# A Critical Review of the Status of Current Greenhouse Technology in China and Development Prospects
## 3 Types of Greenhouses in China  
### Solar Greenhouses  
The development of greenhouses in China has gone through three phases: The first phase during the 1960s involved the gradual emergence of greenhouses in China, which were simple structures, such as plastic greenhouses. In the second phase in the 1970s, considerable attention was given to the structures, which became more complex, and the greenhouses were equipped with control equipment usually introduced from the Netherlands, the United States, and other developed countries at a high cost and which did not meet the national conditions of the time, In the third stage during the 1990s, after long-term national attention and the continuous efforts of Chinese researchers, a series of significant achievements were introduced in the greenhouse sector. The cold winter weather in northern China has hampered the development of Chinese agriculture, and in order to solve this problem, China has designed and introduced a unique facility: the solar greenhouse. Solar greenhouses (Figure 6) are agricultural facilities built using simple but durable materials, consisting of three main parts: the south (transparent) roof, the north roof, and the north wall. The south roof is made of a transparent material (plastic film), the north roof is made of an opaque thermal-insulating material, and movable thermal blankets are placed on the outside of the south roof, which are unfolded at night on the north roof and laid on top of the south roof for thermal insulation. The north wall is made of a passive solar energy storage system [14]. In most commercial solar greenhouses, there is no heating equipment; the north wall and the thermal blankets maintain an adequate level of indoor air temperature to meet the needs of growing vegetable crops. Figure 7 shows the structural sections of a solar greenhouse [15]; the thickness of the north wall base is 0.4-8 m, according to the demand, and the height of the north wall is mostly in the range of 2-4 m. The span of solar greenhouses (north to south length) is 7-12 m. Larger spans improve the efficiency of solar energy utilization and expand the space available for production. In addition to Chinese solar greenhouses, there are also facility cultivation units known as Gobi cropping systems [16]. These cultivation systems used in China make full use of crop straw, animal manure, and other agricultural wastes to create a cultivation substrate for crop cultivation [17]. In western China, the land is not fertile, such as in the Gobi Desert, and this facility cultivation system alleviates the difficulty of growing agricultural crops in western China. The Gobi cultivation system offers the opportunity to produce large quantities of fresh fruits and vegetables year-round on a land area as large as 2.2 million ha [18]. China's facility-based agriculture is booming, and solar greenhouses are an important part of China's facility-based agriculture. In the 1980s, solar greenhouses developed rapidly in northern China's facility-based agriculture, and the application of new solar greenhouses has further facilitated the cultivation of crops. Currently, the north wall of Chinese solar greenhouses is composed of packed earth and soil, and although this structure provides good thermal storage performance, the wall width is too large and wastes land resources. In addition, its construction produces CO\({}_{2}\) emissions, which contribute to the atmospheric greenhouse effect. A lot of research has been conducted in China on the materials used in the north walls, especially with the aim of building the wall using non-soil materials. [PERSON] et al. [19] developed a novel active-passive thermal storage wall system using phase change materials to improve the thermal performance of the wall and increase its internal temperature. Figure 6: Solar greenhouse internal structure diagram. Figure 7: Cross-section of a typical Chinese solar greenhouse.