Clean energies are forms of energy that do not pollute the air， the ground， or the sea， including solar power， wind power， wave power， tidal power， geothermal① power and so on.
Solar power describes a number of methods of harnessing② energy from the light of the Sun. It has been present in many traditional building methods for centuries， but has become of increasing interest in developed countries as the environmental costs and limited supply of other power sources such as fossil fuels are realized. It is already in widespread use where other supplies of power are absent such as in remote locations and in space.
As the Earth travels around the Sun， it receives approximately 1，400 W/m2 of energy as measured upon a surface kept normal (at a right angle) to the Sun (this number is referred to as the solar constant). Of the energy received， roughly 19% of it is absorbed by the atmosphere， while clouds reflect a further 35% of the total energy on average. The generally absorbing standard is 1，020 watts per square meter at sea level.
After passing through the Earth’s atmosphere， most of the sun’s energy is in the form of visible and ultraviolet light. Plants use solar energy to create chemical energy through photosynthesis③. We use this energy when we burn wood or fossil fuels or when we consume④ the plants as a source of food.
① geothermaladj. 地热的
② harnessv. 治理，利用，控制，驾驭
③ photosynthesisn. 光合作用
④ consumev. 消耗，花费，耗尽
什么是清洁能源
清洁能源就是指一种不会对空气、地面、海洋等造成污染的能源形态，包括太阳能、风能、波能、潮汐能和地热能等。
太阳能指的是用很多方法利用来自于太阳光的能量。许多世纪以来，很多传统的建筑方法里经常用到这些，已经逐渐为发展中国家所青睐，被作为保护环境的成本和替代其它有限能源，如矿石燃料的强有力资源。这种能源也它正被广泛运用于能源紧缺的地方，如边远山区和太空中。
地球围绕太阳运行时，会以每平方米1，400瓦的速度吸收能量，作为衡量从一个表面到达太阳时是否保持正常的状态运行（以直角来看），这个数字叫做太阳常数。在被接受到的能量中，大约有19%被大气层吸收，而云层会平均反射总共能量的35%多一点。海平面上每平方米1，200瓦特是大致上的吸收标准。
穿过地球大气层后，大部分太阳能出于可见的形式或为紫外线。植物利用太阳能制造化学能量来进行光合作用。我们燃烧木头或矿石燃料时，或者我们视植物作为食物来源时，也都会使用太阳能。
