During the 100 years of the 20th century, the history of solar technology development can be roughly divided into 7 stages. The last two stages are introduced as follows.

The sixth stage (1980-1992). The development and utilization of solar energy boom in the 1970s began to ebb shortly after entering the 1980s and gradually entered a trough. Many countries in the world have drastically reduced solar energy research funding one after another, of which the United States is the most prominent. The main reason for this phenomenon is that the world oil price has dropped sharply, while the price of solar energy products remains high and lacks competitiveness; There is no major breakthrough in solar energy technology, and the goals of improving efficiency and reducing costs have not been achieved, which has shaken some people’s confidence in the development and utilization of solar energy; nuclear power has developed rapidly, which has played a certain role in restraining the development of solar energy. Affected by the decline of international solar energy in the 1980s, China’s solar energy research work has also been weakened to a certain extent. Some people even pointed out that: solar energy utilization has large investment, poor effect, difficult energy storage, and large area. They believe that solar energy is the future energy and advocate foreign research. After success, China will introduce technology again. Although there are few people holding this view, it is very harmful and has a negative impact on the development of China’s solar energy industry. At this stage, although the solar energy development and research funding has been drastically reduced, the research work has not been interrupted. Some projects are progressing rapidly, and they have prompted people to carefully review the previous plans and goals set, adjust the focus of research work, and strive to achieve greater results with less investment.

The seventh stage (1992-present). Due to the massive burning of fossil energy, it has caused global environmental pollution and ecological destruction, posing a threat to the survival and development of mankind. After 1992, the world’s solar energy utilization has entered a period of development. Its characteristics are: The use of solar energy is closely integrated with the world’s sustainable development and environmental protection, and the world is acting together to achieve the world’s solar energy development strategy; The development goals of solar energy are clear, the key points are prominent, and the measures are effective, which are conducive to overcoming the shortcomings of sudden cold and heat, overheating and overheating in the past, and ensuring the long-term development of the solar energy industry; While increasing the research and development of solar energy, pay attention to the transformation of scientific and technological achievements into productivity, develop the solar energy industry, accelerate the commercialization process, expand the field and scale of solar energy utilization, and gradually improve economic benefits; International cooperation in the field of solar energy is unprecedentedly active, scaled up, and effective.

Through the review of the above seven stages, it can be seen that in the 100 years of this century, the development of solar energy has not been smooth, and generally there will be a low tide period after each high tide period. The development process of solar energy utilization is completely different from that of coal, petroleum, and nuclear energy. People’s understanding of it is very different, repeated, and the development time is long. On the one hand, it shows that solar energy development is difficult and it is difficult to realize large-scale utilization in a short time. On the other hand, it also shows that solar energy utilization is also affected by factors such as mineral energy supply, politics and war, and the development path is relatively tortuous. Nevertheless, from an overall point of view, the technological progress of solar energy in the 20th century is still greater than that of any previous century.