Full sun, half the yield - where is the energy lost?
Just imagine: A sunny day, the display of your PV system shows a stable output – everything seems perfect. ☀
But when the statement arrives at the end of the month, they are in for a surprise:
The yields are significantly lower than expected.
No error, no warning – and yet valuable energy is lost day after day.
The reason? - An idle string.
Silent, invisible, but with serious consequences for your earnings.
Such errors often remain undetected for months, but can cause financial losses or even safety risks.
The solution? - Drone thermography.
It makes invisible weak points visible – quickly, reliably and without long downtimes.
What is an ‘idle string’?
A photovoltaic string consists of several solar modules connected in series, which together generate direct current.
If a string is idle, the circuit is interrupted – whether due to a faulty connection, a defective inverter or a damaged generator connection box.
The affected modules then no longer contribute to power generation.
Common causes of an open-circuit string
- Damaged or loose plug connections – the current flow is interrupted.
- Defective string fuses – DC fuses that protect PV modules can fail.
- Short circuits or thermal overloads – components in junction boxes fail.
- Inverter faults – individual or multiple strings can fail.
- Defective or deactivated generator junction boxes – faulty connections between strings & inverters can cause strings to idle.
How do you recognise an idle string?
🔥 Warmer temperature pattern – Non-working strings heat up more because less radiant energy is converted into electricity.
📷 Thermography as a solution – In thermography, they appear warmer than neighbouring, functioning strings. For clear temperature differences, an irradiation of > 600 W/m² is required.
Why is drone thermography ideal for fault diagnosis?
✅ Fast and large-scale inspection – drones capture PV fields and roofs in just a few minutes.
✅ No system downtime – inspection takes place during operation.
✅ Precise fault detection – empty strings are identified without time-consuming individual measurements.
The consequences of an idle string
🚨 Power loss – lower yields.
🔥 Safety risks – defective cables or connections can lead to thermal problems or even electric arcs.
📢 More interesting Insights?
🔗 Subscribe to the Photovoltaik Vision WhatsApp channel & newsletter!
Author and expert: Jan Wannenwetsch