# Regional Adaptability Analysis of Solar Roof Utilization Technologies in China
## 1 Introduction  
With the development of urbanization in China, numerous buildings have been built. In 2018, more than 400 million square meters of buildings have been completed in China [1]. The current total building area has already achieved about 400 billion square meters. Assuming that all buildings are 10-story, then possible available rooftop area can reach 40 billion square meters. The rooftops of buildings, especially within urban areas, are constantly attracting interests as one important resource. It is a huge waste for the society if the building rooftops are not fully utilized [2, 3]. The buildings typically need heat and electricity, which can be partly covered by the available solar energy on the building roofs using solar utilization technologies [4, 5, 6]. These solar utilization technologies can be categorized into the following two groups:  
1. Solar thermal technology. Sunlight is collected by solar collector panel and then converted into heat, which can be used to meet the demands of domestic hot water services and space heating. 2. Solar PV technology. The solar radiation is converted directly into electricity via the photovoltaic effect of semiconductors to supply power for buildings or be fed directly in the electricity grid. Several researchers have proposed methods to estimate the potentials of solar energy on building rooftops. A method was proposed to estimate the daily or monthly solar energy on individual buildings by LiDAR data and GIS approach for the use of photovoltaic systems on building rooftops. [PERSON] [7] developed a new method for evaluation of the solar potential of a roof surface that combines extracted urban topography from LiDAR data with the measurements of global and diffuse solar radiation. [PERSON] proposed a method based on a statistical calculation model to determine solar potential for applications in a complex urban environment [8]. [PERSON] developed a 3D urban model for the evaluation of solar energy potential of buildings roofs and facades [9]. [PERSON] developed a model of buildings and used it to calculate rooftop areas for PV arrays [10]. [PERSON] built an existing geo-referenced method for determining the available roof area for the installation of solar thermal systems and photovoltaic systems [11]. [PERSON] combined object-oriented image analysis and geographical information systems with remote sensing image data to quantify the rooftop area available for solar energy applications [12]. Then, the simulation is adopted to predict the potential benefits of urban-scale photovoltaic systems. [PERSON] calculated the roof area with sufficient solar energy in Dhaka Megacity [13]. The solar PV systems on these bright rooftops can generate nearly 1000 MW electricity. Several researchers have studied the utilization of solar technology as building energy supply. [PERSON] [14] developed a framework for the analysis of the potential of the rooftop PV system to achieve the net-zero energy solar buildings and verify its feasibility with lots of cases of elementary school facilities located in in South Korea. [PERSON] [15] applied the BPV module on a building and established a multi-index life cycle assessment (LCA) method for BPV modules applied on buildings by combining with the experimental test, simulation, and enterprise investigation. [PERSON] [16; 17] reviewed lots of published documents and revealed that the PV-green roof is an effective strategy for producing clean energy on the building scale with various challenges that hinder the large-scale implementation of PV-green roofs. However, it is certain that the sustainable rooftop can help reduce carbon emissions in urban areas. [PERSON] [18] proposed a solar-borehole thermal energy storage system to replace a natural gas-fired boiler in two residential buildings. The project execution can result in yearly CO\({}_{2}\) emission reductions of 1.1 million kg.