Photovoltaic power generation is a cutting-edge technology in today's world. It will completely solve the three major world problems of "energy crisis", "environmental pollution" and "sustainable development" for all mankind. It will make a historic and intergenerational contribution. Mankind has entered a new era in the use of new energy and new technologies. There are several core issues in the development of reality.
1 Solar resource data and evaluation
1.1 Solar resource data
Solar radiation data can be obtained from the county-level meteorological station or from the National Meteorological Administration. The data obtained from the Bureau of Meteorology is the radiation data of the horizontal plane, including: total horizontal plane radiation, direct horizontal plane radiation and horizontal plane scattered radiation.
The data of solar energy resources mainly include: the total amount of solar energy`s radiation (irradiance) or the monthly average value of the total amount of solar energy and radiation intensity in each month. The data related to the climatic conditions mainly include: annual average temperature, annual average maximum temperature, annual average minimum temperature, the longest number of consecutive cloudy days in a year (including precipitation or snowfall days), annual average wind speed, annual maximum wind speed, annual number of hail , The number of annual sandstorm days. Among them, the monthly value of total solar radiation is indispensable. In addition, the cumulative data of the above data for the last 5 to 10 years should also be provided to evaluate the validity of the solar resource data and climate status data.
1.2 Evaluation of solar resource data validity
The solar resource data provided by the Meteorological Observatory or relevant departments are used in the design of photovoltaic systems, and in some cases their effectiveness must still be evaluated.
First of all, when the solar resource data of a specific site is not complete enough or lacks accumulated data for many years, the effectiveness and magnitude of solar radiation must be evaluated.
Secondly, although the local solar resource data is relatively complete and the solar radiation is also good, the candidate site is located in or near a mountainous area, and there is a topography that significantly affects solar radiation. In this case, the effectiveness of the local solar resource data should be evaluated by studying the average data changes in the neighboring areas around the candidate site.
Third, the data obtained from the meteorological department is the data of the horizontal plane, including: direct radiation of the horizontal plane and scattered radiation of the horizontal plane, so as to obtain the total radiation amount data on the horizontal plane. However, in the practical application of solar photovoltaic power generation, in order to obtain more power generation and the need for self-cleaning of Battery modules, the fixed installation square array is usually inclined, which requires calculation of the amount of solar radiation on the inclined surface ( Usually greater than the amount of radiation on the horizontal plane). However, this calculation process is very complicated, so people often directly use the data on the horizontal plane, or use the 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 often store a large number of solar radiation data in different regions in its database, and some also have the function of photovoltaic system analysis and design.
2 Site selection and site assessment of the photovoltaic system
2.1 It is necessary to eliminate the influence of shadows when selecting the location of the photovoltaic system
Solar cells rely on sunlight to generate electricity. When the sunlight projected on the panel is blocked, the power output characteristics of the square array will be seriously affected. A small shadow on the panel can also make it
The performance is greatly reduced. Therefore, it is extremely important to ensure the rated power of the square array and reduce the power generation cost of the photovoltaic system by carefully determining the sun passage and avoiding shadows during the design and installation of the photovoltaic system.
The shadows that appear on the site often come from trees, plants, nearby buildings, and the poles and wires of the solar collector. As a general rule, make sure that there is no shadow from 9 am to 3 pm. In the winter months, when the elevation angle of the sun is low and the Solar Panel is blocked, it is often a relatively big problem, which should be paid attention to by photovoltaic system designers and photovoltaic power plant operators. China is located in the northern hemisphere of the earth. The most unfavorable shadow for solar cell array power generation appears around December 21 (the winter solstice).
In order to eliminate the influence of shadows, after selecting the site, you must confirm whether the following conditions are met: (1) in any month of the year, the sunlight on the solar cell array will not be blocked; (2) solar energy every day from 9 am to 3 pm No shadow on the battery board; (3) Identify the obstacles that block the solar cell square array from 9 am to 3 pm, and eliminate the source of the shadow; (4) If you cannot eliminate the factors that cause shadow, you can also consider moving the solar cell square array or Increase the capacity to make up for the loss caused by the shadow.
2.2 Evaluation of the photovoltaic system site
When evaluating the photovoltaic system site, the following evaluations should be made.
(1) Evaluation of general sunshine conditions
After collecting the solar resource data of the candidate site according to the requirements, the site should also carefully observe the obstacles near the site, assess the impact of the solar shadow on the solar cell array power generation, and propose to avoid
Suggestions for opening or removing obstacles. By observing directly on the roof, wall, or in the yard, we can find an optimal position for satisfying the annual sunshine conditions of the square array.
South of the northern hemisphere is the most basic orientation of the solar cell square. If you ensure that the square array is facing south or at an azimuth of 0 °, the daily sunshine performance will be the best. However, the impact of local climatic characteristics should be considered and carefully evaluated. For example, if the fog is shrouded near the site in the morning, the square matrix needs to be adjusted slightly to the southwest to obtain more effective solar radiation lagging behind at noon.
(2) Calculate the running time of the square matrix
The longer the solar array is exposed to sunlight, the more energy the system can emit daily. Therefore, when the position and height of the square array at the site are initially determined, it is necessary to evaluate and determine the daily operating time of the solar panel in different seasons.
(3) Sun window
When evaluating the site, you must select a time with good sunlight and no shadows throughout the day as the running time of the solar cell array. This optimal time interval is called "Dayang Window".
The "sun window" concept can show the sunshine time and path conditions of the venue. According to the different sunshine conditions on the site, the sun window can be selected from 9 am to 3 pm, or from 8:20 am to 3:20 pm, etc. In the summer, the sun rises early and the sunset is very late. The sunshine time is much longer than that in winter. Therefore, the sun window in summer is longer than the sun window in winter, that is, the square matrix can run longer. The size of the solar window 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 the solar cell array. One year
The sun window time of the four seasons is different. To accurately measure the solar window, first need to ask the meteorological department for the local solar azimuth at sunrise and sunset in different seasons and the solar altitude at noon, and then modify it according to the specific conditions of the site. If only the approximate "sun window" time of the site is needed, it can be done by visual inspection.
If the site is evaluated only from the length of sunshine, then the "sun window" period reaches 9 a.m. to 3 p.m. already meeting the photovoltaic system power generation conditions. When the time period of the "sun window" reaches 10 am to 2 pm, it means that the sun exposure time of the concubine is too short, you should check or remove the surrounding obstacles or consider choosing another venue.
(4) Transportation conditions
Traffic and transportation conditions should be considered at the installation site, and there should be roads nearby to facilitate unprepared transportation of photovoltaic modules, control cabinets, and storage batteries. If the truck cannot reach the scene, at least the agricultural vehicle can reach the scene.
(5) Power supply conditions
The installation site should be close to the power supply village, and the power supply radius should not exceed 1 kilometer. It is necessary to consider the convenience of operators and the transmission loss of low-voltage cables. In addition, the power supply load and the potential for capacity expansion should be investigated in detail. For off-grid independent village power stations, the power grid will not be extended to this in the short term to avoid unnecessary duplication of construction and future power station relocation issues.
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