Informations sur la centrale photovoltaïque

Analysis of factors affecting the design of photovoltaic power plants and how to calculate the actual annual power production of photovoltaic panels

Photovoltaic (PV) power station is a power station with photovoltaic power generation system as the main component, including all kinds of construction (structures) and auxiliary facilities such as maintenance, repair and living.

When a photon shines on a metal, its energy can be absorbed by an electron in the metal, the electron absorbed energy is large enough to overcome the internal gravitational force of the metal to do work and leave the metal surface to escape and become a photoelectron.

There are many factors to consider in the construction of a photovoltaic power plant. Many factors affect the power generation capacity, such as the quality of modules, inverters, cables, installation orientation azimuth, tilt angle, dust, shadow shading, module and inverter ratio system solution, line design, construction, grid voltage, etc. Various factors are possible.Today we will introduce a part of the factors affecting the photovoltaic power plant and how to calculate the actual annual power generation of photovoltaic panels.

Centrale photovoltaïque
Centrale photovoltaïque

1.Solar photovoltaic power plant design influence factor analysis

1.1 Analysis of the impact of meteorological environmental factors

Meteorological conditions are one of the most significant factors affecting solar photovoltaic power generation. Changes in the meteorological environment are often reflected in the form of changes in the radiation intensity of sunlight reaching the ground, which in turn has a direct impact on solar photovoltaic power generation. In the design of photovoltaic power plant, we should fully consider the natural meteorological and climatic conditions of the area where the power plant is located, scientifically set up the meteorological environment equipment adapted to the local meteorological environment, to ensure that the function of the equipment is compatible with the local meteorological environment, and give full play to the proper performance.


1.2 Analysis of the factors affecting the optimal angle of inclination of solar photovoltaic cells

The power generation of photovoltaic power station depends on the absorption of sunlight by solar cells, which is influenced by the tilt angle of solar photovoltaic cells. Under the premise of sufficient conditions and engineering progress, in order to achieve the best results of the design, the construction unit should set up a solar observatory at the site where the solar PV power plant is located to collect solar resource data of the project site, and the measurement time should reach more than 1 year.

If there is no actual observation data of the project site for a complete year, the long-term photometric data available near the site can be selected to simulate the observatory within the site to assess the solar energy resources of the proposed site. In order to determine the tilt angle of solar photovoltaic cells, professional software is used to adjust the tilt angle of solar photovoltaic cells with the aid of computer, so that the annual power generation of the photovoltaic power plant can be maximized.

Centrale photovoltaïque
Centrale photovoltaïque

2.How to calculate the actual annual power production of photovoltaic panels

After a PV plant is completed or built, it is an important and necessary task to estimate the power generation capacity of the PV plant. This task is usually calculated and analyzed based on the local annual solar radiation and the power generation efficiency of the PV plant.

2.1 Calculation methods

(A) Calculation methods stipulated by national specifications.

According to the latest "Design Code for Photovoltaic Power Station GB50797-2012", Article 6.6: The calculation of power generation stipulates that:

  1. a. The prediction of power generation of PV power station should be based on the solar energy resources of the site, and calculated after considering various factors such as PV power station system design, PV array layout and environmental conditions.
  2. b. the average annual power generation Ep of photovoltaic power station is calculated as follows.


In the formula:

HA - is the total annual horizontal solar irradiation (kW- h/m2);

Ep - is the grid power generation (kW- h);

PAZ - the installed capacity of the system (kW);

K - is the overall efficiency factor.

The combined efficiency factor K is a correction factor that takes into account the effects of various factors, including:

1) Correction factor for PV module type;

2) Correction factor for the tilt and azimuth of the PV array;

3) availability of PV power system;

4) Light utilization rate;

5) Inverter efficiency;

6) Collector line and booster transformer losses;

7) PV module surface contamination correction factor;

8) PV module conversion efficiency correction factor.

This calculation method is the most comprehensive one, but the grasp of the comprehensive efficiency coefficient is a test for non-senior PV practitioners, in general, the value of K2 is between 75%-85%, depending on the situation.

Centrale photovoltaïque
Centrale photovoltaïque

(B) Module area - radiation calculation method

PV power plant feed-in power Ep is calculated as follows.


In the formula:

HA - is the total solar irradiation on the inclined surface (kW- h/m2) ;

S - is the total module area (m2)

K1 - is the module conversion efficiency;

K2 - is the overall system efficiency.

The integrated efficiency factor K2 is a correction factor after taking into account the influence of various factors, which includes.

1) Energy discounting of plant power and line losses

The AC/DC distribution room and transmission line losses account for about 3% of the total power generation, and the corresponding discount correction factor is 97%.

2) Inverter discount

The inverter efficiency is 95%~98%.

3) Operating temperature loss deduction

The efficiency of photovoltaic cell will change with the temperature change of its operation. When their temperature increases, the efficiency of photovoltaic module power generation will tend to decrease. Generally speaking, the average operating temperature loss is around 2.5%.

4) Other factors discount

In addition to the above factors, the impact of photovoltaic power plant power generation also includes unavailable solar radiation loss and maximum power point tracking accuracy impact discount, as well as grid absorption and other uncertain factors, the corresponding discount correction factor is taken as 95%.

This calculation method is the variation formula of the first method, applicable to the project of inclination installation, as long as the tilt irradiance (or according to the horizontal irradiance conversion: tilt irradiance = horizontal irradiance / cosα), can be calculated more accurate data.

Centrale photovoltaïque
Centrale photovoltaïque

(C) Standard sunshine hours - installed capacity calculation method

PV power plant feed-in power Ep is calculated as follows.


In the formula:

P - is the installed capacity of the system (kW) ;

H - is the local standard sunshine hours (h);

K1 - is the overall system efficiency (taken as 75%-85%).

This calculation method is also a variation of the formula of the first method, which is simple and convenient to calculate the average daily power generation and is very practical.

Centrale photovoltaïque
Centrale photovoltaïque

(iv) Empirical coefficient method

The average annual power generation capacity of PV power plant Ep is calculated as follows


 In the formula:

P - is the installed capacity of the system (kW) ;

K1 - is the empirical coefficient (taking the value according to the local insolation condition, generally taking the value of 0. 9~1. 8).

This calculation method is based on the actual operation experience of local PV projects, and is the fastest way to estimate the annual average power generation.

Centrale photovoltaïque
Centrale photovoltaïque

2.2 Calculation Case

Take a 1MWp rooftop project in a certain place as an example. The project uses 4,000 250W modules, with module size 1640*992mm, and is grid-connected with 10KV voltage level. The local horizontal solar radiation is 5199 MJ- m-2, and the system efficiency is calculated at 80%. Then the final results of the four calculation methods are as follows.

Standard method Component Area Method Standard sunshine hour method Empirical coefficient method
Calculation process 1000*5199*0.28*0.8 1.64*0.992*4000*5199*0.28*0.154*0.8


5199*0.28*1000*0.8 1000000*1.15
Calculation results 1164576 kWh 1167089 kWh 1164576 kWh 1150000 kWh


Module efficiency = nominal module power / module area * 1000W/㎡ * 100%

Note: 0.8 is the unit conversion experience factor

Summary:The above calculation shows that the standard method and the standard insolation hour method have the same number, because the concept of the standard insolation hour is defined as follows: the total amount of irradiation is converted into the number of hours converted at 1000W/m2 of irradiation, which is numerically equal to the value of irradiation after unit conversion. In general, the field estimates are used empirical coefficient method, and when organizing written materials, the other three methods can be used.

Centrale photovoltaïque
Centrale photovoltaïque


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