Inverter Guide: String, Hybrid and Micro-Inverters Compared

The inverter is the heart of every photovoltaic system. It converts the direct current (DC) generated by the solar modules into grid-compliant alternating current (AC) — and significantly determines the efficiency, monitoring and flexibility of the entire system. This guide explains the different inverter types, their sizing and what to look for when choosing.

Operating Principle: From DC to AC

The conversion of direct current to alternating current takes place in several stages:

1. DC input side: The modules deliver direct current at typically 30-50 V per module (in series in a string: 200-800 V)
2. MPP tracking: The inverter adjusts voltage and current so that the modules always operate at the Maximum Power Point (MPP)
3. DC/DC conversion: Adapting the input voltage to the required level
4. DC/AC inversion: Generating a sinusoidal 230V alternating voltage using semiconductor bridge circuits (IGBT or MOSFET)
5. Grid filtering: Harmonic filters ensure a clean sine wave and EMC compliance
6. Grid monitoring: Continuous monitoring of frequency, voltage and impedance — during grid failure, the inverter shuts off within milliseconds (anti-islanding protection)

Comparison Table: Inverter Types

Comparison of the three main inverter types | As of January 2026

Feature	String inv.	Micro inv.	Hybrid inv.
Topology	1 device for entire system	1 device per module	1 device + battery connection
Power range	3-25 kW	0.25-0.5 kW per unit	3-15 kW
European efficiency	96-97.5 %	95-96.5 %	95-97 %
MPP tracker	1-3 (depending on model)	1 per module	2-3 + battery MPP
Partial shading	Sensitive (entire string affected)	Very good (module-individual)	Like string inv.
Monitoring	String level	Module level	String + battery
Price (EUR/kW)	80-150	200-350	150-300
Warranty (typical)	5-12 years	15-25 years	5-10 years
Installation	Simple, central location	Complex, at the module	Medium, incl. battery
Expandability	Limited (fixed design)	Expandable per module	Battery can be added later
Backup power possible	No (without add-on)	No	Yes (with battery)

String Inverter

The string inverter is the classic and most widely used type. Multiple modules are connected in series into a “string” and connected to a central inverter.

How a String Works

In a string, modules are connected in series. The voltages add up (e.g. 15 modules x 40 V = 600 V DC), while the current through all modules is identical. This means: the weakest module determines the current of the entire string.

Typical string configurations:

• Small system (5 kWp): 1 string with 12-14 modules, 1 MPP tracker
• Medium system (10 kWp): 2 strings of 12-14 modules each, 2 MPP trackers
• Large system (20+ kWp): 3-4 strings, possibly multiple inverters

When a String Inverter is the Right Choice

• Roof area largely shade-free (no trees, chimneys, dormers)
• All modules on one roof side with the same orientation and pitch
• Cost optimisation is the priority
• Standard system without battery (retrofit possible via AC-coupled storage)

Micro-Inverter

Micro-inverters (micro-inverters) are mounted directly on individual modules or module pairs. Each module operates independently at its own MPP.

When Micro-Inverters are the Best Choice

• Partial shading from trees, chimneys, antennas or neighbouring buildings
• Different roof surfaces (east/west, different pitches)
• Safety requirements (only AC on the roof, e.g. fire protection regulations)
• Gradual system expansion planned
• Maximum transparency through module-level monitoring desired

Hybrid Inverter

The hybrid inverter combines the function of a grid inverter with a battery charge controller. It can feed solar power directly into the grid, charge the battery and serve as a backup power source during grid outages.

DC Coupling vs. AC Coupling

When integrating a battery storage system, there are two basic concepts:

Feature	DC coupling (hybrid inv.)	AC coupling (separate battery inv.)
Efficiency	~95-97 % (1x conversion)	~90-94 % (2x conversion: DC-AC-DC-AC)
Installation	One device, simpler	Two devices, more flexible
Retrofit	Ideal for new systems	Ideal for existing systems
Manufacturer lock-in	Battery often predetermined	Free battery choice
Cost	Cheaper as a package	More expensive due to 2 devices

Sizing: Choosing the Right Size

Correct sizing of the inverter is crucial for the yield and lifespan of the system.

DC/AC Ratio

The DC/AC ratio (also “oversizing factor”) describes the ratio of installed module power (DC) to the rated power of the inverter (AC).

• Recommended range: 1.0 to 1.2 (for Germany/DACH region)
• Example: 10 kWp modules — inverter with 8.5-10 kW AC power

Voltage Window

Every inverter has a defined MPP voltage window (e.g. 150-850 V). The string configuration must be chosen so that:

• The maximum open-circuit voltage (at -10 degrees C) does not exceed the limit
• The minimum MPP voltage (at +70 degrees C) is not undercut
• Manufacturer software (e.g. SMA Sunny Design, Fronius Solar.configurator) calculates the optimal configuration

Number of MPP Trackers

Roof situation	Recommended MPP trackers
One roof surface, no shading	1 MPP tracker is sufficient
Two roof surfaces (e.g. east/west)	2 MPP trackers recommended
Complex roof or partial shading	2-3 MPP trackers or micro inverters
System with battery	Separate battery MPP tracker (hybrid inv.)

Efficiency: European Efficiency vs. Maximum

The maximum efficiency (e.g. 98.3%) is only achieved at optimal partial load. More meaningful is the European efficiency (also “Euro efficiency”), which weights the typical irradiance distribution in Central Europe:

eta_euro = 0.03 x eta_5% + 0.06 x eta_10% + 0.13 x eta_20% + 0.10 x eta_30% + 0.48 x eta_50% + 0.20 x eta_100%

The European efficiency is typically 0.5-1.5% below the maximum value and is the more relevant metric for DACH locations.

String inv. (top models)97,5 %

String inv. (standard)96,5 %

Hybrid inv. (top models)97 %

Hybrid inv. (standard)95,5 %

Micro inv. (top models)96,5 %

Micro inv. (standard)95 %

Manufacturer Comparison

Selected manufacturers | As of January 2026 | Specifications may vary by model

Manufacturer↕	Origin↕	Types	Euro eff. (up to)↕	Warranty↕	Monitoring
SMA (Sunny Boy/Tripower)	Germany	String, Hybrid	97.5%	5+5 yr (extendable 10-20)	Sunny Portal (free)
Fronius (Symo/Gen24)	Austria	String, Hybrid	97.3%	5+5 yr (extendable 10-20)	Solar.web (free)
Huawei (SUN2000)	China	String, Hybrid	97.5%	10 years	FusionSolar App
Kostal (Plenticore)	Germany	Hybrid	97%	10 years	Kostal Solar Portal
GoodWe	China	String, Hybrid	97.2%	10 years	SEMS Portal
Enphase (IQ7/IQ8)	USA	Micro	96.5%	25 years	Enphase Enlighten (module level)
APsystems	China/France	Micro	96%	15-25 years	EMA App (module level)
SolarEdge	Israel	String + optimisers	97%	12-25 years	SolarEdge Monitoring (module level)

Warranty and Lifespan

The lifespan of an inverter is typically 10-15 years — shorter than the modules (25-30 years). A replacement during the system’s lifetime should therefore be planned for.

Inverter type	Typical warranty	Extension possible	Expected lifespan
String inv.	5-10 years	Yes, to 10-20 years	12-15 years
Micro inv.	15-25 years	Usually included	20-25 years
Hybrid inv.	5-10 years	Yes, to 10-15 years	10-15 years

Installation Requirements

Location Selection

• String and hybrid inv.: Cool, dry location (basement, garage, utility room). Operating temperature range typically -25 to +60 degrees C. Ensure adequate ventilation — inverters generate waste heat
• Micro inv.: Directly at the module on the roof. Protection class IP67 (weatherproof). Consider access for maintenance
• All types: Maintain minimum distances to combustible materials. Consider noise levels (fans in string/hybrid inverters, especially in summer)

Grid Connection

• Single-phase (up to ~4.6 kW): For small systems and balcony power stations
• Three-phase (from ~5 kW): Standard for residential roof systems in Germany — avoidance of phase imbalance. Many grid operators require symmetrical feed-in

Monitoring Features Compared

Modern system monitoring is an important factor in inverter selection:

Feature	String inv.	Micro inv.	Hybrid inv.
Generation data	Total + per string	Per module	Total + per string
Consumption overview	With additional sensor	With additional sensor	Integrated
Battery status	—	—	State of charge, cycles
Fault detection	String level	Module level	String + battery
App control	Yes (manufacturer-dependent)	Yes	Yes (incl. storage management)
API access	Partial	Partial	Partial
Historical data	Months/years	Months/years	Months/years

Frequently Asked Questions (FAQ)

How large does my inverter need to be?

As a rule of thumb: the AC rated power of the inverter should be 85-100% of the DC rated power of the modules (DC/AC ratio 1.0-1.2). Example: for 10 kWp of module power, an inverter of 8.5-10 kW is recommended. Use the manufacturer’s planning software for precise sizing.

Can I replace my inverter later?

Yes, replacement is possible and should be planned for string inverters after 12-15 years. Ensure the new inverter matches the string design (voltage, current) and any existing battery. The feed-in tariff is retained when replacing the inverter.

String inverter or micro-inverter — which is better?

There is no “better” — it depends on the situation. For an unshaded roof with uniform orientation, a string inverter is the most cost-effective solution. For partial shading, different roof surfaces or the desire for module-level monitoring, micro-inverters are the better choice. The additional cost of micro inverters pays for itself through increased yield when shading is significant.

Do I need a hybrid inverter for a battery?

Not necessarily. A battery can also be AC-coupled to an existing string inverter. However, the hybrid inverter is more efficient (DC coupling avoids one conversion stage) and cheaper as an overall package for new systems. For retrofitting a battery to an existing system, AC coupling is often the more pragmatic approach.

How loud is an inverter?

String and hybrid inverters have fans that can be audible at high output (35-50 dB). Installation in the bedroom is not recommended. Micro-inverters are fanless and silent. Some high-quality string inverters (e.g. Fronius Gen24) also operate without fans.

What happens during a power outage?

Standard inverters (string and micro) switch off immediately during a grid outage — this is legally required (anti-islanding protection) to prevent feed-in to the disconnected grid. Only hybrid inverters with battery and backup power function can continue supplying electricity in island mode. Distinguish between automatic transfer (automatic switching, milliseconds) and emergency power (manual switching).

Summary and Recommendation

The choice of the right inverter depends on your individual situation:

• Standard pitched roof without shading: String inverter — cost-effective and proven
• Complex roof or shading: Micro-inverters or SolarEdge with optimisers
• System with battery (new build): Hybrid inverter — most efficient solution
• Battery retrofit: AC-coupled battery storage on existing string inverter

Regardless of type: pay attention to the European efficiency (not maximum value), warranty conditions and a good monitoring system with app and, if possible, open API.

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Last update: January 2026. Sources: Fraunhofer ISE “Current Facts about Photovoltaics in Germany”, manufacturer data (SMA, Fronius, Huawei, Enphase, SolarEdge), HTW Berlin “Independence Calculator”.