Modelling East West arrays (version 5.64)

[JPye]

Hello,

We are currently trying to model the differences in output of an array with 2 strings - once facing west and one facing east. We would like to know the difference in performance when they are connected to either a single MPPT, or separate MPPTs. We are expecting to see a small reduction in power when using a single MPPT.

The results we are currently getting is a slight increase in performance when using a single MPPT - only an additional 2kWh over a year with a 4kW system. Although this is negligible, it would indicate the simulation is not accurate as there would be more loss using only a single MPPT. This would indicate the simulation does not represent the situation we are string to simulate!

Is it possible to simulate this in PVsyst?

Regards,

Jono

[André Mermoud]

In the mixed arrays (heterogeneous fields in version 5), the calculation of Pmpp is indeed very different than for a single array: we have to establish 2 I/V curves, mix them and identify the Pmpp of this resulting mixed I/V curve (approximation).

In practice, when mixing different I/V curves with different currents (but about the same voltage), as this arises with mixed orientation, we observe that the result is very close to the sum of both Pmpp. That is, at comparable voltages the mismatch loss is quite negligible (this appears in the loss diagram of the version 6, and is always almost null).

Therefore a little discrepancy (error) in the calculation approximations may indeed lead to a better performance - but not significant - in mixed orientation.