_cc781905-5cde-3194-bb3b-136bad5 Preliminary work on the distributed roof through field survey And communicate with roof owners, collect relevant information, and prepare for the preliminary design of the next technical scheme and the analysis of the project investment income. Various roofs may be encountered in the actual survey, and the owner will also raise technical and business issues such as the feasibility of roof construction, installed capacity, support installation method, investment income, cooperation mode, etc. Taking the color steel tiles and concrete industrial building roofs that are widely used in distributed power stations as objects, the relevant technical content involved in the survey is briefly introduced from the following aspects:

1. Environmental factor assessment
Environmental factors are important issues that must be considered in the construction of photovoltaic power plants and cannot be ignored. Generally, it is necessary to understand the climate conditions of the project site (annual temperature and humidity, whether there are storms, blizzards, earthquakes, etc.), and whether the roof of the industrial plant or nearby areas will be affected. There is a large amount of hot and humid gas or the emission of weak acid and weak alkali gas, etc., because the photovoltaic module itself has certain requirements for the installation environment, installation in an inappropriate environment will affect the reliability of the module, and also provide investors and even the module supply. For example, components without anti-PID function are installed in high temperature and high humidity belts, and PID problems are easily induced by environmental factors without negative grounding or virtual grounding protection treatment. After the environment is assessed, at the component level, in order to avoid the impact of the special environment on the long-term reliability of the component, it is necessary to communicate and confirm between the investor or the builder and the component supplier. Figure 1 shows the climate classification map of different regions in my country. This classification is based on the Köppen climate classification method widely used in the world. The dark green part of the Cfa region is a hot summer climate with normal humidity and warm climate, which belongs to the PID-prone area, followed by Cwa area.

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

Figure 1 Comparison of climate zones in my country (Source: World Maps of Köppen-Geigerclimate classification)

 

 

 

 

 

 

 

 

 

 

 

Table 1 Köppen climate classification description

2. Roof information collection and bracket installation
The collection of roof information needs to know the structure type, building height, construction time, service life, property rights information, roof area, orientation, azimuth, roof access, lightning protection belt, surrounding traffic, etc. The module installation area will generate basic information such as the height of the building shaded by shadows. The relevant dimensions can be measured on the spot or refer to the building structure drawings and floor plans provided by the owner, which is convenient for shadow calculation in the preliminary design to determine the actual installable area.
For the steel structure color steel tile roof, there is generally a certain slope, and the roof with a small slope angle (within 5°) is not suitable for tiling because the power output of the crystalline silicon module is greatly affected by the radiation, and the installation needs to be increased. The inclination angle can improve the power generation of the module, and it is also conducive to the self-cleaning of the module in rainy days. For thin-film modules, the low-light effect is better, and tiling can be considered to increase the installed capacity in a limited roof area.
It is also necessary to understand the types of color steel tiles. Different types determine different bracket installation methods. Common ones are trapezoidal and angle-chilled three types. For trapezoidal color steel tiles, if they cannot be clamped, self-tapping screws need to be used for drilling. , In order to ensure the waterproofing of the roof during the installation of the bracket base, waterproof rubber pads and self-tapping screw waterproof pads can be used, as shown in Figure 2. For the angle chi three type, generally use the clamp and the color steel tile to fix, don't worry about the waterproof problem, as shown in Figure 3. For color steel tiles that have a certain age, during the installation of components and brackets, it is necessary to lay wooden boards or packaging trays for components on the main aisle to prevent repeated manual trampling and damage to the color steel tile roof. The position of the color steel tile fixings is generally on the purlin, and the best position is the junction point of the steel beam and the purlin. During the roof survey, the site situation should be considered and these problems can be thought of to be aware of it.

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

Figure 2 Installation method of trapezoidal color steel tile bracket base

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

In addition, the bearing performance of the roof needs to be considered. It is necessary to know the span between the steel beams and the spacing between the purlins, the specifications of the purlins, the thickness of the color steel tiles, the roof load value provided by the original architectural design institute, etc. from the drawings. Consider The installation of modules on the color steel tile roof will increase the load of the roof structure. The purlin is the direct bearing part of the roof structure, and it is also the weak part of the roof structure. Generally, the module needs to be installed at the load-bearing steel beam to reduce the purlin caused by the increase of load. Deformation, the subsequent load and stress analysis of the roof purlins is required. For the installation of the guide rail, according to the experience we communicated with the bracket manufacturers, if the purlin spacing of the three-type color steel tile roof is less than 1.2m, such as 1m, then the color steel tile fixing parts and the color steel tile can be placed directly after being fixed. Angle rails are used to install photovoltaic modules without additional square rails. If the purlin spacing is more than 1.2m (the actual roof purlin spacing is about 1.5m), and the thickness of a single layer of color steel tiles is less than 0.8mm, square guide rails need to be added. The installation inclination angle of the color steel tile roof is relatively small, generally below 15 degrees. The array installation inclination angle is small, and the wall thickness of the guide rail can be made thinner. If the inclination angle increases, the wall thickness of the guide rail needs to be increased to enhance its load capacity. .
For the cement roof, the fixing of the bracket and the roof is also a very important task. Generally, there are many prefabricated pressing blocks or the overall connection scheme of the brackets. The distance between the front, rear, left and right of the block, the installation of components and brackets needs to meet the load that the roof can bear without destroying the original waterproof layer of the roof. For the overall connection scheme, the parapet walls need to be fixedly connected to the bracket guide rails, and the brackets are horizontal and vertical. To form a whole, the key point is to consider the wind resistance of the bracket, and the installation inclination should not be too large. Figure 4 and Figure 5 are the methods used in the actual project. In fact, each roof has its own characteristics, which requires the design according to During the survey, the specific characteristics of the roof are considered comprehensively, and the most suitable installation scheme is adopted.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4 The overall connection, installation and fixing method of the bracket

 

 

 

 

 

 

 

 

 

 

 

 

 

​

 

 

Figure 5 Prefabricated block type installation and fixing method

3. Access conditions
The grid connection of the system needs to consider the annual power consumption of the enterprise load, the location of the power distribution room and the capacity of the user's transformer. If there is a small amount of electricity or it has been absorbed by other power stations, and whether there are large power-consuming enterprises in the nearby area, the self-generated and self-consumption surplus power grid mode is preferred under the current policy, and the full grid mode is an alternative. In reality, the owner may have multiple factories, and the use area of a single roof is small, and the power distribution rooms are usually scattered in one or several factories. In this case, a multi-point access mode is generally recommended. The network access point or two adjacent plant square arrays are connected to an inverter at the same time, and then connected to the 380V low-voltage bus in the user power distribution room. If there is no space in the power distribution room to place electrical equipment such as inverters, DC cabinets, grid-connected cabinets, etc., can a piece of land be planned for the installation of outdoor rooms outside the power distribution room? Of course, the amount of civil engineering foundation construction will increase. After preliminarily determining the locations of electrical equipment such as inverters and grid-connected cabinets, it is necessary to consider the wiring method and cable laying method from the combiner box to the power distribution room. Whether the original cable trench is feasible or not, according to the structural characteristics of the building, From the shortest route, the lowest cost, convenient construction, wiring specifications and other aspects.

4. A brief review of the roof
The actual roof is complex and diverse. First, it is necessary to evaluate whether the roof can be used for construction, and then consider the installation, design optimization and investment income issues. The following roofs are selected as examples for simple analysis and comparison. The comparison points of each roof refer to the table 2, The roof picture is shown in Figure 6.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

​

Table 2 Comparison of each roof (partly listed for reference)

 

 

 

 

 

 

 

 

 

 

​

​

 

 

 

 

 

 

Figure 6 Partial photos of various roofs

From the above, it can be seen that the roof of A is old, and the expansion bolts on the roof may damage the original waterproof layer. The roof of C will face the replacement of color steel tiles in the next few years. The roof of D needs to prevent PID problems and needs to be done at the system side. The negative pole is grounded. In addition, high temperature and high humidity gas will also have a certain impact on the life of the module. From the comparison of the overall condition of the roof, the B roof in the park is the most suitable for building a photovoltaic power station, and then we will examine the load usage and electricity price on this basis. Level, power distribution room location, property rights, etc., and communicate with the owner on issues related to business cooperation, and then formulate preliminary technical plans, including meteorological resource analysis, shadow calculation, array layout, load calculation, equipment selection and configuration , bracket installation, connection scheme and power generation simulation, etc., and carry out economic evaluation of investment projects, calculate financial internal rate of return, investment payback period and sensitivity analysis and other indicators, which will be used as an important basis for evaluating whether the project is feasible or not. .