In the pre-feasibility study of photovoltaic power stations, theoretical predictions are required of the power generation capacity of the proposed photovoltaic power plant, in order to calculate the investment rate of return, and then decide whether the project is worth building. In general, every experienced photovoltaic company has a simple estimation method that can obtain similar data to the calculated values. Then this summary lists the methods for calculating/estimating the average power generation of photovoltaic power plants. Analyze the difference of each method to facilitate readers to choose the most appropriate calculation method.

First, the calculation method

1) The calculation method prescribed by the national regulations.

According to the latest “Design Specification for Photovoltaic Power Station GB50797-2012” section 6.6:

1. The prediction of the power generation capacity of photovoltaic power stations shall be based on the solar energy resources at the site of the site, and shall be calculated and determined after considering various factors such as the design of the photovoltaic power station system, the layout of the photovoltaic array, and the environmental conditions.

2. The average annual power generation Ep of photovoltaic power stations is calculated as follows:

Ep=HA×PAZ×K

In the formula:

HA - the annual total solar radiation (kW·h/m2) for the horizontal plane;

Ep - power generation for the Internet (kW · h);

PAZ - system installation capacity (kW);

K - is the overall efficiency factor.

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

1) Photovoltaic module type correction factor;

2) The tilt angle and azimuth correction factor of the photovoltaic array;

3) Availability of photovoltaic power generation systems;

4) light utilization;

5) Inverter efficiency;

6) Collector line, step-up transformer loss;

7) Photovoltaic module surface pollution correction factor;

8) Photovoltaic module conversion efficiency correction factor.

This method of calculation is the most comprehensive one, but the grasp of the overall efficiency coefficient is a test for non-senior photovoltaic industry personnel. In general, the value of K2 is between 75% and 85%. It depends on the circumstances.

2) Component Area - Radiation Calculation Method

Photovoltaic power stations on-grid electricity Ep is calculated as follows:

Ep=HA×S×K1×K2

In the formula:

HA - the total amount of solar energy (kW·h/m2) on the inclined plane;

S——Total area of ​​assembly (m2)

K1 - component conversion efficiency;

K2 - for overall system efficiency.

The overall efficiency coefficient K2 is a correction coefficient that takes into account the effects of various factors, including:

1) Energy reduction of power consumption and line loss of the plant

The losses of AC and DC power distribution rooms and transmission lines accounted for about 3% of the total power generation, and the corresponding reduction correction factor was taken as 97%.

2) Inverter reduction

The inverter efficiency is 95%~98%.

3) Working temperature loss reduction

The efficiency of a photovoltaic cell varies with the temperature at which it operates. As their temperature rises, photovoltaic modules generate a decreasing trend in power generation efficiency. In general, the average operating temperature loss is about 2.5%.

4) Reduction of other factors

In addition to the above factors, the generation of electricity that affects the photovoltaic power station also includes the useless solar radiation loss and the impact of the maximum power point tracking accuracy, as well as other uncertainty factors such as power grid absorption, and the corresponding reduction correction factor is taken as 95%.

This calculation method is a variation of the first method. It is applicable to projects that are installed at an angle of inclination, provided that inclined surface irradiance is obtained (or converted according to horizontal irradiance: inclined surface irradiance = horizontal irradiance/cosα). , you can calculate more accurate data.

3) Standard sunshine hours - Calculation method for installation capacity

Photovoltaic power stations on-grid electricity Ep is calculated as follows:

Ep=H×P×K1

In the formula:

P - installation capacity for the system (kW);

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

K1 - for the system overall efficiency (value 75% ~ 85%).

This method of calculation is also a variation of the first method. It is simple and convenient, and can calculate the average daily power output. It is very practical.

4) Empirical coefficient method

The annual average power generation Ep of photovoltaic power stations is calculated as follows:

Ep=P×K1

In the formula:

P - installation capacity for the system (kW);

K1 - is the empirical coefficient (value according to the local sunshine conditions, generally ranging from 0.9 to 1.8).

This calculation method is based on the actual operating experience of the local photovoltaic project and is the quickest way to estimate the average annual power generation.

Second, case analysis

Take the 1MWp roof project in a place in Shandong Province as an example. The project uses 4000 units of 250W components with a component size of 1640*992mm and adopts a 10KV voltage level grid connection. The local level of solar radiation is 5199 MJ·m-2, and the system efficiency is calculated as 80%.

The final results of the four calculation methods are as follows:

From the above calculations, it can be seen that the standard method and the standard sunshine hours method are the same, because the concept of the standard hours of sunshine is defined as: the total amount of irradiation converted to an hour calculated under irradiation of 1000 W/m2 The number is numerically equal to the value of the unit of radiation after the conversion. In general, on-site estimation is based on the empirical coefficient method. When organizing written materials, all three methods are available.

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