There are many influencing factors in the design and calculation of photovoltaic power generation systems. They are not only related to the lighting conditions, geographical location, weather conditions, and air quality of the area where the photovoltaic power station is located, but also related to the electrical load power and time, and also need to ensure The number of rainy days for power supply is related, and other factors are related to the orientation, tilt angle, surface cleanliness, and ambient temperature of photovoltaic modules. Among these factors, the main factors such as lighting conditions, climate, and electrical power consumption are extremely unstable. Strictly speaking, the off-grid photovoltaic power plant must strictly maintain the balance between photovoltaic power generation and power consumption. impossible.
The design of grid-connected photovoltaic power generation system is simpler than that of off-grid photovoltaic power generation system. This is not only because the off-grid photovoltaic power generation system does not require a battery and a charge controller, and its power supply target is a more stable power grid. Therefore, it is not necessary to consider the balance between the amount of power generated and the amount of electricity used, and it is not necessary to consider the resistance and inductance characteristics of the load. Usually, only the total power of the PV modules is used to calculate their power generation. Instead, grid-connected power generation system settings are designed based on the amount of power generated.
The following introduces the design of grid-connected photovoltaic power generation system and the calculation of photovoltaic module squares:
I. Design and calculation of grid-connected photovoltaic power generation system
(a) design depends on:
1) The geographic location (latitude) of the PV system;
2) Annual average annual light radiation;
3) Annual power generation or total power of PV modules or investment scale or floor space, etc.;
4) Grid-connected grid voltage, phase number;
(II) Design calculation of grid-connected power generation system
1) Calculation of power generation or total power of components:
Annual average daily electricity generation g=Pm×h1×y×η (kwh) or
g= Pm×F(MJ/m2 )×y×η/3.6×365×1 (kwh) or
g= Pm×F(kwh/m2 )×y×η/365 (kwh)
Average annual power generation G=g×365 (kwh)
2) Grid-connected inverter selection:
The selection of grid-connected inverters is based on the following requirements:
a) Inverter rated power = 0.85-1.2 Pm;
b) Maximum input DC voltage of inverter > PV array no-load voltage;
c) Inverter input DC voltage range> PV array minimum voltage;
d) Maximum input DC current of the inverter> Photovoltaic matrix short circuit current;
e) Inverter rated input DC voltage = PV array maximum power voltage;
f) Rated output voltage = nominal voltage of the grid;
g) rated frequency = grid frequency;
h) number of phases = number of grid phases;
The output waveform distortion and frequency error of the grid-connected inverter should meet the grid connection technical requirements. In addition, it must have short-circuit, overvoltage, undervoltage protection, and anti-islanding effects.
Second, photovoltaic module square design:
(a) The horizontal tilt angle design of photovoltaic modules:
The design of the horizontal tilt angle of photovoltaic modules depends mainly on the latitude of the photovoltaic power generation system and the requirements for the distribution of power generation in the four seasons.
1) For a situation where the power generation requirements in the four seasons are basically balanced, the component inclination can be selected as follows:
The latitude of the PV system
PV module level inclination
Latitude 0°---25°
Tilt equals latitude
Latitude 26°--- 40°
Tilt equals latitude plus 5° ∽ 10°
Latitude 41°----55°
Tilt equals latitude plus 10° ∽ 15°
Latitude >55°
Tilt equals latitude plus 15° ∽ 20°
2) In most areas of China, the horizontal latitude of the component at the latitude plus 7° can be used.
For the case that more power is required in the winter, the horizontal inclination of the component at the latitude plus 11° can be used.
For the case where more power is required in the summer, the horizontal inclination of the component at the latitude minus 11° can be used.
(II) Influence of the tilt angle and orientation of the photovoltaic array on the power generation:
The tilt angle and direction of the PV array have a great influence on the power generation. In general, the PV array should face the positive south (northern hemisphere). A reasonable dip angle is discussed in the previous section.
However, in some cases, the tilt and orientation of the components may not be ideal. This will have a significant impact on the power generated by the PV array. The following figure shows the general relationship between the tilt angle and the direction of the photovoltaic array.
(3) The spacing between the front and rear rows of the PV array or the distance between the front and the back cover is designed:
If the space between the front and back of the PV array or the distance between the front and the front cover is not designed properly, it will affect the power generation of the photovoltaic system, especially in winter.
The design of the distance between the front and back of the PV array or the distance between it and the front shield is related to the latitude of the photovoltaic system, the front array or the height of the shield.
Let D------- be the pitch before and after;
Φ------ is the latitude of the PV system (positive in the Northern Hemisphere and negative in the Southern Hemisphere);
H------- is the vertical height from the bottom edge of the rear photovoltaic module to the top edge of the front row;
D=0.707H/tan[arc sin(0.648cosΦ—0.399sinΦ)]
Example: Let Φ=32°
D=0.707H/tan[arc sin(0.648cos32°—0.399sinΦ32°)]
=0.707H/tan [arc sin(0.648×0.848—0.399×0.529)]
=0.707H/tan[arc sin(0.549−0.211)= 0.707H/tan[arc sin0.338]
=0.707H/tan18.6°=0.707H/0.336=2.1H
(4) The relationship between the total power of the PV arrays and the floor space:
The relationship between the total power of the PV array and the floor space depends on the installation method of photovoltaic modules, the type of photovoltaic modules (crystal silicon or thin-film batteries) and the photoelectric conversion efficiency of photovoltaic modules. Component installation methods can be divided into two types:
1) Cover type: such as covering the slope roof or flat roof or wall installation. The total power of the photovoltaic array that can be installed in this way is more. Based on the different photoelectric conversion rates of components, the following are roughly:
a) Crystal silicon module (photoelectric conversion rate 15-17%): 130-145WP/m2;
b) Thin-film batteries (photovoltaic conversion rate 5-7%): 43-60 WP/m2
2) Saw-tooth type: Install tilted PV modules on a flat roof or flat ground. This installation method is conducive to increasing the power generated by the photovoltaic array. However, from the foregoing, in order to prevent the front row from obstructing the rear row, there must be a certain distance between the front and rear rows. This spacing increases with the latitude of the PV system. For most parts of China, the power of the components that can be installed per square meter is only half that of the covered type. which is
a) Crystal silicon module (photoelectric conversion rate 15-17%): 65-72 WP/m2;
b) Thin-film batteries (photovoltaic conversion rate 5-7%): 22-30 WP/m2;
With the numbers listed above, it is possible to calculate the total area required for the total power of the PV modules under different installation conditions. Conversely, if you know the area, you can calculate the total power of the largest photovoltaic array that can be installed.
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