This can be due to several reasons. We will examine the various possibilities below:

Inverter is undersized (intentional undersizing)

What is it?

The inverter is deliberately chosen to be smaller than the peak power of your solar panels. For example: 5000 Wp of panels, but a 4000 W inverter.

Why is this done?

• Cost savings: smaller inverters are more affordable.
• Efficiency: Inverters operate more efficiently when running at a higher percentage of their capacity.
• Peak power vs. realistic power: solar panels rarely deliver their maximum power due to temperature losses, sun angle, dirt, etc.

👉 Recommendation: Check the ratio between panel power and inverter power (the “DC/AC ratio”). A ratio of 1.1 to 1.2 is usually optimal for residential installations.

Sun conditions and environment

• Weather conditions: clouds, winter sun, or a low sun position limit the yield.
• Orientation and tilt angle: deviations from the optimal south orientation or tilt reduce power.
• Shading: trees, dormers, and chimneys can partially or temporarily limit power.

👉 Recommendation: Use monitoring data to analyze if there is structural shading. Consider optimizers or micro-inverters if you have significant shading.

Grid limitations (grid congestion or feed-in limitation)

The grid operator throttles the injection if the grid is saturated. Some inverters have a limit for feeding back into the grid.

👉 Recommendation: Check if your inverter or grid operator has set a limit. Some systems show this in the monitoring data. For feed-in limitations, a home battery can be a solution.

Technical limitations or defects

• Outdated firmware or poor configuration
• Loss in cabling (voltage drop)
• Poor ventilation or overheating of the inverter (thermal derating)
• Defective solar panels or strings

👉 Recommendation: Have a specialist perform a technical check or conduct a power analysis yourself via the monitoring portal. Also check if all strings are functioning correctly.

Mismatch in system design

• Multiple orientations on a single MPPT input can cause inefficiency.
• No or poor use of optimizers with string variations

👉 Recommendation: Review the string configuration. Reconfiguring or replacing the inverter with one that has multiple MPPTs can increase efficiency.

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