Photovoltaic power generation is the cutting-edge technology in today's world. It will solve the three major world challenges of “energy crisis”, “environmental pollution” and “sustainable development” for all mankind. It will make a historic and cross-generational contribution. Humankind has entered a new era in the use of new energy sources and new technologies. There are several core issues in the actual development.
1 Solar Resource Data and Assessment
1.1 Solar Energy Resources Data
Solar radiation data can be obtained from county-level meteorological observatories or from the National Weather Service. The data obtained from the Bureau of Meteorology is the radiation data of the horizontal plane, including: total radiation in the horizontal plane, direct radiation in the horizontal plane, and scattered radiation in the horizontal plane.
The solar resource data mainly includes: Monthly solar energy total radiation (irradiance) or total daily solar radiation and radiation intensity. The data related to the climatic conditions mainly include: annual average temperature, annual average maximum temperature, annual average minimum temperature, longest continuous cloudy days in one year (including precipitation or snowfall days), annual average wind speed, annual maximum wind speed, annual hail times , The number of sandstorm days in the year. Among them, the monthly value of total solar radiation is essential. In addition, cumulative data for the last 5 to 10 years of each of the above data should also be provided to assess the validity of data on the number of solar energy resources and climate conditions.
1.2 Evaluation of the validity of solar energy data
The use of solar resource data provided by meteorological observatories or related departments for the design of photovoltaic systems will in some cases still require an assessment of their effectiveness.
First of all, when the solar energy resources data for a specific site is incomplete or lacks years of accumulated data, the effectiveness and magnitude of solar radiation must be evaluated.
Second, although the local solar resource data is relatively complete, and the solar radiation is also better, the candidate site is located in or near the mountainous terrain that has significant effects on solar radiation. In this case, the effectiveness of the local solar resource data should be assessed by studying the average data change in the neighboring areas around the candidate site.
Again, the data obtained from the meteorological department is the data of the horizontal plane, including the direct radiation of the horizontal plane and the scattered radiation of the horizontal plane, thereby obtaining the total amount of radiation data on the horizontal plane. However, in the practical application of solar photovoltaic power generation, in order to obtain more power generation capacity and the need for self-cleaning of the battery assembly, the fixed installation matrix is usually tilted, which requires calculating the amount of solar radiation on the inclined surface ( Usually larger than the amount of radiation on the horizontal surface). However, this calculation process is very complicated, so people often directly use the data on the horizontal plane, or use an empirical coefficient method for simple conversion, which has an impact on the accuracy of the calculation. In recent years, some software has been developed, which not only can easily solve these calculation problems, but also stores a large number of solar radiation data in different regions in the database. Some of them also have the function of photovoltaic system analysis and design.
2 Location and Site Assessment of Photovoltaic System
2.1 Need to eliminate the influence of shadow when selecting the photovoltaic system
Solar cells rely on sunlight to generate electricity. When the sunlight projected onto the panel is blocked, the power output characteristics of the array will be seriously affected. A small shadow on the panel can also greatly reduce its performance. Therefore, The careful determination of the sun path and shadows during the design and installation of the PV system is extremely important for ensuring the power rating of the array and reducing the cost of generating electricity from the PV system.
Shadows on the ground often come from trees, vegetation, nearby buildings, and struts and wires from solar collectors. As a general rule, it is good to determine that there is no shadow from 9:00 am to 3:00 pm. In the winter months, when the sun's elevation angle is low, the obstruction of the solar panels is often a big problem, which should attract the attention of photovoltaic system designers and photovoltaic power plant operators. China is located in the northern hemisphere of the Earth. The most unfavorable shadow of the solar array’s power generation appears sometime around December 21 (ie, the winter solstice).
To eliminate the influence of shadows, after selecting the venue, you must confirm whether the following conditions are met: (1) In any month of the year, the sunlight that is thrown into the solar array will not be blocked; (2) Daily from 9:00 am to 3:00 pm There is no shadow on the panel; (3) Identify obstacles blocking the solar array from 9 am to 3 pm, and eliminate shadow sources; (4) Consider moving a solar array or if moving shadows cannot be eliminated. Increase capacity to compensate for loss due to shadows.
2,2 Assessment of PV System Sites
In the evaluation of photovoltaic system sites, the following assessment should be conducted.
(1) General conditions of sunshine assessment
After collecting the solar energy data of the candidate sites according to the requirements, we should also carefully observe the obstructions near the site to assess the impact of solar shadows on the solar array power generation, and propose to avoid obstacles or remove obstacles. . By looking at the roof, walls or yard or directly, find the best position for satisfying the full-year sunshine conditions of the phalanx.
In the south of the Northern Hemisphere is the most basic orientation of the solar cell array. If you make sure that the square faces a south or 0° azimuth, the daily sunshine performance will be the best. However, the impact of local climate characteristics should be considered and carefully evaluated. For example, if there is fog in the morning near the site, the square array needs to be adjusted slightly southwest to obtain more effective solar radiation that lags behind at noon.
(2) Estimate the running time of the square
The longer the solar cell array is exposed to sunlight, the more electricity the system can deliver per day. Therefore, after the initial determination of the orientation and height of the field on the site, it is necessary to evaluate and determine the daily running time of solar panels in different seasons.
(3) Sun Window
When evaluating the venue, you must choose a time with good sunshine and no shadows throughout the day as the running time of the solar array. This optimal time zone is called the "large window."
The "solar window" concept can show the sunshine time and path conditions of the site. According to the different conditions of sunshine on the site, the solar window can be selected from 9:00 am to 3:00 pm, or from 8:20 am to 3:20 pm. In the summer, when the sun rises early and late, it is very late. In sunshine, it is much longer than in winter. Therefore, the solar window in summer is longer than the sun window in winter, which is the long running time of the square. The size of solar windows is not only affected by the season, but also related to the environmental conditions around the site. For example, the mountains, forests, and tall buildings on the east and west sides of the site will reduce the running time of solar arrays. The solar window time is different throughout the year. To accurately determine the sun window, first of all need to ask the meteorological department about the local sunrise and sunset sun azimuths and noon sun elevation angles in different seasons, and then correct according to the site specific conditions. If only the approximate “sun window” time of the site is required, visual inspection is sufficient.
If the site is evaluated only from the length of sunshine, the solar window period has reached 9:00 am to 3:00 pm and has met the photovoltaic system power generation conditions. When the “Sun Window” time period reaches 10:00 am to 2:00 pm, it means that the sunshine time of the field is too short. Check or remove the surrounding obstacles or consider alternative sites.
(4) Conditions of transport
The transportation site and transportation conditions should be considered at the installation site. There should be roads nearby to facilitate the transportation of photovoltaic modules, control cabinets, and storage batteries. If the truck cannot reach the site, at least the agricultural vehicle can reach the site.
(5) Power supply conditions
The installation site should be closer to the power supply village, and the power supply radius should not exceed 1 km. Considering the convenient and low-voltage cable transmission loss caused by the operating personnel, the power supply load and the capacity expansion potential must be investigated in detail. For off-grid independent village power stations, the power grid will not extend to this point in the short term, so as to avoid unnecessary duplicate construction and future power station relocation issues.
3 Selected battery capacity and battery pack installation
3.1 Selected battery capacity
Designers need to evaluate the system load demand on the battery capacity. When determining the battery capacity, it is first necessary to determine how much power is required for the load of the access system; secondly, it is determined according to the climatic conditions how many days of storage the battery needs to be stored. When measuring, pay attention to the battery capacity will be affected by many prisoners, such as: discharge rate, depth of discharge, temperature, battery aging and controller performance. Of course, the required battery capacity is also affected by the size of the load. Reducing the load will reduce the required battery capacity. At the same time, when determining the battery capacity, the larger the capacity is, the better, and the larger battery capacity scale will also cause problems. Therefore, proper and reasonable determination of the battery capacity of a photovoltaic system is an important and meticulous task that must be taken seriously.
3.2 Installation of battery
(l) The battery to which the electrolyte is added should be tightened with the lid of the filling hole to prevent impurities from falling into the interior of the battery. The vent on the rubber plug must be kept clear.
(2) Each clamp and battery pole must be in close contact. After the connecting wires are connected, a thin layer of petroleum jelly must be applied to each connection point to prevent corrosion of the connection points.
(3) The storage battery should be placed in a well-ventilated place away from direct sunlight. The heat source should not be less than 2 meters and the room temperature should be maintained between 10 and 25C.
(4) Insulation measures shall be taken between the storage battery and the ground. For example, wood or other insulating objects may be placed on the battery to avoid discharge due to short circuit between the storage battery and the ground.
(5) The location where the battery is placed should be selected in a place closer to the solar cell array. The connecting wires should be as short as possible and the diameter of the wires chosen should not be too thin to minimize unnecessary line losses.
(6) Acid batteries and alkaline batteries must not be placed in the same room at the same time.
(7) For the storage battery rooms with more storage batteries, it is not allowed to use open flame heating in the winter, and it is better to use fire walls, solar houses, etc. to increase the indoor temperature and maintain good ventilation conditions.
4 Charging Controller Performance and Protection Against Lightning Strike
4.1 The performance of the charging controller has a great influence on the system
The evaluation of the performance of the photovoltaic charge controller can be mainly considered from three aspects: reliability, ease of maintenance and charging performance. A photovoltaic controller with good quality, safety and reliability, which is not easy to fail, is obviously an effective guarantee for the overall performance of the photovoltaic system. In particular, the stability of key settings such as the charge and discharge voltage control of the battery is directly related to the safety of the battery. life. An easy-to-maintain photovoltaic charging controller that is clearly structured and easy to repair after a failure can also improve the performance of the PV system from another aspect. The excellent energy consumption and charging control strategy of the PV charging controller directly affects the amount of power that the PV system itself can provide. The low-power and high-efficiency photovoltaic charging controller can improve the utilization of the PV modules and improve the efficiency. The overall performance of the photovoltaic system.
4.2 Measures to Prevent Lightning Strike of Charge Controller
To prevent lightning strikes, we must first understand how thunder and lightning people invade the power system. Lightning people invade three types: direct lightning, inductive lightning, and lightning.
Direct lightning strikes directly into the solar cell array, low voltage distribution lines, electrical installations, their wiring, etc., as well as lightning strikes nearby. The direct lightning current peaks about 50% in the range of 15-20 kA, and lightning strikes in the range of 200-30OkA can also be observed. Since the energy of such a lightning strike is very large, lightning rods and the like are installed as measures against direct lightning.
Inductive lightning is divided into lightning caused by electrostatic induction and lightning induced by electromagnetic induction. Thunder formed by electrostatic induction is due to the formation of thunderclouds. For example, the positive charge induced by a cable and the surface charge caused by a lightning strike are neutralized to form lightning surges. Thunder formed by electromagnetic induction is caused by the lightning current generated by a lightning strike that falls near the cable and causes the cable to induce lightning surge.
One end of the PV charging controller is connected to the battery and one end is connected to the solar cell array. Because the battery is installed in a building, as long as the building is equipped with building lightning protection measures in accordance with building codes, the battery is basically not exposed to lightning. Therefore, the charging controller does not require special lightning protection measures on the side that connects to the battery.
The solar cell array is installed outdoors in the open air, and the PV module frame is generally made of aluminum. The PV mounting bracket is generally a steel structural component, which greatly increases the possibility of lightning strikes. In order to prevent direct lightning strikes in the solar cell array, the photovoltaic installation site should be provided with a lightning rod. The lightning rod should be reliably grounded so that the lightning current can be safely and quickly grounded; to ensure the safety of the electrical devices, the grounding of the lightning rod should be protected by the electrical device. Separate them and keep a safe distance. In order to prevent the damage caused by the induced lightning, the photovoltaic cable should be provided with a metal bridge and be reliably grounded; the PV site controller should have a closed metal shell and be reliably grounded, and at the same time ensure the equipotential bonding of the grounding point. In order to prevent damage caused by lightning waves, photovoltaic controllers should install lightning protection devices, such as varistors or lightning protection modules, in the population of PV lines and be reliably grounded.
5 Inverter Overlay Use and Control Inverter-Pros and Cons
5.1 Inverter Overlay
Inverters used in photovoltaic power plants can also be referred to as stand-alone inverters that build their own 220V/50Hz grid while outputting electrical energy.
Under normal circumstances, this type of inverter cannot directly superimpose the AC output of multiple inverters in parallel. Because each inverter has its own independent voltage, frequency, and phase characteristics, even if it is turned on and put into operation at the same time, it cannot guarantee that the voltage, frequency, and phase of each inverter output are exactly the same, resulting in distortion of the power grid waveform, voltage and current. Drift will cause the grid to fail to work. Severely, the output current of the inverter will be reversed and the inverter will be damaged.
If it is indeed necessary to use multiple inverters in parallel to increase the output capacity of the inverter, it is necessary to select inverter models that can work in parallel. In this case, an inverter is called a master and other inverters are called slaves. The host establishes a power grid to determine basic parameters such as voltage, frequency, and phase of the grid. At the same time, the same frequency in-phase command is issued to the slave, and the slave inputs exactly the same AC power to the grid according to the instruction. If the frequency phase of the slave and the master is deviated, the slave should correct the deviation at any time and make it send out. The power parameters are kept consistent with the host. When the host sends the same-phase in-phase command, it also sends power adjustment instructions to the slave to ensure that the output power balances among the inverters, preventing the individual hosts from being overloaded and the others from under-loading. .
5.2 Advantages and Disadvantages of Controlling Inverter
The advantages of controlling the inverter are: the combination of photovoltaic charging and inverter, small size, less wiring, simple to use, easy to maintain, high cost performance, high efficiency of the whole machine, especially suitable for the household system. The inverter protection integrated circuit has a complete internal protection circuit, and has protection measures such as input overvoltage, input undervoltage, output overload, output short circuit, input direct-current reverse, overheat protection and the like, which can effectively guarantee the use safety during use. The disadvantages of controlling the inverter are also obvious. Because the charger capacity and the inverter capacity are fixed and cannot be adjusted, it is not suitable for a system in which the power generation and the power load do not match.
6 Lifespan of Off-grid Photovoltaic Power Generation System
The lifespan of the off-grid PV system is mainly as follows: The service life of the battery is usually about 5 years, the inverter life is about 10 years, and the lifetime of the PV module is 20-25 years. Generally, the lifetime of the off-grid photovoltaic system is considered as It is 20 years, so the battery, controller and inverter need to be replaced during the life cycle.
7 Local grid design
Local grid design needs to consider the construction of power points, the composition of grid architecture, and the matching and management of loads. Planning for power points in local power grids should first consider the construction of local natural resources. Since such power grids are generally located in remote areas, the choice of power station type should be based on renewable energy such as hydropower, photovoltaic, and wind power. The choice of power station capacity should be based on the local socio-economic development level and make a reasonable load forecast to meet the demand for electricity within 5 to 10 years. If possible, it is necessary to plan as many as possible different types of power stations to operate in a networked mode of operation, to make full use of various natural resources, and to use the advantages of complementary resources.
The construction of local grids is generally based on 220v/380V low-voltage power distribution systems, so as to reduce the power loss caused by substations. If there are power points that are too far from the load center, power transmission must be performed, according to the distance. Select a reasonable transmission and distribution voltage level in the distance. The distribution form of the low-voltage power grid is generally based on a tree structure, which facilitates the maintenance of the power grid and the elimination of faults. If there are more than two power point contact lines, they can be connected in a ring network or double return mode to improve the reliability of power supply, power transmission and distribution. In the local power grids, relay protection devices should be set up in stages. Short-circuit currents and other parameters of each protection point should be calculated according to the cable type and length of transmission and distribution lines. Appropriate relay protection products should be selected to set reasonable protection parameters to ensure safe operation of the power grid.
Due to the small range, limited energy sources, and fragile network, local grids must be strictly managed for access to the grid, prohibiting the occurrence of private connections, limiting high-power loads (such as electric stoves, electric heaters, and central air-conditioning systems) and large Impact load (large-capacity motor, welding machine, etc.) use. The grid load should be managed according to the user's different levels, and the key departments such as party and government agencies, military units, schools, and banks should be classified as a first-level load range that guarantees power supply at any time; for residents, shops, etc., classified as non-emergency under normal power supply Secondary loads; for general factories, restaurants, and entertainment venues should be classified as secondary loads that do not guarantee continuous power supply, and achieve a reasonable and orderly allocation of limited power energy.
8 Monitoring and Operational Data Analysis and Evaluation of Photovoltaic Power Plants
Photovoltaic power generation system is still a new thing, but it has not reached the scale of promotion and application. At present, there are disadvantageous conditions such as distant distances, low level of local technology, and limited capacity of independent power grids, which increase the difficulty of managing photovoltaic power plants. Therefore, the implementation of the monitoring of the operation of the power station, through the scientific analysis of the data on the operation of the system, to find out the internal laws, provide a reliable basis for the system optimization design, and contribute to the promotion of an independent photovoltaic power generation system on a larger scale.
8.1 Power Station Monitoring Content
(1) Local lighting and wind resources: the intensity of the sun's radiation and the duration of the light during each day, and the wind speed and direction at various times of the day.
(2) Weather conditions (temperature, lightning, dust, hail, rain, snow, clouds, etc.).
(3) Power generation and power generation of each generation subsystem of the system during each period.
(4) The charging controller's working status in each period.
(5) The battery pack's working status in each period.
(6) The working status of the system load in each period.
(7) System failure statistics.
8.2 Monitoring Means and Methods
(1) For power stations that do not have automatic data acquisition devices installed, manual readings are used to record data. In order to ensure the authenticity (reliability and accuracy) of the data, the station staff must learn how to correctly read the form, measure and fill in the form of the working diary when attending the training. The professional and technical personnel of the owner company regularly proofread and verify the work diary of each power station. The work diary of the power station must be filed for archival purposes, and should not be lost or damaged. The manual recording of the work diary is a daily work that must be done from beginning to end.
(2) For a power station equipped with an automatic data acquisition device, professional technicians regularly read and record, or when the power station staff is specially trained to periodically replace the data recording disk, mail it to a professional data collector.
(3) In the power station with various communication conditions, a remote monitoring system can be established. The professional and technical personnel can perform real-time monitoring and remotely collect data automatically.
8.3 Analysis and Evaluation of Power Station Operation Data
On the basis of obtaining complete data, the following assessments should be analyzed and completed.
(1) The amount of electricity provided by photovoltaic power plants every month and every year.
(2) The monthly electricity consumption of the whole village and the power consumption of each load.
(3) 24 hours per month energy flow chart.
(4) Each system mainly sets its work performance and potential.
(5) Analysis of power supply margin.
(6) Load development forecast.
(7) Failure analysis and preventive measures. The follow-up monitoring and evaluation of photovoltaic power plants will help improve the management system, further improve the photovoltaic power plant, give full play to the potential of the system, and make the system operate under the best conditions to obtain the best economic and social benefits.
9 Cost Analysis of Off-grid Photovoltaic Power Generation System
Investment costs and operating costs constitute the main cost of off-grid photovoltaic power generation systems. However, it should be noted that an off-grid photovoltaic power generation project, especially a rural off-grid photovoltaic power generation project in remote areas, creates additional value for the entire society. This is not simply a sum of local values. . Its external factors include: benefits to the environment, health, safety and education, reduction of urban migration, promotion of national unity, social stability and technological progress. The value of these benefits, in comparison with economic analysis, is more of a concern for social and environmental benefits.
It is very important for the project developers of off-grid photovoltaic power generation systems to submit various cost descriptions related to the project. The cost can be divided into the following five parts:
(1) Initial investment (cost of equipment, infrastructure and installation);
(2) set the replacement cost (set each and installation);
(3) Operation and maintenance costs (salary and material costs);
(4) Energy service fee (inspection and maintenance service fee of owner or energy service company);
(5) Recycling and dismantling costs.
The system cost description submitted to the power plant operation should include at least the following four types;
(1) Annual capital flow;
(2) The total cost of the power plant life cycle;
(3) Calculated power generation costs;
(4) Annual operating maintenance and replacement costs.
According to statistics, since 1998-2008, more than 2% of the 20 off-grid photovoltaic projects that have been completed in China, MMW, are gratis or domestic government grants.
10 Acceptance contents of photovoltaic power generation system
Photovoltaic power generation system
Acceptance mainly includes the following seven parts:
(1) Square base section
· Concrete base and anchor bolt specifications
· The dimensions of the platforms and the specifications of the load-bearing components for the overhead square array
(2) Square array rack section
· The firmness of the installation
Adjustable rack tilt angle adjustment range
(3) Solar cell array
· Wiring of each sub-array
The maximum output power of each sub-matrix
· Component cable and square output cable tie fixing status
(4) Power Feeder Section
· Feeder route
Interline or line-to-ground insulation resistance
·Threading pipe sealing
·Cable end processing
·Power feeder and control cabinet connection
(5) Control cabinet section
·Installation position and firmness of installation
(6) Battery section
·According to the manufacturer's instructions or communication power supply equipment installation engineering construction and acceptance technical specifications
· Sealed battery box processing
The rated capacity of the battery
(7) System Protection Section
Grounding system position and grounding resistance
· Lightning protection grounding device connection method
· Location and height of lightning rods
·Set the seismic fortification of each battery
11 Solar Photovoltaic Architecture - Principles of Humanization
(1) Infiltration of ecologically driven design concepts into conventional building design: The building itself should have an aesthetic form, and the integration of the PV system with the building makes the building appearance more attractive. The use of PV panels in buildings not only makes good use of solar energy, but also greatly saves the building's use of energy. It also enriches the architectural facade design and facade aesthetics. The BIPV design should be based on the principle of not damaging and influencing the building's effect, structural safety, function, and service life. Any BIPV design that causes damage and adverse effects on the building itself is a substandard design.
(2) The integration of traditional building constructions and modern photovoltaic engineering technologies and concepts; the introduction of integrated building design methods and the development of solar energy and building integration technologies. The integrated design of buildings refers to the application of solar energy technology into the entire process of architectural design to achieve the aesthetic, practical and economical requirements of architectural design. BIPV is primarily a building. It is an architect's artwork. The key to its success is the appearance of the building. From the beginning of the design, the building should design all the contents contained in the solar energy system as an indispensable design element of the building, and skillfully integrate the various components of the solar energy system into the design of the building, making the solar energy system an integral part of the building. Part of it, to achieve the perfect combination with the building.
(3) Pay attention to different architectural features and people's living habits; appropriate proportions and scales: The proportion and scale of PV panels must be consistent with the proportions and dimensions of the overall architecture, and be consistent with the functions of the buildings, which will determine the PV panels. The size and form of the grid. The color and texture of the PV panels must be in harmony with the rest of the building, and integrated with the overall style of the building. For example, in a historical building, PV panels integrated tiles may be more suitable than large-scale PV panels, and in a high-tech In architecture, industrialized PV panels better reflect the character of the building.
(4) The organic combination of thermal insulation enclosure technology and natural ventilation and sunshading technology; exquisite detail design: not only refers to the waterproof structure of PV roof, but to pay more attention to the specific details of the design. From a pure architectural technology product is well integrated into architectural design and architectural art.
(5) Photovoltaic systems and buildings are two separate systems. Combining these two systems involves many aspects. It is necessary to develop photovoltaic and building integrated systems. It is not that photovoltaic producers can independently perform their own tasks, and must be connected to buildings. The close cooperation of related materials, architectural design, construction and other related areas can be achieved through joint efforts.
(6) The balance between the initial investment in construction and the investment in photovoltaic engineering in the life cycle; comprehensive consideration of construction operating costs and their external costs. Construction operations are reflected in various activities throughout the life cycle such as planning, construction, use, and renovation, and demolition of buildings. Building energy-saving technologies, solar energy technologies, and ecological building technologies have important implications for construction operations. It is necessary not only to pay attention to an investment in the early stage of construction, but also to pay attention to the later operation and cost of construction, not only to meet the residential needs of the people, but also to pay for the energy consumption of the use of the housing. In addition, consideration should be given to the increase in external environmental costs such as carbon dioxide emissions.
12 Planning first is the key to solar photovoltaic architecture
Solving the integration of solar energy and buildings and solving the harmonization of architectural design and solar energy construction are actually not technical problems. The real difficulty lies in the interests of developers and the public's awareness of energy conservation. This urgently requires government agencies to take a step forward in planning foresight and normativeness. It is suggested that the construction administrative department of the government should propose or stipulate rigid requirements for “synchronous design, simultaneous construction, and simultaneous completion” of building construction and solar energy construction. Therefore, in the face of the increasingly severe energy situation, the introduction of relevant regulations or mandatory standards for energy-saving buildings should be preceded. On the basis of policy orientation and incentive mechanisms at all levels of government, we will raise the level of vocational training and public education, strengthen product (system) testing and certification, and establish a system of admitting people, improve standards and related technical regulations, and make full use of enterprises and owners. The level of enthusiasm to jointly promote the orderly and healthy development of solar photovoltaic buildings.
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