AEP sensitivity from MPPT configuration

Dear All,

I have question regarding the use of MPPT features.
It seem that by utilizing the MPPT inputs, the more input I use, the less overall energy production

I have a system design with
- 90 Modules, 450W
- Inverter with 4 MPPT inputs
- Two Azimuth, 79 and 259 degree.
- Each string have 15 modules in series
- Therefore, we have 6 strings to work with.
- The roof is is allow for 2 string on the 259 degree azimuth and 4 string on the 79 degree azimuth

By common sense, it would be logical to have 2 MPPT input, one for each azimuth.
I have three cases
a) 1 MPPT inputs, 2 subarrays, mismatch
b) 2 MPPT inputs, 2 subarrays, no mismatch
c) 2 MPPT inputs, 2 subarrays, mismatch

The productionwise, (a)>(b)>(c), from inspection the losses diagram, it seem that the main cause of this production lost is the inverter power consumption.
Am I correct that because of the power used by inverter to track the power point (Varying the voltage), the production reduced.

Best,
Potchara S.

Hi Potchara,

The subarray mismatch voltage option at the bottom of the System Design page is intended for modeling inverters with a single MPPT input. We implemented that option before SAM allowed for inverters with up to four MPPT inputs. SAM should probably not allow you to choose the mismatch option for an inverter with more than one MPPT input.

These different options determine the value of the inverter input voltage as follows for a system with two subarrays:

1 MPPT with no mismatch: Inverter input voltage is the average of subarray 1 and subarray 2 operating voltages.

1 MPPT with mismatch: Inverter input voltage is calculated using iterative method described in Dobos (2012) Modeling of Annual DC Energy Losses due to Off Maximum Power Point Operation in PV Arrays .

2 MPPT: Inverter has two inputs with two different voltages allowing each subarray to operate at its maximum power point.

I would expect the total annual output for the three options to be in this order:

2 MPPT > 1 MPPT with mismatch > 1 MPPT with no mismatch

You can explore the effects of these different options by looking at the "Inverter MPPT i]m[/i Nominal DC voltage" and "Subarray i]n[/i Operating DC voltage" outputs. (The MPPT input number may not be the same as the subarray number.)

Best regards,
Paul.