Micro Inverter or String Inverter? Which one performs better?
When we need to lay PV Panels on a complicated roof. For instance the roof comprises multiple faces with different orientation and tilt angle, and each face can only put a few PV panels.
Then the String inverter is not suitable to be used, because you need to combine PV panels from different faces to form a string. This will cause high mixed orientation mismatched loss.
Another instance is that when there is shadow hitting the PV panels, the whole string performance will be affected especially when you have a long string.
Technically, the Micro Inverter shall perform better than String Inverter under these two circumstances.
Other than that, Micro Inverters seem to have no significant advantage over String Inverters in terms of performance.
But how much better is the Micro Inverter performing under the above two circumstances?
I took some time to run the Pvsyst simulations based on the said circumstances for a small system to find out the differences.
A 3D model of about 13kWp Solar PV system is built. 25 nos. of 550Wp PV panels were laid on two faces of the 3D model roof.
An obstacle is purposely created to have the effect of shadow on the PV Panels.
One scenario of the simulation is based on 6 x 2kWac Micro Inverters; and another scenario is based on 1 x 12kWac String inverter.
The simulations were run at a detailed level, which included module layout electrical connection.
Unfortunately, PVsyst didn’t allow me to do electrical connection of PV Panels of different orientations for the String Inverter Scenario.
Thus, I can only compare the scenario of shadows on PV Panels..
And the result?
When there is shadow hitting the PV Panels, both Micro Inverter and String Inverter systems have the same amount of irradiance loss.
But the String inverter system has higher shading- electrical loss, about 0.55%. Probably because I only have 16PV per string. The loss shall be higher if it is a longer string.
While the Micro inverter system has about 0.27% shading- electrical loss..
Micro Inverters also have shading- electrical loss, and mixed orientation mismatched loss though!
Based on PVsyst simulation results, the Micro Inverters have higher inverter loss during operation (efficiency), about 3.91%; while the String inverter scenario is only 1.96%.
Surprisingly, in overall performance, the String Inverter system performs better than Micro Inverter System!
All in all, for small PV systems, the Micro Inverter doesn't seem to have much advantage over the String Inverter on shading- electrical loss.
On the other hand, its efficiency loss seems much higher than the String inverter.
It could be due to the Micro Inverter Model that I used in my simulation..
So next time when you want to install PV modules on a roof with potential shadow, don’t just buy into the idea that the Micro Inverter will be performing better. You can also explore the string inverter performing based on simulation results…
If interested to know more details about the analysis, join my FB group below:-
Disclaimer: I just share the Pvsyst simulation result, and I don’t represent any string inverter supplier.
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