Solar power generation is the cutting-edge technology in the world today. It will completely solve the three major world problems of “energy crisisâ€, “environmental pollution†and “sustainable development†for all mankind. It will make a great contribution to the history and cross-generation. Human beings have entered a new era in the use of new energy and new technologies, and there are several core issues in the development of reality.
1 Solar resource data and assessment
1.1 Solar resource data
Solar radiation data can be obtained from county-level meteorological stations or from the National Weather Service. The data obtained from the Meteorological Bureau are radiation data from the horizontal plane, including: total horizontal radiation, direct horizontal radiation, and horizontal scattered radiation.
The solar energy resource data mainly includes: the monthly total solar radiation amount (irradiance) or the total solar radiation amount and the monthly average value of the radiation intensity. The data related to its climatic conditions mainly include: annual average temperature, annual average maximum temperature, annual average minimum temperature, the longest continuous cloudy days in a year (including precipitation or snowfall days), annual average wind speed, annual maximum wind speed, annual hail times , the number of years of sandstorms. 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 be provided to assess the effectiveness of solar energy resources and climate status data.
1.2 Evaluation of the effectiveness of solar energy data
The solar energy resource data provided by the meteorological observatory or related departments is used for the design of the photovoltaic system, and in some cases, the effectiveness of the evaluation is still required.
First, when the solar energy resource data of a specific site is not complete or lacks accumulated data for many years, the effectiveness and magnitude of solar radiation must be evaluated.
Secondly, although the local solar energy resource data is relatively complete and the solar radiation is also good, the candidate site is located in or near the mountainous area with obvious topographical features that affect solar radiation. In this case, the effectiveness of local solar resource data is assessed by studying the average data changes in the neighborhood around the candidate site.
Again, the data obtained from the meteorological department is the data of the horizontal plane, including: horizontal direct radiation and horizontal plane scattered radiation, so that the total radiation amount data on the horizontal plane is obtained. However, in the practical application of solar photovoltaic power generation, in order to obtain more power generation and self-cleaning of the battery components, the fixed installation square is usually inclined, which requires calculating 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 use data directly 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 can not only solve these calculation problems conveniently. The database also stores a large number of solar radiation data in different regions, and some also have photovoltaic system analysis and design functions.
2 PV system siting and site evaluation
2.1 Eliminate shadow effects when selecting PV systems
Solar cells rely on sunlight to generate electricity. When the sunlight projected onto the panel is blocked, the square matrix power output characteristics will be seriously affected, and a small shadow on the panel can also make it
The performance is greatly reduced. Therefore, careful determination of the solar pathway and avoidance of shadows during the design and installation of the photovoltaic system is extremely important to ensure the rated power of the array and reduce the power generation cost of the photovoltaic system.
The shadows on the site often come from trees, vegetation, nearby buildings, and poles and wires of the sun collector. As a general rule, it is determined 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 occlusion of the panel is often a relatively large problem, which should be paid attention to by PV system designers and PV power plant operators. China is located in the northern hemisphere of the Earth, and the most unfavorable shadow of solar arrays appears on the 21st of December (the winter solstice).
In order to eliminate the influence of shadows, it is necessary to confirm whether the following conditions are met after selecting the venue: (1) In any month of the year, the sunlight that is directed to the solar cell array will not be blocked; (2) Every day from 9 am to 3 pm solar energy There is no shadow on the panel; (3) Identify obstacles that block the solar cell array from 9:00 am to 3 pm, and eliminate the source of shadows; (4) If the factors that cause shadows cannot be eliminated, consider moving the solar array or Increase capacity to compensate for the damage caused by shadows.
2.2 Evaluation of photovoltaic system sites
The following assessments should be made when evaluating PV site sites.
(1) General sunshine condition assessment
After collecting the solar energy resource data of the candidate site according to the requirements, it is also necessary to go to the site to carefully observe the obstacles near the site, evaluate the influence of the sun shadow on the solar cell array power generation, and propose to avoid
Advice on opening obstacles or removing obstacles. Find the best position to meet the square's annual sunshine conditions by looking directly at the roof, on the wall or in the yard.
In the southern hemisphere, the south is the most basic orientation of the solar cell array. If you ensure that the square is facing south or 0° azimuth, the daily sunshine performance will be the best. However, consideration should be given to the impact of local climatic characteristics and careful evaluation. For example, if there is fogging in the morning near the site, the square matrix needs to be adjusted slightly to the southwest to obtain more effective solar radiation that lags behind noon.
(2) Measuring the running time of the square matrix
The longer the solar cell array receives sunlight, the more power the system can emit per day. Therefore, when the square matrix is ​​initially determined at the orientation and height of the site, it is necessary to evaluate and determine the daily run time of the solar panel in different seasons.
(3) Sun window
When evaluating the site, you must choose a day with good sunshine and no shadow for all day as the running time of the solar cell array. This optimal time interval is called the "big sun window."
The “sun window†concept can show the daylight hours and path conditions of the venue. Depending on the conditions of the venue, the sun window can be selected from 9:00 am to 3:00 pm, or from 8:20 am to 3:20 pm. In the summer, the sun rises early and the sunset is very late, the sunshine time is much longer than the winter, so the summer sun window is longer than the winter sun window, which is the long running time of the square. In addition to the seasonal influence, the size of the sun window is also related to the environmental conditions around the site: for example, mountains, trees and tall buildings on both 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 sun window, you first need to ask the meteorological department about the sun azimuth and the midday sun angle at sunrise and sunset in different seasons, and then correct it according to the specific conditions of the site. If only the approximate "sun window" time of the venue is required, it can be visually observed.
If the venue is evaluated only from the length of the sunshine, the "sun window" period will reach the photovoltaic system power generation conditions from 9:00 am to 3:00 pm. When the "sun window" time period reaches 10:00 am to 2:00 pm, it indicates that the sunshine time of the field is too short, and the surrounding obstacles should be inspected or removed or the site selected separately.
(4) Transportation conditions
Traffic and transportation conditions should be considered at the installation site, and there should be roads nearby to facilitate the transportation of PV modules, control cabinets, and storage batteries. If the truck cannot reach the site, at least the farm vehicle can arrive at 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 km. It is necessary to consider the convenience of the operators, the transmission loss of the low-voltage cable, and the detailed investigation of the power supply load and capacity. For off-grid independent village power stations, the power grid will not extend to this in the short term, so as to avoid unnecessary duplication of construction and future power station relocation.
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