PV Temperature Coefficient: Voc, Vmp and Pmp Effects

Quick answer

A temperature coefficient is the rate at which a PV module parameter changes with cell temperature, usually expressed in %/°C relative to the 25 °C rating. Values are measured under IEC 60891 and IEC 60904 procedures; typical crystalline modules lose about 0.29 to 0.40% of Pmax per °C, which matters for hot-climate yield and string sizing.

Module Temperature Coefficients (Typical 2024)

Technology	β_Voc (%/°C)	γ_Pmp (%/°C)
PERC	−0.27 to −0.30	−0.35 to −0.40
TOPCon	−0.25 to −0.27	−0.30 to −0.34
HJT	−0.22 to −0.25	−0.24 to −0.28

Application, Voc Correction

Voc(T) = Voc(STC) × [1 + β_Voc × (T − 25)]

At T = −10°C with β_Voc = −0.0027/°C: Voc rises ~9.5%.

Key Takeaways

Temperature coefficients quantify module response to cell temperature change.
β_Voc and γ_Pmp drive cold/hot-day calculations.
TOPCon and HJT have tighter (better) γ_Pmp than PERC.
Always temperature-correct using site-specific cold and hot temperatures.
Datasheet values are nominal; field variation 5-10%.

Why It Matters for Design Sign-Off

Temperature coefficients aren’t just a datasheet curiosity, they set the hard limits an electrical designer has to work inside. The β_Voc figure defines the cold-day ceiling that keeps string voltage under the inverter’s maximum input rating and the equipment’s DC voltage rating, while γ_Pmp shapes the hot-day power derating that a yield model has to account for.

Both numbers ultimately feed the same string-sizing calculation that shows up on stamped drawings and permit packages, which is why a module swap late in a project (say, PERC to TOPCon) usually forces a re-check of string length rather than a simple like-for-like substitution.

Because temperature coefficients govern the cold-day and hot-day boundaries used in string sizing, they show up directly in Solar SLD software that auto-generates NEC-compliant single-line diagrams, and in the broader PV yield simulation software, where γ_Pmp is one of the loss inputs behind every energy estimate.

Reports that express that estimate as a confidence band, see our breakdown of P50, P90, and P99 solar yield reports, carry temperature-related uncertainty as one of their line items. For a closer look at how string voltage limits and MPPT tracking windows interact once temperature correction is applied, Qbits Energy’s guide on string voltage versus MPPT voltage in solar inverters is a useful companion read.

Disclosure: Qbits Energy is a Heaven Designs group company.

Frequently Asked Questions

3 commonly searched questions about Temperature Coefficient.

What is a good temperature coefficient for solar panels?

Lower magnitude is better. Many TOPCon and heterojunction modules list Pmax coefficients around -0.26 to -0.30%/°C, while older PERC modules are often near -0.34 to -0.37%/°C. In hot climates the difference adds up to measurable annual energy.

Why is the Voc temperature coefficient negative?

Cell voltage falls as temperature rises because higher temperature increases recombination in the semiconductor. The negative coefficient means modules produce higher voltage in cold weather, which is why designers use it to calculate maximum string voltage at the site's lowest expected temperature.

How do you use a temperature coefficient in a calculation?

Multiply the coefficient by the difference between cell temperature and 25 °C, then apply that percentage to the STC value. For example, a -0.30%/°C module at 65 °C cell temperature loses about 12% of its rated power.

Need engineering-backed solar designs?

Heaven Designs prepares solar drawings, structural calculations, electrical engineering documents, and project-specific permit plan sets.

Solar 3D Pre-Design Solar Permit Design Electrical CEIG Drawings

Get a project quote See all services