Quick answer
A solar module temperature coefficient describes how maximum power, open-circuit voltage or short-circuit current changes with cell temperature relative to a reference condition. The quantity, sign and units must be read together.
What Is a Solar Panel Temperature Coefficient?
Answer: A solar module’s temperature coefficient describes how a specified electrical quantity changes with cell temperature relative to a reference condition. Datasheets distinguish maximum power (Pmax), open-circuit voltage (Voc) and short-circuit current (Isc) coefficients. Read the quantity, sign and units together: a power coefficient is useful for energy modeling, while voltage and current coefficients serve different electrical-design checks.
The reference for standard test conditions (STC) is 25°C cell temperature, not 25°C outdoor air temperature. STC also specifies irradiance and spectrum; see standard test conditions.
Pmax, Voc and Isc Coefficients
| Datasheet quantity | What the coefficient describes | Why it matters |
|---|---|---|
| Pmax | Change in maximum power with temperature | Helps estimate the temperature contribution to power and energy output. |
| Voc | Change in open-circuit voltage with temperature | Used in evaluating cold-condition maximum voltage; it is not the MPPT operating voltage. |
| Isc | Change in short-circuit current with temperature | One input to current assessment; it does not replace required current-sizing rules. |
As a verified example, Canadian Solar’s May 2026 CS6.2-66HB-HP datasheet lists −0.255%/°C for Pmax, −0.230%/°C for Voc and +0.044%/°C for Isc. These values belong to that published product family and revision; they are not universal coefficients for all HJT modules.
The different signs explain why warmer cells can have lower maximum power and open-circuit voltage while short-circuit current increases slightly. Do not substitute one coefficient for another because they appear next to each other on the datasheet.
Percentage Versus Absolute Units
A coefficient in %/°C is relative to the reference value. For a calculation that uses a fractional coefficient, divide the percentage by 100:
−0.35%/°C = −0.0035 per °CA coefficient in W/°C, V/°C or A/°C expresses an absolute change. Those numbers cannot be inserted directly into a formula expecting a fractional coefficient.
For example, a hypothetical 400 W module with −0.35%/°C has an equivalent reference-power slope of −1.4 W/°C: 400 × −0.0035. Likewise, convert mV to V or mA to A before using an absolute voltage or current slope. Record both the original datasheet units and the units used by the model to prevent silent conversion errors.
A Simple Temperature-Only Power Calculation
A linear estimate at the reference irradiance is:
P(Tcell) ≈ PSTC × [1 + γP × (Tcell − 25°C)]Here γP is the fractional Pmax coefficient per °C. This estimates the temperature effect under the stated assumptions; it is not a complete prediction of measured field output.
Retaining a useful arithmetic example from this guide, assume a hypothetical 400 W module, γP = −0.0035/°C and cell temperature of 55°C:
Temperature difference = 55 − 25 = 30°C
Power factor = 1 − 0.0035 × 30 = 0.895
Estimated temperature-adjusted power = 400 × 0.895 = 358 WThe modeled reduction is 42 W, or 10.5%, at that operating point. It does not establish a 10.5% annual energy loss. Annual energy needs time-varying irradiance, temperature and the other system-loss inputs. The same linear example at 15°C gives 414 W at the reference irradiance; an STC rating is not an unconditional cap under every weather condition.
Cell Temperature Is Not Ambient Temperature
Outdoor air temperature alone does not determine the cell temperature. Sandia’s cell-temperature overview identifies irradiance, weather and module construction as influences. Its module-temperature model includes ambient temperature and wind, with parameters that depend on construction and mounting.
Do not add a fixed number of degrees to the forecast air temperature for every roof. Select a thermal model appropriate to the installation and document its inputs. A temperature measured on the back of a module is also a different measurement location from the cell itself; record how the model relates those quantities.
NOCT or NMOT is an operating-temperature characterization under specified conditions, not the cell temperature the module will always reach. Use the relevant datasheet definition rather than treating the number as a constant for an annual simulation.
Cold Voltage and String Sizing
For a module with a negative Voc coefficient, lower temperature raises open-circuit voltage in the linear approximation. That is why using only STC voltage—or assuming a hot climate permits longer strings—can miss a cold-condition limit.
Use the selected module’s Voc data and the temperature method required by its applicable instructions and local rules. Check the limits of the complete connected equipment, not just one inverter field. Do not substitute Pmax coefficient for Voc coefficient, or use a yearly average temperature for an extreme-condition check.
Canadian Solar’s 2020 standard-module installation manual illustrates manufacturer guidance using the lowest expected ambient temperature, the selected module’s voltage coefficient and competent engineering review. It is a historical manual for its covered products, not installation approval for the 2026 datasheet example or every solar module. Obtain the correct current instructions for the actual equipment.
Cold-voltage assessment does not complete string design. Operating voltage across temperature and irradiance, the inverter’s MPPT range and current limits, module and component ratings, and applicable electrical rules still need assessment.
Comparing Modules and Mounting Options
For two negative Pmax coefficients, the value closer to zero describes less modeled power reduction per degree above the reference, all else equal. It does not establish the best annual yield, value or lifetime performance on its own.
Compare exact products using their rated power, coefficients, relevant warranties, price and a consistent project model. Avoid ranking an entire cell technology from a generic coefficient range. The HJT solar-cell definition provides context, while panel derate factor covers the broader loss concept.
Mounting can affect the thermal model, but clearance and attachment must follow the applicable module/racking instructions and structural requirements. This glossary does not prescribe a universal roof gap or promise a particular cooling gain.
For a SurgePV demo, bring the actual datasheets and ask how the available workflow represents coefficient units, thermal inputs and electrical checks. Confirm those details before relying on a proposal or string-design result.
Frequently Asked Questions
Is a more negative power coefficient better?
For modeled power retention above the reference temperature, a negative coefficient closer to zero means a smaller reduction, all else equal. Product selection still requires a complete project comparison.
Should I use outdoor air temperature in the power formula?
The temperature-only power formula uses cell temperature. Estimate it using an appropriate thermal model or a justified measurement method; do not substitute ambient temperature without explanation.
Can the power coefficient be used for maximum string voltage?
No. The Pmax and Voc coefficients describe different quantities. Maximum-voltage assessment needs the appropriate voltage data, temperature method, equipment limits and applicable rules.
Does the coefficient describe permanent degradation?
No. It describes temperature-dependent electrical behavior. Long-term degradation is a separate change in performance and should not be combined with the temperature coefficient as though they were the same loss.
Related Glossary Terms
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