How Solar Irradiance Affects PV Panel Output – UNI-T UT381PV Malaysia
How Solar Irradiance Affects PV Panel Output – UNI-T UT381PV Malaysia
Content
Solar panel output changes according to the amount of solar energy reaching the panel surface. When irradiance increases, the panel can normally produce more current and power. When irradiance decreases, output also falls.
The UNI-T UT381PV Solar Irradiance Meter measures the available solar energy in watts per square metre, helping technicians interpret PV electrical readings more accurately.
What Is Solar Irradiance?
Solar irradiance is the amount of solar power reaching a surface.
It is normally expressed in:
Watts per square metre – W/m²
The UT381PV measures solar irradiance from 0 to 1400 W/m².
The reading represents the sunlight condition at the time and position of the measurement. It may change because of weather, shading, panel orientation and time of day.
Why PV Output Changes with Irradiance
A photovoltaic panel converts solar energy into electrical energy.
When more sunlight reaches the cells, the panel can normally generate more electrical current. When less sunlight is available, the generated current and power decrease.
Irradiance may be reduced by:
- Cloud cover
- Haze
- Rain
- Dust or dirt
- Partial shading
- Early-morning sunlight
- Late-afternoon sunlight
- Incorrect panel inclination
- Incorrect panel direction
This is why a panel’s electrical output should not be evaluated without considering the irradiance present during the test.
Rated Power and Actual Field Output
Solar panel rated power is determined under specified test conditions. Actual rooftop or solar farm conditions are rarely identical to laboratory conditions.
Field output may differ because of:
- Actual irradiance
- Panel temperature
- Cable losses
- Inverter losses
- Panel mismatch
- Shading
- Contamination
- Installation angle
- Module ageing
- Measurement uncertainty
A panel producing below its nameplate rating is not automatically defective.
A Simple Irradiance Comparison
A simplified field estimate may compare the measured power with the available irradiance.
For example, a panel rated at 450 W is tested at 800 W/m².
Ignoring temperature and system losses, a rough proportional estimate would be:
450 W × 800 ÷ 1000 = 360 W
The actual result may be lower because of panel temperature, wiring losses, inverter efficiency and other site conditions.
This calculation is only a basic screening method. It does not replace formal PV performance testing or an I-V curve analysis.
Why Panel Temperature Must Also Be Measured
Strong irradiance heats the solar panel. As the panel temperature increases, its voltage and overall power may decrease.
Therefore:
- Higher irradiance may increase available power
- Higher panel temperature may reduce voltage
- Both effects may occur at the same time
The UT381PV measures temperature from −40°C to 120°C and includes a suction-cup probe for panel-surface measurement.
Record irradiance and panel temperature together for a more meaningful comparison.
Correct Sensor Positioning
Position the UT381PV sensor in the same plane as the solar panel.
Avoid:
- Shading the sensor
- Holding it vertically beside a tilted panel
- Measuring under a roof structure
- Placing it far from the tested array
- Allowing dirt to cover the sensor
- Comparing readings taken at different times
Incorrect sensor positioning may produce an irradiance value that does not represent what the panel is receiving.
Compare Similar Panels
When comparing two panels:
- Check that both receive similar sunlight.
- Record irradiance at each location.
- Measure the panel temperatures.
- Confirm that neither panel is shaded.
- Use identical electrical test points.
- Complete both tests within a short period.
- Record the weather conditions.
If one panel produces less output under similar irradiance and temperature, further electrical or thermal inspection may be required.
Use Data Logging for Changing Sunlight
The UT381PV stores up to 12,800 measurement sets, with intervals from one second to 60 minutes.
Data logging helps show how irradiance changes because of:
- Passing clouds
- Moving shadows
- Haze
- Time of day
- Weather changes
The recorded irradiance trend can be compared with inverter or PV output data.
Bluetooth connection to the UNI-T iENV App supports convenient measurement review.
When Low Output Requires Further Inspection
Further testing may be required when:
- Irradiance is suitable but output remains low
- Similar panels produce different results
- Output is unstable under steady sunlight
- Panel temperature does not explain the difference
- Voltage or current is abnormal
- Visible damage is present
- Cleaning does not restore performance
Possible causes include:
- Loose connectors
- Damaged cables
- Panel mismatch
- Defective bypass diode
- Insulation problems
- Inverter faults
- Defective solar modules
Use appropriate electrical, thermal or I-V curve instruments for further diagnosis.
For assistance using the UNI-T UT381PV to compare solar irradiance with PV panel output in Malaysia, contact MTM Precision.
MTM Precision Sdn Bhd
Showroom & Service Centre: No. 29-1 & 29-2, Jalan Bandar 18, Pusat Bandar Puchong, 47160 Puchong, Selangor, Malaysia
Tel: 03-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com
Website: www.mtmpre.com.my
30 Sep 2026
