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Above about 150 kW the questions change. You stop asking “how many strings fit” and start asking about grid support functions, where the units physically sit, and what it costs you when one of them is down for a week. A 250 kW string inverter sits right in that transition, which is why the specification has more to it than a power rating.
This page is for EPCs and developers specifying inverters for large commercial roofs, ground-mount blocks and utility-scale arrays in the multi-megawatt range. It covers the decisions that are expensive to revisit once the block is built.
Why 1500 V at this size
A 1500 V DC platform lets you run longer strings, which means fewer combiner points, less DC cable and fewer losses. On a large block that is a meaningful saving in both material and labour. It also raises two requirements: the modules and DC components all have to be rated for 1500 V, and the string open-circuit voltage at the coldest expected temperature has to stay under the limit with margin.
On smaller roofs, compare the DC voltage platform and input arrangement of the selected 100 kW inverter. Higher DC voltage may reduce cable and string count on some layouts, but power rating alone does not determine the platform.
MPPT count usually decides before power does
On anything other than a single-plane array, the number of independent MPPT inputs is the binding constraint. Each orientation needs its own input, and each input has a maximum DC current. A 250 kW unit with twelve inputs can handle a complex roof or a block with varied tilt; the same power in a unit with four inputs cannot.
The practical sequence is: fix the string layout from the site geometry, count the orientations, and let that decide the unit count and the model. Starting from “we need 2 MW” and working backwards gives the wrong answer.
Grid support is a specification, not a feature list
Modern interconnection agreements require specific behaviours: volt-var and volt-watt response, frequency-watt, and low- and high-voltage ride-through. The utility specifies which curves and which settings, and the inverter has to be capable of them and commissioned to them.
Confirm the applicable listing and grid-code compliance evidence for the selected model, firmware and utility. Where the interconnection agreement specifies particular settings, record them in the commissioning documents rather than relying on factory defaults.
Where the units sit: centralised or distributed
Two approaches, and the right one depends on the site:
- Distributed on the block — shorter DC runs, no inverter station building, but units are exposed to the weather and servicing means walking the array. Common on ground-mount.
- Centralised in a station — easier servicing and a controlled environment, but longer DC runs and more DC cable and losses. Common where the array feeds a substation anyway.
On large roofs the answer is usually forced by where there is space and how far the AC run is. Deciding before the conduit is drawn avoids the most common mid-project change.
Derating in hot climates
An inverter’s rating is quoted at an ambient temperature, and output falls above it. A block in a hot climate with units in full sun will derate during exactly the hours you most want production. Shading the units, orienting them away from the afternoon sun, or specifying a higher-temperature rating are all cheaper than discovering the derating after commissioning.
Redundancy and what downtime costs
One 2 MW of capacity can be eight 250 kW units or two 1 MW central inverters. The distributed option costs slightly more per watt and gives you something valuable: losing one unit costs you an eighth of the plant rather than half of it. On sites where an outage is expensive relative to the premium, that is the whole argument.
It also changes spares. With distributed units, holding one spare is affordable and meaningful; with central inverters it usually is not.
Specifications at a glance
Configuration reference
Swipe horizontally to view all columns →
| Parameter | Typical value | What it depends on |
|---|---|---|
| Rated AC power | 250 kW at 480 V or 600 V three-phase | Block size and the plant voltage |
| DC platform | 1500 V DC | String length and cable economics |
| MPPT inputs | Up to 12, with per-input DC current monitoring | Orientations and string layout |
| Maximum DC voltage | 1500 V DC | Coldest expected temperature and string length |
| Maximum efficiency | Up to 99.0 percent | Load level and DC voltage |
| Grid support | Volt-var, volt-watt, frequency-watt, ride-through | Interconnection agreement and grid code |
| Cooling | Forced air with variable speed, or liquid on some models | Ambient temperature and derating strategy |
| Enclosure | IP66, outdoor rated | Whether it sits on the block or in a station |
| Communication | Modbus TCP, IEC 60870-5-104, or SunSpec | Plant controller and SCADA |
| Protection | DC and AC surge protection, anti-islanding, string fault detection | Grid code and site exposure |
| Compliance documents | Confirm applicable listing, grid-code compliance and safety documents | Exact model, firmware and utility interconnection requirements |
| Warranty | Confirm manufacturer warranty term and any extension options for the selected model | Selected 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.
Questions buyers ask about 250 kW inverters
Can we mix 250 kW with smaller units on one site?
Yes, and it is common — larger units on the main plane, smaller ones on secondary orientations or shaded sections. What matters is that each unit is sized to its own strings and that the plant controller can see all of them.
What does the utility need to see?
Confirm the required listing, grid-code compliance records and commissioning test scope with the utility before ordering. The quotation should identify the documents available for the exact model and the project drawings included in the supply.
Do we need a separate MV transformer?
At 480 V or 600 V output feeding a medium-voltage collection system, yes — that is where our distribution transformers come in. Whether the step-up sits at each unit or centrally depends on the collection design.
How do we monitor string-level faults?
Monitoring resolution depends on the selected inverter. Confirm whether current measurements are provided per MPPT, per input or per string; specify additional combiner-level monitoring where the fault-location requirement needs it.
What spares should we hold?
On larger plants where outage cost justifies it, one spare unit. Beyond that, fuses, surge cartridges and connectors. Modules are better held at the supplier because matching model and power bin matters more than having one on a shelf.
What to send us
Send the block size and layout, the plant voltage, the interconnection requirements if you have them, and your target date. We confirm the unit schedule, the MPPT allocation, the certification package and the delivery date in writing.
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