical, not highly energy-efficient and are not considered potential sources of auxiliary energy.

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