Along with the increasing human demands for energy during the process of pursuing better lives， the excessive consumption of natural resources has led to depleted energy and irreversible impacts such as environmental pollution， extreme natural disaster， and abnormal climate. That’s why experts and scholars have been constantly calling for energy saving and carbon reduction in order to slow down the global warming on the planet of Earth. Along with the technology advancement， the conditions for development and utilization of solar energy have been improved， thus leading to great potential for future development of solar energy. Countries with matured technologies and abundant solar energy have already listed the development and utilization of solar energy on their national agenda， and some have achieved a certain degree of success.
The key feature of solar energy is that it is an unlimited source of energy with nothing comparable on Earth. Solar energy is the radiation energy released by the high temperature nuclear fusion reaction inside the sun. The solar radiation energy reaching the Earth every year is roughly equivalent to 130 trillion tons of standard coal， which is 10，000 times the sum of annual energy consumption by the entire world.
Nowadays solar modules are usually installed on the building， which are known as building integrated photovoltaics (BIPV) capable of generating electricity from the sunlight. According to the Renewable Energy Development Act， the owner of a solar energy system can sign a power purchase agreement (PPA) with Taiwan Power Company which is valid for 20 years. In addition to making a vacant space profitable， the heat insulation feature of this system can also effectively reduce the temperature inside the building and thus reducing the energy consumption by home appliance. It can achieve both the energy saving carbon reduction and the secondary use of vacant rooftop space.