Belonging the qucik development of teachnology, people use more and more energy these days. No matter transportation, home or workplace, the use of energy is needed. For example, when we take the tram, the lighting, the air cnditioner even the tram itself, both need to use energry. To maintain our life quality, we need to maintain the engry supply. And now, more and more people are discussing using renewable engry rather than tranditional unrenewable ergry, which is prodcued by oil.