Why Do Solar Panels Lose Power in Malaysia's Heat?
Published by Quinn Lai | By InverPower Technical Team
Published 14 August 2026 · Last updated 14 August 2026
DIRECT ANSWER
A module's temperature coefficient states how much output it loses for every degree above 25 °C. Datasheet wattage is measured at a 25 °C cell temperature, and a Malaysian rooftop runs far hotter than that all day — so the rated number is a laboratory figure, not a prediction of what the roof will produce.
Every module is sold on a number measured in conditions Malaysia never provides. Standard test conditions specify 1,000 W/m² of irradiance and a cell temperature of 25 °C. We get the irradiance. We do not get the 25 °C — not at midday, not on a roof, not in any month of the year.
What does the coefficient actually state?
Three coefficients sit on a datasheet and they are commonly confused. The one that matters for yield is the coefficient of maximum power, expressed as a percentage loss per degree Celsius above 25 °C. The coefficient of open-circuit voltage matters for string sizing rather than yield. The coefficient of short-circuit current is a small positive number and can be set aside for most purposes.
Take the Trina Vertex S+ N-type i-TOPCon module we distribute. Its published figures are −0.29 %/°C on maximum power, −0.24 %/°C on open-circuit voltage and +0.04 %/°C on short-circuit current. The first of those is the yield number: every degree above 25 °C costs a little under a third of a percent of output.
That sounds trivial until you count the degrees. A cell running at 62 °C is 37 degrees above the test condition, which at −0.29 %/°C is roughly an eleven percent reduction in output — happening at exactly the hour when irradiance is highest and the array should be at its best.
How hot does a Malaysian rooftop module actually get?
Not as hot as the roof surface, and much hotter than the air. The datasheet gives you the honest answer under a different name: NOCT, the nominal operating cell temperature, is the temperature the module reaches at 800 W/m² irradiance, 20 °C ambient and 1 m/s wind. For the Trina module above, NOCT is 43 °C — the module runs 23 degrees above the air around it under those conditions.
Scale that to a Malaysian midday. Higher irradiance and a 33 °C ambient rather than 20 °C put cell temperature somewhere around 60 °C on a well-ventilated array, and higher on a badly mounted one. This is why NOCT is the most useful number on the thermal part of a datasheet: it is the manufacturer's own statement about how hot their product runs in service.
There is a seasonal wrinkle too. Malaysia's hottest cell temperatures do not arrive in the wettest months, when cloud cover cuts irradiance before heat can build. They arrive on clear days in the drier stretches, which are also the highest-irradiance days of the year. The thermal penalty is therefore concentrated in exactly the periods a yield model counts on most, rather than spread evenly across the twelve months.
Which datasheet numbers should you compare?
When two modules are quoted at the same wattage, the thermal figures are where they stop being equivalent:
| Datasheet line | Trina Vertex S+ figure | Why it matters here |
|---|---|---|
| Coefficient of Pmax | −0.29 %/°C | The yield number — output lost per degree above 25 °C |
| Coefficient of Voc | −0.24 %/°C | Drives string sizing, not yield |
| Coefficient of Isc | +0.04 %/°C | Small and positive; rarely decisive |
| NOCT | 43 °C (±2 °C) | How hot the module runs in service, per the manufacturer |
| Operating temperature range | −40 to +85 °C | The envelope, not a performance figure |
| Test condition for rated watts | 25 °C cell, 1,000 W/m² | The condition Malaysia never delivers |
A module with a −0.29 %/°C coefficient and one with −0.40 %/°C will diverge by roughly four percent of output at the same 37-degree rise. Over a twenty-five year asset that is not a rounding error, and it does not appear anywhere in the headline wattage both products are sold on.
What reduces the loss in practice?
- Mounting clearance. Air moving under the modules carries heat away; a tight-to-the-roof installation traps it and runs hotter for the same weather.
- Cell technology. N-type designs generally carry gentler temperature coefficients than older p-type PERC, which is a real advantage in a tropical market rather than a marketing line.
- Roof surface and colour beneath the array, which sets how much reflected and re-radiated heat the modules sit in.
- Airflow around the array edges — a parapet or plant enclosure that blocks the prevailing breeze raises cell temperature across the whole section.
- Realistic modelling. Using NOCT and the Pmax coefficient in the yield model rather than the rated wattage, so the client's expectation matches the roof.
The last point is the commercial one. Heat loss is not a defect to be engineered away; it is a known, quantified property of the product. The failure is not that the array runs hot, it is that someone promised a number calculated as though it would not.
How does InverPower help you compare modules?
We distribute Trinasolar and hold the current datasheets, so when you are comparing modules at the same wattage you can put the actual thermal figures side by side rather than working from a summary. The yield model and the client conversation stay with the EPCC. If you need the datasheet revision that matches the stock you are quoting, ask before the tender rather than after.
Frequently Asked Questions
Does a lower temperature coefficient always mean a better panel for Malaysia?
It means better behaviour in heat, which matters more here than in temperate markets. It does not settle the decision on its own — degradation rate, warranty terms, bankability and price all sit alongside it. But between two otherwise similar modules, the gentler coefficient is worth real yield in Malaysia.
What is NOCT and why does it matter more than the operating temperature range?
NOCT is the cell temperature the module reaches at 800 W/m², 20 °C ambient and 1 m/s wind — the manufacturer's statement of how hot it runs in service. The operating range is only the envelope the product survives, which tells you nothing about performance.
Does mounting height affect real-world temperature?
Yes. Clearance under the modules allows air to carry heat away. A flush installation with little airflow runs hotter than a rail-mounted array with a gap beneath it, in the same weather, on the same day.
Should I use the datasheet wattage in a yield estimate?
Not on its own. Rated wattage is measured at a 25 °C cell temperature. A Malaysian yield model needs the temperature coefficient and a realistic cell temperature applied to it, or it will overstate output at exactly the hours that matter most.
Sources
- Trinasolar — Vertex S+ NEG9R.28 datasheet, APAC 2024 (temperature coefficients, NOCT, STC and NOCT test conditions) — http://static.trinasolar.com/sites/default/files/Vertex%20S+_NEG9R.28_EN_2024_APAC_A_web.pdf
- IEC 61215 — Terrestrial photovoltaic modules: design qualification and type approval (the standard behind STC ratings) — https://webstore.iec.ch/publication/61345
- Sungrow — SG125CX-P2 inverter datasheet, Version 13 (MPP voltage range referenced for sizing context) — https://info-support.sungrowpower.com/application/pdf/2023/02/28/DS_20230227_SG125CX-P2_Datasheet_V13_EN.pdf
About InverPower
InverPower is Malaysia's A–Z solar component distributor — Sungrow Preferred Distributor and Sunkean Sole Distributor — supplying EPCCs, installers, and government projects nationwide.
Explore the InverPower resource hub at inverpower.com.my
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