## 4 Discussion  
Both Light and Temperature Factors Should Be Considered When Studying the Adaptivity of the Photovoltaic Greenhouse  
The deployment of photovoltaic modules on the daylighting surface of a greenhouse would definitely reduce the daylighting of the greenhouse. It is hard to achieve a scale effect of power generation when deployed a small-scale of photovoltaic modules. However, a large proportion of photovoltaic modules may occupy the light resources rather than leave it for the crops in the greenhouse. Therefore, the intensity of daylighting in a photovoltaic greenhouse has become a key issue in the research of photovoltaic greenhouses. [PERSON] et al. investigated the light environment of a photovoltaic solar greenhouse in summer as well as its effect on the growth of tomato [17]. Their findings showed that the photovoltaic solar greenhouse is effective in cooling down the greenhouse in summer and the indoor light environment can satisfy the growth requirement of tomato. [PERSON] et al. studied the growth, photosynthesis, yields, and quality of Chinese cabbage which were grown in a single photovoltaic greenhouse with double-slope roofs under two different coverage modes of photovoltaic modules (33% and 50%) during October-November (Changzhou, Jiangsu) [18]. The results showed that a 33% coverage of the photovoltaic greenhouse can be used for normal Chinese cabbage cultivation and production. [PERSON] et al. measured and simulated (Ecotect) the average light transmittance of a photovoltaic greenhouse with different coverage methods and coverage rates of the photovoltaic greenhouse and analyzed the light transmittance in the photovoltaic solar greenhouse with different coverages and deployment methods of photovoltaic modules [19]. The results showed that the light  
Figure 12: Temperature and humidity change curves of the photovoltaic greenhouse in summer.  
transmittance of a traditional greenhouse was 58.87%, the overall light transmittance of a photovoltaic greenhouse with a coverage of 58% longitudinally spaced photovoltaic modules was 38.45%, and the overall light transmittance of a photovoltaic greenhouse with coverages of 58% and 81% horizontally spaced photovoltaic modules were 29.00% and 24.21%, respectively. The above studies have made detailed investigation on the illuminance of photovoltaic greenhouses with different coverage of modules as well as their impacts on the production in the greenhouses from the perspective of light.  
Environmental factors inside greenhouses are mutually restricted and related, so the shade created by photovoltaic modules certainly will affect the indoor temperature. The adaptability of a photovoltaic greenhouse should be studied synchronously from light and temperature environment. Especially for the winter production of solar greenhouses in North China, light not only is used for the photosynthesis of crops, but can also be used as a heat resource for the wall and ground of greenhouses to achieve the purpose of no or less heating in winter production. The winter in tropical areas is warm with an average temperature of above 10 \({}^{\circ}\)C, so there is no need to consider heat storage or use of heat-preservation equipment. The shading of photovoltaic modules will not only affect the heating demand of the greenhouse, but also can create shades in summer, so that it can help to alleviate the high temperature inside the greenhouse.