Inverters & Controllers

100 kW String Inverter

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Equipment selection5 min readGTP Solar

A 100 kW three-phase string inverter is the workhorse for commercial rooftops, carports and mid-size ground-mount blocks. It is the rating where a single unit covers a substantial roof without the cost and complexity of a central inverter, and where multiple MPPT inputs let one unit handle a roof with more than one orientation.

This page covers the inverter as supplied: the electrical window that has to match your array, the protection and grid-code functions your utility will ask for, and what has to be confirmed before it ships.

The window that has to match your array

An inverter is not sized to a round number. It is matched to the array through four checks, and all four are done at temperature extremes rather than at datasheet conditions.

  • String voltage at the coldest temperature. Open-circuit voltage rises as temperature falls. The string length has to keep Voc inside the maximum DC voltage at the lowest expected temperature for the site.
  • MPPT voltage range under load. The operating voltage has to stay inside the MPPT window at the hottest expected temperature, when voltage sags.
  • Current per MPPT. Check operating-current and maximum permissible short-circuit-current limits separately for each input and MPPT, including parallel strings. Select string protection using the module and cable ratings, the inverter manual and applicable design rules.
  • DC-to-AC ratio. A ratio above one is normal and deliberate; it shifts production into the morning and evening. It also means the inverter clips on the best days, which is a design choice and not a fault.

Specifications

Configuration reference

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ParameterTypical valueWhat it depends on
Rated AC power100 kW at 480 V three-phaseArray size and the DC-to-AC ratio you design to
MPPT inputsUp to 10Number of roof orientations and string voltages
MPPT voltage range200 to 1 000 V DCString length at the coldest expected temperature
Maximum DC voltage1 100 V DCInverter platform and local code
Maximum current per MPPTUp to 40 AModule short-circuit current and string fuse
Maximum efficiencyUp to 98.8 percentLoad level and DC input voltage
Output480 V three-phase, 60 HzPlant voltage and utility standard
EnclosureConfirm the selected IP and/or NEMA enclosure ratingManufacturer model rating and installation instructions
Surge protectionType II on DC and ACLightning exposure of the site
CommunicationsRS485, Ethernet, Wi-Fi, Modbus or SunSpecMonitoring and SCADA requirements
Compliance documentsConfirm applicable listing, grid-code compliance and safety documentsExact model, firmware and utility interconnection requirements
WarrantyConfirm manufacturer warranty term and any extension options for the selected modelSelected model and written order terms

Figures are selection references. Confirm the final ratings, dimensions, available certifications and warranty against the current datasheet and written proposal for the selected model or system.

What arrives in a typical order

  • The inverter with the DC isolator and the AC connection arranged for your cable entry.
  • Wall or pad mounting bracket and the drilling template.
  • Commissioning tool access, firmware current at the time of shipping, and the monitoring credentials.
  • Installation manual, grid-code settings guide and warranty terms.

Where the project needs it, the modules, the mounting, the AC combiner panel and the monitoring are quoted on the same order so the string configuration is confirmed once rather than by three suppliers.

Where a 100 kW unit usually goes

  • Commercial rooftops split across two or three orientations, where several MPPT inputs avoid the mismatch loss of a single-input design.
  • Carports and canopies in the 80 to 130 kW range.
  • Mid-size ground-mount blocks where a string architecture is preferred to a central inverter for serviceability.
  • Storage-coupled projects where an AC-coupled battery connects on the AC side of the unit.

Sizing notes before you order

  • Check the inverter operating-current and permitted short-circuit-current limits for the selected module and string arrangement. Cell size alone does not establish compatibility.
  • Confirm the grid code, voltage level and protection settings your utility requires. Verify the applicable listing and compliance documents for the exact model and firmware before ordering.
  • Decide where the unit sits. IP66 allows outdoor mounting, but the cable runs, the service access and the afternoon sun all affect where it should go.
  • Confirm the monitoring interface. Modbus or SunSpec matters if the site has a SCADA system that has to read it.

Documentation to confirm for your order

  • Datasheet and the installation manual with the wiring diagram.
  • Grid-code certification for your market, and the test report matching it.
  • Settings guide for the protection functions your utility requires.
  • Packing list, delivery documentation and warranty registration.

Questions buyers ask

String inverter or central inverter?

At this rating a string unit usually wins on cost and on serviceability: a failed unit takes out 100 kW rather than the whole block, and a spare sits on the shelf. Central inverters start to make sense where the block is large and the service is centralised.

What DC-to-AC ratio should we design to?

Commonly 1.2 to 1.4 on commercial roofs. It lifts production in the morning and evening and improves the inverter utilisation, at the cost of some clipping on the best days. It is a modelled trade-off, not a default.

Will clipping show up as a fault in the monitoring?

It will show up as a flat top to the midday curve. That is the design working as intended. Reading it as a fault leads to replacing equipment that is behaving exactly as specified.

Can a battery be added later?

An AC-coupled battery may be added after reviewing the distribution capacity, protection, controls and any required islanding or transfer arrangement. Compare AC-coupled and hybrid options against the actual site design; neither architecture guarantees higher efficiency in every application.

How fast can it ship?

Stocked specifications ship from U.S. warehouse inventory with dispatch timing confirmed for the selected model and delivery address. Confirm the grid-code variant you need at enquiry stage, because that is what determines whether it is a stock item.

What to send us

Send the module model and quantity, the string layout if you have it, the utility and the grid code, and your target date. We check the voltage and current window against your modules before you order, so the unit arrives matched to the array.

EXPLORE FURTHER

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Send the service voltage and the string layout

With the service voltage, string configuration and which circuits need backup, we confirm the right unit, the grid-support settings required in your utility area, and current availability.

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Or reach us directly: +86 136 7367 3267 · sales@gtpsolar.com

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