How to Choose a Solar Inverter: A Specifier's Guide
A working guide to specifying your first PV inverter: the four topologies, how AC power relates to array size, why the MPPT voltage window decides which strings will run, and what to check before you order.
What an inverter is actually doing
A photovoltaic array delivers direct current at a voltage that swings with irradiance and, above all, with temperature. The inverter turns that into alternating current the grid can accept, doing three jobs at once: holding the array at its maximum power point, synchronising its waveform with the grid, and disconnecting when the grid moves outside permitted limits. Almost every line on a datasheet describes one of those three jobs.
So design the array first, then find the inverter that fits it. Choosing a model on brand or headline efficiency and then bending the string layout to suit it is how systems end up unable to start on cold mornings, or throttling through every clear summer afternoon.
The four topologies
| Topology | Where MPP tracking happens | Example from the database | Best fit |
|---|---|---|---|
| String | One or more channels inside the inverter | Huawei SUN2000-3-6KTL-L1 — 6,000 W, 2 MPPT | Simple, unshaded roofs, one or two orientations |
| Module-level (optimisers) | Per module, via DC-DC converters | SolarEdge SE6000H — 6,000 W, 99.2% peak | Complex roofs where individual modules are shaded |
| Microinverter | Per module or pair, on the roof | GoodWe MIS — 800 W, IP67 | Shaded or multi-orientation arrays; staged expansion |
| Hybrid | Inverter, plus a battery port | Deye Sun3 3 6 5 6Ksg04Lp1 — 6,000 W, MPPT 150–425 V | Self-consumption with storage, backup circuits |
| Off-grid | Inverter, with no grid to synchronise to | Victron Inverter Rs Smart Solar — 6,000 W, MPPT 80–450 V | No grid connection, or one too weak to rely on |
A string inverter is one box on a wall, fed by series strings of modules. Cheapest per watt and easiest to service, but every module in a string shares one operating point: the Huawei SUN2000-3-6KTL-L1 gives two independent MPPT channels for 6,000 W of output, so you can split a roof two ways, not sixteen.
Microinverters move conversion onto the roof, one unit per module or pair. The GoodWe MIS is 800 W with two MPPT inputs, 18 A per input and an IP67 enclosure; the Growatt Neo 1000M X is 1,000 W at 97.3% peak, also IP67. Set those against the 98%-plus typical of larger string units: you trade conversion efficiency for per-module tracking and AC-only roof cabling.
A middle path puts module-level electronics on a string inverter. The SolarEdge SE6000H is single phase, 6,000 W, 99.2% peak efficiency, 480 V maximum DC input, designed to work with per-module optimisers.
A hybrid adds a battery port and self-consumption logic. The SMA Sunny Boy Smart Energy is single phase with three MPPT channels and a 500 V DC maximum; the Deye Sun3 3 6 5 6Ksg04Lp1 is 6,000 W nominal against 6,600 W maximum AC, MPPT 150–425 V, 13 A per MPPT.
An off-grid inverter forms voltage and frequency itself. The Victron Inverter Rs Smart Solar is 6,000 W at 230 V, MPPT 80–450 V, 450 V DC ceiling; the Growatt Spf 6000 Es Plus is 6,000 W with two MPPT channels. For the full comparison, see string vs microinverter vs hybrid.
Matching AC power to array size
Nameplate AC power is what the utility cares about and what your export limit is written against. It is almost never equal to the array's DC rating: a DC/AC ratio of 1.1 to 1.3 is standard practice, because an array reaches its STC rating only a handful of hours a year.
Datasheets carry two AC numbers. Nominal is the continuous rating; maximum is what the unit delivers briefly or in favourable conditions. The Huawei SUN2000-3-10KTL-M1 is 10,000 W nominal with an 11,000 W maximum; the Deye Sun18 20 22 23 25Kg05 is 20,000 W nominal and 22,000 W maximum. Size against nominal and treat the maximum as headroom. The ratio is the single decision with the largest effect on annual yield, and it is worked through in how to size a solar inverter.
The MPPT window decides which strings will work
This is the specification that most often makes a chosen inverter unusable. Every inverter has an MPPT voltage range within which it can track, and a separate, higher absolute maximum DC input voltage that must never be exceeded.
The two pull in opposite directions. On a cold clear morning, module open-circuit voltage rises well above its rated value, and a string sized comfortably at 25 °C can overshoot the DC maximum at −10 °C. On a hot afternoon voltage sags, and a string that is too short falls below the bottom of the window and stops producing.
The windows differ enormously. The Fronius Symo GEN24 3.0 Plus tracks 125–800 V with a 1,000 V ceiling, forgiving of short and long strings alike. The Fronius Primo GEN24 3.0 tracks only 190–530 V with a 600 V ceiling, which fixes string length within a narrow band. Neither is better; they are different design targets. MPPT explained covers the mechanism.
Efficiency: read the second number
| Model | Nominal AC power | Peak efficiency | European efficiency |
|---|---|---|---|
| Fronius Primo GEN24 3.0 | 3,000 W | 97.6% | 96.7% |
| SolarEdge SE3000H | 3,000 W | 99.2% | 97.5% |
| Fronius Symo GEN24 10.0 Plus | 10,000 W | 98.2% | 97.9% |
| Huawei SUN2000-3-10KTL-M1 | 10,000 W | 98.6% | 98.1% |
| Fronius Tauro ECO 100-3-P | 100,000 W | 98.5% | 98.2% |
Peak efficiency is measured at one convenient operating point. European efficiency is a weighted average across realistic part-load conditions, and it is the figure that predicts annual yield. The SE3000H shows why the distinction matters: 99.2% peak against 97.5% European is a 1.7-point spread, while the Huawei SUN2000-3-10KTL-M1 sits at 98.6% and 98.1%. See solar inverter efficiency explained for the weighting.
Single phase or three phase
Below roughly 5 kW, single phase is normal and often the only supply available. Above it, three phase spreads the load evenly and many distribution operators require it. The Huawei SUN2000-3-6KTL-L1 is single phase at 220/230/240 V, while the Solis S5-GR3P and the Fronius Symo GEN24 10.0 Plus are three phase, the latter at 400/230 V. Your existing service connection usually settles this before anything else does.
Grid code and certification
A grid-connected inverter must be certified for the network it feeds: anti-islanding protection, defined ride-through behaviour, reactive power control, and a country-specific grid code setting. Waveform quality is part of the same requirement — total harmonic distortion is quoted at 3% for the Huawei SUN2000-3-6KTL-L1 and 2% for the Solis S5-GR3P, against a typical 5% grid-code cap.
Check the enclosure and temperature ratings against where the unit will live. The Fronius Primo GEN24 3.0 is IP66 and rated −40 °C to +60 °C; the SolarEdge SE3000H uses a NEMA 4X enclosure. An outdoor wall in full sun is harsher than a garage.
Specification checklist
- Nominal AC power — against your export limit and the array's DC rating, at a ratio of 1.1–1.3.
- Maximum AC power — headroom, not capacity.
- MPPT voltage range — string voltage inside it at the hottest expected cell temperature.
- Maximum DC input voltage — string open-circuit voltage at the coldest expected temperature below it, with margin.
- MPPT channels — at least one per orientation or shading zone.
- Maximum input current per MPPT — against the short-circuit current of the strings paralleled there.
- Phases and output voltage — matched to your service connection.
- European efficiency — not just the peak figure.
- Grid code compliance — for your country and network operator.
- IP rating and operating temperature range — matched to the mounting location.
- Battery port — only if you intend to store energy, now or later.
Work through the list in that order and the shortlist usually collapses to two or three models.