String Inverter vs Microinverter: A Guide for Solar Installers

Choosing between string inverters and microinverters is one of the most common design decisions in residential solar. The right choice depends on the property, the customer's priorities, and the installer's operational preferences.

For most UK residential installations on unshaded roofs, a string inverter with power optimisers offers the best balance of cost, performance, and serviceability. Microinverters are the better choice for complex roof layouts, significant shading, or customers who want panel-level monitoring. Neither is universally "better". The right answer depends on the specific installation.

How string inverters work

A string inverter is a single centralised unit, typically wall-mounted near the consumer unit or in a garage, that converts DC electricity from a series-connected "string" of solar panels into AC electricity for the home.

How panels connect

Panels are wired in series to form strings. A typical UK residential system (3-4 kWp) might have a single string of 8-12 panels. Larger systems may use two or more strings connected to a single inverter or a multi-MPPT (Maximum Power Point Tracking) inverter.

Pros for installers

• Lower hardware cost: a single inverter is cheaper than one microinverter per panel
• Faster installation: one unit to mount, wire, and commission
• Easier troubleshooting: centralised point of access for diagnostics
• Familiar technology: most installers have extensive string inverter experience
• Straightforward replacement: a single swap if the unit fails after warranty

Cons for installers

• Shading sensitivity: a shaded panel reduces output across the entire string
• Single point of failure: if the inverter fails, the whole system goes down
• Roof DC wiring: high-voltage DC runs from roof to inverter location
• Less design flexibility: string voltage and current limits constrain panel layouts

Leading string inverter brands

SolarEdge, GoodWe, Solis, Fox ESS, and Huawei are among the most commonly used string inverters in the UK market. Many now include hybrid functionality for battery storage integration.

How microinverters work

A microinverter is a small inverter attached to each individual panel (or sometimes shared between two panels). DC-to-AC conversion happens at the panel level, and AC power is sent directly down from the roof.

How panels connect

Each panel operates independently with its own microinverter. Panels connect in parallel on an AC bus cable that runs along the roof and down to the consumer unit. This means each panel's output is independent of every other panel.

Pros for installers

• Shade tolerance: a shaded panel only affects its own output, not the rest of the system
• Panel-level monitoring: precise diagnostics for each panel individually
• Design flexibility: panels can face different directions and angles without string-matching constraints
• No high-voltage DC on roof: AC output from each panel improves safety during installation and for fire services
• System expandability: easy to add panels later without redesigning string configurations

Cons for installers

• Higher hardware cost: one unit per panel adds up, especially on larger systems
• More components on roof: more potential failure points in harder-to-access locations
• Longer installation time: each panel needs its own microinverter mounted and connected
• Roof access for servicing: any microinverter replacement requires scaffold or roof access
• Battery integration: less straightforward than hybrid string inverters (though AC-coupled solutions exist)

Leading microinverter brands

Enphase dominates the microinverter market globally. AP Systems (APsystems) and Hoymiles are also gaining market share, particularly in the UK and European markets.

Power optimisers: the middle ground

Power optimisers sit between string inverters and microinverters. They are DC-DC converters attached to each panel that optimise output before sending it to a centralised string inverter.

SolarEdge is the most well-known example. Their system pairs panel-level optimisers with a dedicated string inverter.

What optimisers give you

• Panel-level optimisation (similar to microinverters for shading)
• Panel-level monitoring
• Centralised inverter for easier servicing
• Rapid shutdown compliance (relevant for some markets)

The trade-off

• Cost sits between pure string and microinverter systems
• You still have a centralised inverter as a single point of failure
• More components than a basic string setup
• Vendor lock-in (optimisers must match the inverter brand)

Decision matrix: when to recommend each

Factor	String inverter	String + optimisers	Microinverters
Unshaded, simple roof	Best choice	Overkill	Overkill
Partial shading	Poor choice	Good choice	Best choice
Multiple roof faces	Limited	Good choice	Best choice
Budget-conscious customer	Best choice	Mid-range	Most expensive
Customer wants panel monitoring	Not available	Available	Available
Large system (10+ panels)	Good choice	Good choice	Cost adds up
Small/complex system	May not fit	Good choice	Best choice
Battery storage planned	Hybrid inverter (simple)	Hybrid inverter (simple)	AC coupling needed
Future expansion likely	Requires planning	Easier	Easiest

Rules of thumb

1. Simple roof, no shading, budget matters → string inverter
2. Some shading or multiple orientations → string inverter with optimisers
3. Heavy shading, complex roof, or customer wants maximum flexibility → microinverters
4. Battery storage is part of the project → hybrid string inverter (with or without optimisers) is usually simplest

Cost comparison

Exact pricing varies by manufacturer and supplier, but here is a general guide for a typical 4 kWp (10-panel) residential system:

Component	Approximate cost
String inverter only	£500 - £1,000
String inverter + optimisers	£1,200 - £1,800
Microinverters (10 units)	£1,500 - £2,500

The cost difference narrows on smaller systems and widens on larger ones. Labour time also differs: microinverter installs typically take 30-60 minutes longer due to per-panel mounting.

For installers, the key question is not just hardware cost but total project margin. Microinverter systems can command a premium from customers who value monitoring and shade tolerance, potentially improving margin despite higher component costs.

Warranty and maintenance considerations

String inverters

• Typical warranty: 5-12 years (extendable to 20-25 years with some manufacturers)
• Replacement is straightforward. Swap the unit, recommission.
• Inverter is accessible (wall-mounted indoors or in garage)
• Average lifespan: 10-15 years (expect at least one replacement over a 25-year panel warranty)

Microinverters

• Typical warranty: 20-25 years (Enphase offers 25 years standard)
• Longer warranty aligns with panel lifespan, which is a strong selling point for customers
• Replacement requires roof access, and scaffold cost can exceed the microinverter cost itself
• Individual failure only affects one panel, not the whole system

Impact on callbacks

String inverter failures take the whole system offline, which means an urgent callback. Microinverter failures affect a single panel, which customers may not notice for weeks, meaning less urgent but potentially harder to identify without monitoring.

For installation businesses managing a growing portfolio of systems, the warranty and callback profile should factor into the recommendation. Fewer callbacks means lower servicing costs and better customer satisfaction.

Making the right recommendation

The best inverter choice is the one that matches the specific installation. Rather than defaulting to one technology for every job, consider building a standard assessment into your site survey:

1. Assess shading using shading analysis tools during the survey
2. Map the roof and count usable faces and orientations
3. Understand the customer's priorities: budget vs monitoring vs future plans
4. Factor in battery. If storage is planned, hybrid string inverters simplify the design
5. Consider your margin. Microinverters cost more but can command a premium

Whichever technology you recommend, being able to clearly explain the trade-offs builds trust with customers and reduces post-installation queries.

Related reading: Best types of solar panels | Software for solar installers | Book a demo