Temperature Driven Derating in Solar Inverter Installations
Johannesburg’s heat changes the engineering rules.
A 15 kW Sigenergy inverter — like all power electronics — is rated at 25 °C, yet our real world ambient temperatures regularly reach 35–40 °C, with enclosed inverter spaces climbing to 45–55 °C. At these temperatures, no inverter can safely deliver its full rated output without derating.
This is not a design preference.
It is a risk management requirement.
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Why Derating Is Essential
High ambient temperatures reduce an inverter’s ability to cool itself. When heat sinks saturate and switching components run hotter, the inverter automatically reduces output to protect itself. In Johannesburg conditions, a 15 kW inverter typically delivers 12–13 kW continuously.
Failing to derate leads to:
• Overheating and shutdowns
• Accelerated component aging
• Reduced system efficiency
• Premature inverter failure
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Breaker Derating: Preventing Nuisance Trips
Circuit breakers are also temperature sensitive.
At 40–55 °C, their effective current capacity drops by 15–30%.
Always On Energy derates input and output breakers to 85% for Johannesburg installations to prevent:
• Unnecessary tripping under normal load
• Heat induced breaker fatigue
• Safety risks during peak generation
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Wiring Must Be Rated for 55 °C — Not 25 °C
Standard cable ratings assume 30 °C ambient. Johannesburg routinely exceeds this.
At 55 °C ambient:
• Design Cable capacity should drop by 20–30%
• Other wise Insulation softens
o Voltage drop increases
o Heat buildup accelerates
o Heat transfer to terminals increases
If wiring reaches 70 °C — the PVC limit — insulation hardens, cracks, and can expose conductors, creating a fire and equipment damage risk.
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Impact on Sigenergy Inverters
Sigenergy inverters are high performance units, but like all electronics, they rely on:
• Correct ambient temperature
• Correct breaker sizing
• Correct cable sizing
• Correct installation environment
Ignoring temperature realities results in:
• Derating events
• Breaker trips
•

• Overheating

• Long term damage
A 15 kW inverter only delivers 15 kW when the environment allows it.
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Always On Energy: Engineering Grade Installations
We design systems around real Johannesburg conditions, not theoretical datasheet values. Our installations ensure:
• No nuisance tripping
• No overheating
• No premature inverter failure
• No melted terminals
• No hidden thermal risks
Temperature is the silent killer in solar systems — unless it is engineered correctly.