Photovoltaic Building

Photovoltaic Building 
In the 1980s, in addition to being widely used in remote areas without electricity, nomadic families, nautical lighthouses, isolated island residents and some special fields, photovoltaic ground systems have begun to enter general individual users, networked users and commercial buildings. After entering the 1990s, with the increasing cost of power generation caused by the depletion of conventional energy sources and the increasing awareness of people's environment, some countries have begun to implement and promote building integrated photovoltaic (BIPV) systems. China has a large population and a high population density. The BIPV system combines buildings with photovoltaic systems or photovoltaic modules, which can not only save the area occupied by photovoltaic power generation systems, but also reduce its cost, which is in line with China's national conditions. Therefore, it has a broad market in China. Expansion capacity. [5]
In June 2021, the Comprehensive Department of the National Energy Administration issued the "Notice on Submitting the Pilot Plan for the Development of Distributed Photovoltaic on the Roof of the Whole County (City, District)" (hereinafter referred to as the "Notice"), pointing out that China's building roof resources are rich and widely distributed. , The development and construction of rooftop distributed photovoltaic has great potential. Carrying out entire counties (cities, districts) to promote roof distributed photovoltaic construction is conducive to integrating resources to achieve intensive development, reducing peak power loads, saving and optimizing distribution network investment, and guiding residents to consume green energy. It is an important measure of the two major national strategies of carbon peaking, carbon neutrality and rural revitalization. Among them, the proportion of photovoltaic power generation installed on the total roof area of ​​the party and government organs in the pilot counties (cities, districts) of the project application shall not be less than 50%. [10]
Photovoltaic grid-connected power generation applications centered on photovoltaic building integration account for most of the current photovoltaic market share. BIPV has the following advantages: the building can provide enough area for the photovoltaic system without occupying additional land; it can save the supporting structure of the photovoltaic system and the cost of power transmission; the photovoltaic array can replace conventional building materials and save materials Cost; the combination of installation and building construction saves installation costs; decentralized power generation avoids transmission and power distribution losses (5% to 10%), reduces power transmission, power distribution investment and maintenance costs; makes the appearance of buildings more attractive. Additionally, a building's photovoltaic system can be a reliable power source where power outages are a constant hassle. Combining solar energy with buildings and developing houses into new self-circulating buildings with independent power sources is the necessity of human progress and the development of society and science and technology. According to the survey report of the United Nations Energy Agency, BIPV will become one of the most important emerging industries in the 21st century. [5]
1. Main forms of BIPV [5] 
The combination of photovoltaics and buildings currently mainly has the following two forms: [5]
(1) Combination of buildings and photovoltaic systems. The combination of buildings and photovoltaic systems is to install packaged photovoltaic modules (flat or curved panels) on the roofs of residential buildings or buildings, and then connect them with inverters, batteries, controllers, loads and other devices, and can Connected to the external grid, the photovoltaic system and the grid are connected in parallel to supply power to the residence (user), the excess power is fed back to the grid, and the insufficient power is taken from the grid. [5]
(2) Combination of buildings and photovoltaic modules. The further combination of architecture and photovoltaics is to integrate photovoltaic devices with building materials. Generally, paint, decorative tiles or curtain wall glass are used on the outer surface of the building to protect and decorate the building. If photovoltaic devices are used to replace some building materials, that is, photovoltaic modules are used to make roofs, exterior walls and windows of buildings, which can be used as both building materials and power generation. To use photovoltaic devices as building materials, several conditions required by building materials must be met: sturdy and durable, thermal insulation, waterproof and moisture-proof, appropriate strength and rigidity and other properties. If it is used for windows, skylights, etc., it must be able to transmit light, that is to say, it can generate electricity and receive light. In addition, factors such as safety performance, appearance and ease of construction should also be considered. [5]
In addition, when photovoltaic modules are used in combination with buildings, two important factors should also be considered: 1) In order to ensure a high photoelectric conversion efficiency of photovoltaic modules, the ambient temperature around photovoltaic modules must be kept as low as possible. This requires better ventilation conditions around the photovoltaic modules, so when designing and installing photovoltaic modules, you can consider adopting overhead forms, double-layer ventilated roofs or double-layer glass curtain walls; 2), the life of photovoltaic modules is usually 15 to 25 years, and the life of the building envelope is usually 50 years. When designing, the disassembly and replacement requirements after the failure of photovoltaic modules must be considered. [5]
2. Several Influencing Factors of BIPV Design [5] 
The design of BIPV grid-connected power generation needs to consider the following factors: [5] 
(1) Consider the surrounding environment of the building and try to avoid or stay away from shading objects. [5]
(2) The orientation of the building should be as east-west or north-south as possible. [5]
(3) Determine the inclination angle of the roof according to the local latitude and longitude. In general, since the earth is constantly revolving around the sun, the inclination angle of the roof has little effect on the overall solar power generation, generally no more than 5%. With the same angle and the same power of solar cells, the power generation of the east and west roofs is almost equal. [5]
(4) According to the size of the components, calculate the total number and arrangement of components that can be installed on each roof. [5]
(5) According to the input DC voltage of the inverter, determine the total number of each group that can be connected in series. Since the orientation of each roof is different, the amount of light and the time of light are different. Generally, one roof corresponds to one inverter to improve the inverter. efficiency. [5]
3. Impact on the environment [5] 
The general ground solar photovoltaic power generation system and building integrated photovoltaic system use solar energy, a renewable clean energy, to generate electricity, which is of great significance to promote the sustainable development of energy and the environment; at the same time, if [5] photovoltaic power generation Improper use or recycling of photovoltaic devices in the system will also cause some negative impacts on the environment. The favorable and unfavorable factors of its impact on the environment are listed as follows: [5]
(1) Favorable factors: [5]
① Cutting-edge technological design and craftsmanship can make up for the cost of traditional building materials; [5] 
② No noise during operation; [5] 
③ During the power generation process, no additional transportation costs are required; [5] 
④Without any moving parts, it requires minimal maintenance during its 20-year working life; [5]
⑤ Will not cause air pollution. Solar cells generate lkWp of electricity, which can avoid the generation of 1000kg of carbon dioxide; [5]
⑥ Independent power supply, thus reducing the cost of power transmission and distribution; [5] 
⑦ A set of standardized design and debugging methods has been formed, so installation and use can be carried out in batches, thereby avoiding the financial pressure caused by excessive one-time investment. [5]
(2) Unfavorable factors: [5]
① Photovoltaic cells need to consume relatively high energy in the production process. If they are used unreasonably, it may lead to the phenomenon that the power generation in the life cycle is lower than the production energy consumption; [5] 
② Improper utilization or recycling of acid lead-acid batteries may easily cause environmental problems; [5] 
③ If the heavy metals (such as cadmium) contained in photovoltaic cells are not recycled properly, it is easy to cause serious environmental problems; [5] 
④ Discarded photovoltaic cells and their battery components may leak mercury, lead, and cadmium, causing harm to the environment. [5]