1.1 Selection and design of leading equipment in the photovoltaic field
The grid-connected photovoltaic power station comprises a square array of photovoltaic modules, a combiner box, an inverter, a step-up transformer, and a power distribution cabinet at the grid-connected point. This project's leading equipment in the photovoltaic field area includes photovoltaic modules, inverters, box-type transformers, and AC and DC cables. The configuration diagram of the photovoltaic power station system is shown in Figure 2.
(1) Photovoltaic modules
The photovoltaic modules used in grid-connected photovoltaic power stations in my country mainly include three types: monocrystalline silicon modules, polycrystalline silicon modules, and thin-film modules. Among them, monocrystalline silicon modules have high conversion efficiency. Still, the cost of a single module is relatively high, and they are primarily used in power station systems with a small installation area such as rooftop distributed power stations; compared with crystalline silicon modules, thin-film modules have low light conditions. Better power generation performance and the shape of the finished thin-film module is flexible, which can be adjusted according to the actual needs of the building, and is widely used in systems such as building curtain walls; the conversion efficiency of polycrystalline silicon modules is between monocrystalline silicon modules and thin-film modules, with mature technology and high performance. Stable, easy to transport and install on a large scale, and more cost-effective than monocrystalline silicon and thin-film modules. Therefore, large-scale ground power stations mostly use polysilicon components. Considering the large number of photovoltaic modules installed in this project, the remote location of the site, and the harsh installation conditions, the selection design adopts domestic high-quality polysilicon modules, and the module power is 270W. In a photovoltaic power generation system, the installation scheme of photovoltaic modules directly determines the amount of solar radiation that the array can receive, which affects the power generation efficiency of the entire power station. In the mountain photovoltaic power station, the factors to measure the pros and cons of the photovoltaic module installation plan should be considered from the selection of the array installation inclination and the land utilization rate of the site. For the installation inclination of modules, the industry generally believes that it should be consistent with the latitude of the project location. Still, too large installation inclination for high latitude areas means longer shadow shielding distance and more bracket steel consumption, which is not conducive to site utilization. Rates and stent costs are both adversely affected.
On the contrary, if we consider improving land utilization by reducing the installation inclination and shortening the shadow shielding distance, the amount of solar radiation received by the array will be significantly reduced, which will seriously affect the power generation efficiency of the collection. Therefore, an excellent component installation solution must find an appropriate balance between the array inclination and the land utilization, which can ensure that the components receive the best radiation amount and take into account the reasonable utilization of the land. The latitude of the component installation site in this project is about 43.5°. Suppose the conventional bracket installation scheme is adopted. In that case, the shadow shielding of the array will have a more significant impact on the land utilization rate, which is unacceptable for the tight project land situation. Therefore, in the pre-design process of the project, this project abandoned the conventional component installation method and switched to a new installation mode: first, the module installation inclination was reduced to 40°, on the one hand, the length of the array shadow can be shortened, and the other On the other hand, it can also reduce the cost of the bracket; secondly, in the conventional installation scheme, the mode of installing 2-row components in 1 group of arrays is changed to 1 group of displays and 3-row members. As a result, the number of features installed in a single collection group increases; generally, the number of components installed per unit area is more than that of the conventional installation scheme. The land utilization rate is also reasonably guaranteed.
(2) Inverter
The inverters used in photovoltaic power plants in my country are mainly divided into centralized inverters and string inverters. The centralized Inverter is large in capacity and volume, has better schedulability, and is cost-effective. Still, the centralized Inverter has a small number of MPPT and high requirements for installation conditions, which is more suitable for uniform installation of components and equipment—centralized large-scale power stations. String inverters have a small capacity, lightweight per device, good protection performance, low requirements for external use environment, easy transportation and installation, and string inverters generally have a large number of MPPTs, which can maximize the It can effectively reduce the adverse effects caused by component differences and shadow shading, and improve the efficiency of photovoltaic power generation. It is suitable for power station systems with complex component installation conditions, and in areas with more rainy and foggy days, the power generation time of string inverters is shorter. Long. The selection of photovoltaic power station inverters should be selected according to factors such as the scale of the power station, the geographical environment of the site, the system form, and grid connection requirements. The project is located in a mountain forest area, the equipment installation area is scattered, and the terrain severely restricts the component installation. Therefore, to reduce the loss of module series and parallel mismatch and optimize the power generation capacity of the photovoltaic power station, this project adopts a domestic high-quality string inverter with a 4-channel MPPT function in the inverter selection, and a single inverter is used. The rated power is 50kW. In addition, the open-circuit voltage and short-circuit current of photovoltaic modules will change with the fluctuation of the ambient temperature, especially the open-circuit voltage will increase with the decrease of the ambient temperature. Therefore, the serial number of components connected to the inverter MPPT must be calculated and demonstrated to ensure that it does not exceed the upper limit of the inverter MPPT working voltage under extremely low-temperature conditions; At the same time, it is also necessary to ensure that the capacity of the components connected to the Inverter is not higher than the maximum DC input power of the Inverter. In this project, each Inverter is associated with eight photovoltaic string circuits, each circuit is connected to 21 photovoltaic modules, and the DC input power of the Inverter is 45.36kW
(3) Field transformer
Domestic photovoltaic field transformer products mainly include oil-immersed transformers and dry-type transformers. Because photovoltaic power station transformers are mostly installed outdoors, oil-immersed box-type combined transformers with good protection performance and easy construction and installation are generally used. When designing and selecting a transformer, it is necessary to comprehensively consider the electrical design type of the photovoltaic system, the voltage transformation ratio, and the environmental conditions of installation and use, and select the most suitable product for the type of photovoltaic system while taking into account the enthusiasm. Oil-immersed transformers are widely used in photovoltaic systems due to their low cost, easy maintenance, flexible voltage level, and transformer capacity configuration. However, due to their large size and the risk of environmental pollution and fire due to leakage of insulating oil, they are generally suitable for Large-scale ground photovoltaic power station systems with sufficient installation sites and low fire rating requirements.
The photovoltaic field of this project is located on the mountain, and there is ample space for electrical equipment transportation and installation. Therefore, the oil-immersed box-type transformer of model ZGS11-ZG (referred to as "box-type transformer") is designed and designed to ventilate the transformer foundation. The oil pool can prevent environmental pollution and fire hazards caused by the leakage of insulating oil in the box changer.
Considering the scattered distribution of components in mountain power stations and the inconsistent installed capacity of power generation units, this project is designed to use box transformers with two degrees of 1000kVA and 1600kVA. According to the actual installed capacity of each power generation unit, each box transformer is connected to 20-38 units Inverter, the ratio of PV access capacity to box transformer rated capacity should not exceed 1.2.
(4) AC and DC cables
There are generally two types of cable laying in the field for mountain power stations: overhead and buried. For routes that need to cross ravines, woodlands, and rivers, overhead wires are generally used, while for areas with short distances, flat sites, and convenient ground construction, buried laying is used. This method has the advantages of a short construction period and low cost. The cables used in the photovoltaic field of this project mainly include photovoltaic DC cables between modules and inverters, AC cables between inverters and box transformers, and between box transformers and booster stations. The considerations for cable selection mainly include withstanding voltage rating, cross-sectional area, and cable type. Among them, the cables between the modules and the inverters are designed with photovoltaic special DC cables, which are arranged along with the purlins of the back brackets of the modules; the AC cables between the inverters and the box-type transformers and the box-type transformers are laid underground, considering the summer in the area where the power station is located. However, it is rainy and humid. The temperature is low in winter, so use an armored XLPE insulated polyethylene sheathed power cable (YJY23) with better moisture and low-temperature resistance. To make a selection.
Before laying buried cables, the appropriate buried depth must be determined. According to the requirements of the specification, the buried depth of directly buried lines should not be less than 0.7m, and when crossing farmland, the depth should not be less than 1.0m; at the same time, in cold regions, the thickness of the frozen soil layer in winter must also be considered, and the directly buried cables should be at the maximum depth of the firm soil layer—the following. The extreme minimum temperature in winter in the area where the project is located is -37.5°C, and the maximum thickness of the frozen soil layer is 1.8m. Therefore, the design depth of the cable trench in the photovoltaic field area should reach 2.0m. At the same time, the part passing through the road needs to be protected by steel pipes. Large-scale photovoltaic power plants cover a large area, with a large number of equipment, and the amount of AC and DC cables is enormous. Therefore, it is essential to reasonably estimate the number of wires used in the early stage of construction.
On the other hand, due to mountain power stations' complex terrain and construction conditions, it is difficult to estimate the number of cables based on the so-called "similar project" experience and construction drawings. Therefore, in the actual construction process of this project, the method of "construction drawing + experience value + on-site sampling value" is adopted to comprehensively count the cable engineering quantity. On the one hand, the construction drawings and the cable consumption data of previous mountain power stations are used to estimate; With the advancement of the project, the reference samples of cables will become more and more abundant and representative and the estimated value of cable usage will become more and more accurate.
1.2 PV field operation and maintenance management
Since the construction of photovoltaic power station projects and on-grid electricity prices in my country are greatly affected by policies, the construction period of most projects is short, and the design and construction of power stations cannot be fully scientifically and effectively controlled. Therefore, management has caused particular difficulties and hidden dangers. At the same time, due to the explosive growth of photovoltaic projects in recent years, a large number of power stations have been put into operation, while the training and reserve of professional process and maintenance personnel in the industry is relatively backward, resulting in the tension of photovoltaic power station operation and maintenance personnel, and the uneven operation and maintenance level and quality. Therefore, strengthening and improving power plants' operation and maintenance management is of great significance to ensure the service life and economic benefits of photovoltaic power plants.
(1) Field equipment management
The leading equipment in the photovoltaic field area includes photovoltaic modules, string inverters, and box transformers. The management of this equipment is mainly through the data collection and monitoring of the site and regular on-site inspections, etc., to understand the operating parameters and conditions of the equipment, analyze potential safety hazards and eliminate faults promptly.
The leading equipment in the photovoltaic field is equipped with data acquisition terminals. The real-time transmission of data and instructions can be realized through the RS485 communication cable and optical fiber ring network laid in the field and the central control room of the booster station. The operation and maintenance personnel are in the central control room. The operating parameters of all electrical equipment in the field can be tested indoors, including parameters such as inverter power generation, box-changing power, etc., as shown in Figure 3 and Figure 4; The equipment is remotely controlled to realize the automatic management of the leading electrical equipment in the photovoltaic field.
At the same time, the inspection of the leading equipment should be strengthened, and the operation and maintenance personnel should be regularly arranged to conduct on-site checks of the photovoltaic modules, inverters, and box transformers in the photovoltaic field and record the operating conditions and relevant parameters of each equipment.
Fig.3 Typical daily power generation distribution of inverter
Problems found in the investigation are classified, summarized, and sorted promptly, and targeted solutions are formulated according to the seriousness of the situation. For photovoltaic power plants in high-altitude areas, due to the large inclination of the module installation, special attention should be paid to the force of the module bracket, and the loose connection parts should be tightened in time. For photovoltaic power stations in areas with a significant temperature difference between day and night, special attention should be paid to the frost condensation in the electrical equipment box, especially the inside of the box transformer. It is necessary to focus on checking whether there is frost and condensation on the surface of each terminal and circuit breaker in and timely if necessary. Remove ice on the inner wall of the box, and ensure smooth ventilation of the box to prevent the electrical equipment in the box from being damp and affecting the insulation performance. The inspection period is generally 1 to 2 weeks, which can be determined according to the actual operation of the power station and the weather and environmental conditions of the site. For newly put into operation, after maintenance and equipment with a history of failure, inspections should be strengthened; at the same time, checks should be maintained before and after extreme weather such as snowfall, rainfall, gale, and hail.
(2) Cleaning of photovoltaic modules
Photovoltaic power stations constructed and operated in my country use crystalline silicon modules with a glass substrate. This module mainly comprises tempered glass, backplane, aluminum alloy frame, crystalline silicon cells, EVA, silica gel and junction box, etc. Light receiving area and photoelectric conversion efficiency, but its tempered glass surface is also prone to accumulation of dust and dirt. An obstruction such as dust on the surface of the module will reduce its photoelectric conversion efficiency and cause a hot spot effect in the shaded part of the module, which may cause severe damage to the photovoltaic module. Therefore, it is necessary to formulate corresponding measures and plans to regularly clean the surface of photovoltaic modules installed in the power station to ensure the modules' conversion efficiency and operation safety. The commonly used cleaning technologies for photovoltaic modules in my country's photovoltaic power plants mainly include manual cleaning technology with high-pressure water guns, onboard robot cleaning technology, photovoltaic module self-cleaning technology, electric curtain dust removal technology, and vehicle-mounted mobile cleaning technology. The characteristics of various cleaning technologies are introduced in Table 1.
Table 1 Commonly used photovoltaic module cleaning technologies
The project is located in a forest area far away from the urban area. There are no air pollution sources such as thermal power plants and mining fields around the site. Therefore, the air cleanliness is high, and the photovoltaic modules are less affected by dust. However, the temperature of the project site is low in winter, and the snowfall time is extended. Therefore, module cleaning mainly considers the impact of snow on PV modules. In response to this problem, combined with the actual situation of the project location and the module installation mode, this project adopts a combination of passive cleaning and active cleaning to clean and maintain the photovoltaic modules in the field.
Passive cleaning combines the characteristics of the high installation height and large inclination angle (40°) of the photovoltaic modules of this project. Under the influence of its gravity, the snow on the surface of the modules in winter is challenging to adhere to the glass surface of the modules. When the sunlight hits the modules, The increased surface temperature of the components will help shed snow ice. Judging from the actual operation of the power station, in early December, after the snowfall in the field at night, the thickness of the snow on the surface of the photovoltaic modules is about 2-5 cm in the morning. It falls off by itself, and the remaining snowfalls off after 2 hours. Similarly, in other seasons, debris such as dust or leaves falling on the surface of the module can also smoothly slide off the surface of the module under the action of rain and wind.
Active cleaning Considering the requirements of economy and applicability, for those snow and dust debris that their weight cannot remove, this project adopts the method of regularly arranging cleaning personnel to remove snow and dust to clean the components manually. For areas with abundant water sources, pressurized water guns can be used to rinse, and the other regions can be cleaned manually with tools such as rags. The cleaning time of the modules should be selected in the early morning, evening, night, or cloudy days to avoid the adverse effects of the shadows of equipment and personnel on the power generation efficiency of photovoltaic modules during the cleaning process. The selection of the cleaning cycle should be determined according to the degree of contamination on the surface of the component. Under normal circumstances, for dust attachments, the number of cleanings should be no less than twice a year; for snow, it should be arranged promptly according to the thickness of the accumulation on the surface of the module and the recent snowfall.
The quality of operation and maintenance personnel training of photovoltaic power station operation and maintenance management depends on the skill and quality of process and maintenance personnel. Photovoltaic power generation technology is a new form of energy utilization. Most power stations' operation and maintenance management teams are relatively young and lack photovoltaic operation and maintenance experience and technology. Therefore, the power station operation and maintenance unit should strengthen the professional training of operation and maintenance personnel. During the operation and maintenance of photovoltaic power plants, according to relevant laws and regulations and the provisions of the local power department, combined with the rules and regulations of power station operation, formulate training programs that meet their characteristics and Detailed rules, continuously improve the technical level of employees, and strengthen their awareness of learning and innovation. At the same time, attention should be paid to technical disclosure and training from professional subcontracting units or equipment manufacturers. There are many professions and industries involved in constructing photovoltaic power plants, and the pre-project design, construction, and operation and maintenance management are often not completed by the same company or department. Therefore, professional subcontracting is required when the power station is completed and handed over to the operation and maintenance unit. The unit and equipment supplier shall make technical disclosure to the operation and maintenance unit and provide necessary training services to ensure that the operation and maintenance personnel are familiar with the performance of the system and equipment and master the operation and maintenance methods.
2.Photovoltaic power generation and benefit analysis
2.1 Theoretical power generation calculation
According to the "Design Specifications for Photovoltaic Power Stations," the forecast of the power generation of photovoltaic power stations should be calculated and determined according to the solar energy resources at the site. After considering various factors such as photovoltaic power station system design, photovoltaic array layout, and environmental conditions, the calculation formula is: :
In the formula, EP is the on-grid power generation, kWh; HA is the total solar irradiance on the horizontal plane, which is 1412.55kWh/m² in this project; ES is the irradiance under standard conditions, with a constant of 1kWh/m²; PAZ is the component The installation capacity is 100000kWp in this project; K is the comprehensive efficiency coefficient, which is 0.8. Therefore, the theoretical power generation capacity of the power station in the first year of this project is
Due to the aging of the primary material and ultraviolet radiation, the power of photovoltaic modules will decline year by year during use. The power attenuation rate of the modules used in this project is 2.5% in the first year, 0.7% in each year after the first year, 8.8% in 10 years, and 19.3% in 25 years. Therefore, the system's life is calculated as 25 years, and Table 2 is the calculation result of the 25-year power generation of the project.
According to the analysis, the cumulative total power generation of the project in 25 years is 2,517.16 million kWh, the average annual power generation in 25 years is 100.69 million kWh, and the annual power generation per watt of installed capacity is about 1.007 kWh.
2.2 Benefit Analysis
The power station is located in Yanbian Prefecture, Jilin Province. According to the "Notice of the National Development and Reform Commission on the Price Policy of Photovoltaic Power Generation Projects in 2018" (Fa Gai Price Regulation [2017] No. 2196), the photovoltaic power station put into operation after January 1, 2018, The benchmark on-grid electricity prices for Class I, Class II, and Class III resource areas are adjusted to 0.55 yuan/kWh, 0.65 yuan/kWh, and 0.75 yuan/kWh (tax included), respectively. This area is a Class II resource area, and the benchmark on-grid electricity price for photovoltaic power plants is 0.65 yuan/kWh. At the same time, according to Jilin Province's "Proposal on Accelerating the Application of Photovoltaic Products to Promote the Healthy Development of the Industry (No. 128)", Jilin Province implements a policy of electricity subsidy for photovoltaic power generation projects and based on national regulations, additional support of 0.15 yuan/kWh. Therefore, the photovoltaic power station can enjoy a 0.8 yuan/kWh subsidy.
The installed capacity of the first phase of the project is 100MW. According to the cost estimate of 8 yuan/W, the initial budget investment is about 800 million yuan, and the actual acquisition of the project is 790 million yuan, which is slightly lower than the previous budget investment. According to estimates, the average annual power generation of the project is 100,686,564 kWh. According to the policy, subsidies can be obtained at 0.8 yuan/kWh, and the photovoltaic power station's average yearly electricity fee income is about 80.549 million yuan.
According to the estimate of the actual investment, the project will recover the cost in about ten years. The cumulative total power generation of the power station in 25 years is 2.517 billion kWh, and the total income is about 2.014 billion yuan. During the 25-year service life, the profit of this project is about 1.224 billion yuan. At the same time, the project can realize 14 million yuan in local taxes and 12 million yuan in poverty alleviation funds each year, and 4,000 registered poor households can be successfully lifted out of poverty, with an average annual income increase of 3,000 yuan.
In addition, since the photovoltaic power station consumes less power and does not emit pollutants such as carbon dioxide, sulfur dioxide, and nitrogen oxides to the external environment, it has high environmental protection value and social benefits. The photovoltaic power station generates an average of nearly 100 million kWh per year. According to the relevant conversion rules, it can save 36247.16t of standard coal every year, which means reducing the emission of carbon dioxide 100384.5t, sulfur dioxide 1188.1t, and nitrogen oxides 432.9t, and can reduce the generation of thermal power generation. In addition, 27386.7t of dust saved nearly 400 million L of purified water.
3.Summary
After the explosive growth of the photovoltaic industry in recent years, the lag in the construction of power grids in individual regions has become increasingly prominent. Coupled with the acceleration of industrial transformation and upgrading in my country, the national electricity demand has slowed down. As a result, photovoltaic power curtailment has occurred in various places. At the same time, to achieve the goal of photovoltaic grid parity, the benchmark on-grid electricity price for photovoltaics has entered a downward channel. According to the "Notice of the National Development and Reform Commission on the Price Policy of Photovoltaic Power Generation Projects in 2018", the benchmark on-grid electricity price in 2018 was reduced by 0.1 compared to 2017. Yuan/kWh. In this context, photovoltaic companies will face more significant pressure to reduce costs. In contrast, the raw materials (such as components, steel, etc.) and labor costs required to construct photovoltaic power plants remain high. Balancing the relationship between costs and benefits is a complex problem that the photovoltaic industry needs to think about and solve next.
1. Classification and composition of solar photovoltaic power stations
Solar photovoltaic power stations can be divided into independent and grid-connected types according to whether they are connected to the public grid. The type of solar photovoltaic power generation system needs to be selected based on the reference power supply demand, and the most reasonable solar photovoltaic power generation system is established.
2. Key points of site selection for solar photovoltaic power stations
Solar photovoltaic power stations are distributed all over the world. In my country's construction of solar photovoltaic power stations, sufficient attention should be paid to the site selection of solar photovoltaic power stations. In the site selection of solar photovoltaic power stations, light conditions need to be considered to ensure sufficient light shining on the solar panel to provide the power generation effect. The solar photovoltaic power station is located in an area with flat terrain. Therefore, it is not prone to natural disasters to avoid the severe impact of natural disasters on the equipment of the solar photovoltaic power station. Avoid large numbers or buildings around the solar photovoltaic power station site that will shade the solar photovoltaic power station and affect the illumination of the solar photovoltaic power station.
3. Design points of the independent solar photovoltaic power generation system
When designing a solar photovoltaic power generation system, it mainly focuses on the capacity of the solar photovoltaic power generation system, the selection of power electronic equipment in the solar photovoltaic power generation system, and the design and calculation of ancillary facilities. Among them, the capacity design is mainly aimed at the capacity of the battery components and batteries in the solar photovoltaic power generation system. The focus is to ensure that the electricity stored in the batteries can meet the work requirements. For the selection and configuration of system components in the solar photovoltaic power generation system, it is necessary to ensure that the selected equipment matches the capacity design of the solar photovoltaic power generation system to ensure that the solar photovoltaic power generation system can work typically.
4. Main points of capacity design of independent solar photovoltaic power generation system
When designing the capacity of an autonomous solar photovoltaic power generation system, the load and local dimensions of the separate solar photovoltaic power generation system should be listed first, and the load size and power consumption of the independent solar photovoltaic power generation system should be determined. On this basis, the battery capacity of the separate solar photovoltaic power generation system is selected. Then, the optimal current of the different solar photovoltaic power generation systems is determined by calculating the square array current of the independent solar photovoltaic power generation system. Then the square array voltage of the battery of the independent solar photovoltaic power generation system is selected. Finally, the battery of the separate solar photovoltaic power generation system is determined of power. When designing the power of the battery square array of the independent solar photovoltaic power generation system, the design of the solar battery square array of the separate solar photovoltaic power generation system can be completed according to the principle of series boosting and parallel rectification.
5. Main points of installation of the independent solar photovoltaic power generation system
5.1 Stand foundation construction of stand-alone solar photovoltaic power generation system
The battery matrix base of the independent solar photovoltaic power generation system should be made of concrete. The concrete floor's ground height and horizontal deviation should meet the design requirements and specifications. The battery matrix base should be fixed with anchor bolts. The leakage must meet the requirements of the design specification. After the concrete pouring and fixing of the anchor bolts, it needs to be cured for at least five days to ensure its solidification strength before the stand-alone solar photovoltaic power generation system rack can be completed.
When installing the solar bracket of the independent solar photovoltaic power generation system, attention should be paid to: (1) The azimuth angle and inclination angle of the square array frame of the independent solar photovoltaic power generation system needs to meet the design requirements. (2) When installing the rack of the independent solar photovoltaic power generation system, it is necessary to pay attention to the need to control the levelness of the bottom within the range of 3mm/m. When the levelness exceeds the allowable range, a horn should be used for leveling. (3) The surface of the fixed part of the stand-alone solar photovoltaic power generation system rack should be as flat as possible to avoid damage to the cells. (4) For the fixed part of the stand-alone solar photovoltaic power generation system rack, anti-loose gaskets should be installed to improve the reliability of its connection. (5) For the solar cell array with the sun-tracking device in the independent solar photovoltaic power generation system, the tracking device should be checked regularly to ensure its sun-tracking performance. (6) For the stand-alone solar photovoltaic power generation system, the angle between the rack and the ground can be fixed or adjusted according to seasonal changes so that the solar panel can most likely increase the receiving area and lighting time of sunlight and improve the independence of the solar panel—the power generation efficiency of the solar photovoltaic power generation system.
5.2 Installation points of solar modules of the stand-alone solar photovoltaic power generation system
When installing the solar modules of the stand-alone solar photovoltaic power generation system, please pay attention to: (1) When installing the solar modules of the stand-alone solar photovoltaic power generation system, it is necessary to measure and check the parameters of each component first to ensure that the parameters meet the User requirements to measure the open-circuit voltage and short circuit current of the solar module. (2) Solar modules with similar working parameters need to be installed in the same square array to improve the power generation efficiency of the square array of the independent solar photovoltaic power generation system. (3) During the installation of solar panels, etc., bumps should be avoided to avoid damage to solar panels, etc. (4) If the solar panel and the fixed frame are not closely matched, they need to be leveled with iron sheets to improve the tightness of the connection between the two. (5) When installing the solar panel, it is necessary to use the prefabricated installation on the solar panel frame for connection. When connecting with screws, pay attention to the tightness of the connection, and pay attention to the relaxation work in advance according to the standards used. (6) The position of the solar module installed on the rack should be as high quality as possible. The gap between the solar module installed on the rack and the rack should be greater than 8mm to improve the heat dissipation capacity of the solar module. (7) The junction box of the solar panel needs to be protected from rain and frost to avoid damage caused by rain.
5.3 Main points of cable connection of solar photovoltaic power generation system
When laying the connecting cables of the solar photovoltaic power generation system, pay attention to the principle of first outdoor, then indoor, first simple, and then complicated. At the same time, pay attention to the following when laying cables: (1) When laying cables on the sharp edge of the wall and bracket, pay attention to the protection of the cables. (2) Pay attention to the direction and fixation of the cable when laying the cable, and pay attention to the moderate tightness of the cable layout. (3) Pay attention to protection at the joint of the cable to prevent oxidation or fall off at the joint, which affects the connection effect of the cable. (4) The feeder and return line of the same circuit should be twisted together as much as possible to avoid the influence of the electromagnetic interference of the cable on the cable.
5.4 Do an excellent job of lightning protection for solar photovoltaic power generation systems
During installing the solar photovoltaic power generation system, attention should be paid to the lightning protection and grounding of the solar photovoltaic power generation system. The grounding cable of the lightning rod should be kept at a certain distance from the bracket of the solar photovoltaic power generation system. For the lightning protection of the solar photovoltaic power generation system, two lightning protection methods can be used to install the lightning rod or the lightning protection line to protect the safety of the solar photovoltaic power generation system.
Epilogue
The development and utilization of solar energy is the focus of energy development and even in the future. Based on the analysis of the composition and characteristics of the solar photovoltaic system, this paper analyzes and expounds on the critical points of the design and installation of the solar photovoltaic system.
The grid-connected photovoltaic power station comprises a square array of photovoltaic modules, a combiner box, an inverter, a step-up transformer, and a power distribution cabinet at the grid-connected point. This project's leading equipment in the photovoltaic field area includes photovoltaic modules, inverters, box-type transformers, and AC and DC cables. The configuration diagram of the photovoltaic power station system is shown in Figure 2.
(1) Photovoltaic modules
The photovoltaic modules used in grid-connected photovoltaic power stations in my country mainly include three types: monocrystalline silicon modules, polycrystalline silicon modules, and thin-film modules. Among them, monocrystalline silicon modules have high conversion efficiency. Still, the cost of a single module is relatively high, and they are primarily used in power station systems with a small installation area such as rooftop distributed power stations; compared with crystalline silicon modules, thin-film modules have low light conditions. Better power generation performance and the shape of the finished thin-film module is flexible, which can be adjusted according to the actual needs of the building, and is widely used in systems such as building curtain walls; the conversion efficiency of polycrystalline silicon modules is between monocrystalline silicon modules and thin-film modules, with mature technology and high performance. Stable, easy to transport and install on a large scale, and more cost-effective than monocrystalline silicon and thin-film modules. Therefore, large-scale ground power stations mostly use polysilicon components. Considering the large number of photovoltaic modules installed in this project, the remote location of the site, and the harsh installation conditions, the selection design adopts domestic high-quality polysilicon modules, and the module power is 270W. In a photovoltaic power generation system, the installation scheme of photovoltaic modules directly determines the amount of solar radiation that the array can receive, which affects the power generation efficiency of the entire power station. In the mountain photovoltaic power station, the factors to measure the pros and cons of the photovoltaic module installation plan should be considered from the selection of the array installation inclination and the land utilization rate of the site. For the installation inclination of modules, the industry generally believes that it should be consistent with the latitude of the project location. Still, too large installation inclination for high latitude areas means longer shadow shielding distance and more bracket steel consumption, which is not conducive to site utilization. Rates and stent costs are both adversely affected.
On the contrary, if we consider improving land utilization by reducing the installation inclination and shortening the shadow shielding distance, the amount of solar radiation received by the array will be significantly reduced, which will seriously affect the power generation efficiency of the collection. Therefore, an excellent component installation solution must find an appropriate balance between the array inclination and the land utilization, which can ensure that the components receive the best radiation amount and take into account the reasonable utilization of the land. The latitude of the component installation site in this project is about 43.5°. Suppose the conventional bracket installation scheme is adopted. In that case, the shadow shielding of the array will have a more significant impact on the land utilization rate, which is unacceptable for the tight project land situation. Therefore, in the pre-design process of the project, this project abandoned the conventional component installation method and switched to a new installation mode: first, the module installation inclination was reduced to 40°, on the one hand, the length of the array shadow can be shortened, and the other On the other hand, it can also reduce the cost of the bracket; secondly, in the conventional installation scheme, the mode of installing 2-row components in 1 group of arrays is changed to 1 group of displays and 3-row members. As a result, the number of features installed in a single collection group increases; generally, the number of components installed per unit area is more than that of the conventional installation scheme. The land utilization rate is also reasonably guaranteed.
(2) Inverter
The inverters used in photovoltaic power plants in my country are mainly divided into centralized inverters and string inverters. The centralized Inverter is large in capacity and volume, has better schedulability, and is cost-effective. Still, the centralized Inverter has a small number of MPPT and high requirements for installation conditions, which is more suitable for uniform installation of components and equipment—centralized large-scale power stations. String inverters have a small capacity, lightweight per device, good protection performance, low requirements for external use environment, easy transportation and installation, and string inverters generally have a large number of MPPTs, which can maximize the It can effectively reduce the adverse effects caused by component differences and shadow shading, and improve the efficiency of photovoltaic power generation. It is suitable for power station systems with complex component installation conditions, and in areas with more rainy and foggy days, the power generation time of string inverters is shorter. Long. The selection of photovoltaic power station inverters should be selected according to factors such as the scale of the power station, the geographical environment of the site, the system form, and grid connection requirements. The project is located in a mountain forest area, the equipment installation area is scattered, and the terrain severely restricts the component installation. Therefore, to reduce the loss of module series and parallel mismatch and optimize the power generation capacity of the photovoltaic power station, this project adopts a domestic high-quality string inverter with a 4-channel MPPT function in the inverter selection, and a single inverter is used. The rated power is 50kW. In addition, the open-circuit voltage and short-circuit current of photovoltaic modules will change with the fluctuation of the ambient temperature, especially the open-circuit voltage will increase with the decrease of the ambient temperature. Therefore, the serial number of components connected to the inverter MPPT must be calculated and demonstrated to ensure that it does not exceed the upper limit of the inverter MPPT working voltage under extremely low-temperature conditions; At the same time, it is also necessary to ensure that the capacity of the components connected to the Inverter is not higher than the maximum DC input power of the Inverter. In this project, each Inverter is associated with eight photovoltaic string circuits, each circuit is connected to 21 photovoltaic modules, and the DC input power of the Inverter is 45.36kW
(3) Field transformer
Domestic photovoltaic field transformer products mainly include oil-immersed transformers and dry-type transformers. Because photovoltaic power station transformers are mostly installed outdoors, oil-immersed box-type combined transformers with good protection performance and easy construction and installation are generally used. When designing and selecting a transformer, it is necessary to comprehensively consider the electrical design type of the photovoltaic system, the voltage transformation ratio, and the environmental conditions of installation and use, and select the most suitable product for the type of photovoltaic system while taking into account the enthusiasm. Oil-immersed transformers are widely used in photovoltaic systems due to their low cost, easy maintenance, flexible voltage level, and transformer capacity configuration. However, due to their large size and the risk of environmental pollution and fire due to leakage of insulating oil, they are generally suitable for Large-scale ground photovoltaic power station systems with sufficient installation sites and low fire rating requirements.
The photovoltaic field of this project is located on the mountain, and there is ample space for electrical equipment transportation and installation. Therefore, the oil-immersed box-type transformer of model ZGS11-ZG (referred to as "box-type transformer") is designed and designed to ventilate the transformer foundation. The oil pool can prevent environmental pollution and fire hazards caused by the leakage of insulating oil in the box changer.
Considering the scattered distribution of components in mountain power stations and the inconsistent installed capacity of power generation units, this project is designed to use box transformers with two degrees of 1000kVA and 1600kVA. According to the actual installed capacity of each power generation unit, each box transformer is connected to 20-38 units Inverter, the ratio of PV access capacity to box transformer rated capacity should not exceed 1.2.
(4) AC and DC cables
There are generally two types of cable laying in the field for mountain power stations: overhead and buried. For routes that need to cross ravines, woodlands, and rivers, overhead wires are generally used, while for areas with short distances, flat sites, and convenient ground construction, buried laying is used. This method has the advantages of a short construction period and low cost. The cables used in the photovoltaic field of this project mainly include photovoltaic DC cables between modules and inverters, AC cables between inverters and box transformers, and between box transformers and booster stations. The considerations for cable selection mainly include withstanding voltage rating, cross-sectional area, and cable type. Among them, the cables between the modules and the inverters are designed with photovoltaic special DC cables, which are arranged along with the purlins of the back brackets of the modules; the AC cables between the inverters and the box-type transformers and the box-type transformers are laid underground, considering the summer in the area where the power station is located. However, it is rainy and humid. The temperature is low in winter, so use an armored XLPE insulated polyethylene sheathed power cable (YJY23) with better moisture and low-temperature resistance. To make a selection.
Before laying buried cables, the appropriate buried depth must be determined. According to the requirements of the specification, the buried depth of directly buried lines should not be less than 0.7m, and when crossing farmland, the depth should not be less than 1.0m; at the same time, in cold regions, the thickness of the frozen soil layer in winter must also be considered, and the directly buried cables should be at the maximum depth of the firm soil layer—the following. The extreme minimum temperature in winter in the area where the project is located is -37.5°C, and the maximum thickness of the frozen soil layer is 1.8m. Therefore, the design depth of the cable trench in the photovoltaic field area should reach 2.0m. At the same time, the part passing through the road needs to be protected by steel pipes. Large-scale photovoltaic power plants cover a large area, with a large number of equipment, and the amount of AC and DC cables is enormous. Therefore, it is essential to reasonably estimate the number of wires used in the early stage of construction.
On the other hand, due to mountain power stations' complex terrain and construction conditions, it is difficult to estimate the number of cables based on the so-called "similar project" experience and construction drawings. Therefore, in the actual construction process of this project, the method of "construction drawing + experience value + on-site sampling value" is adopted to comprehensively count the cable engineering quantity. On the one hand, the construction drawings and the cable consumption data of previous mountain power stations are used to estimate; With the advancement of the project, the reference samples of cables will become more and more abundant and representative and the estimated value of cable usage will become more and more accurate.
1.2 PV field operation and maintenance management
Since the construction of photovoltaic power station projects and on-grid electricity prices in my country are greatly affected by policies, the construction period of most projects is short, and the design and construction of power stations cannot be fully scientifically and effectively controlled. Therefore, management has caused particular difficulties and hidden dangers. At the same time, due to the explosive growth of photovoltaic projects in recent years, a large number of power stations have been put into operation, while the training and reserve of professional process and maintenance personnel in the industry is relatively backward, resulting in the tension of photovoltaic power station operation and maintenance personnel, and the uneven operation and maintenance level and quality. Therefore, strengthening and improving power plants' operation and maintenance management is of great significance to ensure the service life and economic benefits of photovoltaic power plants.
(1) Field equipment management
The leading equipment in the photovoltaic field area includes photovoltaic modules, string inverters, and box transformers. The management of this equipment is mainly through the data collection and monitoring of the site and regular on-site inspections, etc., to understand the operating parameters and conditions of the equipment, analyze potential safety hazards and eliminate faults promptly.
The leading equipment in the photovoltaic field is equipped with data acquisition terminals. The real-time transmission of data and instructions can be realized through the RS485 communication cable and optical fiber ring network laid in the field and the central control room of the booster station. The operation and maintenance personnel are in the central control room. The operating parameters of all electrical equipment in the field can be tested indoors, including parameters such as inverter power generation, box-changing power, etc., as shown in Figure 3 and Figure 4; The equipment is remotely controlled to realize the automatic management of the leading electrical equipment in the photovoltaic field.
At the same time, the inspection of the leading equipment should be strengthened, and the operation and maintenance personnel should be regularly arranged to conduct on-site checks of the photovoltaic modules, inverters, and box transformers in the photovoltaic field and record the operating conditions and relevant parameters of each equipment.
Fig.3 Typical daily power generation distribution of inverter
Problems found in the investigation are classified, summarized, and sorted promptly, and targeted solutions are formulated according to the seriousness of the situation. For photovoltaic power plants in high-altitude areas, due to the large inclination of the module installation, special attention should be paid to the force of the module bracket, and the loose connection parts should be tightened in time. For photovoltaic power stations in areas with a significant temperature difference between day and night, special attention should be paid to the frost condensation in the electrical equipment box, especially the inside of the box transformer. It is necessary to focus on checking whether there is frost and condensation on the surface of each terminal and circuit breaker in and timely if necessary. Remove ice on the inner wall of the box, and ensure smooth ventilation of the box to prevent the electrical equipment in the box from being damp and affecting the insulation performance. The inspection period is generally 1 to 2 weeks, which can be determined according to the actual operation of the power station and the weather and environmental conditions of the site. For newly put into operation, after maintenance and equipment with a history of failure, inspections should be strengthened; at the same time, checks should be maintained before and after extreme weather such as snowfall, rainfall, gale, and hail.
(2) Cleaning of photovoltaic modules
Photovoltaic power stations constructed and operated in my country use crystalline silicon modules with a glass substrate. This module mainly comprises tempered glass, backplane, aluminum alloy frame, crystalline silicon cells, EVA, silica gel and junction box, etc. Light receiving area and photoelectric conversion efficiency, but its tempered glass surface is also prone to accumulation of dust and dirt. An obstruction such as dust on the surface of the module will reduce its photoelectric conversion efficiency and cause a hot spot effect in the shaded part of the module, which may cause severe damage to the photovoltaic module. Therefore, it is necessary to formulate corresponding measures and plans to regularly clean the surface of photovoltaic modules installed in the power station to ensure the modules' conversion efficiency and operation safety. The commonly used cleaning technologies for photovoltaic modules in my country's photovoltaic power plants mainly include manual cleaning technology with high-pressure water guns, onboard robot cleaning technology, photovoltaic module self-cleaning technology, electric curtain dust removal technology, and vehicle-mounted mobile cleaning technology. The characteristics of various cleaning technologies are introduced in Table 1.
Table 1 Commonly used photovoltaic module cleaning technologies
The project is located in a forest area far away from the urban area. There are no air pollution sources such as thermal power plants and mining fields around the site. Therefore, the air cleanliness is high, and the photovoltaic modules are less affected by dust. However, the temperature of the project site is low in winter, and the snowfall time is extended. Therefore, module cleaning mainly considers the impact of snow on PV modules. In response to this problem, combined with the actual situation of the project location and the module installation mode, this project adopts a combination of passive cleaning and active cleaning to clean and maintain the photovoltaic modules in the field.
Passive cleaning combines the characteristics of the high installation height and large inclination angle (40°) of the photovoltaic modules of this project. Under the influence of its gravity, the snow on the surface of the modules in winter is challenging to adhere to the glass surface of the modules. When the sunlight hits the modules, The increased surface temperature of the components will help shed snow ice. Judging from the actual operation of the power station, in early December, after the snowfall in the field at night, the thickness of the snow on the surface of the photovoltaic modules is about 2-5 cm in the morning. It falls off by itself, and the remaining snowfalls off after 2 hours. Similarly, in other seasons, debris such as dust or leaves falling on the surface of the module can also smoothly slide off the surface of the module under the action of rain and wind.
Active cleaning Considering the requirements of economy and applicability, for those snow and dust debris that their weight cannot remove, this project adopts the method of regularly arranging cleaning personnel to remove snow and dust to clean the components manually. For areas with abundant water sources, pressurized water guns can be used to rinse, and the other regions can be cleaned manually with tools such as rags. The cleaning time of the modules should be selected in the early morning, evening, night, or cloudy days to avoid the adverse effects of the shadows of equipment and personnel on the power generation efficiency of photovoltaic modules during the cleaning process. The selection of the cleaning cycle should be determined according to the degree of contamination on the surface of the component. Under normal circumstances, for dust attachments, the number of cleanings should be no less than twice a year; for snow, it should be arranged promptly according to the thickness of the accumulation on the surface of the module and the recent snowfall.
The quality of operation and maintenance personnel training of photovoltaic power station operation and maintenance management depends on the skill and quality of process and maintenance personnel. Photovoltaic power generation technology is a new form of energy utilization. Most power stations' operation and maintenance management teams are relatively young and lack photovoltaic operation and maintenance experience and technology. Therefore, the power station operation and maintenance unit should strengthen the professional training of operation and maintenance personnel. During the operation and maintenance of photovoltaic power plants, according to relevant laws and regulations and the provisions of the local power department, combined with the rules and regulations of power station operation, formulate training programs that meet their characteristics and Detailed rules, continuously improve the technical level of employees, and strengthen their awareness of learning and innovation. At the same time, attention should be paid to technical disclosure and training from professional subcontracting units or equipment manufacturers. There are many professions and industries involved in constructing photovoltaic power plants, and the pre-project design, construction, and operation and maintenance management are often not completed by the same company or department. Therefore, professional subcontracting is required when the power station is completed and handed over to the operation and maintenance unit. The unit and equipment supplier shall make technical disclosure to the operation and maintenance unit and provide necessary training services to ensure that the operation and maintenance personnel are familiar with the performance of the system and equipment and master the operation and maintenance methods.
2.Photovoltaic power generation and benefit analysis
2.1 Theoretical power generation calculation
According to the "Design Specifications for Photovoltaic Power Stations," the forecast of the power generation of photovoltaic power stations should be calculated and determined according to the solar energy resources at the site. After considering various factors such as photovoltaic power station system design, photovoltaic array layout, and environmental conditions, the calculation formula is: :
In the formula, EP is the on-grid power generation, kWh; HA is the total solar irradiance on the horizontal plane, which is 1412.55kWh/m² in this project; ES is the irradiance under standard conditions, with a constant of 1kWh/m²; PAZ is the component The installation capacity is 100000kWp in this project; K is the comprehensive efficiency coefficient, which is 0.8. Therefore, the theoretical power generation capacity of the power station in the first year of this project is
Due to the aging of the primary material and ultraviolet radiation, the power of photovoltaic modules will decline year by year during use. The power attenuation rate of the modules used in this project is 2.5% in the first year, 0.7% in each year after the first year, 8.8% in 10 years, and 19.3% in 25 years. Therefore, the system's life is calculated as 25 years, and Table 2 is the calculation result of the 25-year power generation of the project.
According to the analysis, the cumulative total power generation of the project in 25 years is 2,517.16 million kWh, the average annual power generation in 25 years is 100.69 million kWh, and the annual power generation per watt of installed capacity is about 1.007 kWh.
2.2 Benefit Analysis
The power station is located in Yanbian Prefecture, Jilin Province. According to the "Notice of the National Development and Reform Commission on the Price Policy of Photovoltaic Power Generation Projects in 2018" (Fa Gai Price Regulation [2017] No. 2196), the photovoltaic power station put into operation after January 1, 2018, The benchmark on-grid electricity prices for Class I, Class II, and Class III resource areas are adjusted to 0.55 yuan/kWh, 0.65 yuan/kWh, and 0.75 yuan/kWh (tax included), respectively. This area is a Class II resource area, and the benchmark on-grid electricity price for photovoltaic power plants is 0.65 yuan/kWh. At the same time, according to Jilin Province's "Proposal on Accelerating the Application of Photovoltaic Products to Promote the Healthy Development of the Industry (No. 128)", Jilin Province implements a policy of electricity subsidy for photovoltaic power generation projects and based on national regulations, additional support of 0.15 yuan/kWh. Therefore, the photovoltaic power station can enjoy a 0.8 yuan/kWh subsidy.
The installed capacity of the first phase of the project is 100MW. According to the cost estimate of 8 yuan/W, the initial budget investment is about 800 million yuan, and the actual acquisition of the project is 790 million yuan, which is slightly lower than the previous budget investment. According to estimates, the average annual power generation of the project is 100,686,564 kWh. According to the policy, subsidies can be obtained at 0.8 yuan/kWh, and the photovoltaic power station's average yearly electricity fee income is about 80.549 million yuan.
According to the estimate of the actual investment, the project will recover the cost in about ten years. The cumulative total power generation of the power station in 25 years is 2.517 billion kWh, and the total income is about 2.014 billion yuan. During the 25-year service life, the profit of this project is about 1.224 billion yuan. At the same time, the project can realize 14 million yuan in local taxes and 12 million yuan in poverty alleviation funds each year, and 4,000 registered poor households can be successfully lifted out of poverty, with an average annual income increase of 3,000 yuan.
In addition, since the photovoltaic power station consumes less power and does not emit pollutants such as carbon dioxide, sulfur dioxide, and nitrogen oxides to the external environment, it has high environmental protection value and social benefits. The photovoltaic power station generates an average of nearly 100 million kWh per year. According to the relevant conversion rules, it can save 36247.16t of standard coal every year, which means reducing the emission of carbon dioxide 100384.5t, sulfur dioxide 1188.1t, and nitrogen oxides 432.9t, and can reduce the generation of thermal power generation. In addition, 27386.7t of dust saved nearly 400 million L of purified water.
3.Summary
After the explosive growth of the photovoltaic industry in recent years, the lag in the construction of power grids in individual regions has become increasingly prominent. Coupled with the acceleration of industrial transformation and upgrading in my country, the national electricity demand has slowed down. As a result, photovoltaic power curtailment has occurred in various places. At the same time, to achieve the goal of photovoltaic grid parity, the benchmark on-grid electricity price for photovoltaics has entered a downward channel. According to the "Notice of the National Development and Reform Commission on the Price Policy of Photovoltaic Power Generation Projects in 2018", the benchmark on-grid electricity price in 2018 was reduced by 0.1 compared to 2017. Yuan/kWh. In this context, photovoltaic companies will face more significant pressure to reduce costs. In contrast, the raw materials (such as components, steel, etc.) and labor costs required to construct photovoltaic power plants remain high. Balancing the relationship between costs and benefits is a complex problem that the photovoltaic industry needs to think about and solve next.
1. Classification and composition of solar photovoltaic power stations
Solar photovoltaic power stations can be divided into independent and grid-connected types according to whether they are connected to the public grid. The type of solar photovoltaic power generation system needs to be selected based on the reference power supply demand, and the most reasonable solar photovoltaic power generation system is established.
2. Key points of site selection for solar photovoltaic power stations
Solar photovoltaic power stations are distributed all over the world. In my country's construction of solar photovoltaic power stations, sufficient attention should be paid to the site selection of solar photovoltaic power stations. In the site selection of solar photovoltaic power stations, light conditions need to be considered to ensure sufficient light shining on the solar panel to provide the power generation effect. The solar photovoltaic power station is located in an area with flat terrain. Therefore, it is not prone to natural disasters to avoid the severe impact of natural disasters on the equipment of the solar photovoltaic power station. Avoid large numbers or buildings around the solar photovoltaic power station site that will shade the solar photovoltaic power station and affect the illumination of the solar photovoltaic power station.
3. Design points of the independent solar photovoltaic power generation system
When designing a solar photovoltaic power generation system, it mainly focuses on the capacity of the solar photovoltaic power generation system, the selection of power electronic equipment in the solar photovoltaic power generation system, and the design and calculation of ancillary facilities. Among them, the capacity design is mainly aimed at the capacity of the battery components and batteries in the solar photovoltaic power generation system. The focus is to ensure that the electricity stored in the batteries can meet the work requirements. For the selection and configuration of system components in the solar photovoltaic power generation system, it is necessary to ensure that the selected equipment matches the capacity design of the solar photovoltaic power generation system to ensure that the solar photovoltaic power generation system can work typically.
4. Main points of capacity design of independent solar photovoltaic power generation system
When designing the capacity of an autonomous solar photovoltaic power generation system, the load and local dimensions of the separate solar photovoltaic power generation system should be listed first, and the load size and power consumption of the independent solar photovoltaic power generation system should be determined. On this basis, the battery capacity of the separate solar photovoltaic power generation system is selected. Then, the optimal current of the different solar photovoltaic power generation systems is determined by calculating the square array current of the independent solar photovoltaic power generation system. Then the square array voltage of the battery of the independent solar photovoltaic power generation system is selected. Finally, the battery of the separate solar photovoltaic power generation system is determined of power. When designing the power of the battery square array of the independent solar photovoltaic power generation system, the design of the solar battery square array of the separate solar photovoltaic power generation system can be completed according to the principle of series boosting and parallel rectification.
5. Main points of installation of the independent solar photovoltaic power generation system
5.1 Stand foundation construction of stand-alone solar photovoltaic power generation system
The battery matrix base of the independent solar photovoltaic power generation system should be made of concrete. The concrete floor's ground height and horizontal deviation should meet the design requirements and specifications. The battery matrix base should be fixed with anchor bolts. The leakage must meet the requirements of the design specification. After the concrete pouring and fixing of the anchor bolts, it needs to be cured for at least five days to ensure its solidification strength before the stand-alone solar photovoltaic power generation system rack can be completed.
When installing the solar bracket of the independent solar photovoltaic power generation system, attention should be paid to: (1) The azimuth angle and inclination angle of the square array frame of the independent solar photovoltaic power generation system needs to meet the design requirements. (2) When installing the rack of the independent solar photovoltaic power generation system, it is necessary to pay attention to the need to control the levelness of the bottom within the range of 3mm/m. When the levelness exceeds the allowable range, a horn should be used for leveling. (3) The surface of the fixed part of the stand-alone solar photovoltaic power generation system rack should be as flat as possible to avoid damage to the cells. (4) For the fixed part of the stand-alone solar photovoltaic power generation system rack, anti-loose gaskets should be installed to improve the reliability of its connection. (5) For the solar cell array with the sun-tracking device in the independent solar photovoltaic power generation system, the tracking device should be checked regularly to ensure its sun-tracking performance. (6) For the stand-alone solar photovoltaic power generation system, the angle between the rack and the ground can be fixed or adjusted according to seasonal changes so that the solar panel can most likely increase the receiving area and lighting time of sunlight and improve the independence of the solar panel—the power generation efficiency of the solar photovoltaic power generation system.
5.2 Installation points of solar modules of the stand-alone solar photovoltaic power generation system
When installing the solar modules of the stand-alone solar photovoltaic power generation system, please pay attention to: (1) When installing the solar modules of the stand-alone solar photovoltaic power generation system, it is necessary to measure and check the parameters of each component first to ensure that the parameters meet the User requirements to measure the open-circuit voltage and short circuit current of the solar module. (2) Solar modules with similar working parameters need to be installed in the same square array to improve the power generation efficiency of the square array of the independent solar photovoltaic power generation system. (3) During the installation of solar panels, etc., bumps should be avoided to avoid damage to solar panels, etc. (4) If the solar panel and the fixed frame are not closely matched, they need to be leveled with iron sheets to improve the tightness of the connection between the two. (5) When installing the solar panel, it is necessary to use the prefabricated installation on the solar panel frame for connection. When connecting with screws, pay attention to the tightness of the connection, and pay attention to the relaxation work in advance according to the standards used. (6) The position of the solar module installed on the rack should be as high quality as possible. The gap between the solar module installed on the rack and the rack should be greater than 8mm to improve the heat dissipation capacity of the solar module. (7) The junction box of the solar panel needs to be protected from rain and frost to avoid damage caused by rain.
5.3 Main points of cable connection of solar photovoltaic power generation system
When laying the connecting cables of the solar photovoltaic power generation system, pay attention to the principle of first outdoor, then indoor, first simple, and then complicated. At the same time, pay attention to the following when laying cables: (1) When laying cables on the sharp edge of the wall and bracket, pay attention to the protection of the cables. (2) Pay attention to the direction and fixation of the cable when laying the cable, and pay attention to the moderate tightness of the cable layout. (3) Pay attention to protection at the joint of the cable to prevent oxidation or fall off at the joint, which affects the connection effect of the cable. (4) The feeder and return line of the same circuit should be twisted together as much as possible to avoid the influence of the electromagnetic interference of the cable on the cable.
5.4 Do an excellent job of lightning protection for solar photovoltaic power generation systems
During installing the solar photovoltaic power generation system, attention should be paid to the lightning protection and grounding of the solar photovoltaic power generation system. The grounding cable of the lightning rod should be kept at a certain distance from the bracket of the solar photovoltaic power generation system. For the lightning protection of the solar photovoltaic power generation system, two lightning protection methods can be used to install the lightning rod or the lightning protection line to protect the safety of the solar photovoltaic power generation system.
Epilogue
The development and utilization of solar energy is the focus of energy development and even in the future. Based on the analysis of the composition and characteristics of the solar photovoltaic system, this paper analyzes and expounds on the critical points of the design and installation of the solar photovoltaic system.