Прочтите и переведите текст; выпишите ключевые слова, относящиеся к теме

1. Over the past three decades the feasibility of using ocean tides to generate electric power has been investigate d at many sites.

2. By far the largest tidal plant in service is Rance (France), with a capacity of 240 MW and an annual output exceed ing 500 GWh. Others include the 20 MW Annapolis plant in Canada, several small units in China with total capacity of about 5 MW and a 400 kW experimental unit near Murmansk in Russia.

3. Most designs, existing or proposed, have opted for a single tidal basin to create hydraulic heads and propeller turbines to extract energy therefrom. Linked and paired basins have also been considered. Innovative approache s have included extract ion of energy directly from tide races using a variety of prime movers.

4. The main obstacle to development is economic. Capital costs are high in relation to output: a consequence of the low and variable heads available at even the best sites. Heads available at the turbine vary throughout each tidal cycle, averaging less than 70% of the maximum. As a result, installed capacity is underutilized, typical capacity factors lending to fall in the range 0.23 to 0.37. Low heads imply that civil as well as mechanical engineering components must be large in comparison to output. For such reasons, tidal plants are likely to be practicable

only where energy is concentrated by large tides and where physical features permit construction of tidal basins at low cost.

5. Significant capital-cost reductions through improved design and construction techniques have been achieved over the past three decades. In China a somewhat different approach has been taken: tidal plants have been built as part of broader schemes of resource utilization – typically land reclamation or aquaculture.

6. In a world increasingly sensitive to environmental factors, tidal plants must avoid unacceptable impacts. Tidal power is non-polluting and in this respect superior to thermal generation. Beyond that, it is difficult to generalize. No serious long-term impacts are known to have been caused by the Rance tidal power plant, but large developments in the Bay of Fundy would, it has been predict ed, perturb the tidal regime, with impacts on New England shorelines.

7. In recent years, commercial acceptance of combined-cycle generation based on combustion turbines has reduced the potential economic and environmental costs of meeting future capacity and energy demands through thermal plants wherever natural gas is available at competitive prices. This has tended to increase the economic bias against tidal power.

8. Another development with adverse implications for tidal power is the trend in many countries to adopt market pricing of electric energy and dispense with regulatory pricing. This in almost every case entails competition in the generation function. Under such conditions, competitors will be under strong compulsion to choose plant types having the shortest construction times and the lowest unit capital costs.

9. Such factors render construction of new tidal generation capacity unlikely during the near future, unless strong incentives such as emission caps or carbon taxes are imposed.

Примечания

1. to investigate – исследовать

2. to exceed – превышать

3. innovative approach – новаторский подход

4. to extract – извлекать

5. to imply – подразумевать

6. to predict – предсказывать

7. to perturb – нарушать

8. to dispense – распределять