And at the same time, there are two main deficiencies in this renewable energy. The first one is dispersion, which is caused by the low solar energy flux density.
Near the tropic of cancer, the mean solar energy flux density is 200W per day, but only half of that in winter and about 1/5 of that in cloudy day. Therefore, in the utilization of solar energy, it is necessary to provide a set of collection and
conversion equipment with large area to get enough switching power, but the cost is high. Another disadvantage
of solar energy is discontinuity and instability, and it is caused by the natural conditions, such as day and night,
season, geographic latitude and altitude, and it is influenced by the random factors, such as the weather. So the
discontinuous and unstable solar irradiance will increase the difficulty to the large-scale application of solar energy
[6,8,9].