Microinverters vs string inverters: which should you choose?
String inverter, optimisers or microinverters: how the three set-ups compare on shade, grid limits, monitoring, repairs, batteries and warranties, and how to test the choice on your own roof.
On a simple roof, with the panels on one slope and little shade, a well-designed string inverter is usually the natural choice: fewer parts, and the inverter sits somewhere you can reach it. Microinverters or power optimisers earn their place when the panels face different ways, are shaded at different times, are split into small groups, or you want to see each panel's output.
No option wins on every roof. Ask for two designs on the same layout and compare the estimated yearly output, the full price, what sits on the roof, how a fault would be fixed, the monitoring included and how a battery would fit later. That comparison shows which set-up suits your home. For how inverters work in general, see solar inverters.
The three set-ups in brief
- String inverter. Panels are wired together in one or more strings that carry direct current (DC) to a single inverter, usually in the loft, garage or utility room, which converts it to alternating current (AC) for the house. A model with several independent MPPT inputs can run strings on different roof slopes separately.
- String inverter with power optimisers. A small device under each panel (or under the panels that need it, where the system allows) adjusts that panel's DC output before it goes to a central inverter. Optimisers and inverter have to be a compatible pair.
- Microinverters. Each small inverter under the panels converts DC to AC on the roof, so there is no central inverter. Depending on the model, one microinverter serves one, two or four panels.
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An MPPT (maximum power point tracker) is the circuit that keeps a group of panels working at the point where they give the most power. The number of panel connectors on a device does not tell you how many independent MPPTs it has. Some current examples:
| Microinverter (datasheet) | Panels per unit | Independent MPPTs |
|---|---|---|
| Enphase IQ8 series (UK datasheet, March 2026) | 1 | 1 |
| APsystems DS3 series (EMEA datasheet Rev 1.7, 2025) | 2 | 2 |
| Hoymiles HMS-1600/1800/2000-4T | 4 | 4 |
Ask for the datasheet of the exact model proposed, not just the word "microinverter". MCS-certified installers must give you the datasheets for the panels, the inverter and any optimisers or microinverters before you sign.
How they compare
| What matters | String inverter | String with optimisers | Microinverters |
|---|---|---|---|
| Where DC becomes AC | One box, usually indoors | One box, with DC adjusted under each panel | Under the panels, on the roof |
| Simple roof, one slope, little shade | The natural option to price first | Worth it only for a specific need | Possible, but the benefit should be shown for your roof |
| Panels facing different ways | Put each slope on its own MPPT | Handled panel by panel, within the system's design rules | Depends on panels and MPPTs per unit |
| Partial shade | Depends on string layout, MPPTs and the inverter's shade handling | Can reduce losses from mismatched panels | Can separate shaded panels if the MPPTs are independent |
| DC voltage on the roof | Strings can reach several hundred volts | Strings still run at string voltage | Limited to one panel's voltage, up to 60 V on the IQ8 and DS3 |
| Monitoring | Usually whole system or per string | Per panel, within that brand's system | Per panel or per input, with a gateway |
| If a converter fails | The whole inverter's strings stop until it is replaced | One optimiser affects its panel; the central inverter is still shared | One unit affects its panels; wiring, protection and gateway are shared |
| Getting to it | Indoors, if sited well | Roof work for optimisers, indoors for the inverter | Roof work |
| Adding panels later | Limited by the inverter's inputs and rating | Depends on the system's design rules | Often modular, but check the AC circuit, gateway and grid limit |
| Battery | Hybrid inverter or AC-coupled battery | Depends on the inverter and brand | AC-coupled battery |
| Comparing prices | Inverter, isolators, monitoring, fitting | Add optimisers, communications, fitting | Every microinverter, cabling, gateway, protection, fitting |
The table does not rank reliability. More devices on the roof do not prove a system will fail more often, and a single central inverter does not prove it will wear out sooner. Without comparable failure data by model and conditions, the useful question is: what happens if this particular part fails, and how is it replaced?
On the DC voltage row: panels in a string add their voltages together. Ten LONGi Hi-MO X6 455 W panels, for example, each with an open-circuit voltage of 40.13 V, give about 401 V at standard test conditions. With microinverters, the DC side stays at the level of a single panel.
Grid limits: why microinverters count differently
On a single-phase supply, systems whose inverters can together deliver up to 16 A (3.68 kW) are connected under G98: the installer notifies the network operator within 28 days (30 days in Northern Ireland, under G98/NI). Above that, G99 applies and the network operator has to approve the connection first. What counts is the combined AC output of all the inverters, battery inverters included, not the panels' kWp.
That changes the sums for each set-up:
- String inverter. A 3.68 kW inverter can be fed by a slightly larger array, such as 4.4 kWp of panels, and the system stays within G98.
- Microinverters. Their AC ratings add up. Ten Enphase IQ8AC units (1.59 A each) come to 15.9 A, or 3,660 W, within G98. Twelve IQ8HC units (1.67 A each) come to about 20 A, or 4,608 W, so the installer has to apply under G99 before connecting.
Neither route is a problem in itself, but G99 can add time. Ask which applies to your design; G98 and G99 explains the process.
Shade and MPPTs
Shade on a panel reduces the light it gets. The electronics can limit some of the knock-on losses when panels are mismatched, but they cannot bring back sunlight that is blocked. The effect depends on the shape of the shadow, how it moves through the day, the wiring, the panel's bypass diodes and the MPPT arrangement.
Put groups of panels that behave differently on separate MPPTs, where the design and the model allow it. East and west slopes, for example, should not be wired together as if they got the sun at the same time.
Ask for a simulation of each design using the same panels, the same layout and the same shade model. Compare the difference in kWh per year, then the difference in price. A general promise of "up to X% more" does not describe your roof.
This matters for your MCS quote. The standard MCS shade method does not credit optimisers or microinverters, because their benefit varies too much between projects. It does allow the shade factor to be worked out separately for each group of panels on its own MPPT. A benefit from optimisers or microinverters can be shown with proprietary software, modelling the system with and without them. Under the current MCS scheme's standard (MIS 3002 issue 6.0), any such extra estimate must not be more prominent than the standard MCS estimate and must carry a warning if it is much better. Solar panel shading explains the MCS method step by step.
Access and fault-finding
Where the electronics sit changes what a fault looks like. A string inverter in the loft or garage can be checked and swapped without touching the panels. An optimiser or microinverter under a panel means finding the right device, arranging safe access to the roof (often scaffolding) and sometimes lifting a panel.
Spreading the electronics across the roof limits what one failure takes out, but not everything is separate. A microinverter serving four panels takes all four down, and the AC cable, protection devices, communications or gateway serve a larger part of the system. A failed string inverter, on the other hand, stops every string connected to it until it is replaced.
Ask who watches for alerts, who diagnoses faults remotely, who goes up on the roof, and who pays for access, removal and refitting.
Monitoring you actually get
Per-panel monitoring can help you spot a panel that has stopped or a persistent drop. On its own it does not prove a device is faulty: orientation, passing shade, dirt or normal panel tolerances can explain a difference.
Check what is included: gateway, meters, an account in your name, history, alerts, data export and any subscription. Ask for a map linking each panel to its device ID. With two or four panels per microinverter, check whether the app shows each input or only each unit.
Warranties can depend on monitoring too. Enphase's UK warranty gives IQ8 microinverters 25 years, but only while they stay connected to the internet through an IQ Gateway, and only in England, Scotland and Wales. APsystems' EMEA datasheet for DS3 requires the microinverters to be monitored through its EMA portal to be covered. Make sure the account stays in your name after handover.
Batteries and power cuts
Choosing microinverters does not rule out a battery, and choosing a string inverter does not make every battery compatible. DC-coupled batteries usually connect through a hybrid inverter with a list of approved batteries. AC-coupled batteries have their own inverter and can work alongside any of the three set-ups, subject to the design and compatible equipment. Remember that a battery inverter counts towards the G98 limit: a 3 kW solar inverter plus a 3 kW AC-coupled battery on one single-phase supply needs G99.
Backup during a power cut is a separate feature again. It needs dedicated hardware and wiring, whichever set-up you choose, and it is specific to each brand's system. Ask for the design without a battery, then the planned design with one: compatible models, metering, power, which circuits are backed up and what disconnects the house from the grid. See solar battery storage and do solar panels work in a power cut?.
Read the warranties part by part
A long manufacturer's warranty is not proof of lifespan. It applies to listed models, from a start date, in a territory and on conditions. The two microinverter examples above show how much the terms vary. Enphase's UK limited warranty (effective 30 September 2025) gives IQ8 microinverters 25 years from activation, provided they are registered and stay continuously connected to the internet through an IQ Gateway. It covers England, Scotland and Wales; Northern Ireland is not listed. APsystems' EMEA warranty gives DS3 12 years as standard, extendable to 25 years if bought within six months of registration. The microinverters must stay connected to the internet through APsystems' ECU gateway; otherwise cover drops to two years. Optimisers and the central inverter in the same system can have different terms from each other, so read each one.
Ask what the manufacturer covers and what the installer covers: diagnosis, the replacement part, delivery, labour, scaffolding or roof access, removal and refitting. Ask what happens if the installer stops trading and whether the warranty transfers when you sell the house.
Keep the invoices, serial numbers, commissioning date, registration and app logins. "25-year warranty" on a quote, without the model and conditions, is not enough to compare two offers. Solar panel warranties covers panels, workmanship and insurance-backed guarantees.
Compare two like-for-like quotes
Ask for at least two designs on the same roof: the same panels, the same number, the same layout and the same output assumptions. One can use a string inverter with its strings sensibly split across MPPTs; the other adds optimisers or microinverters where they solve an identified problem.
Then compare:
- the estimated yearly output and the losses put down to shade;
- every model number, the number of inputs and the independent MPPTs;
- the full price, with monitoring, protection devices, fitting and paperwork (installed solar panels and batteries are zero-rated for VAT until 31 March 2027, then due to be 5% unless extended; kits bought without installation carry 20%);
- where each device goes and how it will be reached;
- whether the design falls under G98 or G99;
- the monitoring included, accounts and any subscription;
- the battery and backup plan;
- each component's warranty and who pays for call-outs.
Comparing solar quotes helps you line up the rest of each offer.
Your checklist before you sign
- How many strings, inputs and truly independent MPPTs are planned?
- Which panels share an MPPT, a microinverter or an AC cable?
- What difference in kWh per year do two like-for-like simulations show?
- Does the design fall under G98 or G99, and does that include a future battery?
- Which devices are on the roof, and how will they be replaced?
- Does the monitoring show each panel, input, unit, string or only the total?
- Are the exact models compatible with the panels and a future battery?
- What extra hardware would backup in a power cut need?
- Do the warranties match the models, the UK and your commissioning date, and what conditions apply?
- Does the price include the gateway, cabling, protection, access, commissioning and an account in your name?
Frequently asked questions
Does each panel get its own microinverter?
Not always. Some models serve one panel, others two or four. Check the number of independent MPPTs, and whether the monitoring shows each panel, for the exact model quoted.
Do microinverters always produce more electricity?
No. They can reduce some losses from mismatched or shaded panels, but the gain depends on your roof and on how well the string alternative is designed. Compare simulations with the same layout and shade model.
Do I need optimisers on a roof with no shade?
Not automatically. They can add per-panel monitoring or features in a particular brand's system, but they should meet a specific need and be compared with a well-designed string system.
Can I add a battery later?
In many cases, yes, but not with any combination. Get the future design documented now, including compatible models, the extra hardware for any backup, and whether the total inverter output would move the system from G98 to G99.
Which set-up lasts longest?
Manufacturer warranties do not tell you that. Compare the models, installation conditions, how faults are diagnosed and how easy replacement really is.