Photovoltaic! 6 methods for calculating the power generation of photovoltaic power plants

With the rapid development of new energy, photovoltaic power generation has become ubiquitous, Many customers want to know how the power generation of photovoltaic power plants is calculated. Today I'm here to organize for you:

After the completion of a photovoltaic power station, estimating its power generation is a very important and necessary task, which usually requires calculation and analysis based on various factors such as the local annual solar radiation and the power generation efficiency of the Guangfa power station!

• Theoretical calculation method

The theoretical power generation (E) of a photovoltaic power station can be calculated using the following formula:

 

E=Pr×H×PRE =Pr×H×PR

 

E: Electricity generation (kWh)

 

Pr: The rated power of the photovoltaic system (kW), which is the total power of all photovoltaic modules under standard test conditions (STC)

 

H: Annual average solar radiation (kWh/㎡), usually expressed as daily radiation multiplied by 365 days

 

PR: Performance Ratio, which represents the overall efficiency of the system, including photovoltaic module efficiency, inverter efficiency, line loss, etc

 

Calculation steps:

 

 

Determine the rated power Pr of the photovoltaic system. The rated power of the photovoltaic system is the total power of the photovoltaic modules under standard test conditions (irradiance of 1000 W/㎡ and temperature of 25 ℃). If 1000 modules with a rated power of 300W are installed in the photovoltaic power station, the total rated power is Pr=1000 × 0.3kW=300kW

 

The average annual solar radiation (H) can be obtained through meteorological data, measured in kWh/㎡. For example, the average annual solar radiation in a certain area is 1500 kWh/㎡.

 

The computational performance ratio (PR) is the overall efficiency of a photovoltaic system, typically ranging from 0.75 to 0.85. The calculation of PR takes into account the following factors: assuming PR is set to 0.8

 

Photovoltaic module efficiency: about 15% to 20%

 

Inverter efficiency: approximately 95% to 98%

 

Other losses such as line loss, dust cover, temperature impact, etc

 

give an example:

 

Assuming the parameters of a certain photovoltaic power station are as follows:

 

Rated power of photovoltaic system (Pr}): 300 kW

 

Annual average solar radiation (H): 1500 kWh/㎡

 

Performance ratio (PR): 0.8

 

The annual power generation (E) is:

 

E=300kW×1500kWh/m²×0.8 =360,000kWh

 

2. Actual measurement method

 

Using actual measurement methods to calculate the power generation of photovoltaic power plants is an accurate method to ensure system performance. This method can evaluate the impact of various factors on power generation during actual operation. Usually, the following data is collected

 

Electric energy meter: used to measure the total power generation.

 

Solar radiometer: used to measure the actual amount of solar radiation.

 

Environmental monitoring equipment: including sensors for temperature, humidity, wind speed, etc.

 

The calculation formula is as follows:

P (ti) - instantaneous power at time point P (ti) (kW)

 

△ t - Time interval (hours)

 

3. Empirical estimation method

 

This method estimates the potential power generation of newly built photovoltaic power plants by analyzing historical power generation data of other photovoltaic power plants in the same region or under similar conditions, combined with local factors such as sunshine conditions and climate characteristics. This method relies on sufficient historical data and professional experience, and accuracy depends on the relevance and sufficiency of the reference data.

4. Software simulation method

 

The calculation of the power generation of photovoltaic power plants can be carried out through software simulation, which is a commonly used method in modern photovoltaic system design and analysis. This method can predict the power generation of photovoltaic systems by simulating solar radiation, system component characteristics, and other environmental factors through professional software. At present, there are mainly PVSyst, HOMER, SAM (System Advisor Model), PV * SOL on the market

 

General steps

Enter system parameters

 

Photovoltaic module parameters: including module type, power, efficiency, temperature coefficient, etc.

 

Inverter parameters: including efficiency, power, input voltage range, etc.

 

System layout: including the arrangement, inclination, azimuth, etc. of components.

 

Input meteorological data

 

Use local meteorological data, including annual average solar radiation, temperature, humidity, wind speed, etc.

 

These data can usually be obtained from meteorological databases or solar resource assessment agencies.

 

Set system loss

 

System losses include cable losses, dust cover, shading effects, temperature effects, etc.

 

These losses can be adjusted through default values in the software or manually set according to the actual situation.

 

Run simulation

 

Use software to run simulations and calculate the annual power generation of the system under given conditions.

 

The software will generate detailed power generation reports and performance analysis by simulating the operation of a day or a year.

 

Analysis results

 

Analyze simulation results and view detailed data such as power generation, performance ratio, and system losses.

 

Optimize system design based on the results, adjust component arrangement, select more efficient inverters, etc.

 

Example:

 

Assuming we use PVSyst software to simulate a 1 MW photovoltaic power plant, the steps are as follows:

 

Input photovoltaic module and inverter parameters: module power: 300 W, module efficiency: 18%, inverter efficiency: 97%

 

Input meteorological data: Annual average solar radiation: 1600 kWh/㎡, annual average temperature: 25 ℃

 

Set system loss: cable loss: 2%, dust cover: 3%

 

Run simulation: The software calculates the annual power generation and performance ratio.

 

Analysis result: Based on the annual power generation report, assuming the calculated annual power generation is 1,280,000 kWh.

 

5. Calculate according to the National standard GB/T50797-2012

 

The calculation of power generation based on Article 6.6 of the national standard "Design Code for Photovoltaic Power Stations GB50797-2012" is shown in the screenshot below

 

6.6 Calculation of power generation

 

6.6.1  The prediction of the power generation of a photovoltaic power station should be based on the solar energy resources of the site, and various factors such as the design of the photovoltaic power station system, the layout of the photovoltaic array, and environmental conditions should be considered before calculation and determination.

 

6.6.2 The grid connected electricity of photovoltaic power plants can be calculated according to the following formula:

 

E=HA × P_AZ/Es × K

 

In the formula:

H - total solar radiation on the horizontal plane (kW · h/m2, peak hours);

 

E_P — On grid power generation (kW · h);

 

E_S — Irradiance under standard conditions (constant=1kW · h/m2);

 

P_AZ —Component installation capacity (kWp);

 

K —Comprehensive efficiency coefficient. The comprehensive efficiency coefficient K includes: correction coefficient of photovoltaic module type, correction coefficient of inclination angle and azimuth angle of photovoltaic array, availability rate of photovoltaic power generation system, light utilization rate, inverter efficiency, power collection line loss, step-up transformer loss, official account number of photovoltaic module surface pollution correction, wind and solar storage knowledge sharing coefficient, and correction coefficient of photovoltaic module conversion efficiency.

 

6. PV module area - radiation calculation method

 

Ep=HA*S*K1*K2

 

HA - total solar radiation on inclined surface (kW. h/m ²)

 

S - Total area of components (m ²)

 

K1- Component Conversion Rate

 

K2- System Comprehensive Efficiency

 

The comprehensive efficiency coefficient K2 is a correction coefficient that takes into account various factors, including:

 

1) Energy reduction for factory electricity, line losses, etc

 

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

 

2) Inverter discount

 

The inverter efficiency is between 95% and 98%.

 

3) Reduction of working temperature losses

 

The efficiency of photovoltaic cells will vary with the temperature changes during their operation. When their temperature increases, the power generation efficiency of photovoltaic modules tends to decrease. Generally speaking, the average operating temperature loss is within 2 About 5%.

 

4) Other factors reduced

 

In addition to the above factors, the factors that affect the power generation of photovoltaic power plants also include the reduction of unusable solar radiation losses and the impact of maximum power point tracking accuracy, as well as other uncertain factors such as grid absorption. The corresponding reduction correction factor is taken as 95%.

 

This calculation method is a variation formula of the first method, applicable to projects with inclined installation. As long as the inclined surface irradiance is obtained (or converted based on horizontal irradiance: inclined surface irradiance=horizontal surface irradiance/cos α),

 

More accurate data can be calculated.

 

Actual case calculation

 

Taking the 1MWp rooftop project in a certain location as an example. The project uses 4000 pcs of 250W PV panels with dimensions of 1640 * 992mm, connected to the grid at a voltage level of 10KV. The local level solar radiation is 5199 MJ • m-2, and the system efficiency is calculated at 80%.

 

Firstly, it is necessary to convert the solar radiation from MJ • m^-2 to kWh • m^-2, as 1MJ=0.27778kWh. Next, based on the total installed capacity of the system (1MWp), solar radiation, and system efficiency, we can estimate the annual power generation.

 

Convert solar radiation

 

5199MH/cdotpm^-2=5199×0.27778kWh/codtp m^-2

 

Calculate annual power generation

 

Annual power generation (kWh)=installed capacity (MWp) × solar radiation (kWh \ cdotpm^-2) × 365 × system efficiency

 

Among them, the installed capacity is 1MWp and the system efficiency is 80%.

Let's do the calculations.

 

Taking the 1MWp rooftop photovoltaic project as an example, considering the local level solar radiation of 5199 MJ • m ^-2 and a system efficiency of 80%, the theoretical annual power generation of the project is approximately 421,700 kWh.