Solar PVMeasured in %/°C

Temperature Coefficient

Also called: Pmax temperature coefficient · Temp co

In one line

The percentage change in a module's power, voltage or current for each degree Celsius the cell rises above 25°C — the single most useful datasheet number for hot climates.

TOPCon Pmax

−0.29 to −0.32 %/°C

HJT Pmax

−0.24 to −0.26 %/°C

PERC Pmax

−0.34 to −0.38 %/°C

Typical Voc

−0.24 to −0.28 %/°C

What it means

Silicon cells lose power as they heat. The Pmax temperature coefficient expresses that loss as a percentage per degree above the 25°C STC reference — modern n-type modules sit around −0.29 to −0.34%/°C, older p-type PERC nearer −0.34 to −0.38%/°C. Separate coefficients exist for open-circuit voltage (strongly negative, typically −0.24 to −0.28%/°C, which governs cold-weather string sizing) and short-circuit current (slightly positive). In a market like India or the Gulf, where cells routinely operate 30°C above the reference, a 0.05%/°C difference between two modules translates into roughly 1.5% of annual energy — often more than the efficiency difference buyers focus on.

Worth knowing

Power falls as cells heat; voltage falls fastest, current rises slightly.
N-type TOPCon and HJT hold a real advantage over PERC in hot climates.
The Voc coefficient drives cold-climate string sizing; the Pmax coefficient drives hot-climate yield.
A 30°C rise above STC costs roughly 9–11% of power on a typical module.

How it's calculated

P_actual ≈ P_STC × [1 + γ × (T_cell − 25)]

P_STC — nameplate power at Standard Test Conditions

γ — Pmax temperature coefficient, e.g. −0.0030 for −0.30 %/°C

T_cell — operating cell temperature in °C, typically ambient + 25–35°C at full sun

Field notes

1In hot markets, compare candidate modules on Pmax coefficient before comparing efficiency — it usually matters more to annual energy.
2Use the Voc coefficient and the record low site temperature to check that string voltage stays under the 1,000 V or 1,500 V system limit.
3Elevated mounting with rear ventilation reduces cell temperature; flush rooftop mounting raises it, sometimes by 10°C.

Common mistakes

Using the Pmax coefficient for string-voltage checks — voltage has its own, different coefficient.
Ignoring that HJT's superior temperature behaviour can outweigh a lower headline efficiency in tropical sites.

Frequently asked

What is a good temperature coefficient for a solar panel?

For Pmax, anything better than about −0.32 %/°C is competitive in 2026. HJT modules lead at roughly −0.24 to −0.26 %/°C, TOPCon sits at −0.29 to −0.32, and older PERC products are −0.34 or worse.

How much power do solar panels lose in heat?

At a cell temperature of 60°C — common on a hot rooftop — a module with a −0.30 %/°C coefficient loses about 10.5% of its rated power compared with the 25°C reference.

Sources

[1]PV module temperature effects on performance — NREL
[2]IEC 61853 — PV module performance testing and energy rating — IEC

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