The so-called energy, refers to the ability to directly or through conversion to provide energy natural resources. Recently can provide human use of energy, such as firewood, coal, petroleum, natural gas,
Hydropower, solar energy, wind energy, geothermal energy, wave energy, tidal energy, ocean energy deposition, nuclear power.
In the above all kinds of energy, the energy of the sun, its annual projected to the surface of the earth's energy is consumed every year tens of thousands of times the energy, but it is non-polluting, renewable sources of energy. Solar energy enters and leaves the ground energy flow as shown in Figure L - 2 - 1.

As mentioned before, the energy types is very large, in order to facilitate the use, we can put the ammonium energy on earth the source of every hue classified as Figure 1 - 2 - 2

Usually, we take ready-made form exists in the nature of energy known as the primary energy, the need to rely on other sources of energy to manufacture or production of energy known as the two energy. Once the energy can also according to regeneration and further classification. The so-called renewable energy, is not with the use of its own transformation or human the dwindling energy. Non renewable energy refers to those and less energy. With the development of society, its classification as shown in Figure 1 - 2 - 3.

In short, the energy has a variety of classification methods, but Baconian rise, basically have the following kinds:
(1) according to the source can be divided into: ① ② from the sun, from the earth itself
Interaction of the earth and the other planets from.
(2) according to the origin can be divided into: primary energy; the two energy.
(3) by nature can be divided into: the fuel energy; ② non fuel energy.
(4) by the use of state can be divided into: conventional energy; new energy.
(5) according to whether the pollution can be divided into the environment; the clean energy; the non clean energy.