Bright sunshine is not the whole story — heat is the hidden culprit that cuts photovoltaic output, especially in silicon modules, which account for more than 90 % of today’s market and are highly temperature-sensitive.
The Role of the Temperature Coefficient (Pmax)
Every module datasheet lists a Temperature Coefficient, Pmax (% / °C).
It quantifies the power loss for each 1 °C the cell temperature rises above the 25 °C standard-test condition (STC). The value varies by manufacturer and cell technology.
Example
Parameter | Value |
Nameplate power | 550 W |
Pmax | –0.40 % / °C |
Midday cell temperature | 40 °C (ΔT = +15 °C) |
Power loss = 15 °C × 0.40 % = 6 %
Loss in watts = 6 % × 550 W ≈ 33 W
Net output ≈ 517 W
Mitigation Measures
- Improve ventilation
Mount modules with adequate gaps between roof and panel, and between module rows, to let hot air escape. - Specify low-Pmax modules
Technologies with a smaller (less negative) coefficient lose less power in high temperatures. - Avoid heat traps
Do not place modules flush against surfaces that store or radiate heat.
High summer temperatures can noticeably reduce PV performance. Selecting modules with a favourable Pmax and installing them for effective cooling will keep your system producing at its best, even in extreme heat.
Tips: Checklist For a Solar PV System
▢ Check module Pmax — Ensure Temperature Coefficient (Pmax) is less than -0.35 % / °C
▢ Analyze average rooftop cell temperature (Tcell) — Focus on summer conditions
▢ Design for airflow — Mounting rail height ≥ 100 mm and side gap between panels ≥ 20 mm
▢ Prepare an IR camera — For use during commissioning tests to verify thermal performance
Contact Us
West Coast Engineering Company Limited (WCE)
🌐 www.wce.co.th
✉️ international@wce.co.th
📞 +66 (0) 65-9376283
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