The Evolution of Agricultural Greenhouses: From Primitive Hotbeds to Photovoltaic Greenhouses

    Today, we can enjoy fresh and delicious out-of-season fruits and vegetables even in the cold winter, and greenhouse agriculture certainly deserves much of the credit. Many people assume that greenhouses must be a product of modern scientific progress. However, as early as more than 2000 years ago, our great ancestors were already able to use certain protective structures (the prototype of greenhouses) to cultivate a variety of vegetables. With the passage of time, agricultural greenhouses have long since transformed magnificently from primitive hotbeds into photovoltaic greenhouses, opening up a broader path for green agricultural growth and distinctive development. Today, let us take a “journey through time” to experience the self-evolution of greenhouses.

    Greenhouses Through a Millennium: East and West Take Turns on Stage

    China is one of the earliest countries in the world to originate greenhouse cultivation, with a very long history of using protective structures to grow vegetables. According to the Biographies of Upright Officials in the Book of Han, “In the Imperial Kitchen Garden, winter scallions, chives, and mushrooms were grown, covered with roofed structures, with warm fires burning day and night, waiting for the warm air to bring them to life; Xin Chen considered these all to be out-of-season items.” This shows that as early as the Western Han Dynasty, the ancients had already begun to build simple structures and use fire to heat the interiors of buildings, cultivating out-of-season crops for people to enjoy.

    In 3rd-century Europe, the ancient Roman emperor Tiberius, who loved to eat snake gourd (American cucumber, which closely resembles a cucumber) all year round - a plant native to the tropics that thrives in hot, humid conditions - had it planted in wooden boxes filled with soil after its normal growing season ended, and placed the boxes in a room. As glass had not yet been invented, he fitted the room with thin sheets of mica, which allowed sunlight to enter and let the snake gourd absorb the sun's light and heat while also maintaining the room's temperature. From today's perspective, the principles behind growing snake gourd at that time were essentially the same as those of modern greenhouses.

    Early greenhouses often faced the challenge of heat retention, and the history of greenhouse technological progress is also a history of research and exploration into greenhouse heating equipment. The ancient Romans built pipes under greenhouse floors to convey hot air, the French once burned dung to heat greenhouses, and the English used charcoal and hot water in the 17th century to maintain indoor temperatures. Similarly, during the Ming and Qing dynasties in China, there were earthen-wall greenhouses with paper windows and fire heating, which could be heated by burning fires and were generally also banked with horse dung. Earthen walls were erected on the east, north, and west sides to block the wind, and inclined oiled paper windows were installed on the south side, making it possible both to heat with fire and to make full use of solar energy - the most advanced greenhouse of its time.

    By contrast, Europe began using the heat of solar radiation to raise greenhouse temperatures only after 1851, when Britain abolished William III's window tax and glass came into large-scale use. Glass greenhouses were prized for their energy efficiency, environmental friendliness, and ease of ventilation and moisture removal. With advances in production technology, greenhouse construction entered a true golden age, leaving many models for later generations. China's modern greenhouses, however, did not begin until the 1950s, when large ridge-style glass greenhouses were built in North China. The development histories of Chinese and Western greenhouses are histories of taking turns on stage, gradually forming today's modern distinctive agricultural system represented by specialization, intensification, and large-scale operation over a millennium of development.
 

    A Clever Technological Makeover: Photovoltaic Greenhouses Open a New Chapter

    In the course of modern agricultural development, the share of scientific and technological investment in total agricultural investment has grown ever larger, and the results brought by technological development to agricultural industry growth have become increasingly remarkable. Traditional greenhouses have continuously adopted changes brought by various technological innovations during their development, pushing agricultural industry development to one historical peak after another - and photovoltaic greenhouses are yet another successful “makeover” in greenhouse development.

    Photovoltaic agricultural greenhouses are greenhouses that integrate solar photovoltaic power generation, intelligent temperature control systems, and modern high-tech cultivation. The greenhouse is covered with solar photovoltaic modules, which, while ensuring solar photovoltaic power generation, can also meet the lighting needs of all the crops in the greenhouse. This not only saves arable land, alleviates the human-land conflict, and produces clean energy, but can also support the greenhouse's irrigation system, supplement light for plants, meet the winter heating needs of greenhouses, provide greenhouse temperature, and promote rapid crop growth.

    In the practice of combining photovoltaics with agriculture, photovoltaic agricultural greenhouses use solar thin films as a new covering material and adopt multiple modes of construction tailored to local conditions, maximizing the assurance of the greenhouse's various functions. Among them, Hanergy, the world's leading thin-film solar manufacturer, has already taken the lead in photovoltaic agricultural greenhouse construction through continuous innovation in its own technology. Laminated safety glass no thicker than 5mm ensures that light transmittance does not decay for 20 years, and can also guarantee good power generation efficiency under high-temperature and high-humidity conditions. At the same time, in terms of light classification, Hanergy truly achieves “taking what I can use.” Its uniform red light and infrared transmission capacity ensures the growth needs of most cash crops and avoids wavy growth in crops; the compound eyes of most insects can distinguish colors and are relatively sensitive to short-wavelength blue, green, and yellow light, while they cannot see beyond red light. Therefore, using thin-film solar glass that blocks the violet-to-yellow light range can achieve insect prevention through ecological means, reducing pest worries. At the same time, it effectively blocks ultraviolet rays, reducing the occurrence of plant diseases. The thin film's promotion of benefits and avoidance of harms makes greenhouses more practical and adds new safeguards for agricultural development.
 

    The photovoltaic agricultural greenhouses covered with Hanergy thin films have also done a great deal when it comes to “saving.” First, installing the thin film can help shade the greenhouse in summer, thereby reducing water evaporation and cutting irrigation water use, thus saving users an expense. Second, while serving as a greenhouse covering material, the thin film can also generate electricity; the dual safeguard of cultivation and power generation not only saves bit by bit but also yields benefits over the long term. Third, in alleviating land shortages, the thin film makes full use of the space above agricultural land without occupying land resources separately, achieving the positive development of intensive agriculture and creating additional benefits. With all three working together, saving is a real gain - saving is a real gain. Technology has helped greenhouses achieve a “makeover” and has also created a profit model for new ecological agriculture. Hanergy is working through its own efforts to let more people benefit in agricultural development and gain tangible advantages.
 

    From primitive hotbeds to photovoltaic greenhouses, a millennium-long history of greenhouse evolution lets us feel humanity's wisdom and innovation in the use of technology. All applications of new technology are meant to better serve agriculture and promote the healthy development of the agricultural industry. With the growing popularity of Hanergy thin-film solar energy, I believe that in the not-too-distant future, we will be able to see the flourishing scene of China's agricultural photovoltaic greenhouses.