Before, there have been two articles written about the new technology: "The 100% increase in photovoltaic power generation may not be a fantasy! 》, "PV modules: Inverter = 1:1? You OUT! Improve the project revenue by changing equipment ratios."
The previous article is based on a patented technology of Li Moran, the chief engineer of Xingyineng (Beijing) Energy Technology Co., Ltd., to double the amount of radiation received by photovoltaic modules by simply modifying the brackets and adding reflectors. Also doubled.
The latter article is a combination of technological changes in the work plan. We believe that our commonly used PV modules: Inverter = 1:1 may not be the most economical solution.
In response to these two new technologies, many people gave me a reply. Among them, the most questionable question is: Whether it is the first increase in the amount of reflection or the second increase in the ratio of PV modules, the result is that the output power of photovoltaic modules will exceed the inverter power, and the inverter can withstand the ? Will it be burned?
In response to this problem, I discussed with a number of experts and talked about the results.
I. Preconditions for calculation
To illustrate the problem, make such an assumption.
Assumption 1: PV module power P1, inverter power P0;.
Assumption 2: Basic scheme: P1: P0 = 1:1, P1 = P0
Solution one: After adding reflectors, assuming that the output power of the PV modules is doubled, P2:P0=2:1, P2=2P0
Solution 2: PV modules and inverters are installed in a ratio of 1.2:1. P3:P0=1.2:1, P3=1.2P0
Second, the impact of solar energy resources
The following figure is selected from the observation data of solar energy resources in 2011 in a place in Qinghai Province, which are the maximum daily radiation, annual average, and the time-of-use irradiance of the winter solstice.
Fig. 1 Solar radiation intensity of different days in a certain place in Qinghai
As can be seen from the above figure,
On the maximum day of total radiation, only within 4 hours of the maximum noon of total radiation, the irradiation intensity is above 900W/m2;
For the whole year, the total amount of radiation in the whole day is within 750W/m2;
On the winter solstice day, the daily irradiance is below 500W/m2.
Of course, since the above observation data is the data of the horizontal plane; when the fixed inclination angle is adopted, the amount of radiation received on the photovoltaic module will be greater than the above-mentioned level data. Therefore, an irradiation intensity calculation was performed on an inclined surface and the results are shown in the following table.
Table 1 Irradiation intensity table on inclined plane
Explanation: k is the ratio of "average amount of radiation on the inclined plane to the amount of radiation on the horizontal plane" on a monthly average at the best inclination angle.
Third, the impact of comprehensive system efficiency
According to statistics from the National Renewable Energy Information Center, the integrated system efficiency of photovoltaic power plants is shown in the figure below.
Figure 2 System efficiency statistics of photovoltaic power plants
From the above figure, the overall system efficiency of the project is 89%. The loss of system efficiency is mainly caused by the previous stage of the inverter. After the inverter, there is only one inverter's efficiency loss, box change conversion loss and AC line loss, as shown in the figure below.
Therefore, before the inverter, the efficiency loss should be above 8%, that is, the system efficiency of the part before the inverter is below 92%.
Table 2 Various efficiency loss standards
IV. The actual output power of photovoltaic power plants
Only when the irradiation intensity is 1000 W/m2, the output of the photovoltaic module is the nominal power, the irradiance is reduced, and the output power is also reduced. The following figure shows the IV curve of a component.
Figure 3 IV curve of PV modules
P=IU. From the IV curves it can be seen that when the irradiance is above 400 W/m2, the output power is basically proportional to the irradiance. Therefore, the ratio of the actual input power Pa of the inverter to the nominal power P1 is the "actual irradiance Fa: 1000 W/m2 on the inclined plane."
According to the above assumptions, the nominal power of photovoltaic modules:
The basic scheme is P1, scheme 1 (increasing reflectors) is P2, and scheme 2 (increasing photovoltaic modules) is P3.
Option 1: Inverter actual input power Pa=(Fa:1000)*P1*η
Let η = 92%, P1 = 2P0, when Fa = 543W/m2, Pa = P0
That is, when the irradiance Fa ≤ 543 W/m2, no light will be generated;
Option 2: Inverter actual input power Pa=(Fa:1000)*P2*n
Let η=92%, P1=1.2P0, when Fa=905W/m2, Pa=P0
That is, when the irradiance Fa is ≤ 905 W/m2, no light emission occurs.
From Table 1, it can be seen that only two hours with the maximum amount of radiation are slightly larger than 905 W/m2. It can be seen that if the ratio of "PV modules: inverter = 1.2:1" is adopted, only light emission will occur within a short time in the summer at noon. At other times, the input inverter power is lower than its nominal power. .
However, if the "increase reflection plate" scheme is adopted, the power input to the inverter will be higher than its nominal power most of the time except for winter. Therefore, measures should be taken to increase the tilt angle of PV modules to reduce the output in summer and increase the output in winter.
Five, summary
In general terms:
If the "Photovoltaic module: Inverter = 1.2:1" ratio is used, only a small amount of light will be generated in the two hours of the summer noon. Most of the time, the input power is lower than the nominal value of the inverter. power.
If the "increase reflection plate" scheme is adopted, the power of photovoltaic modules will be doubled, and most of the time, the input power will be higher than the nominal power of the inverter. Therefore, it is necessary to increase the tilt angle of the photovoltaic module, reduce the output in summer, and increase the output in winter.
By consulting experts in the inverter, you can set the MPPT tracking of the inverter. When the input power is greater than the nominal power, MPPT tracking is not used and the inverter will not burn. (Wang Shujuan)
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