Abstract: In the feasibility evaluation of the photovoltaic power plant in the early stage of construction, it is of great significance to estimate the power generation capacity of the photovoltaic power plant because this will directly affect the project's expected revenue. Currently, system designers often use software to simulate the amount of power generated in the first year. This article will be based on the estimated power generation in the first year and try to calculate the amount of power generated in the following 24 years.
1 Introduction
As a result of the global energy crisis, new sources of energy, such as wind power and solar energy, gradually occupy an important position. The world's solar photovoltaic power generation system has maintained sustained high-speed growth in recent years. By 2012, the cumulative installed capacity of photovoltaic power generation in the world has reached 102GW, and it has become the fastest growing power generation technology. Photovoltaic power generation has achieved parity access in more than 20 countries.
With the continuous breakthrough in the technology of core device photovoltaic modules, and the continuous improvement in efficiency, the cost of electricity for photovoltaic systems will gradually approach the cost of traditional thermal power generation. At the same time, with the continuous development of energy storage technologies, by then, photovoltaic power generation systems will The advantages of a system of arbitrary scale, low installation requirements, and the like will be applied to more general applications around the world.
In the entire photovoltaic system application market, the current grid-connected photovoltaic system occupies an absolutely dominant position, all relying on the continuous development and maturation of grid-connected photovoltaic technology, the continuous R&D progress of corresponding equipment performance costs, and the active promotion of policies by various governments.
2. The principle of photovoltaic power generation system
Since photovoltaic power generation systems are generally divided into grid-connected systems and independent systems according to actual applications, the application of grid-connected systems occupies a large share. This paper focuses on the analysis of power generation estimates for grid-connected systems.
At the same time, due to the differences in system size and application conditions, the grid-connected system also has a variety of system forms. The evaluation of the power generation volume in this paper is based on a relatively large-scale photovoltaic power station as a model, and the environmental conditions of the photovoltaic power station are relatively good.
Figure 2-1 shows the block diagram of a typical large-scale ground power station.
Figure 2-1 Diagram of the principle of power generation for large-scale power plants
The entire system is mainly composed of photovoltaic square arrays and alternating current (straight-stream) transmission and transformation. The DC output from photovoltaic arrays is converted into waveform-regulated and frequency-stabilized alternating current through the inverter through a DC line and then boosted locally. After medium pressure, conduct confluence on the medium-voltage AC line before conducting secondary centralized boost, and finally connect to the grid for grid connection.
According to the illustration, an effective energy meter is usually installed at the property rights point to measure the power generated by the photovoltaic power plant. This is the most accurate statistical data. The analysis and correction of the simulated data based on the statistical data of the first few years can provide a more accurate estimate of future generations.
3, analysis of loss factors of photovoltaic power generation
To accurately estimate the amount of power generated by a photovoltaic power plant in the early stages of the project, in addition to a deep understanding of the system structure of the photovoltaic power plant, it is necessary to have a deep understanding of the major equipment performance parameters. At the same time, if you want to estimate the amount of power generation for a longer period of time, you must fully consider the influence of external environmental factors and the estimation of the operation status of the power plant for a long time.
When analyzing the first year's power generation estimation of photovoltaic power plants, the usual loss factors that need to be considered are as follows:
(1) Correction of solar radiation exposure on inclined surfaces;
(2) The influence of foreign materials such as dust on the surface of the module blocks light;
(3) The effect of temperature on the output of photovoltaic modules;
(4) self-attenuation of photovoltaic modules;
(5) Matching loss of components within a string;
(6) Shadow shading loss between front and rear rows of square arrays;
(7) DC line loss;
(8) Inverter conversion efficiency loss;
(9) Local transformer losses;
(10) AC line loss;
(11) main transformer loss;
(12) Power consumption of the power station;
(13) Loss of downtime;
When PVSYST software is commonly used to simulate power generation, the loss of self-consumption and downtime is not considered, but it is only a comprehensive data considering Other factors.
When analyzing the power generation of photovoltaic power plants in the following 24 years, operation management is the most important influencing factor, but the predictability is poor, and it is usually assumed that it does not change with other factors, but only considers the attenuation of photovoltaic modules themselves.
4. Attenuation analysis of PV module power
In practice, photovoltaic modules have been attenuated since they were manufactured. However, when the light is not visible in the package, it attenuates very slowly. Once it begins to receive sunlight, the attenuation will rapidly increase, gradually decay after a certain percentage of attenuation. Figure 4-1 illustrates the first year decay curve model:
Figure 4-1 First-year decay curve model of photovoltaic modules
The total 3% attenuation data in the first year of Figure 4-1 is taken from the 25-year attenuation guarantee of the solar polysilicon module from Zhengtai. The 25-year attenuation guarantee is shown in Figure 4-2.
Figure 4-2 Photovoltaic module attenuation curve
From Figure 4-2, it can be seen that the maximum attenuation value of PV modules in the first year is 3%, and the attenuation value is 0.7% in the next 24 years.
Since the attenuation in the initial stage has a direct relationship with the light intensity, in the first year, under the condition of average light intensity, the early stage shows a sharp decay, and the stage is gradually stable. However, in fact, the time span for a photovoltaic power plant from the beginning of the installation of components to the start of grid-connected power generation is not necessarily. By the time of starting to measure the power generation, the components may have already undergone a certain proportion of attenuation, in order to reduce the actual situation. With the error of the theoretical estimation, in addition to the requirements for the warranty start time, the general component will have a certain percentage of positive power deviation at the factory. This positive power deviation can cover part of the components caused by some human factors without power generation. Some attenuation loss.
Therefore, in the theoretical calculation, the starting point of the rated power for the power generation simulation calculation can be equivalent to the rated power of the photovoltaic module at the time of delivery, and the attenuation of the components in one year can be regarded as a linear attenuation.
5. Estimation of photovoltaic power generation
The annual power generation of photovoltaic power plants is actually a function of the real-time output power of photovoltaic power plants as a function of time, as shown in Figure 5-1.
Figure 5-1 Photovoltaic power-time curve
For ease of calculation, the above figure is generally equivalent to a rectangular plot of the output power and peak sunshine hours under standard light intensity, as shown in Figure 5-2.
Figure 5-2 Photovoltaic power-time equivalent rectangle
Therefore, the annual photovoltaic power plant power generation Q = equivalent power P′ × peak sunshine duration H × 365 days, in which the equivalent power P′ is a fluctuating value during the actual day, the formula can be used (Equation 5-1) Said that
Equivalent power P'= rated installed power P × system overall efficiency η (Equation 5-1)
To facilitate the calculation of the amount of power generated by the photovoltaic power plant for 25 years, formula 5-1 can be expressed as formula 5-2 as follows:
Equivalent power P' = rated installed power P × average efficiency of the module η1 × system other loss factor comprehensive efficiency η2 (Equation 5-2)
Taken together, the annual power generation of photovoltaic power plant Q = rated installed power P × average efficiency of the module η1 × system other loss factor comprehensive efficiency η2 × peak sunshine time H × 365 days, in the 25-year period, in addition to the average efficiency of the component η1, other items The product of can be regarded as an invariable constant Q, then the final expression is the annual power generation of photovoltaic power plant Q = Q × average efficiency of the component η1 (Equation 5-3).
Average efficiency of the component η1 - (proportion of the rated capacity of the component at the beginning of the year + proportion of the rated capacity of the component at the end of the year)/2
The positive power deviation of the proportion, this positive power deviation can cover a part of some attenuation factors caused by some artificial factors in the absence of power generation.
Therefore, in the theoretical calculation, the starting point of the rated power for the power generation simulation calculation can be equivalent to the rated power of the photovoltaic module at the time of delivery, and the attenuation of the components in one year can be regarded as a linear attenuation.
To sum up, taking the attenuation guarantee of the solar polysilicon component of Zhengtai as an example, the average annual component efficiency for 25 years is shown in the following table:
If PVSYST software is used to estimate the first year's power generation of the PV power plant, the system efficiency does not take into account both the power consumption of the power station and the downtime, but it does not affect the estimation of the next 24 years based on the first year's estimate. Power generation. According to the previous statement, when using PVSYST to estimate the first year power generation, if the Module efficiency loss is set to 1.5% in Detailed losses, it means that the average efficiency of the component calculated in the first year is 98.5%, then the estimated annual power generation in the second year. The figure is 98.12% for the first year, 97.41% for the first year in the third year, and 96.70% for the first year in the fourth year. About 0.7% on the basis of the previous year.
6. Summary
Based on the above calculations, the following conclusions are generally drawn: Under the same conditions, the power generation of a photovoltaic power plant is roughly in proportion to the attenuation of photovoltaic modules. However, in the actual operation, the cleanliness of the component surface, the failure rate of the equipment, and the management of the power plant are the main factors affecting the power generation of the power plant in the later period. The degree of influence of the loss factor in the actual operation of the power plant is recorded, and then the estimated power generation amount is modified to have very Significance.
kaiping aida sanitary ware technology co.,ltd , https://www.kpfaucets.com