Inverter MPPT voltage ranges

Are the inverter MPPT voltage ranges in SAM informational only (for system sizing), or do/should they affect the modeled array performance?

Specifically, can I use SAM to model the clipping effect when the array voltage deviates from the MPPT tracking limits of the inverter? (Presumably, the inverter would clamp the voltage at the limit, resulting in a production loss. I would like to model that loss.)

A couple quick tests suggest that the inverter MPPT voltage range has no effect on modeled DC power production.

Hi Steve,

For now, SAM only uses the MPPT voltage ranges for sizing. SAM does prevent the inverter from operating above its rated capacity (power in W or kW), but does not model the clipping effect due to inverter operating voltages exceeding the MPPT voltage limits.

Best regards,
Paul.

Ok, then I have a related question: is it possible to extract time series of the temperature-adjusted PV model parameters at every timestep? If so, then it should be possible to estimate the MPPT clipping using an external script / post-processing.

SAM does report the operating DC string voltage for each subarray and the inverter DC input voltage, which you could compare to the inverter MPPT limits to determine when clipping would occur.

For systems with one subarray, the subarray DC string voltage is the product of the module maximum power point voltage and number of modules per string: The inverter input voltage is equal to the subarray string voltage.

For systems with more than one subarray, when the subarrays have different orientations or tracking options, SAM estimates the inverter's input voltage by averaging each subarray's string voltage. The cell temperature of modules in each subarray will be slighlty different because each subarray is exposed to different incident irradiance levels.

If you use the CEC module model option, you can enable the subarray voltage mismatch calculation option on the System Design page to use a more accurate method to estimate the inverter's input voltage.

Best regards,
Paul.

Hi Paul/SAM team,

My question is a follow-up to this 2014 topic.  Are there any plans to add calculation of losses for out-of-MPPT-window array voltage?  The specific scenario I'm considering is low array voltage, where DC operating voltage goes below the bottom of the inverter MPPT window, and the inverter must boost voltage at the expense of shifting off of peak power.

Much appreciated,
Ben

Hi Ben,

More recent versions of SAM do take the inverter MPPT voltage range into account during the simulation to ensure that the inverter input voltage is within the MPPT voltage window.

SAM reports the power loss associated with adjusting the inverter input voltage in each time step as "Inverter clipping loss DC MPPT voltage limits." It also reports the total loss on the Losses tab of the Results page and as an annual kWh and % of total output value as "DC inverter MPPT clipping loss" under Single Values on the Data Tables tab.

In the most recent version, SAM 2022.11.21 r1, we made the inverter voltage ratings editable on the System Design page, so you can use different values than those in the CEC inverter library.

Best regards,
Paul.