Start from the plant architecture, not the inverter brand
An inverter is not selected in isolation. It is the component that has to reconcile the module you chose, the array geometry the site allows, the grid connection the utility grants and the operating strategy the owner wants. Buyers who start with a brand preference usually end up revising the string design; buyers who start with the array and the grid connection usually only need to compare products once.
This guide covers the three architectures a C&I or utility buyer will actually evaluate, how to set the DC/AC ratio, and the compatibility checks that decide whether a design is viable. The SolarXport inverter portfolio currently spans microinverter, three-phase string, hybrid and utility-scale string platforms alongside storage conversion, so the examples reference real listed products rather than generic power classes.
String, central and microinverter architectures
The three architectures differ in where conversion happens and therefore in how failures, maintenance and MPPT granularity behave. The table gives the practical distinctions; the notes after it explain when each one tends to win.
| Criterion | String inverter | Central inverter | Microinverter |
|---|---|---|---|
| Typical unit power class | From a few kW up to roughly 350 kW per unit | Commonly around 1 MW and above per unit | Commonly a few hundred watts up to a few kW per unit |
| MPPT granularity | Several MPPT inputs per unit | Few MPPT inputs for a large array | Module level |
| Effect of one failure | Loses one inverter, part of the plant keeps producing | Loses a large block until repaired or replaced | Loses a single module position |
| Service model | Unit swap by two technicians, spares held on site | Component-level repair, often by the manufacturer service team | Replace individual units, roof access required |
| DC cabling | Shorter DC runs to distributed inverters | Long DC runs to a central point, or DC combiners | Minimal DC, AC from each module |
| AC collection | AC combiner panels, then the transformer | Directly to a dedicated MV step-up block | AC branch circuits to a distribution board |
| Best-fit projects | C&I rooftops and modern utility blocks | Large ground-mount plants with MV blocks | Small, shaded, complex or retrofit arrays |
Why string inverters dominate C&I
Commercial rooftops rarely offer one clean plane. Multiple orientations, shading from plant rooms and staged construction all favour an architecture with several MPPT inputs and modest unit size. Distributed string units also fail gracefully: a plant with several inverters keeps producing when one is offline, which matters when a replacement takes weeks to arrive. In the SolarXport library, three-phase platforms such as the GoodWe SDT G3 and Growatt MID KTL3-X2 at 30-50 kW illustrate the class used for this work.
Where central inverters still make sense
For large ground-mount plants, concentrating conversion reduces the number of devices to commission, monitor and maintain, and pairs naturally with a medium-voltage block. The trade-off is coarse MPPT granularity and concentrated risk. Note that high-power string inverters have absorbed much of this territory: utility-scale string platforms such as the Growatt MAX KTL3-X HV at 185-253 kW and the Sineng SP275K-H1 in the 275 kW class serve large plants while keeping the failure of a single unit proportionate.
When microinverters are the right answer
Module-level conversion is the correct choice when the array is small, irregular or shaded, when high-voltage DC on a roof is undesirable, or when a system must grow one module at a time. The economics rarely favour it at C&I scale, but for balcony and small residential channels it removes string design entirely. The Growatt NEO M-X at 600-1,000 W is the microinverter class listed for that use in this library, and it is the basis of the balcony solar packages.
Sizing the DC/AC ratio
The DC/AC ratio compares installed array capacity in kWp with inverter rated AC output in kW. A 1,200 kWp array on 1,000 kW of inverters is a ratio of 1.2. Oversizing the array relative to the inverter raises energy capture in the many hours when irradiance is below peak, at the cost of clipping the top of the curve on the best days.
There is no universal correct value. The optimum depends on the irradiance profile, the module temperature coefficient and operating temperature, tilt and tracking, soiling, the shape of any export limit and the relative cost of DC and AC capacity. The ranges below are common starting points that should then be confirmed by yield modelling for the specific site.
| Application | Common starting range | Main driver |
|---|---|---|
| C&I rooftop, self-consumption led | About 1.05 to 1.2 | Matching generation to an on-site load curve, limited roof area |
| C&I rooftop, export or high-yield site | About 1.1 to 1.25 | Maximising annual yield within the connection limit |
| Utility fixed-tilt | About 1.2 to 1.35 | Flatter production curve makes clipping cheaper than idle inverter capacity |
| Utility single-axis tracker | About 1.15 to 1.3 | Trackers already broaden the curve, so less oversizing is needed |
| Export-limited or storage-coupled plants | Often higher | Surplus DC energy is curtailed, shifted into storage or absorbed by tariff design |
- Confirm the maximum DC input power the inverter accepts, which is a hard limit and separate from the ratio you choose.
- Check whether the manufacturer places a warranty or operating condition on sustained clipping.
- Model the loss from clipping against the gain in low-irradiance hours rather than assuming either dominates.
- Where an export limit applies, remember that surplus DC is only valuable if storage or on-site load can absorb it.
- Re-check the ratio if the module power class changes late in design, because piece count and array capacity move together.
MPPT window and string sizing checks
String sizing is where most inverter selections succeed or fail. Two temperature extremes govern it: the coldest expected condition sets the maximum voltage the string can reach, and the hottest operating condition sets the minimum voltage the inverter must still track.
- Cold-condition voltage: module Voc corrected to the record low temperature, multiplied by modules in series, must stay below both the module maximum system voltage and the inverter maximum DC input voltage.
- Hot-condition voltage: module Vmp corrected to the highest expected cell temperature, multiplied by modules in series, must stay inside the inverter MPPT window with margin.
- Current per MPPT: module Imp multiplied by parallel strings on that input, checked against the maximum input current the MPPT accepts.
- Short-circuit current: module Isc multiplied by parallel strings, checked against the maximum short-circuit current rating of the input.
- Bifacial headroom: rear-side irradiance increases operating current, so leave margin rather than designing to front-side STC values.
- String balance: keep strings on one MPPT equal in length and orientation wherever possible, and use separate MPPTs for different planes.
- Fusing and cabling: fuse ratings, combiner design and DC conductor sizing all follow from the final string current.
Compatibility checks beyond the DC side
A design that satisfies the MPPT window can still fail at commissioning. The AC side, the communications layer and the installation environment carry their own requirements.
Grid code and AC connection
Ask for a valid grid-code certificate for the destination country and the specific model, not a generic compliance statement. Confirm reactive power capability and the power factor range required, fault ride-through behaviour, anti-islanding, protection settings, and whether the utility requires an export limitation device or a certified controller. Then check the transformer arrangement, the AC cable and breaker sizing at the derated output you actually expect, and whether the inverter can be configured for the local voltage and frequency band.
Communications and monitoring
Confirm the physical interface and protocol available, commonly RS485 with Modbus, and whether the platform supports the SunSpec model set your monitoring system expects. Check how many devices can share a bus, what the datalogger supports, whether the plant controller can write setpoints and not just read data, and what happens to logging and control when the internet connection drops.
Environment and installation
Rated power is quoted at reference conditions. Confirm the derating curve for high ambient temperature and for altitude, since both reduce usable output. Check the ingress protection rating against the mounting location, the cooling method and the clearances it needs, the noise level where people work nearby, mounting orientation limits, and the weight for lifting and structural support. Finally, confirm spare-part availability and who performs warranty service in the destination country, because service response is part of the specification.
C&I and utility selection patterns
In practice, project type narrows the field quickly. Commercial rooftops favour distributed three-phase string inverters in the tens of kilowatts, because roof planes are irregular, DC runs should be short, units must be carried by hand through a building, and the owner needs the plant to keep producing during a repair. Where local rules require module-level shutdown or rapid shutdown, that requirement can also drive the architecture.
Utility plants favour high-power string inverters or central units organised into repeatable electrical blocks. The engineering task shifts from roof geometry to block design: string length, combiner layout, MV transformer pairing, cable losses across long DC and AC runs, and the availability guarantee the offtaker expects. Spares strategy becomes commercial rather than technical, because a plant with a hundred identical units can hold two spares, while a plant with four central units cannot afford one to be down.
The commercial rooftop solar and utility-scale equipment application pages set out the wider requirement list that surrounds these choices.
Where hybrid inverters and storage conversion fit
If batteries are part of the design, the architecture question changes. A hybrid inverter manages PV, battery, grid and backup loads through one device and suits residential and smaller C&I systems. A larger battery system is normally built around a dedicated bidirectional PCS with its own EMS, coupled to the PV plant on the AC side. The GoodWe ET Series at 25-50 kW is the hybrid class listed here for C&I systems.
The choice between adding a battery to an existing string plant through AC coupling or building around a hybrid platform from the start is covered in the dedicated string inverter versus hybrid inverter comparison. For larger systems, review the battery energy storage portfolio and the C&I storage application guide, where PCS power and battery energy are sized separately.
A practical inverter selection checklist
Before issuing a purchase order, the following points should all be answered from documents rather than from a conversation.
- Array capacity, module model, string layout and the resulting DC/AC ratio are all fixed and consistent with each other.
- Cold-condition string voltage and hot-condition MPPT voltage have been calculated with site temperature data.
- Current per MPPT and maximum short-circuit current are within the input ratings, with bifacial margin included.
- A grid-code certificate valid for the destination country covers the exact model, with the required protection and reactive power functions.
- Derating at design ambient temperature and site altitude has been applied to the AC output used in the yield model.
- The monitoring interface, protocol and plant-control requirements are confirmed, including behaviour on loss of connectivity.
- Mechanical fit is confirmed: dimensions, weight, mounting orientation, clearances, cooling and noise at the intended location.
- Warranty terms, extension options, spare-part availability and the service entity in the destination country are documented.
- For storage projects, battery voltage range, communication protocol and an approved compatibility list have been verified.
Turning the selection into a bill of materials
The output of an inverter selection is not a model name; it is a coordinated bill of materials in which module current, string design, protection, cabling, monitoring and the AC connection all agree with one another. That coordination is the work, and it is where most retrofitted design changes are avoided.
Send your array layout, module datasheet, connection limits and destination country through the contact form, and SolarXport will review MPPT compatibility, string design and grid-code documentation against the current inverter library before quoting.