The selection of the array form of photovoltaic power stations needs to be comprehensively considered from several aspects such as initial investment, power generation, and operation and maintenance costs. Combined with the actual data of a photovoltaic power station in northwest China designed by a design institute, the power generation characteristics of the four forms of optimal inclination fixed type, single-axis tracking type, dual-axis tracking type and concentrating tracking type are analyzed as the selection of photovoltaic array. form of reference.
1. Initial investment
The optimal tilt angle fixed array can greatly simplify the structure of the support system because the position and angle of the photovoltaic modules are fixed, and the initial investment cost is the lowest. Fixed adjustable type is divided into jack type, hydraulic rod type, push rod type and arc type. The first two forms need to install jacks or hydraulic equipment, which increases equipment investment; the latter two only change the connection form of the bracket, and the cost increase is not obvious.
The flat single-axis tracking type is similar to the flat single-axis tracking type with an inclination angle, and the structure is relatively simple and the stability is good. Since the tilted flat single-axis tracking style requires slightly more brackets than the standard flat single-axis tracking style, the tilted flat single-axis tracking style is slightly more expensive. In order to increase the use efficiency of the tracking system, the inclined single-axis tracking system usually adopts the arrangement of one axis and multiple components. Due to the increase in the height of the photovoltaic bracket, a larger distance between modules is required, and the space required for the rotation of the photovoltaic modules increases, resulting in a decrease in the installed photovoltaic capacity per unit area, which will increase the cost of the unit installation site; installation cost.
The dual-axis tracking system uses two rotating shafts to track sunlight in real time, so its own cost is high. The space required for the rotation of the dual-axis tracking system increases, resulting in a decrease in the installed photovoltaic capacity per unit area, which will increase the cost of the unit installation site. The installation of the dual-axis tracking bracket is difficult and requires hoisting, which increases the installation cost.
Concentrator tracking photovoltaic arrays use inexpensive materials to manufacture concentrators, so that sunlight can be concentrated on solar cells with a small area, which can reduce the use of expensive solar cell materials and the cost of photovoltaic power generation systems.
The upper part of Figure 1 is a low-magnification concentrating light tracking type component system, and the lower part is a flat panel type component system. It can be seen from the figure that compared with the flat-panel photovoltaic module system, the low-power concentrator tracking system has a small footprint. Generally speaking, the flat-panel tracking module system covers an area of about 50m² per kilowatt, while the system using the low-power concentrator tracking cell module only needs about 25.5m², that is, the footprint per kilowatt is almost reduced by half. Therefore, photovoltaic power stations using low-power concentrating tracking battery modules will greatly reduce land acquisition costs.
Through the analysis of site investment and the form of components and their brackets, it can be seen that the initial investment costs of the four types of photovoltaic arrays are in descending order: dual-axis tracking type> single-axis tracking type> concentrating tracking type> optimal inclination fixed Mode.
2. Comparison of power generation
Due to the fixed position and angle of photovoltaic modules in the optimal inclination-fixed bracket system, the power generation of these bracket systems is relatively small. The fixed adjustable type can be divided into three categories according to the number of adjustments per year: three angles (adjusted 3 times a year), which can increase power generation by 5% to 7%; two angles (adjusted twice a year), which can increase power generation by 1% ~4%.
The standard flat single-axis tracking photovoltaic power station tracks the change of the incident angle of the sun throughout the day. Since photovoltaic modules have no inclination in the north-south direction, the increase in power generation in this form is significantly better in low-latitude regions than in high-latitude regions. Compared with the fixed bracket system, the power generation of the standard flat single-axis tracking photovoltaic power station will increase by 10%~15%. On the basis of the standard flat uniaxial tracking photovoltaic power generation station, the inclination angle of the north-south direction is increased, so the power generation will be increased by 15%~20% compared with the fixed type.
The tracking axis of the inclined single-axis tracking bracket system rotates in the east-west direction while setting a certain inclination angle to the south, and rotates around the inclined axis to track the azimuth of the sun to obtain greater power generation, which is suitable for application in higher latitudes. Compared with the fixed bracket system, the power generation of the inclined single-axis tracking system can generally be increased by 20% to 25%.
The dual-axis tracking system uses two axes of rotation (vertical axis and horizontal axis) to track the sun rays in real time to ensure that the sun rays are perpendicular to the panel surface of the module at every moment, so as to obtain the maximum power generation, which is suitable for use in various latitudes. . Compared with the fixed bracket system, the photovoltaic power generation of the dual-axis tracking system can be increased by 30%~40%.
Compared with the photovoltaic array in fixed operation mode, the single-axis tracking type increases the power generation by about 18% compared with the fixed type, and the dual-axis tracking type increases the power generation by about 25% compared with the fixed type.
Compared with the fixed installation with the optimal tilt angle, the power generation of horizontal single-axis tracking is increased by 17%~30%, the power generation of single-axis tracking with a tilt of 5° is increased by 21%~35%, and the power generation of dual-axis tracking is increased. 35%~43%. However, under different latitudes, the power generation rate of various operation modes is obviously different. Compared with the horizontal fixed installation method, the power generation increase of various installation methods has the following rules:
(1) The optimal inclination angle fixed type (hereinafter referred to as “method 1”): in low latitude areas, due to the small optimal inclination angle, the power generation increase is very small (for example, at 8°, it is almost constant); In high latitudes, the optimal inclination angle is large, and the power generation is significantly improved (for example, at 50°, it is increased by about 25%).
(2) Flat uniaxial tracking type (hereinafter referred to as “mode 2”): This operation mode tracks the change of the incident angle of the sun within a day, and its rate of increase in power generation is significantly better in low latitude areas than in high latitudes. area. It is generally believed that this mode of operation is more suitable for use in areas with latitudes below 30°, and can increase power generation by 20% to 30% compared to “Mode 1”. Of course, in high latitude regions, the relative “method 1” can also be improved by nearly 20%.
(3) Inclined single-axis tracking type (hereinafter referred to as “mode three”): This operation mode obviously combines the advantages of “mode one” and “mode two”. Just as “mode one” is not suitable for low latitudes, this mode of operation is not much better than “mode two” in low latitudes. Therefore, it is more suitable for high latitude regions.
In this way, the forces on the support structures (brackets, rotating shafts) on both sides of the array must be different. Since the optimal inclination angle in high latitudes is large, if the “optimal inclination angle of the single axis” is adopted, the unbalanced force on both sides will be very large. Therefore, a smaller inclination angle is generally adopted in the project.
(4) Dual-axis tracking type (hereinafter referred to as “method 4”): Since the change of the incident angle of the sun within one day and one year is tracked, this method obviously has the highest increase in power generation.
(5) Fixed and adjustable type (hereinafter referred to as “mode 5”): This operating mode adjusts the inclination of the bracket according to the change of the sun’s radiation angle within a year, so as to achieve an increase in power generation.
Compared with the horizontal plane radiation, the fixed type improves the power generation in spring, autumn and winter, while sacrificing the power generation in summer; the curve of the single-axis tracking is almost completely parallel to the horizontal plane curve; the dual-axis tracking is relative to the single-axis tracking, Increased power generation in spring, autumn and winter. The tracking type (single-axis, dual-axis) is relative to the fixed type, which improves the power generation in the morning and evening.
3. Operation and maintenance costs
The high tracking failure rate is a common feedback problem. In addition to the failure rate, the tracking accuracy is not ideal, especially for dual-axis tracking. Therefore, the increase in power generation will be lower than originally expected.
The optimal inclination fixed type adopts a relatively fixed installation method. Generally, it is directly fixed by fasteners such as clips, pressing blocks, and bolts. The installation is simple, the fixing method is safe and reliable, the overall reliability is high, and the later operation and maintenance are simple. The aspects that need to be operated and maintained in the later stage of the fixed-support photovoltaic power station may include: ① photovoltaic module replacement; ② photovoltaic equipment maintenance; ③ photovoltaic support maintenance.
Standard flat single-axis tracking, tilted flat single-axis tracking and inclined single-axis tracking photovoltaic power stations all use tracking systems to track sunlight in real time, but the tracking system has a high failure rate and frequent maintenance.
4. kWh electricity cost
Fixed, inclined single-axis tracking, and dual-axis tracking use the same photovoltaic modules, so the cost difference per MW power generation unit is mainly reflected in the photovoltaic support foundation and tracking system. Due to the difference in system design and fixed and tracking photovoltaic power generation systems, the main cost difference is reflected in photovoltaic modules and bracket systems.
Although the total investment of the inclined single-axis and dual-axis tracking system is higher during the project construction, it still has advantages over the fixed photovoltaic power generation system, and its electricity cost per kWh is lower than that of the fixed type. Therefore, in terms of economy, the advantages of the inclined single-axis tracking power generation system are slightly larger, and the dual-axis tracking power generation system is second. However, the control equipment of single-axis and dual-axis tracking systems is more complicated than that of fixed ones, and the workload of operation and maintenance is larger, so many projects use fixed photovoltaic power generation systems. It can be expected that with the advancement of technology and technology, when the cost and failure rate of the tracking system are reduced, the advantages of the tracking power generation system can be reflected.
Due to the immature technology and process of the low-power concentrating photovoltaic power generation system adopted, and the local wind and sand are relatively large and the climate conditions are relatively bad, the failure rate of the low-power concentrating photovoltaic power generation system is relatively high. When its technology and process are perfected, there is still a large application space due to the low consumption of crystalline silicon and the low cost of low-power concentrating tracking photovoltaic modules.
5. Overall comparison
By comparing the power generation of different operating modes and monitoring the operating conditions, it can be seen that the power generation benefits of the single-axis tracking type and the dual-axis tracking type are better than those of the fixed photovoltaic power generation system. Considering the operating mechanism of the dual-axis tracking photovoltaic system And the control is more complicated, and the single-axis tracking photovoltaic power generation system is more convenient to promote.
In terms of comprehensive cost-effectiveness of the three products of the flat single-axis, inclined single-axis and dual-axis tracking systems, the flat single-axis has advantages. Although the power generation efficiency of the double shaft is higher, the cost of the support reaches 0.85~1.15 yuan/W, and the land resource occupation is two or three times that of the fixed support. Although the efficiency is improved, the initial investment cost is very large; the inclined single shaft is between Between the flat single shaft and the double shaft, the stent input cost and land resource occupation are about twice as much as the flat single shaft. The flat uniaxial system is divided into standard flat uniaxial and flat uniaxial with inclination angle. Under the same platform, the power generation efficiency of the flat uniaxial with inclination angle can be improved by 5%~10% compared with the standard flat uniaxial, while Compared with the traditional bracket, the standard flat uniaxial can achieve 10%~15% increase, and the inclined one can achieve 18%~23%. Therefore, an appropriate phalanx operation mode should be selected from multiple perspectives such as the initial investment cost and economic benefits of the entire photovoltaic power station.