Which current is compared with which inverter limit?

The sum of Imp across an input's parallel strings is compared with that input's maximum input current. The sum of Isc is compared with its maximum short-circuit current. Series modules do not add current, so only parallel strings are summed.

Are the currents temperature-corrected?

Only Isc, and only when you enter alpha, the Isc temperature coefficient. It is then corrected to your hot design temperature. Without alpha the current checks are labelled STC values only, not temperature-corrected. Imp is always the STC value, because alpha belongs to Isc.

Does the planner apply a safety factor or default temperatures?

No. No current multiplier is applied, and the design temperatures, datasheet values and inverter limits all start empty. Every figure compared comes from what you enter, so confirm the limits against the inverter documentation and the DC design against AS/NZS 5033.

Does it estimate the loss from mixing faces on one MPPT?

No. It says when strings on one input span faces with different azimuth or tilt, or when parallel strings have different module counts, and leaves the judgement to you. It does not model yield.

Design Check

Multi-Face MPPT Allocation Planner

Allocate strings from several roof faces across one inverter's MPPT inputs, and check temperature-corrected voltages and summed currents against the limits you enter.

Sources listedReviewed September 2026Our methodology

Inputs

View result

Module datasheet, shared by every face

Voc (open-circuit)Datasheet STC value.

Vmp (at max power)Datasheet STC value.

Isc (short-circuit)Datasheet STC value.

Imp (at max power)Datasheet STC value.

Module power (Pmax)Used for the array total only.

Voc temperature coefficientType it as printed. The sign is normalised.

Vmp temperature coefficientType it as printed. The sign is normalised.

Isc temperature coefficient, alpha (optional)Without it, the current checks read STC values only, not temperature-corrected.

Design temperatures

Cold design cell temperatureYour figure for this site. No default is supplied.

Hot design cell temperatureYour figure for this site. No default is supplied.

Inverter datasheet

Maximum DC input voltage

AC ratingUsed for the DC:AC ratio only.

MPPT operating minimum

MPPT operating maximum

MPPT inputs in useOne inverter only. Current limits are entered per input below.

Roof faces (1 of 8)

Face name
Azimuth (optional)Degrees clockwise from true north.
Tilt (optional)Degrees from horizontal.
Different modules on this face

Live result

Edit inputs

Choose how many MPPT inputs are in use, then enter the module, temperature and inverter values from the datasheets.

Key takeaways

Checks each MPPT input of one inverter: the highest string Voc at your cold design temperature, the Vmp window at both design temperatures, and the currents of its parallel strings.
Sums Imp against the maximum input current and Isc against the maximum short-circuit current. Without an Isc temperature coefficient both read STC values only, not temperature-corrected.
Describes, without estimating a loss, strings that span faces with different orientation and parallel strings with different module counts on one input.
Every datasheet value, limit and design temperature starts empty, and no current multiplier is applied. Results read within or outside the limit you entered.

How it works

Each string's voltages start from the datasheet values you enter and are corrected to your design temperatures with the same helper the string sizing calculator uses:

V(T) = modules × V_datasheet × (1 − |β| ÷ 100 × (T − T_STC)), where T_STC is the datasheet reference cell temperature and β is the temperature coefficient for that voltage.

Cold Voc. The highest string Voc on each MPPTinput at your cold design temperature, compared with the inverter's maximum DC input voltage.
Vmp window. The lowest string Vmp at your hot design temperature against the MPPT minimum, and the highest string Vmp at your cold design temperature against the MPPT maximum.
Current.Parallel strings add current. The sum of Imp is compared with the input's maximum input current, and the sum of Isc with its maximum short-circuit current. Both are STC values only, not temperature-corrected, unless you enter alpha, the Isc temperature coefficient. Then each Isc becomes Isc × (1 + |α| ÷ 100 × (T_hot − T_STC)), the temperature term of the Sandia PV Array Performance Model. Imp has its own coefficient that datasheets rarely print, so alpha is never applied to it. No current multiplier is applied to either sum.
Allocation notes. The planner describes, without estimating a loss, when strings on one input span faces with different azimuth or tilt, when parallel strings have different module counts, and when a face uses different modules.
Array total. Module power times modules, over every string, divided by the inverter AC rating you enter gives the DC:AC ratio, as in the DC:AC ratio calculator.

Every datasheet value, limit and design temperature starts empty and comes from you. Results read within entered limit or outside entered limit. This is a check of one inverter's allocation, not design software: there is no layout drawing and no energy-yield estimate. For a single string with voltages already at design conditions, the module and inverter compatibility worksheet is quicker. The DC design itself sits under AS/NZS 5033.

Estimates only: for guidance, not a quote or a compliance certificate. Verify against the current AS/NZS standards and a licensed design. The maths runs in your browser. Nothing is sent to Wattbench unless you sign in and deliberately save the result.

Source ledger4 sources

ResearchSandia PV Array Performance Model — Sandia PV Performance Modeling Collaborative
Standards bodyAS/NZS 5033:2021 — Standards Australia catalogue
Standards bodyIEC 62109-1:2010 — IEC Webstore
Standards bodyIEC 62109-2:2011 — IEC Webstore

Best next action

AS/NZS 5033Do this next

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Good to know

Frequently asked

Which current is compared with which inverter limit?: The sum of Imp across an input's parallel strings is compared with that input's maximum input current. The sum of Isc is compared with its maximum short-circuit current. Series modules do not add current, so only parallel strings are summed.
Are the currents temperature-corrected?: Only Isc, and only when you enter alpha, the Isc temperature coefficient. It is then corrected to your hot design temperature. Without alpha the current checks are labelled STC values only, not temperature-corrected. Imp is always the STC value, because alpha belongs to Isc.
Does the planner apply a safety factor or default temperatures?: No. No current multiplier is applied, and the design temperatures, datasheet values and inverter limits all start empty. Every figure compared comes from what you enter, so confirm the limits against the inverter documentation and the DC design against AS/NZS 5033.
Does it estimate the loss from mixing faces on one MPPT?: No. It says when strings on one input span faces with different azimuth or tilt, or when parallel strings have different module counts, and leaves the judgement to you. It does not model yield.
Is my data stored or sent anywhere?: The calculation runs in your browser. Nothing is sent to Wattbench unless you sign in and deliberately select Save result.

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