Solar panels often produce less power as their cells become hotter, even in bright sunlight. Panel temperature and sunlight strength are separate influences; there is no universal percentage loss for an SUV roof or balcony.
Editorial correction: Earlier versions included unsupported testing, experience or performance claims. This research guide replaces those claims. Examples below are calculations, not measurements made by Wild Smart Gear.
Use the panel’s temperature coefficient
Find the datasheet’s maximum-power temperature coefficient and rated test temperature. Cell temperature can be higher than ambient air temperature, especially with restricted airflow.
For a hypothetical coefficient of −0.35% per °C and cells 30°C above the stated reference, the temperature-related power change would be approximately −10.5%, holding other conditions equal. Those values are an example, not specifications or measurements for a named panel.
Do not confuse heat with other losses
Shade, orientation, irradiance, wiring and station input limits can reduce observed power. Compare the same arrangement under similar light before attributing everything to temperature.
A panel’s peak watt rating does not predict daily Wh. Log input energy over the available day and compare it with actual loads.
Vehicle and balcony placement
Use the panel maker’s mounting and clearance guidance. A fixed roof panel can have different airflow and exposure from a portable panel positioned while parked. Keep the battery station within its own charging and storage temperature limits.
Do not place the station in direct sun merely because the panel needs light. Do not pour water on energized equipment or improvise rooftop attachments to cool it.
Cold-weather voltage is another limit
Although this page concerns heat and power, cold cells can increase open-circuit voltage. Check the complete panel configuration against maximum input voltage using the datasheet coefficient and expected minimum temperature.