With the adjustment of the national energy structure, new energy such as photovoltaic power generation has become a substitute for fuel energy. Nowadays, the capacity of the PV and the capacity of the transformer in the power station built by Hami are 1:1.
1. Hami radiation analysis According to the law of the four seasons, the longest sunshine time and the largest amount of radiation in the days near the summer solstice, the shortest sunshine duration in the days near the winter solstice, and the smallest amount of radiation, were compared through the 2009 data provided by the Hami Meteorological Bureau. The maximum amount of radiation was reported on July 22, 2009, and the minimum on December 22. The following is the first analysis of the daily variation curve of radiation:
Radiation intensity refers to the solar radiation energy that is projected perpendicularly to a certain unit area of ​​the earth within a unit of time. In the physical sense, the irradiation of the sun is the direct influence of the photovoltaic effect on the photovoltaic cell. The magnitude of the irradiation intensity directly affects the output of the photovoltaic cell. Figure 1 is a scatter plot of measured radiation intensity of a photovoltaic power plant in Hami and actual active power of a photovoltaic power plant. It can be seen that the irradiation intensity is directly proportional to the output of the photovoltaic power plant. FIG. 2 is a V/A characteristic diagram of a battery module provided by a well-known manufacturer, according to the data on the figure. In addition to the intensity of radiation, the output power of photovoltaic modules is related to the temperature of the components.
With the decline in the price of photovoltaic modules, a large number of large-scale photovoltaic power plants started construction, and Hami Xinjiang has become a hot spot for photovoltaic electric fields. Fully consider the acceptance capacity of the power grid and some of the country's incentive policies for photovoltaics. For the moment, the access resources of Hami are limited. Reasonable configuration of main transformers is particularly important for the access and delivery of photovoltaic power plants. This paper mainly predicts the output curve of photovoltaic power plant from the measured radiation dose of Shichengzi, and finally determines the optimal ratio of the photovoltaic power plant to the main transformer capacity. Further introduced the total capacity of the largest access PV power station in the Shichengzi photovoltaic collection station.
2. Analysis of actual power of photovoltaic modules From the above figure, it can be seen that the maximum actual power of a photovoltaic field of 30 MWp is close to 28,000 kW. The curve is parabolic in shape throughout the day. The highest point of power occurred around 1 o'clock noon. The area formed by the output curve and the horizontal axis is the amount of power generated on this day. July 22 is the day with the highest amount of power generation, so the output curve of July 22 is used as the benchmark for the theoretical power generation of this article. The output of photovoltaic modules is related to the light intensity and also related to the temperature of the battery. When the temperature decreases, the voltage across the photovoltaic cell increases, the current decreases, and the power increases accordingly. When the temperature rises high, the voltage across the photovoltaic cell will be low, the current will increase, and the power will decrease accordingly. The maximum power point occurs around 13 noon, corresponding to this time period is the highest temperature period in the day. So the maximum output will drop a little. Since the amount of descent is small, it cannot be counted.
The inverter is a device that converts direct current generated by a photovoltaic cell into alternating current in a photovoltaic field. The inverter is one of the key equipments for converting the direct current into alternating current in the photovoltaic power generation system. The selection of the inverter plays an important role in the conversion efficiency and reliability of the power generation system. Conversion efficiency and maximum power point tracking play a crucial role in the benefits of photovoltaic electric fields. The following figure shows the efficiency curve provided by a well-known manufacturer. According to the above curve, when the output power reaches 50% of the rated power, the conversion efficiency is the highest, as high as 98.7%. When the actual capacity of the panel is more than 40% of the capacity of the inverter, the efficiency of the inverter is the highest. According to the 92% capacity of photovoltaic cells. The ratio of the capacity of the inverter to the photovoltaic cell is 1:1.08. The highest processing point is around 13 o'clock and the maximum power is 18442.8 kW. Compared with the rated capacity of 30456 MWp under the illumination of 1000kw/m2. It reached 92% of the peak value of 30456kwp. From 9 o'clock in the afternoon to 4 o'clock in the afternoon. It can be seen from Fig. 3 that the electric power reaches 80% of the rated power from 10 o'clock to noon.
Photovoltaic electric field covers a large area, the DC side voltage is low, the current is large, the wire has a certain loss, where the loss value takes 2%; a large number of solar panels have certain differences in characteristics, the inconsistency loss factor takes 3%; Considering that there is still a certain amount of dust on the surface of the solar panel even if it is cleaned, the shadow loss factor is taken as 3%; the efficiency of the photovoltaic grid-connected inverter (no isolation transformer, European efficiency) is about 98.7%, taking into account the night-time loss taking 98% into account The efficiency of dry-type transformers reaches 98%; solar radiation loss factor 3% cannot be used sooner or later; the temperature coefficient of photovoltaic cells is considered as 1%. The system efficiency is: 98%×97%×97%×96%×98%×98%×97%×99%=81.64%
To sum up, the photovoltaic power plant with a rated power of 0.92×0.8164 = 0.76, so 30456kW, has a maximum output of only 23,146 kW. The corresponding main transformer capacity is 23146KVA. Therefore, the transformer capacity corresponding to 30456 MWp can be selected to meet the power transformation requirements by 24000KVA. The ratio of photovoltaic cell capacity to transformer is 23146/30456=1/1.32. Similarly, the Hami Shichengzi 220KV photovoltaic aggregation station installed 3*150MVA substation can be installed photovoltaic power station 592MWP. Hami Shichengzi PV has built and planned a total of 500MW, so the Shichengzi 220kv substation can also access 92MW of photovoltaic power stations.
3. Effect of Temperature on Photovoltaic Electric Field Output Power As mentioned above, the output power of a photovoltaic cell is related to the temperature in addition to the light intensity. According to the data provided by the RYQ-3 Photovoltaic Station Environmental Monitor, the Hami City has -33°C to 45°C. Only a decrease in temperature causes a rise in power, so only the increased power at -33°C is checked. According to the data provided by the above manufacturers, the temperature coefficient is -0.43%/°C. Therefore, the calculated Pmax = P + ΔP is calculated by the installed 592 MWp. ΔP=-33°C×592MWp×−0.43%/°C=84.0048 MWp.
Pmax=P+ΔP=592+84.0048=676MWp. Although the rated power is as high as 676 MWp, the coldest time occurs in winter, and the light intensity in winter is low. The actual output does not reach 60% of the rated power, and is calculated as 60%: Ps = 676 MWp × 60% = 405.6 MWp. Therefore, the maximum output of 592 MWp is still 500 MWp.
4. Conclusion As mentioned in the above, the ratio of transformer to photovoltaic cell is 1/1.32, which is the best ratio. Determining the best ratio can alleviate some of the access and delivery problems, and also reduce the investment for the owner. Provide reference for the overall planning of photovoltaic electric field.
1. Hami radiation analysis According to the law of the four seasons, the longest sunshine time and the largest amount of radiation in the days near the summer solstice, the shortest sunshine duration in the days near the winter solstice, and the smallest amount of radiation, were compared through the 2009 data provided by the Hami Meteorological Bureau. The maximum amount of radiation was reported on July 22, 2009, and the minimum on December 22. The following is the first analysis of the daily variation curve of radiation:
Radiation intensity refers to the solar radiation energy that is projected perpendicularly to a certain unit area of ​​the earth within a unit of time. In the physical sense, the irradiation of the sun is the direct influence of the photovoltaic effect on the photovoltaic cell. The magnitude of the irradiation intensity directly affects the output of the photovoltaic cell. Figure 1 is a scatter plot of measured radiation intensity of a photovoltaic power plant in Hami and actual active power of a photovoltaic power plant. It can be seen that the irradiation intensity is directly proportional to the output of the photovoltaic power plant. FIG. 2 is a V/A characteristic diagram of a battery module provided by a well-known manufacturer, according to the data on the figure. In addition to the intensity of radiation, the output power of photovoltaic modules is related to the temperature of the components.
With the decline in the price of photovoltaic modules, a large number of large-scale photovoltaic power plants started construction, and Hami Xinjiang has become a hot spot for photovoltaic electric fields. Fully consider the acceptance capacity of the power grid and some of the country's incentive policies for photovoltaics. For the moment, the access resources of Hami are limited. Reasonable configuration of main transformers is particularly important for the access and delivery of photovoltaic power plants. This paper mainly predicts the output curve of photovoltaic power plant from the measured radiation dose of Shichengzi, and finally determines the optimal ratio of the photovoltaic power plant to the main transformer capacity. Further introduced the total capacity of the largest access PV power station in the Shichengzi photovoltaic collection station.
2. Analysis of actual power of photovoltaic modules From the above figure, it can be seen that the maximum actual power of a photovoltaic field of 30 MWp is close to 28,000 kW. The curve is parabolic in shape throughout the day. The highest point of power occurred around 1 o'clock noon. The area formed by the output curve and the horizontal axis is the amount of power generated on this day. July 22 is the day with the highest amount of power generation, so the output curve of July 22 is used as the benchmark for the theoretical power generation of this article. The output of photovoltaic modules is related to the light intensity and also related to the temperature of the battery. When the temperature decreases, the voltage across the photovoltaic cell increases, the current decreases, and the power increases accordingly. When the temperature rises high, the voltage across the photovoltaic cell will be low, the current will increase, and the power will decrease accordingly. The maximum power point occurs around 13 noon, corresponding to this time period is the highest temperature period in the day. So the maximum output will drop a little. Since the amount of descent is small, it cannot be counted.
The inverter is a device that converts direct current generated by a photovoltaic cell into alternating current in a photovoltaic field. The inverter is one of the key equipments for converting the direct current into alternating current in the photovoltaic power generation system. The selection of the inverter plays an important role in the conversion efficiency and reliability of the power generation system. Conversion efficiency and maximum power point tracking play a crucial role in the benefits of photovoltaic electric fields. The following figure shows the efficiency curve provided by a well-known manufacturer. According to the above curve, when the output power reaches 50% of the rated power, the conversion efficiency is the highest, as high as 98.7%. When the actual capacity of the panel is more than 40% of the capacity of the inverter, the efficiency of the inverter is the highest. According to the 92% capacity of photovoltaic cells. The ratio of the capacity of the inverter to the photovoltaic cell is 1:1.08. The highest processing point is around 13 o'clock and the maximum power is 18442.8 kW. Compared with the rated capacity of 30456 MWp under the illumination of 1000kw/m2. It reached 92% of the peak value of 30456kwp. From 9 o'clock in the afternoon to 4 o'clock in the afternoon. It can be seen from Fig. 3 that the electric power reaches 80% of the rated power from 10 o'clock to noon.
Photovoltaic electric field covers a large area, the DC side voltage is low, the current is large, the wire has a certain loss, where the loss value takes 2%; a large number of solar panels have certain differences in characteristics, the inconsistency loss factor takes 3%; Considering that there is still a certain amount of dust on the surface of the solar panel even if it is cleaned, the shadow loss factor is taken as 3%; the efficiency of the photovoltaic grid-connected inverter (no isolation transformer, European efficiency) is about 98.7%, taking into account the night-time loss taking 98% into account The efficiency of dry-type transformers reaches 98%; solar radiation loss factor 3% cannot be used sooner or later; the temperature coefficient of photovoltaic cells is considered as 1%. The system efficiency is: 98%×97%×97%×96%×98%×98%×97%×99%=81.64%
To sum up, the photovoltaic power plant with a rated power of 0.92×0.8164 = 0.76, so 30456kW, has a maximum output of only 23,146 kW. The corresponding main transformer capacity is 23146KVA. Therefore, the transformer capacity corresponding to 30456 MWp can be selected to meet the power transformation requirements by 24000KVA. The ratio of photovoltaic cell capacity to transformer is 23146/30456=1/1.32. Similarly, the Hami Shichengzi 220KV photovoltaic aggregation station installed 3*150MVA substation can be installed photovoltaic power station 592MWP. Hami Shichengzi PV has built and planned a total of 500MW, so the Shichengzi 220kv substation can also access 92MW of photovoltaic power stations.
3. Effect of Temperature on Photovoltaic Electric Field Output Power As mentioned above, the output power of a photovoltaic cell is related to the temperature in addition to the light intensity. According to the data provided by the RYQ-3 Photovoltaic Station Environmental Monitor, the Hami City has -33°C to 45°C. Only a decrease in temperature causes a rise in power, so only the increased power at -33°C is checked. According to the data provided by the above manufacturers, the temperature coefficient is -0.43%/°C. Therefore, the calculated Pmax = P + ΔP is calculated by the installed 592 MWp. ΔP=-33°C×592MWp×−0.43%/°C=84.0048 MWp.
Pmax=P+ΔP=592+84.0048=676MWp. Although the rated power is as high as 676 MWp, the coldest time occurs in winter, and the light intensity in winter is low. The actual output does not reach 60% of the rated power, and is calculated as 60%: Ps = 676 MWp × 60% = 405.6 MWp. Therefore, the maximum output of 592 MWp is still 500 MWp.
4. Conclusion As mentioned in the above, the ratio of transformer to photovoltaic cell is 1/1.32, which is the best ratio. Determining the best ratio can alleviate some of the access and delivery problems, and also reduce the investment for the owner. Provide reference for the overall planning of photovoltaic electric field.
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