How Clouds, Haze and Weather Affect Solar Irradiance & PV Testing Malaysia
How Clouds, Haze and Weather Affect Solar Irradiance & PV Testing Malaysia
Why can solar panel output change significantly even when there is no obvious problem with the PV system?
One major reason is the environment.
Clouds, haze, time of day, solar angle and changing atmospheric conditions can affect the solar radiation reaching a PV module.
For solar installers and maintenance technicians in Malaysia, this is why recording solar irradiance in W/m² can be useful when carrying out PV inspection.
A portable instrument such as the VICI LX-107 Solar Power Meter allows technicians to take solar radiation spot measurements directly at the site.
Why Weather Matters in Solar PV Testing
Solar PV modules depend on incoming solar radiation.
If environmental conditions change during an inspection, PV electrical measurements can change as well.
Consider a technician who takes:
Measurement A at 11:00 AM
and
Measurement B at 11:20 AM
If cloud conditions changed between those measurements, directly comparing the electrical results without considering irradiance may lead to an incomplete conclusion.
For better field records, measure irradiance close to the corresponding PV test.
How Do Clouds Affect Solar Irradiance?
Clouds can reduce the direct solar radiation reaching the measurement surface.
But real outdoor conditions can be complex.
Different cloud types, thicknesses, positions and movement can produce rapidly changing irradiance.
This means a technician should not simply record:
“Cloudy.”
A measured value such as:
Solar irradiance: ___ W/m²
provides more useful quantitative information.
Why Passing Clouds Are Important During Troubleshooting
Passing clouds can create a common field-testing problem.
Imagine this sequence:
10:30 AM – Irradiance measurement taken.
10:35 AM – Clouds move across the sun.
10:40 AM – PV electrical measurement taken.
The irradiance measured at 10:30 AM may no longer represent the conditions at 10:40 AM.
This is why technicians should take related environmental and electrical measurements as close together in time as practical.
Can Solar Irradiance Change Within Minutes?
Yes.
Outdoor solar radiation can change rapidly, especially under variable cloud conditions.
For PV troubleshooting, technicians should therefore avoid relying on one irradiance reading to represent an entire inspection period.
If conditions change noticeably, repeat the measurement.
How Does Haze Affect Solar Radiation?
Haze consists of particles suspended in the atmosphere.
These particles can scatter and absorb solar radiation.
As atmospheric conditions change, the amount and characteristics of solar radiation reaching the ground can also change.
For solar technicians, the practical lesson is straightforward:
Do not assume that a bright daytime sky always means identical solar irradiance conditions. Measure when the value matters.
Haze and Solar PV Performance
During hazy conditions, PV performance should be evaluated together with actual environmental measurements rather than relying only on visual observation.
Useful field information can include:
Solar irradiance
Module temperature
Time
Weather condition
Visible haze condition
PV voltage
PV current
Relevant system information
This creates a stronger technical record when investigating changes in solar output.
Solar Irradiance Meter vs Air Quality Monitor
These instruments measure completely different parameters.
Solar Irradiance Meter
Measures solar radiation, typically in W/m².
Air Quality Monitor
Measures selected air-quality parameters depending on the instrument, potentially including particulate matter such as PM2.5.
A haze event may be relevant to both areas, but one instrument does not replace the other.
For example:
Air quality instrument → How much particulate pollution is present?
Solar irradiance meter → How much solar radiation is reaching the measurement surface?
This distinction is important when selecting equipment.
Does Rain Affect Solar PV Testing?
Rain is associated with cloud conditions that can substantially change available solar radiation.
During or around rain events, technicians may encounter rapidly changing irradiance.
There are also important electrical and working-at-height safety considerations for rooftop PV work.
Do not carry out unsafe rooftop or electrical testing simply to obtain a measurement.
Follow appropriate site safety procedures and postpone work when conditions are unsafe.
What About Temperature?
Temperature is another important environmental variable.
A PV module exposed to strong sunlight can operate at a temperature substantially different from ambient air temperature.
For more meaningful PV troubleshooting, technicians may need to consider:
Solar irradiance + module temperature + electrical measurements
rather than irradiance alone.
This is particularly relevant when comparing field measurements with PV module reference specifications.
Why 1000 W/m² Does Not Tell the Whole Story
PV module specifications commonly use 1000 W/m² as part of Standard Test Conditions.
However, measuring approximately 1000 W/m² outdoors does not mean every other STC condition has also been reproduced.
Other factors include:
Cell temperature
Solar spectrum
Electrical operating conditions
Module condition
Shading
Contamination
System losses
Therefore:
1000 W/m² in the field does not automatically mean the PV module must produce exactly its nameplate STC power.
How to Measure Irradiance During Changing Weather
A practical procedure is:
Step 1 – Observe the Sky
Note whether conditions are clear, hazy, cloudy or rapidly changing.
Step 2 – Position the Sensor
For PV-related measurements, use an orientation appropriate to the measurement objective and module plane.
Step 3 – Avoid Local Shading
Do not allow your body, equipment or nearby structures to shade the sensor.
Step 4 – Record W/m²
Take the solar irradiance measurement.
Step 5 – Record the Time
Timing becomes particularly important under changing weather.
Step 6 – Take the Related PV Measurement
Perform the corresponding electrical measurement as close in time as practical.
Step 7 – Repeat When Conditions Change
If a cloud passes or sunlight changes significantly, take another irradiance measurement.
Example PV Maintenance Record
For Malaysian outdoor conditions, a useful record may include:
Date: __________
Time: __________
Weather: Clear / Partly Cloudy / Cloudy / Hazy
Solar irradiance: __________ W/m²
Module temperature: __________ °C
DC voltage: __________ V
DC current: __________ A
Array / String: __________
Visible shading: __________
Module condition: __________
Remarks: __________
This is much more useful than recording only “sunny” or “cloudy”.
VICI LX-107 Solar Power Meter
The VICI LX-107 is a portable instrument designed for solar power measurement.
Its field functions include:
W/m² Measurement
Provides a direct solar radiation measurement useful for PV-related applications.
BTU Display
Provides an alternative measurement unit for relevant applications.
MAX / MIN
Useful for observing variations in solar radiation.
Data Hold
Allows the displayed reading to be held for convenient recording.
According to VICI, applications include solar installation, solar radiation measurement, solar research, meteorology, agriculture, physics and optical laboratories, industrial applications and high-performance window identification.
MAX/MIN During Variable Cloud Conditions
MAX/MIN can be useful when solar radiation is changing.
For example, the technician can observe how much the reading varies during a period of intermittent cloud cover.
However, the MAX value should not automatically be used as the irradiance corresponding to an electrical test performed at another time.
For troubleshooting, timing still matters.
Solar Irradiance Testing for Factory Rooftops
Factories and warehouses are particularly relevant because maintenance teams may be working across large rooftop areas.
Conditions can vary because of:
Cloud movement
Haze
Roof orientation
Building structures
Exhaust equipment
Water tanks
Adjacent buildings
Local shading
Portable spot measurements allow technicians to check conditions at the area being inspected.
Solar Irradiance Testing for Solar Farms
Large ground-mounted PV sites may also experience changing environmental conditions during maintenance.
A handheld irradiance meter can support spot measurements at specific locations.
It should not, however, be confused with a permanent solar monitoring system designed for continuous plant data collection.
Can Weather Alone Explain Low PV Output?
Not always.
Weather and irradiance are important, but low PV performance can also be associated with other factors such as:
Dirty modules
Shading
Module temperature
Module condition
Connector issues
Cable problems
String differences
Inverter conditions
Other system faults
Irradiance measurement helps establish the environmental conditions—it does not replace a complete PV diagnosis.
Solar PV Environmental Measurement Malaysia
A more systematic PV inspection may combine several types of information:
Solar Radiation
Measured in W/m².
Temperature
Relevant to module operating conditions.
Electrical Parameters
Relevant to PV system performance.
Thermal Patterns
Useful for investigating abnormal heating.
Environmental Conditions
Including weather, cloud and haze observations.
This provides a more complete picture than relying on one measurement alone.
Who Can Use the VICI LX-107?
The LX-107 can be relevant for:
Solar installers
PV O&M contractors
Electrical contractors
Factory engineers
Facility maintenance teams
Solar farm technicians
Energy engineers
Universities and researchers
Agricultural applications
For users requiring portable W/m² spot measurements, it provides a straightforward solar power measurement option.
VICI LX-107 Solar Power Meter Supplier Malaysia
MTM Precision supplies testing and measurement instruments for solar PV, factory maintenance, environmental measurement, electrical testing and industrial applications in Malaysia.
Customers can contact MTM Precision for the VICI LX-107 Solar Power Meter and additional instruments required for PV and environmental testing.
Contact MTM Precision
MTM Precision Sdn Bhd
Website: www.mtmpre.com.my
Email: mtmpre@yahoo.com
WhatsApp: 016-660 7346
Showroom & Service Centre
No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia.
Serving customers throughout Selangor, Kuala Lumpur, Johor, Penang, Perak, Negeri Sembilan, Melaka, Pahang, Kedah, Perlis, Terengganu, Kelantan, Sabah and Sarawak.
Need to measure solar irradiance during changing Malaysian weather conditions? Contact MTM Precision for VICI LX-107 availability and suitable solar and environmental testing instruments.
08 Sep 2026
