GC: n

CT: The amount of electricity a hydropower plant produces depends on two factors:
  • How Far the Water Falls. The farther the water falls, the more power it has. Generally, the distance that the water falls depends on the size of the dam. The higher the dam, the farther the water falls and the more power it has. Scientists would say that the power of falling water is "directly proportional" to the distance it falls. In other words, water falling twice as far has twice as much energy.
  • Amount of Water Falling. More water falling through the turbine will produce more power. The amount of water available depends on the amount of water flowing down the river. Bigger rivers have more flowing water and can produce more energy. Power is also "directly proportional" to river flow. A river with twice the amount of flowing water as another river can produce twice as much energy.
S: http://www.wvic.com/content/how_hydropower_works.cfm(external link) (last access: 26 February 2015)

N: 1. c.1300, "ability; ability to act or do; strength, vigor, might," especially in battle; "efficacy; control, mastery, lordship, dominion; legal power or authority; authorization; military force, an army," from Anglo-French pouair, Old French povoir, noun use of the infinitive, "to be able," earlier podir (9c.), from Vulgar Latin potere, from Latin potis "powerful".
2. Let's say that there is a small dam in your area that is not used to produce electricity. Maybe the dam is used to provide water to irrigate farmlands or maybe it was built to make a lake for recreation. As we explained above, you need to know two things:
  • How far the water falls. From talking to the person who operates the dam, we learn that the dam is 10 feet high, so the water falls 10 feet.
  • Amount of water flowing in the river. We contact the United States Geological Survey, the agency in the U.S. that measures river flow, and learn that the average amount of water flowing in our river is 500 cubic feet per second.
Now all we need to do is a little mathematics. Engineers have found that we can calculate the power of a dam using the following formula:
Power = (Height of Dam) x (River Flow) x (Efficiency) / 11.8
Power The electric power in kilowatts (one kilowatt equals 1,000 watts).
Height of Dam The distance the water falls measured in feet.
River Flow The amount of water flowing in the river measured in cubic feet per second.
Efficiency How well the turbine and generator convert the power of falling water into electric power. For older, poorly maintained hydroplants this might be 60% (0.60) while for newer, well operated plants this might be as high as 90% (0.90).
11.8 Converts units of feet and seconds into kilowatts.
For the dam in our area, lets say we buy a turbine and generator with an efficiency of 80%.
Then the power for our dam will be:
Power = (10 feet) x (500 cubic feet per second) x (0.80) / 11.8 = 339 kilowatts
To get an idea what 339 kilowatts means, let's see how much electric energy we can make in a year.
Since electric energy is normally measured in kilowatt-hours, we multiply the power from our dam by the number of hours in a year.
3. Collocations:
- force:
  • Adj.: great | destructive, terrible. The destructive power of a hurricane.
- energy:
  • Adj.: full. The plane was still climbing at full power. | reduced. The transmitter is operating on reduced power. | electric, electrical, hydroelectric, nuclear, solar, steam, tidal, water, wind.
  • Verb + power: generate, produce They use these streams to generate power for the mill. | provide (sb/sth with), supply (sb/sth with). This wheel provides the power to the cutting machine. | use | harness | turn on | cut off, turn off.
  • Power + verb: drive sth. Wind power is used to drive the machinery.
  • Power + noun: cable, line, point, supply | tool. DIY grew in popularity with the advent of power tools. | plant, station | worker | cut, failure.
  • Prep.: ~ for. Supplying power for the grinding process.
  • Phrases: A source of power.
S: 1. OED - http://www.etymonline.com/index.php?allowed_in_frame=0&search=power&searchmode=none(external link) (last access: 26 February 2015). 2. http://www.wvic.com/content/how_hydropower_works.cfm(external link) (last access: 26 February 2015). 3. http://oxforddictionary.so8848.com/search1?word=power(external link) (last access: 20 May 2015).


CR: energy, hydroelectric power, small hydropower plant.


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