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Solar Panel Temperature Coefficient Calculator

Calculate the power, voltage, and current derate your PV module sees at any cell temperature. Free 2026 calculator using the IEC 61853-2 NOCT thermal model with MCS-aligned defaults for UK climate conditions.

Solar Panel Temperature Coefficient Calculator

Cell temperature
52 °C
ΔT vs STC
27 °C
Power change vs STC
-9.18%
Actual Pmax at conditions
367.8 W
Actual Voc at conditions
45.89 V
Actual Isc at conditions
10.61 A

Negative ΔT means the cell is below STC 25°C — Pmax exceeds the rated value.

Show derivation
T_cell = 22 + (44 − 20) / 800 × 1,000 = 52 °C
ΔT = 52 − 25 = 27 °C
Pmax = 405 × (1 − 0.34 × 27 / 100) = 367.8 W
Voc = 49.5 × (1 − 0.27 × 27 / 100) = 45.89 V
Isc = 10.5 × (1 + 0.04 × 27 / 100) = 10.61 A

How the calculator works

This calculator returns six numbers: cell temperature, ΔT vs STC, percent change in Pmax, and the actual Pmax, Voc, and Isc at your specified conditions. You enter nine inputs:

  1. Pmax at STC (W) — module rated power at 25°C, 1000 W/m², AM 1.5.
  2. Voc at STC (V) — open-circuit voltage at STC.
  3. Isc at STC (A) — short-circuit current at STC.
  4. γ Pmax (%/°C) — power temperature coefficient, absolute value.
  5. β Voc (%/°C) — voltage temperature coefficient, absolute value.
  6. α Isc (%/°C) — current temperature coefficient, absolute value.
  7. NOCT (°C) — Nominal Operating Cell Temperature.
  8. Ambient temperature (°C) — site ambient.
  9. Irradiance G (W/m²) — plane-of-array irradiance, 1000 W/m² at STC peak.

The math

T_cell      = T_amb + (NOCT − 20) × G / 800            (IEC 61853-2 NOCT thermal model)
ΔT          = T_cell − 25                              (signed)

Pmax_actual = Pmax_stc × (1 + γ_pmax × ΔT / 100)       (γ_pmax negative)
Voc_actual  = Voc_stc  × (1 + β_voc  × ΔT / 100)       (β_voc negative)
Isc_actual  = Isc_stc  × (1 + α_isc  × ΔT / 100)       (α_isc positive)

Worked example: 405 W JA Solar JAM54S30 on a London summer day

  • Pmax 405 W, Voc 49.5 V, Isc 10.5 A
  • γ Pmax = 0.34 %/°C, β Voc = 0.27 %/°C, α Isc = 0.04 %/°C
  • NOCT 44°C, ambient 22°C July afternoon, G = 1000 W/m²
  • T_cell = 22 + (44−20)/800 × 1000 = 52°C
  • ΔT = 27°C
  • Pmax_actual = 405 × (1 − 0.34 × 27 / 100) = 405 × 0.9082 = 367.8 W (loss 9.2%)
  • Voc_actual = 49.5 × (1 − 0.27 × 27 / 100) = 49.5 × 0.9271 = 45.9 V
  • Isc_actual = 10.5 × (1 + 0.04 × 27 / 100) = 10.5 × 1.0108 = 10.61 A

A 4 kWp UK system shedding 9% at peak insolation matches the MCS PV Guide assumption for typical summer-afternoon yield in the South East.

Worked example: same module on a cold Scottish winter morning

  • Same module, ambient −5°C, G = 600 W/m² (low winter sun)
  • T_cell = −5 + (44−20)/800 × 600 = −5 + 18 = 13°C
  • ΔT = −12°C
  • Pmax_actual = 405 × (1 − 0.34 × −12 / 100) = 405 × 1.0408 = 421.5 W (gain 4.1%)
  • Voc_actual = 49.5 × (1 − 0.27 × −12 / 100) = 49.5 × 1.0324 = 51.1 V

The instantaneous module power at 600 W/m² is still only 60% of rating (243 W actual), but the per-W output is 4% above nameplate. This is also why a 13-module string can clip the cold-Voc inverter limit in a Scottish winter even when the STC-rated string voltage is well within the inverter range.

What γ Pmax means for UK annual energy

UK annual cell temperatures average 28–32°C across England, Wales, and Scotland — ΔT 3–7°C above STC. That translates to 1–2.5% annual yield loss to temperature, well below the 5–10% experienced in the U.S. Southwest, Australia, or Spain. PVGIS-SARAH3 and the MCS PV Guide both bundle a 4% temperature loss into their default model.

In purely UK terms, the gap between a γ Pmax = −0.36 mono-PERC module and a γ Pmax = −0.29 TOPCon module is worth about 0.5–1.0 percentage points of annual yield. On a 4 kWp system that is 20–40 kWh/yr — under £10/year at the April 2026 Ofgem cap (27.03 p/kWh). The technology choice is rarely driven by temperature coefficient alone in UK installs; price-per-W, MCS certification status, and warranty terms usually dominate.

Where temperature coefficient really matters: string Voc compliance

Under BS 7671 and the IET Code of Practice Edition 4, string-Voc verification at minimum design temperature is mandatory. CIBSE Guide A minimum design ambient temperatures (Tmin) for selected UK locations:

  • Penzance, Cornwall: −3°C
  • London Heathrow: −5°C
  • Birmingham: −6°C
  • Manchester: −7°C
  • Edinburgh: −8°C
  • Aviemore, Scottish Highlands: −15°C

At Tmin and 1000 W/m², the cell temperature is approximately Tmin + 31°C (NOCT rise at full sun). For Birmingham Tmin = −6°C, T_cell = 25°C — almost exactly STC, so no cold-Voc concern. For Aviemore Tmin = −15°C, T_cell = 16°C, ΔT = −9°C, and a 49.5 V module reaches 50.7 V. A 13-module string fits a 700 V optimiser there (659 V); a 14-module string does not (710 V). This is the calculation MCS-certified installers run during string sizing — our string sizing calculator automates it.

Three levers in UK design

  1. Pick TOPCon or HJT if you also want low-light performance — HJT bifacial modules deliver 2–4% more annual kWh than mono-PERC in UK climates, mostly from better low-light response rather than temperature.
  2. In-roof systems trade aesthetic for yield — adding 3–5°C to NOCT cuts another 1–2% annual yield. Verify with our system efficiency calculator.
  3. String-Voc check at Tmin — the single most common MCS inspection failure for DIY installs. Always run it before final clamp-on.

Sources

  • IEC 61853-2:2016 Photovoltaic Module Performance Testing — Part 2.
  • IEC 61215-1-1:2021 Terrestrial Photovoltaic Modules — Design Qualification.
  • IET Code of Practice for Grid-connected Solar Photovoltaic Systems, Edition 4 (2024).
  • BS 7671:2018+A2:2022 Requirements for Electrical Installations.
  • MCS Installation Standard MIS 3002 (PV Systems) and MCS PV Guide v4.1 (2025).
  • Energy Saving Trust Solar Energy Calculator and PV Performance datasets.
  • BRE Solar / National Solar Centre PV Performance Testing reports 2024.
  • CIBSE Guide A: Environmental Design (2021), Table 2.13 design ambient temperatures.
  • PVGIS-SARAH3 European Commission Joint Research Centre 2024 release.

For annual kWh impact, run your numbers through our system efficiency calculator and output calculator.

Frequently asked questions

What is the temperature coefficient of a solar PV module?
The temperature coefficient is a datasheet number that tells you how much a module's power, voltage, or current shifts as the cell temperature drifts away from Standard Test Conditions (STC, 25°C). Three coefficients matter to UK installs: γ Pmax (typically −0.30 to −0.36 %/°C), β Voc (typically −0.25 to −0.30 %/°C), and α Isc (typically +0.04 to +0.06 %/°C). A module rated 400 W at 25°C loses around 5–7% of its power on a typical UK summer afternoon when the cell sits at 45–50°C. Voc moves in the same direction at a slower rate; Isc actually rises slightly with temperature. The MCS PV Guide and BRE Solar testing both reference these coefficients in the standard PVGIS yield model used for SAP calculations.
What is a typical Pmax temperature coefficient on a 2026 UK-market module?
Mono-PERC modules from JA Solar, Trina, JinkoSolar, Q Cells, and Longi run γ Pmax = −0.34 to −0.36 %/°C. The 2024–2026 TOPCon generation (Longi Hi-MO 6, JinkoSolar Tiger Neo, Trina Vertex N) runs −0.29 to −0.32 %/°C. REC Alpha Pure-R heterojunction modules — common on premium MCS-certified installs — run −0.24 %/°C. For the typical UK climate the difference between these technologies is worth 1–2% of lifetime kWh, far less than in Spain or Australia. The MCS Product Database (mcscertified.com) lists γ Pmax for every certified module if your installer's quote omits it.
What is NOCT and why does the module run hotter than the UK ambient?
NOCT (Nominal Operating Cell Temperature) is the cell temperature a module reaches in 20°C ambient, 800 W/m² irradiance, 1 m/s wind, open-rack mounting. Most monofacial mono-Si modules ship at NOCT 44–47°C, meaning the cell sits 24–27°C above ambient even at moderate sun. The IEC 61853-2 NOCT thermal-rise model scales linearly: T_cell = T_amb + (NOCT − 20) × G / 800. On a 22°C London summer afternoon at 800 W/m², the cell sits at 46°C — modest by Mediterranean standards but enough to cut a 400 W module to 372 W. Close-to-roof in-roof systems popular on UK new-builds add another 3–5°C compared with on-roof rail systems.
How does γ Pmax affect UK system design?
Less than it affects designs in hot climates, but still measurably. The Energy Saving Trust (energysavingtrust.org.uk) PV calculator and PVGIS use a default temperature loss of around 4% across the UK because annual mean cell temperatures sit at 28–32°C — only 3–7°C above STC on an annual average. A switch from mono-PERC (−0.35 %/°C) to TOPCon (−0.30 %/°C) recovers about 0.5–1 percentage point of annual yield, or roughly 50–80 kWh/yr on a 4 kWp system. The bigger lever for UK installs is correct string sizing using the BS 7671 / IET Code of Practice for Grid-connected Solar PV minimum design temperature (typically −5 to −10°C depending on region).
How does the cold-Voc rule affect string design under BS 7671?
The IET Code of Practice for Grid-connected Solar PV (Edition 4, 2024) requires you to verify that the maximum string Voc at minimum design temperature does not exceed the inverter input rating or 1000 V DC, whichever is lower. For most UK locations the minimum design temperature is taken from CIBSE Guide A — typically −5°C for southern England, −8°C for the Midlands, and −10 to −12°C for Scotland. At −8°C, ΔT = −33°C below STC, and a 49.5 V Voc module climbs to 49.5 × (1 + 0.27 × 33 / 100) = 53.9 V. A 13-module string that just fits a 700 V optimiser at STC reaches 700.7 V at the cold-Voc design point — a one-module-too-many string. Our [string sizing calculator](/calculators/solar-string-sizing-calculator/) walks through the full math.

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