Solis 25kW S5 3 Phase Triple MPPT - DC

The Solis 25kW S5 three-phase inverter, model S5-GC25K, is a transformerless grid-tie string inverter and the smallest of the S5-GC(25-40)K range. Its three MPPT trackers share six DC inputs, so one unit follows three roof pitches or three ground-mount rows, with Solis recommending up to 37.5 kW of panels behind the 25 kW nameplate.

Rated output is 36.1 A a phase at 400 V, 41.8 A maximum, and Solis's grid protection table puts the 25 kW on a 50 A breaker rating where the 30 and 33 kW take 63 A and the 36 and 40 kW take 80 A. It is the only model in the range on a 50 A device, which makes it the usual first step onto three-phase commercial PV where the existing switchgear, rather than the roof, sets the limit.

Commercial three-phase, at a glance

This is the 230/400 V unit, not the S5-GC25K-LV, the AU version or the S6. Conversion peaks at 98.5%, 98.1% by the EU measure: the 25 and 30 kW share the lowest pair of figures in the range, and the 36 and 40 kW reach 98.7%.

Is 25 kW the right size?

• A good fit: a supply that can take 36.1 A a phase, and Solis's recommended 37.5 kW of panels across no more than three orientations — which also keeps a single-inverter system inside the 50 kWp scope of MCS MIS 3002.
• Past 37.5 kW: the 30 kW S5-GC30K, same three trackers, 45 kW of panels recommended, but a 63 A breaker and the cable to match.
• Four orientations: the 36 and 40 kW add a fourth tracker and eight inputs, on 80 A.
• Smaller: the 20 kW S5-GR3P20K, 30 kW of panels on two trackers, and 20 kg to lift instead of 38.2 kg.
• Modules over 16 A: string current is the ceiling here, not power. Solis's own answer is the S6-GC3P25K03-NV-ND, listed at 20 A a string across 42 A trackers.

Laying out the strings

Two strings land on each tracker. Hold any single string at or under 16 A working current, and the pair on one tracker at or under 32 A working and 40 A short-circuit — roughly 20 A of Isc each once a bifacial module's rear-side gain is counted. On high-current modules that 16 A string limit is reached well before the 25 kW is full, and that, rather than any shortage of power, is the usual reason to step up.

Size each string to sit near the 600 V rated DC voltage and to stay under 1,100 V open-circuit on the coldest morning of the year; the trackers hold from 200 V to 1,000 V, and the unit initialises at 180 V. Spread evenly, Solis's recommended 37.5 kW works out at about 6.25 kW a string across the six inputs. Being transformerless, neither PV pole may be earthed.

This one needs a G99 application

Fitted and supplied

• Integrated DC switch, the -DC in the part number, with Type II surge arresters on both the DC and the AC terminals
• Six MC4 connectors, the back plate and its screws, the AC terminal cover, an RJ45 plug for the DRM port and the pluggable RS485 terminals
• Arc-fault detection, fitted but inactive until it is switched on under Special Settings — which MCS MIS 3002 requires on any inverter that has it
• Wall fixings: the M10×70 expansion bolts are the installer's
• A three-phase meter, if the DNO caps export
• A data logger, and a 4-pin one: the USB sticks the S6 range uses do not fit

On the wall

Solis's 2024 manual and its December 2025 UK flyer both give 38.2 kg; the older datasheet in the Documents tab says 37 kg. Either way it is a two-person lift onto the back plate, which goes up on M10×70 expansion bolts in 10 mm holes drilled 60 mm deep. Mount it vertical, or tilted back by no more than 15 degrees, never forward and never flat, and leave 500 mm above, below and to each side, 1,000 mm in front, and 500 mm between the bottom of the case and the floor.

The AC gland closes on a 22 to 32 mm outer diameter, 27 mm being Solis's recommendation, so check a planned SWA against that before ordering it. Cores are copper, 10 to 35 mm² with 25 mm² recommended, landing on crimped ring terminals with the terminal-block screws taken to 3 to 4 Nm. Besides the PE core, the manual wants a second earth of at least 16 mm² outdoor copper on the heat-sink stud. For residual current, Solis recommends an external Type A device at 300 mA for this model — the same figure as its maximum continuous residual current under IEC 62109, where the 30 kW's is 330 mA — on top of the monitoring already inside the unit, and its note says stricter local rules take precedence, so BS 7671 has the last word.

Order alongside

• Export meter, DTSD1352 with three CTs

  The meter type named in the installation manual and on this inverter's G100 registration, supplied with 150 A:5 A CTs. It drives one inverter, not a row of them. Put it on the grid side and, once a logger is in the COM port, SolisCloud shows site consumption against generation as well as holding the export cap.

• Wi-Fi and 4G data logging stick, 4-pin

  Solis files the S5-GC(25-40)K under 4-pin loggers, never the USB type. This one covers all S5 inverters and carries 4G behind the Wi-Fi, but it ships without a SIM, so a yard with no router needs a data SIM putting into it.

• Wi-Fi and wired LAN stick, 4-pin

  The same 4-pin COM port, for a plant room with a network cable already run to it. The meter's own listing names this stick as one of the two loggers to pair with it.

• Cover to 10 years, claimed in year one

  The standard warranty runs 5 years from commissioning, or from 6 months after the unit leaves the factory if that comes first, which is worth knowing when a pack is held between jobs. The extension has to be claimed within 12 months of installation against the serial number, and a 20-year version of the same certificate is written for the 25 to 40 kW S5 GC.