A Historical Review of Solar Energy Utilization
According to records, humans have been utilizing solar energy for over 3000 years. However, the use of solar energy as a source of power and energy has only been around for about 300 years. The recognition of solar energy as an "urgent supplementary energy source" and a "foundation for future energy structures" is a more recent development. Since the 1970s, advancements in solar technology have been rapid, leading to increasingly innovative applications of solar energy.
The modern history of solar energy utilization can be traced back to 1615 when French engineer Solomon de Caux invented the world's first solar-powered engine. This invention was a machine that used solar energy to heat air, causing it to expand and perform work to pump water. Between 1615 and 1900, several solar-powered devices and other solar apparatuses were developed worldwide. These engines mostly employed concentration methods to collect sunlight, had relatively low power output, primarily used steam as their working fluid, were expensive, and had limited practical value, often being personal research projects by solar enthusiasts.
During the 20th century, the development of solar technology can be roughly divided into seven stages, which are outlined below:
**First Stage (1900-1920):**
In this stage, the focus of global solar energy research remained on solar-powered engines, but with more diverse concentration techniques. Flat plate collectors and low-boiling-point working fluids began to be adopted, leading to larger-scale devices. The largest output reached up to 73.64 kW, with more defined practical purposes, though costs were still high. Notable developments included: In 1901, a solar-powered water pumping system was built in California using a truncated cone concentrator with a power output of 7.36 kW; between 1902 and 1908, five dual-cycle solar engines using flat plate collectors and low-boiling-point working fluids were constructed in the U.S.; and in 1913, a solar-powered water pump composed of five parabolic trough mirrors, each 62.5 meters long and 4 meters wide, with a total light collection area of 1250 square meters, was built south of Cairo, Egypt.
**Second Stage (1920-1945):**
For these two decades, solar energy research entered a lull period with significantly fewer researchers and projects. This decline was mainly due to the extensive exploitation of fossil fuels and the outbreak of World War II (1935-1945), during which solar energy could not meet the urgent energy demands, leading to its gradual neglect.
**Third Stage (1945-1965):**
In the 20 years following the end of World War II, some forward-thinking individuals noticed the rapid depletion of oil and natural gas resources, urging people to pay attention to this issue. This gradually revived and promoted solar energy research, leading to the establishment of academic organizations, conferences, and exhibitions, reigniting the solar energy research movement. Significant progress was made during this stage, including: In 1955, Israeli scientist Taber proposed the basic theory of selective coatings at the First International Conference on Solar Thermal Science, developing practical selective coatings like black nickel, paving the way for efficient collectors; in 1954, Bell Labs in the U.S. developed a practical silicon solar cell, laying the foundation for large-scale photovoltaic applications. Other important achievements included: In 1952, the French National Research Center built a 50 kW solar furnace in the eastern Pyrenees; in 1960, the world's first ammonia-water absorption cooling system using flat plate collectors with a refrigeration capacity of 5 tons was built in Florida, USA; in 1961, a Stirling engine with a quartz window was developed. During this stage, significant breakthroughs were achieved in fundamental theories and materials, such as selective solar coatings and silicon solar cells. Flat plate collectors saw substantial development and technological maturity. Advances were made in solar absorption cooling, experimental solar houses were constructed, and initial research began on challenging technologies like Stirling engines and tower-based solar thermal power generation.
**Fourth Stage (1965-1973):**
During this period, solar energy research stagnated due to immature utilization technology, high investment requirements, and unsatisfactory results, making it difficult to compete with conventional energy sources. Consequently, it received little attention or support from the public, businesses, or governments.
**Fifth Stage (1973-1980):**
Since oil became the dominant player in the global energy structure, it became a key factor affecting economies and determining the survival, development, and prosperity or decline of nations. In October 1973, the Middle East war broke out, and OPEC implemented measures like production cuts and price hikes to support the struggle of the Middle Eastern people and protect their interests. This resulted in severe economic blows to countries heavily reliant on cheap oil imports from the Middle East.
As a result, some Western voices cried out that the world faced an "energy crisis" (or "oil crisis"). This "crisis" objectively made people realize that the existing energy structure must be fundamentally changed and the transition to future energy structures accelerated. Many countries, especially industrialized ones, renewed their support for the development of solar energy and other renewable energy technologies, sparking another wave of enthusiasm for solar energy development globally. In 1973, the U.S. established a government-level sunshine power generation plan, significantly increasing solar research funding and establishing a solar development bank to promote the commercialization of solar products. Japan, in 1974, announced its government-developed "Sunshine Plan," which included research and development projects such as solar houses, industrial solar systems, solar thermal power generation, solar cell production systems, decentralized and large-scale photovoltaic systems. To implement this plan, the Japanese government invested substantial human, material, and financial resources. The solar energy development craze that emerged in the early 1970s also greatly influenced China. Forward-thinking scientists actively engaged in solar energy endeavors, offering suggestions to relevant government departments, publishing books and journals, and introducing international developments in solar energy utilization. They promoted solar cookers in rural areas and researched solar water heaters in urban areas, while terrestrial applications of space-grade solar cells began... In 1975, the "First National Solar Energy Utilization Experience Exchange Conference" was held in Anyang, Henan Province, further promoting the development of China's solar energy industry. After this conference, solar energy research and promotion were incorporated into the Chinese government's plans, receiving dedicated funding and material support. Universities and research institutes began setting up solar energy project teams and laboratories, and some places started building solar energy research institutes. At that time, China also experienced a solar energy development boom.
During this period, solar energy utilization underwent unprecedented growth, characterized by: Countries strengthening the planning of solar energy research, with many nations formulating short-term and long-term sunshine plans. Governments becoming more involved in solar energy development with increased support. Active international cooperation, with some third-world countries beginning to participate actively in solar energy development. Expanding research fields and deepening research efforts, yielding significant results such as CPC, vacuum collector tubes, amorphous silicon solar cells, water splitting for hydrogen production, and solar thermal power generation. Most national solar energy development plans set overly ambitious and hasty goals, underestimating the difficulties in implementation, hoping to replace fossil fuels and achieve large-scale solar energy utilization within a short time. For example, the U.S. planned to build a small solar demonstration satellite power station by 1985 and a 5 million kW space-based solar power station by 1995. In fact, this plan was later adjusted, and the space-based solar power station has yet to be launched. Solar water heaters, solar electricity, and other products began to be commercialized, initially establishing a solar energy industry, albeit on a small scale with unsatisfactory economic benefits.
**Sixth Stage (1980-1992):**
The solar energy development boom that began in the 1970s started to wane shortly after entering the 1980s, gradually falling into a low point. Many countries drastically cut solar energy research funding, most notably the U.S. The main reasons for this phenomenon were: A sharp drop in world oil prices, while solar energy product prices remained high, lacking competitiveness; no major breakthroughs in solar technology, failing to achieve goals of improving efficiency and reducing costs, thus shaking some people's confidence in solar energy development; rapid nuclear power development inhibiting solar energy progress to some extent. Influenced by the downturn in international solar energy development in the 1980s, China's solar energy research also suffered to some extent. Some even suggested that solar energy utilization involves large investments, poor effects, difficult storage, and extensive land use, viewing it as a future energy source and advocating the introduction of foreign technology once they succeed. Although this view was held by a minority, it was quite harmful and had adverse effects on the development of China's solar energy industry. Despite the significant reduction in solar energy development funding, research did not stop entirely; some projects even made considerable progress, prompting people to critically review previous plans and goals, adjust research priorities, and strive for greater results with less investment.
**Seventh Stage (1992-Present):**
The extensive burning of fossil fuels has caused global environmental pollution and ecological destruction, threatening human survival and development. Against this backdrop, the United Nations convened the "World Environment and Development Conference" in Brazil in 1992. The conference adopted several important documents, including the Rio Declaration on Environment and Development, Agenda 21, and the United Nations Framework Convention on Climate Change, integrating environment and development into a unified framework and establishing a model of sustainable development. After this conference, countries worldwide strengthened the development of clean energy technologies, linking the use of solar energy with environmental protection, helping solar energy utilization emerge from its low point and gradually gain strength. Following the World Environment and Development Conference, the Chinese government placed great emphasis on the environment and development, proposing ten countermeasures and measures, clearly stating the need to "develop and promote solar energy, wind energy, geothermal energy, tidal energy, biomass energy, and other clean energies according to local conditions." It formulated the "China Agenda 21," further clarifying key solar energy development projects. In 1995, the National Planning Commission, the National Science and Technology Commission, and the National Economic and Trade Commission formulated the "Outline for the Development of New and Renewable Energy" (1996-2010), explicitly outlining China's development goals, tasks, and corresponding strategies and measures for new and renewable energy from 1996 to 2010. The formulation and implementation of these documents played a crucial role in further promoting China's solar energy industry.
In 1996, the United Nations convened the "World Solar Summit" in Zimbabwe. Following the summit, the "Harare Declaration on Solar Energy and Sustainable Development" was issued, discussing important documents such as the "World Solar Ten-Year Action Plan" (1996-2005), the "International Solar Energy Convention," and the "World Solar Strategy Plan." This conference further demonstrated the UN and various countries' firm determination to develop solar energy, calling for global joint action to widely utilize solar energy. After 1992, the utilization of solar water heaters in Shandong, China, entered another development phase, characterized by: the close integration of solar energy utilization with global sustainable development and environmental protection, global joint action to achieve the world's solar energy development strategy; clear solar energy development goals, prominent priorities, effective measures, overcoming past issues of fluctuation and excessive haste, ensuring the long-term development of the solar energy industry; while intensifying solar energy research and development, emphasizing the conversion of scientific and technological achievements into productive forces, developing the solar energy industry, accelerating commercialization, expanding the scope and scale of solar energy utilization, and gradually improving economic benefits; unprecedentedly active international cooperation in the solar energy field, expanded scale, and noticeable results.
From the above review, it is evident that the development path of solar energy in the last 100 years has not been smooth. Generally, after each peak period, there would be a trough period, with about 45 years spent in low periods. The development process of solar energy utilization differs entirely from coal, oil, and nuclear energy. People's understanding varies greatly, with many repetitions and a long development time. On one hand, this indicates that solar energy development is challenging, making large-scale utilization difficult in a short time; on the other hand, it shows that solar energy utilization is also influenced by fossil fuel supply, political, and war factors, resulting in a tortuous development path. Nevertheless, overall, the scientific and technological progress in solar energy in the 20th century surpasses any previous era.
By: http://www.oketyn.com/