Solar Panel Temperature Coefficient: What It Means and How to Calculate Power Loss

Answer: A solar panel’s temperature coefficient of Pmax (maximum power) is how much power it gains or loses for each °C of cell temperature above or below 25°C. The datasheets in this guide list −0.24% to −0.34%/°C. A value closer to zero means less power lost to heat.

The coefficient explains only the heat part of a panel’s output. Yearly energy also depends on sunlight, mounting and weather. So run both panels through the same site model before you pick on the coefficient alone.

What Is a Solar Panel Temperature Coefficient?

A temperature coefficient shows how much a panel’s output changes for each °C of cell temperature. Datasheets list three. Pmax is the maximum power. Voc is the open-circuit voltage, the voltage when nothing is drawing current. Isc is the short-circuit current, the current when the panel is shorted. The Pmax and Voc coefficients are negative, so power and voltage fall as cells heat up. The Isc coefficient is slightly positive.

The reference point is 25°C cell temperature. This is the temperature used in standard test conditions (STC), the lab test that datasheets quote. A Pmax coefficient of −0.30%/°C means the panel loses 0.30% of its STC power for every °C its cells run above 25°C. It gains the same amount for every °C below 25°C.

The temperature-coefficient glossary entry covers the definition and unit conversions. This guide shows how to use the values when you choose panels and run the numbers.

Pmax Temperature Coefficients on Manufacturer Datasheets

The table lists the coefficients printed on eight manufacturer datasheets, in alphabetical order by manufacturer. Each value comes from the manufacturer’s own site. The products differ in power class, size and other specifications. So the table lists stated values. It is not a ranking and not an independent test.

Sources, all manufacturer sites: Canadian Solar HiHero datasheet, Canadian Solar HiKu6 PERC datasheet, Canadian Solar TOPBiHiKu6 datasheet, Jinko Tiger Neo datasheet, LONGi Hi-MO 7 datasheet, Maxeon 6 DC datasheet, REC Alpha Pure-R datasheet and Trina Vertex S+ datasheet.

In this set, the two heterojunction sheets list the values closest to zero (−0.24 and −0.255%/°C). The PERC sheet lists the largest loss (−0.34%/°C). Four sheets list −0.29%/°C: Canadian Solar TOPBiHiKu6, Jinko, Maxeon 6 and Trina. LONGi lists −0.28%/°C.

Manufacturers revise datasheets. The Jinko and PERC sheets date from 2022 and 2023. The LONGi sheet prints no date. So check the current revision for the exact model you quote.

Many people search for the SunPower temperature coefficient. Maxeon names its SunPower Performance panels in a press release. Its Maxeon 6 sheet above lists −0.29%/°C. Its other lines have their own datasheets. Only the Maxeon 6 sheet was read for this guide.

For panel efficiency by manufacturer, see the solar panel efficiency ranking 2026. Cell format is another difference to compare. See half-cut vs full-cell solar panels.

When you buy, keep the exact model, revision and local documents in the project record. Then confirm that the delivered panels match the model you used in your design.

Read the Three Coefficients Before Comparing Panels

Record the sign and the units of each coefficient. −0.38%/°C means −0.0038 per °C in a formula that uses fractions. A value in W/°C or V/°C is an absolute change. It needs a different calculation. Do not mix these forms when you enter a panel into design software.

Calculate Temperature Derating From the Coefficient

Derating means the drop in power. A simple power estimate at standard sunlight looks like this:

P(Tcell) ≈ PSTC × [1 + γP × (Tcell − 25°C)]

γP is the fractional Pmax coefficient per °C. The temperature is cell temperature, not outdoor air temperature. The formula looks at temperature only. Real output also depends on sunlight, shade, the electrical setup and other effects.

Worked Example: A 400 W Panel at 65°C Cell Temperature

Take a 400 W panel with cells at 65°C. Compare a −0.40%/°C coefficient with −0.30%/°C. The inputs are examples, not a measured site:

Temperature difference = 65 − 25 = 40°C
A, −0.40%/°C: factor = 1 − 0.0040 × 40 = 0.840, power = 400 × 0.840 = 336.0 W
B, −0.30%/°C: factor = 1 − 0.0030 × 40 = 0.880, power = 400 × 0.880 = 352.0 W

Panel A loses 64.0 W (16.0%) against the 400 W rating. Panel B loses 48.0 W (12.0%). So B gives 16.0 W more than A at this moment.

That gap is 4.0 percentage points of the 400 W rating. It is also 4.76% more than A’s 336.0 W (16.0 ÷ 336.0). The two percentages use different bases.

A third option at −0.255%/°C, the value on the Canadian Solar HiHero sheet, gives 1 − 0.00255 × 40 = 0.898 and 359.2 W.

The same formula works below 25°C. For option B at 5°C cell temperature, the factor is 1 − 0.0030 × (5 − 25) = 1.060. So 400 × 1.060 = 424.0 W. This covers temperature only. It does not predict winter daily output. It also does not raise the limits of the connected equipment.

Estimate Cell Temperature With a Suitable Thermal Model

The 65°C above is a number you pick. For a site estimate, use a thermal model. Sandia’s module-temperature model uses sunlight, air temperature and wind. It has settings for how the panel is built and mounted. Its cell-temperature model links cell temperature and module temperature through one more setting.

Write down the weather source, the thermal model, the mounting assumptions and how you treat cell versus back-of-module temperature. A fixed rule such as “roof panels run 35°C hotter than air” does not hold on every installation.

NMOT is a panel temperature measured under stated test conditions. The sheets above print 41 ± 3°C (the three Canadian Solar sheets) and 44 ± 2°C (REC). REC’s conditions are 800 W/m² of sunlight, 20°C air and 1 m/s wind. Read the definition on each sheet before you use the number. Do not use it in place of a site simulation.

The NMOT power tables on the same sheets differ from the STC tables. The test conditions differ, not only the temperature.

Panel and racking instructions, structure needs and local rules set the roof clearance. A general cooling benefit is not a reason to improvise how you attach the panels.

Cold Voc and Hot Operating Voltage Need Separate Checks

A negative Voc coefficient means lower temperature raises open-circuit voltage. The temperature-only form is:

Voc(T) ≈ Voc,STC × [1 + βVoc × (T − 25°C)]

βVoc is fractional per °C. The design temperature and the allowed method come from the equipment instructions and the local rules. They do not come from a universal climate table or the site’s average temperature.

Voltage Arithmetic for a Cold-Condition Check

This example is made up. Voc,STC = 38.8 V and βVoc = −0.24%/°C. The method uses −20°C as its temperature input.

Voltage factor = 1 + (−0.0024 × (−20 − 25)) = 1.108
Corrected module Voc = 38.8 × 1.108 = 42.9904 V

Take a made-up 600 V ceiling. 13 such panels give 558.8752 V (13 × 42.9904). 14 give 601.8656 V. The example shows the math and why early rounding misleads.

A real string length also depends on other limits, required allowances, equipment instructions, current checks and whether the operating voltage fits the inverter.

Canadian Solar’s 2020 standard-module manual shows one maker’s cold-voltage method. It uses the lowest expected air temperature, and it calls for review by a competent engineer. That manual is from 2020. So get the current manual for the product you choose and for your area.

For the hot operating-voltage check, use Vmp data or a checked panel model. Do not use the Pmax coefficient in place of Vmp. Do not assume the Voc coefficient gives a good Vmp estimate.

An inverter has two different limits. One is the top DC voltage it can take. The other is its MPPT operating range, the voltage window where it tracks the best power point.

Continue with the solar string-design workflow and the inverter sizing guide. Inverters have heat limits too. See solar inverter high temperature in India.

Decide Whether a Lower Coefficient Justifies the Price

Model both proposed systems with the same site inputs over a full year. Compare the usable energy after other losses and operating limits. Keep the layout, panel count and installed DC capacity in view. That way, a gain from extra capacity is not credited to temperature behavior.

Then weigh the extra cost against the project’s money assumptions. Here is a screening example. An upgrade costs 600 currency units. It gives an extra 200 kWh a year in a separate model, valued at 0.15 currency units per kWh. That is 200 × 0.15 = 30 currency units a year. And 600 ÷ 30 = a 20-year simple payback. The example leaves out discounting, price changes and degradation.

Check the extra energy and its value before you quote a premium. Do not multiply a peak power gap by a guessed number of hot hours. That does not give a yearly saving for a real site.

Temperature behavior is separate from permanent degradation. An n-type label or a good Pmax coefficient does not make a panel immune to light-induced degradation, LeTID, PID or other aging. Keep warranty terms and long-term loss assumptions apart from the operating-temperature model.

Installer Handoff Checklist

Before you finalize the proposal or electrical design:

• Keep the exact panel datasheets, revisions, manuals and equipment ratings.
• Record the Pmax, Voc and Isc coefficients with their original units and the converted model inputs.
• Write down the weather and thermal-model assumptions, including mounting and cell-temperature treatment.
• Compare yearly usable energy with the same inputs, and explain changes in capacity or layout separately.
• Send the cold-voltage check, the hot operating-voltage check and the current checks for qualified review.
• State the cost assumptions behind any premium recommendation.

To see how a design tool handles panel data and loss assumptions, book a free demo. Ask to see where SurgePV’s energy-yield modeling takes panel coefficients. Ask how the temperature assumption shows in the result. Ask which inputs and outputs your plan supports before you rely on a proposal figure.

For the wider production result, see solar system losses and performance ratio.

Frequently Asked Questions

What is a good temperature coefficient for solar panels?

A Pmax coefficient closer to zero loses less power in heat. The datasheets in this guide run from −0.24%/°C (REC Alpha Pure-R) to −0.34%/°C (Canadian Solar HiKu6 PERC). No single cutoff makes a panel the right buy. Compare exact products and modeled yearly energy.

What is the temperature coefficient of Pmax?

It is the change in a panel’s maximum power for each °C of cell temperature, measured against 25°C. A coefficient of −0.30%/°C means the panel loses 0.30% of its rated power for every °C its cells run above 25°C.

How do you calculate temperature derating for solar panels?

Turn the Pmax coefficient from percent per degree into a fraction. Multiply it by cell temperature minus 25°C. Then apply the result to rated power. A 400 W panel at −0.30%/°C and 65°C cell temperature gives 400 × (1 − 0.003 × 40) = 352.0 W. That is a 12.0% drop at that moment.

Do solar panels work better in cold weather?

Lower cell temperature raises power and voltage when other conditions are similar. A 400 W panel at −0.30%/°C and 5°C cell temperature gives 424.0 W on the temperature factor alone. Yearly output still depends on sunlight and weather. Cold voltage also needs its own string check.

What is the difference between STC and NMOT for solar panels?

STC is the reference test: 1000 W/m² of sunlight and 25°C cell temperature. NMOT is a cell temperature measured under a different stated condition. REC’s sheet gives 44 ± 2°C at 800 W/m², 20°C air and 1 m/s wind. The two power tables differ because the test conditions differ.

How does temperature coefficient affect string sizing?

The Voc coefficient shows how far open-circuit voltage rises in cold weather. That limits string length. For hot operating voltage, you need Vmp data or a checked panel model. The Pmax and Voc coefficients cannot replace a Vmp coefficient.

Which solar panel technology has the lowest temperature coefficient?

Among the eight datasheets in this guide, the two heterojunction sheets list the values closest to zero (−0.24 and −0.255%/°C). The PERC sheet lists the largest loss (−0.34%/°C). Eight sheets are not a market ranking. Check the datasheet for the exact model.

What is the SunPower or Maxeon temperature coefficient?

The Maxeon 6 DC 425–440 W datasheet (March 2024) lists −0.29%/°C for Pmax, −0.239%/°C for Voc and +0.057%/°C for Isc. Other Maxeon and SunPower-brand lines have their own datasheets.