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Mismatch Losses


Hayder Ali
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Hi Hayder Ali,

there are several mismatch effects that we consider: In all projects we assume a standard factor for the mismatch losses in PV modules due to the small deviations of the nominal power of the PV modules. That means, that if you buy a set of PV modules labelled with 250 Wp, you will get some that have exactly 250 Wp, but others that have slightly more, perhaps sometimes even a bit less. Due to these differences, the PV modules will not react equally to irradiance or temperature changes, small inhomogenities occur in the field, and so you will have small mismatch losses. You can change the default value of 2% (which is very conservative) in the simulation options:

image.png

 

Another type of mismatch, and the more important one, is a consequence of inhomogeneous shading on the modules, or different orientations of the module areas. So the shading effect can only be simulated when using the 3D environment. Modules in PV systems with near shading objects will always receive different levels of solar irradiance, and in consequence the feature varying i-v characteristics. For all PV modules in a string, the i-v characteristics are superposed, and when there are parallel strings, these i-v curves are superposed as well. The MPP tracker only sees the superposed i-v curve of the PV field and searches for the point of maximum power on this curve. This point will be the maximum for the PV field, but it will be less than the sum of all individual points of maximum power per PV module most of the time. This difference is the mismatch loss due to configuration or shading.

You can read more on the superposition of the i-v curves here:

https://help.valentin-software.com/pvsol/2018/calculation/pv-field/

You find both mismatch losses in the energy balance at the end:

image.png

 

I hope this helps. If you have further question, please don't hesitate to ask.

Kind regards,

Martin

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