Solar Array Output

The amount of power a solar array generates is directly proportional to the solar resource available throughout the day. Two critical calculations can be performed to determine the system yield:

Power output (instantaneous output)
Power output = instantaneous solar radiation (kW/m²) x rated array power (kW) x system efficiency

Energy output (output over time)
Hourly energy output = hourly solar radiation (kWh/m²) x rated array power (kW) x system efficiency
Daily energy output = daily solar radiation (kWh/m² or PSH) x rated array power (kW) x system efficiency

Note: The total array power equals the sum of all the solar modules’ power.

System efficiency relates to factors that reduce the power/energy output of the solar modules. Several factors can affect solar system efficiency. They include:
1. Temperature – a higher cell temperature will reduce the power output.
2. Shading – any shading will reduce the power output.
3. Dirt – any soiling of the modules will reduce the power output.
4. Cable losses – power is lost as electricity runs through cables.
5. Orientation and tilt losses – the orientation and tilt of the modules affect the amount of solar radiation that hits the modules, affecting the power output.

solar panel power output, solar array output

Is PV System Efficiency Different from Module Efficiency?

PV system efficiency relates to losses in the equipment’s operation. This differs from PV module efficiency, which relates to how well a solar PV module converts solar radiation into electricity. The array’s rated power already considers the PV module’s efficiency.

Example 1
A 1.2kW array has been installed to run a bore pump. The measured sunlight intensity is 0.76kW/m², and the system efficiency has been calculated to be 70%. The power output of the array is:
1.2kW x 0.76kW/m² × 0.7 = 0.638kW

Example 2
The 1.2kW system installed to run a bore pump is exposed to 5.0kWh/m² over the course of one day, with a system efficiency of 70%. The energy output of the array over the day is:
1.2kW x 5.0kWh/m² × 0.7 = 4.2kWh

For some low-volume solar pumping installations, the solar array is intended to drive a DC pump directly. In such an installation, the PV array’s power output must match the start-up power required. A pump motor will have an initial start-up power requirement greater than the motor’s running power. If the solar PV array cannot supply that initial power requirement, the pump will not start even if the array has enough power to run the motor once started.

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