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风能

维基百科,自由的百科全书

这是本页的一个历史版本,由118.168.39.111留言2008年4月30日 (三) 02:59 生態顧慮编辑。这可能和当前版本存在着巨大的差异。

多座风力发电机组成风力电厂

风能资源风力做功而提供给人类的一种可利用的能量。风具有的动能称风能。风速越高,动能越大。人们可以用风车把风的动能转化为旋转的动作去推动发电机,以产生电力。方法是透过传动轴,将转子(由以空气动力推动的扇叶组成)的旋转动力传送至发电机。到2008年为止,全世界以风力产生的电力约有 94.1 百万千瓦,供应的电力已超过全世界用量的1%。风能虽然对大多数国家而言还不是主要的能源,但在1999年2005年之间已经成长了四倍以上。

多数现代风力产生以电的形式由转换涡轮刀片的自转成电流通过一台电子发电器。在风车(更旧的技术里) 风能量使用转动机械机械完成物理工作, 像击碎五谷或抽水。

风力被使用在大规模风农场为全国电子栅格并且在小各自的涡轮为提供电在被隔绝的地点。

风能量是丰富, 无尽的, 广泛分布, 干净, 和缓和温室效应。 我们把地球表面一定范围内。经过长期测量,调查与统计得出的平均风能密度的概况称该范围内能利用的依据,通常以能密度线标示在地图上。

人类利用风能的历史可以追溯到西元前,但数千年来,风能技术发展缓慢,没有引起人们足够的重视。但自1973年 世界石油危机以来,在常规能源告急和全球生态环境恶化的双重压力下,风能作为新能源的一部分才重新有了长足的发展。风能作为一种无污染可再生的新能源有著巨大的发展潜力,特别是对沿海岛屿,交通不便的边远山区,地广人稀的草原牧场,以及远离电网和近期内电网还难以达到的农村、边疆,作为解决生产和生活能源的一种可靠途径,有著十分重要的意义。即使在发达国家,风能作为一种高效清洁的新能源也日益受到重视,比如:美国能源部就曾经调查过,单是德克萨斯州南达科他州两州的风能密度就足以供应全美国的用电量。

德国一处风力发电机。从旁边的树可知其约略的大小。

经济性

近年, 大致上来说,利用风来产生电力所需的成本已经降低许多, 即使不含其他外在的成本,在许多适当地点使用风力发电的成本已低于燃油的内然机发电了。[1]自2004 年起,风力发电更成为在所有新式能源中已是最便宜的了。风力发电在2002 年时约25%,现在则是38%的比例快速成长。2003年美国的风力发电成长就超过了所有发电机的平均成长率。在2005 年风力能源的成本已降到1990 年代时的五分之一,而且随著大瓦数发电机的使用,下降趋势还会持续。.[2][3] 风能发电正成长,幅度高逹 38%,[4] 超越2002年时的 25%。在美国,2003年以年增率来看,风力是各种发电方式之中成长最快的。[5] 在2005年,风力发电的成本己降到1990年代后期的五分一,而随著大型百万瓦等级的风力转子进入量产阶段,估计成本还会持续下降。[6]

风的能量

估计地球吸收的太阳能有1%到3%转化为风能,总量相当于地球上所有植物通过光合作用吸收太阳能转化为化学能的50到100倍。 上了高空就会发现风的能量,那儿有时速超过160公里 (100 英哩160 km/h 100 mph)的强风。这些风的能量最后因和地表及大气间的摩擦力而以各种热能方式释放。

风的成因:因太阳照射极地赤道的不均匀使得地表的不受热;地表温的速度较海面快;大气中同温层如同天花板的效应加速了气体的对流;季节/的变化;科氏效应;月亮的反射比率,形成了风。

风能可以通过风车来提取。当风吹动风轮时,风力带动风轮绕轴旋转,使得风能转化为机械能。而风能转化量直接与空气密度、风轮扫过的面积和风速的平方成正比。The mass flow of air that travels through the swept area of a wind turbine varies with the wind speed and air density. As an example, on a cool 15°C (59°F) day at sea level, air density is about 1.22 kilograms per cubic metre (it gets less dense with higher humidity). An 8 m/s breeze blowing through a 100 meter diameter rotor would move about 1,000,000,000 kilograms of air per second through the swept area.

The kinetic energy of a given mass varies with the square of its velocity. Because the mass flow increases linearly with the wind speed, the wind energy available to a wind turbine increases as the cube of the wind speed. The power of the example breeze above through the example rotor would be about 2.5 megawatts.

As the wind turbine extracts energy , the air is slowed down, which causes it to spread out and diverts it around the wind turbine to some extent. A German physicist, Albert Betz, determined in 1919 that a wind turbine can extract at most 59% of the energy that would otherwise flow through the turbine's cross section. The Betz limit applies regardless of the design of the turbine. More recent work by a theoretical limit of about 30% for propeller-type turbines.[7] Actual efficiencies range from 10% to 20% for propeller-type turbines, and are as high as 35% for three-dimensional vertical-axis turbines like Darrieus or Gorlov turbines.

Distribution of wind speed (red) and energy (blue) for all of 2002 at the Lee Ranch facility in Colorado. The histogram shows measured data, while the curve is the Rayleigh model distribution for the same average wind speed. Energy is the Betz limit through a 100 meter diameter circle facing directly into the wind. Total energy for the year through that circle was 15gigawatt-hours.

Windiness varies, and an average value for a given location does not alone indicate the amount of energy a wind turbine could produce there. To assess the climatology of wind speeds at a particular location, a probability distribution function is often fit to the observed data. Different locations will have different wind speed distributions. The distribution model most frequently used to model wind speed climatology is a two-parameter Weibull distribution because it is able to conform to a wide variety of distribution shapes, from gaussian to exponential. The Rayleigh model, an example of which is plotted to the right against an actual measured dataset, is a specific form of the Weibull function in which the shape parameter equals 2, and very closely mirrors the actual distribution of hourly wind speeds at many locations.

Because so much power is generated by higher windspeed, much of the average power available to a windmill comes in short bursts. The 2002 Lee Ranch sample is telling: half of the energy available arrived in just 15% of the operating time. The consequence of this is that wind energy is not dispatchable as for fuel-fired power plants; additional output cannot be supplied in response to load demand.

Since wind speed is not constant, a wind generator's annual energy production is never as much as its nameplate rating multiplied by the total hours in a year. The ratio of actual productivity in a year to this theoretical maximum is called the capacity factor. A well-sited wind generator will have a capacity factor of as much as 35%. When comparing the size of wind turbine plants to fueled power plants, it is important to note that 1000 kW of wind-turbine potential power would be expected to produce as much energy in a year as approximately 350 kW. Though the short-term output of a wind-plant is not completely predictable, the annual output of energy tends to vary only a few percent points between years.

当储藏,如此的关于〔〔用唧筒抽水-储藏水力电气|用唧筒抽水水力电气的储藏〕〕, 或其他形式的世代被用来 " 塑造 " 风力量 (藉著保证持续的递送可信度),商业的递送代表大约 25% 的费用增加,屈从的有活力的商业表现。

风力的分级

风进入风力量密度的七个班级之内在美国区域中映射,这在区域中提供风力量资源的品质指示。

每个班级是多种的力量密度,所以评价当做班级 4 的一个区域,举例来说,将会在地面上面的 10 m 有来自 200 到 250 W/m 的平均的力量密度。 通常,风力量的经济发展为在被评价班级 3 的区域中发生或比较高的。

风能应用

风能优点

  • 风能为干净的能量来源。
  • 风能设施日趋进步,大量生产降低成本,成本已低于内燃机。
  • 风能设施多为立体化设施,可保护陆地和生态。

风能缺点

  • 风力发电在生态上的问题是可能干扰鸟类,目前的解决方案是离岸发电,离岸发电也可以增加效率。
  • 在一些地区、风力发电的经济性不足,例如台湾在电力需求较高的夏季及白日、是风力较小的时间。

注释

  1. ^ Mitchell, Chris. Price of Wind-Generated Electricity Plummeting. March 23, 2006 [2006-04-21]. 
  2. ^ Chakrabarty, Gargi. Powering up. Rocky Mountain News. March 27, 2004 [2004-04-05].  (Internet Archive version)
  3. ^ E-Letter responses to: The Real Cost of Wind Energy. Science. [2006-04-21]. 
  4. ^ Alternate Power: A Change Is In The Wind. Business Week. July 4, 2005 [2006-04-21]. 
  5. ^ Renewable Energy Trends 2003 (PDF). DOE/EIA. July 2004 [2006-04-21]. 
  6. ^ Helming, Troy. Uncle Sam's New Year's Resolution. February 2, 2004 [2006-04-21].  已忽略未知参数|publsiher=(建议使用|publisher=) (帮助)
  7. ^ Gorban, Alexander N. Limits of the Turbine Efficiency for Free Fluid Flow (PDF). Journal of Energy Resources Technology. 2001, 123: 311–317 [2006-04-21].  已忽略未知参数|month=(建议使用|date=) (帮助)

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