A well designed solar system that uses quality components should generate electricity very close to the expectation. However, a variation of up to 10% in monthly generation is quite normal. There may be a few months where even 20% variation in generation is possible. As far as the yearly generation is concerned, up to 10% variation in actual generation is quite possible. The variation could take place due to normal variation in weather. There will be some months where the system generates more than the predicted amount while during others, the generation is lower. However, variation more than these numbers must be examined closely. Specifically, if generation is significantly less than the expected generation, the system installation must be analyzed. Some reasons for low generation are following:

• One or more of strings could be disconnected
• Panel rows placed too close, resulting in shadows
• Incorrect tilt for panels for the given location. A tilt same as latitude of the location may not be best for the given installation
• Nearby objects causing shadow
• Incorrect string design in which each panel does not generate an identical current
• Poor cleaning of panels
• Grid voltage crossing inverter threshold, resulting in frequent disconnections
• Incorrect orientaion of panels (not the tilt)
• Using poor quality panels.
• Excessive loss in wiring
• Using inefficient inverter

Reasons why generation may be legitimately low:
• Cloudy/Rainy Weather.
• Excessively high temperatures
• Pollution

In case you need further assistance for your system, please reach me via email.