What Reduces Solar Output in Malaysia? Heat, Haze, Shading, Soiling and Degradation

By: Progressture Solar | Last verified: 29 July 2026

Solar output in Malaysia falls when less sunlight reaches the cells, when cell temperature rises, or when the system has electrical, inverter or availability losses. Heat, haze, shade, surface soiling and gradual module degradation all matter, but their size is site- and time-specific. The defensible approach is to compare monitored production with a weather-adjusted expectation and investigate the loss mechanism before promising a recovery percentage.

First distinguish normal weather from a performance fault

A rainy or cloudy month can reduce irradiation and energy without indicating defective equipment. Compare kWh/kWp, irradiance where available, inverter availability, alarms and production by string/MPPT against the same season or a validated model. Do not diagnose “degradation” from one month’s bill.

Heat: panel temperature, not just air temperature

PV module nameplate power is measured at standard test conditions, including a cell temperature of 25°C. In operation, modules can be materially hotter than ambient air; most silicon module data sheets show a negative power-temperature coefficient. Use the exact module’s coefficient and a site production model rather than applying one generic percentage to every Malaysian roof.

Practical response: retain rear ventilation, avoid unnecessary roof heat traps, choose an appropriate mounting design and compare actual temperature/irradiance-normalised performance with the model.

Haze: reduces available sunlight and can add deposits

A peer-reviewed Southeast Asian study using PV arrays at Universiti Putra Malaysia examined the 2013 haze and found air pollution reduced energy yield, with the fixed-flat system more affected than the tracking array. The result supports haze monitoring and cleaning/inspection after severe events; it does not justify a universal Malaysian haze-loss percentage for every system.

Practical response: watch irradiance, PV output and local air-quality/haze conditions; inspect modules and compare clean-versus-soiled performance safely after an event.

Shading: small obstruction, disproportionate effect

Shade from trees, parapets, rooftop equipment, cable trays, new neighbouring construction or even accumulated leaves can reduce output and, depending on module/string design, contribute to mismatch and hot-spot risk. The cited Southeast Asian research notes that a shaded cell can behave as resistance and heat up; bypass diodes mitigate some conditions but do not make shade harmless.

Practical response: conduct a shade survey before design and repeat it after rooftop alterations or vegetation growth. Compare underperforming strings/MPPTs rather than judging the whole plant from total kWh alone.

Soiling: dust, soot, pollen, bird droppings and haze residue

Soiling is not a fixed annual loss. Local construction, industrial emissions, road traffic, roof pitch, rainfall, wind and cleaning access can make one roof very different from another. Cleaning too often can waste money or damage equipment; cleaning too rarely can lose energy.

Practical response: establish a baseline after cleaning, monitor an equivalent clean reference or use before/after measurements, inspect visually, and schedule cleaning from measured site economics and safe working procedures—not a generic calendar interval.

Degradation: slow, but design for it

PV output normally declines over time. The National Laboratory of the Rockies notes that modules typically degrade slowly, often losing less than 1% of performance per year. Use the specific module warranty and a conservative project model; then distinguish gradual fleet-wide change from a sudden fault, PID, broken glass, connector issue, inverter outage or shading change.

A practical diagnostic sequence

1. Confirm inverter uptime, grid outages, alarms and communications before attributing a loss to weather.

2. Compare production with irradiance/weather and the expected seasonal profile.

3. Check string/MPPT comparison for shading, mismatch, soiling or equipment patterns.

4. Inspect safely for dirt, bird droppings, damage, vegetation and new obstructions.

5. Record cleaning and repairs; validate whether output recovered against comparable conditions.

Internal-link opportunities

• Link “commercial solar monitoring and O&M” to the current O&M/service page.

• Link “commercial solar feasibility” to the commercial PV page.

• Link “solar + BESS savings” to article 1 for factories seeking a system-level model.

• CTA: “Request a solar performance review using monitoring and site data.”

Sources and update warning

• Official climate context: METMalaysia—Malaysia’s Climate: https://www.met.gov.my/en/pendidikan/iklim-malaysia/

• Official air-quality monitoring: Department of Environment—MyEQMS/APIMS: https://eqms.doe.gov.my/APIMS/main

• Peer-reviewed independent source: Evaluation of the 2013 Southeast Asian Haze on Solar Generation Performance (PubMed/PLoS One): https://pubmed.ncbi.nlm.nih.gov/26275303/

• Independent research source: National Laboratory of the Rockies—PV Lifetime Project: https://www.nlr.gov/pv/lifetime

• International independent technical source: IEA PVPS report on soiling losses: https://iea-pvps.org/wp-content/uploads/2023/01/IEA-PVPS-T13-21-2022-REPORT-Soiling-Losses-PV-Plants.pdf

Evidence warning: no Malaysia-wide official factor was found that safely quantifies heat, haze, shade, soiling or degradation losses for every roof. Keep the article qualitative unless a site-specific study and measured data support a number.