Example Of Roof Photovoltaic Capacity Calculation

Example of roof photovoltaic capacity calculation

1. Capacity calculation method

The capacity calculation of rooftop photovoltaic projects needs to consider multiple factors, including roof area, lighting resources, photovoltaic module efficiency, installation angle, etc.

1.1 Roof area

Measure roof area: Use drones, laser rangefinders, or blueprints to measure the available area of the roof.

Deducting obstacles: Deducting the area occupied by obstacles on the roof (such as chimneys, ventilation openings, air conditioning outdoor units, etc.).

1.2 Lighting Resources

Obtain lighting data: Obtain the local annual average solar radiation (kWh/m ²/day) through meteorological stations or online platforms.

Consider seasonal changes: The light intensity in winter and summer is different, and the annual average value needs to be taken into account.

1.3 Photovoltaic module efficiency

Select component type: Choose monocrystalline silicon, polycrystalline silicon, or thin-film components according to project requirements.

Component power: Select the nominal power (Wp) of the component.

1.4 Installation angle and direction

The optimal inclination angle is usually ± 10 ° of the local latitude.

Orientation: South is the best, followed by east and west, and north is the worst.

1.5 System losses

Temperature impact: High temperatures can reduce the power generation efficiency of components.

Shadow impact: Shadows on the roof can affect power generation.

Electrical losses: Losses of inverters, cables, etc.

2. Capacity calculation formula

System capacity (kW)=Available roof area (m2) x Component power density (W/m2) 1000 System capacity (kW)=1000 Available roof area (m2) x Component power density (W/m2)

Among them, the power density of the components is calculated based on the nominal power and size of the components.

3. Case examples

3.1 Project Background

Roof type: Flat roof

Roof area: 1000 m ²

Annual average solar radiation: 4.5 kWh/m ²/day

Component type: monocrystalline silicon component

Component power: 350 Wp

Component size: 1660 mm × 992 mm

Component efficiency: 18%

Installation angle: 20 °

Orientation: Southward

3.2 Calculation steps

Calculate component area

Component area=1.66 m × 0.992 m=1.64672 m2

Calculate component power density

Component power density=350 Wp1.64672 m2 ≈ 212.5 W/m2

Calculate the number of available components

Number of available components=available roof area Component area=1000 m2 1.64672 m2 ≈ 607 pieces

Calculate system capacity

System capacity=number of available components x component power=607 blocks x 350 Wp=212450 Wp ≈ 212.45 kWp

Consider system losses

Temperature impact: Assuming a 5% reduction

Shadow impact: Assuming a 3% reduction

Electrical loss: Assuming a 2% reduction

Actual system capacity=212.45 kWp × (1-0.05-0.03-0.02) ≈ 192.6 kWp

3.3 Results

System capacity: 192.6 kWp

Annual power generation estimation:

Annual power generation=System capacity x Annual average solar radiation x 365 Annual power generation=System capacity x Annual average solar radiation x 365

Annual power generation=192.6 kWp × 4.5 kWh/m2/day × 365 days ≈ 316000 kWh/year

4. Parameter Summary