# A Critical Review of the Status of Current Greenhouse Technology in China and Development Prospects
## 5 Research on Chinese Greenhouse Technology  
### Energy Supply and Storage  
The heating methods used in Chinese greenhouses are constantly changing and improving with the development of science and technology. In the 1960s, greenhouse cultivation used no heating, and during the winter, cultivation was affected by the weather [37]. With the development of technology, greenhouse heating has been gradually implemented, and equipment such as boilers and electric heaters are now being used to maintain suitable air temperature levels in greenhouses [38]. Heating sources used include coal or oil, electricity, and even open-fire heating, which is very polluting to the environment. Currently, a variety of equipment is used to heat greenhouses, such as solar collectors, biomass boilers, water-source heat pumps, and air-source heat pumps. This new equipment is safe, energy-saving, and environmentally friendly and may be conveniently used by growers. One of the more researched areas is the combination of greenhouses with several types of solar collectors. It is well known that 1 kg of coal combustion produces about 2.5 kg of carbon dioxide. Solar energy is a recognized renewable energy source, and the use of vacuum tube solar collectors placed onto the south side of a typical Chinese solar greenhouse, such as those shown in Figure 14, can be used to collect and store heat from the sun. The solar thermal industry in China is working toward that direction, and systems are being developed to make use of surplus solar energy during the daytime but also for seasonal storage. Mr. [PERSON], from Binzhou Xinrui New Energy Technology Co., Ltd., Weifang, China, stated that _\"there are many locations in China with excellent solar energy potential which are still unexploitable. We are working intensively to develop a system for solar thermal storage to exploit that potential\"_ (Figure 14). The use of solar energy for greenhouse heating can reduce CO\({}_{2}\) emissions and heating costs through the use of vacuum tube solar collectors as solar water heaters to assist electric heat pumps for greenhouse heating, and the internal air temperature of the heated greenhouse is 2 to 3 \({}^{\circ}\)C higher than that of an unheated greenhouse [39]. In addition to solar thermal energy, adopting solar photovoltaics for electric heating as auxiliary heat sources and also for supplementary lighting can greatly contribute to solving the problems relating to energy consumption and pollution and lower the costs and greatly improve the reliability, economics, and convenience of greenhouse heating. [PERSON] et al. [40] developed and analyzed an active solar heating system (ASHS) consisting of five solar water heaters equipped with vacuum tube solar collectors, a hot water storage tank, and a heating system that included a booster pump and heating tubes. During the day, water is heated in the solar collectors and stored in the tank, which is then circulated into the heating tubes to distribute heat to the aerial and root environment of the plants. The results of the study showed that the ASHS was successful in providing 76% of the annual heating demand, heating the solar greenhouse for four months and keeping the temperature inside the greenhouse above 8 \({}^{\circ}\)C at right. Latent heat energy storage technology with phase change materials (PCMs) as the energy storage carrier is a relatively mature and efficient energy storage technology that utilizes the heat absorption and release of these materials during the phase change process to achieve energy storage and efficient utilization. Phase change energy storage technology has the advantages of high energy storage density, low costs, and constant temperature heat release. Incorporating phase change materials into greenhouse solar walls improves the wall's thermal insulation and heat storage capacity, and when the ambient temperature changes, it releases or stores the heat in the room to control the temperature, thus reducing the use of auxiliary equipment [41]. [PERSON] et al.