Fronius Inverter - Review

Fronius is highly regarded in the solar world and generally considered the world’s leading string solar inverter manufacturer. This reputation is not based on sales volume, but service, quality and most importantly reliability. With the solar inverter being the most complex component in any solar systems, it is also the part most likely to develop problems. Inverter faults can be extremely frustrating for installers and customers alike and often result in complete system shutdown, hence why reliability is crucial.

Fronius International professional welding.jpg

All Fronius solar inverters are engineered, designed and manufactured in Austria. With over half a century of experience in inverter (welder) design and manufacturing it’s not surprising Fronius is considered an industry leader in power conversion equipment. Fronius’s history in designing high performance welding inverters provided the ideal background for moving into the solar inverter production over two decades ago with the first Fronius solar inverter released in 1994.

Fronius continued to develop a number of solar inverters but wasn’t until the release of the snap-in inverter (snapINverter) range in 2012 that Fronius really created a stir and quickly developed a strong following around the world. Up until this point SMA was widely regarded as the industry leader. SMA experienced some issues during the transition to the new generation AV series inverters and lost a lot of ground to Fronius. However, they are one of the few manufacturers which can still compete with Fronius on quality and reliability.

The current Fronius snapINverter range, including the Primo, Symo and ECO have become the inverters of choice for many domestic and commercial solar installations. The high demand for the popular Fronius Primo solar inverters used for residential installations has resulted in some supply issues at times and there have been a few minor issues, but overall feedback is extremely positive and any issues have been promptly addressed by the Fronius service network.

Fronius Primo Inverters

Residential single-phase string inverters, 3kW to 8.2kW

Fronius Primo solar inverter image.jpg

The Fronius Primo ‘SnapINverters’ surged in popularity after the release of the new design 8 years ago and are widely regarded as one of the best quality and most reliable residential string solar inverters. While larger and heavier than most modern inverters available today at 21.5kg, the unique snap-in design makes installation and servicing easy. Inverter monitoring and setup is quick and easy via the large clear display and four multi-function buttons.

Primo inverters are cooled via an active cooling system using fan-forced air. Active cooling, while being a little more complex, is claimed to increases performance and reliability when compared to the more common passive cooling systems. As further examined below, we believe this is a key reason behind Fronius’s reliability and low recorded failure rate.

Key features

  • Unique Snap-in design for easy installation & service

  • High input current - 18A per MPPT (5kW+ SC version)

  • Integrated DC isolator (CEC certified)

  • Fan forced active cooling system

  • External relay control - Digital output

The Primo range of single phase transformerless inverters are available in a wide range of power ratings from 3.0kW to 8.2kW, all featuring dual MPPT inputs and wide operating voltage range. More importantly the larger inverters, rated 5kW and above have a high input current rating of 18A per MPPT and Isc of 27A. This allows two strings of panels to be connected in parallel. Note, this is now referred to as the Superior Current (SC) version in Australia.

See the Fronius Primo Solar Inverter Specification sheet here.

Fronius Galvo Inverter

Residential single-phase string inverters, 1.5kW to 3.1kW

Fronius Galvo solar inverter range.jpg

The Galvo range of single phase transformer based inverters use the same snap-in chassis and are available with power ratings from 1.5kW to 3.1kW. Utilising the ‘old’ transformer (isolated) topology, the Galvo inverters are perfect for retrofitting to older systems and are widely used as replacement inverters for old small capacity solar systems.

See the Fronius Galvo Solar Inverter Specification sheet here.

Fronius Symo & ECO Inverters

3-phase string inverters, 3.0kW to 27kW

Fronius Symo solar inverter range.jpg

The Fronius Symo three phase inverters are built around the same snap-in design and available in an impressive range of sizes to suit both residential and commercial applications. Symo inverters range from 3.0kW up to 20kW, while the ECO’s are available in 25kW or 27kW sizes.

Fronius Symo inverter temperature derating chart

Fronius Symo inverter temperature derating chart

Many commercial inverters are located in exposed locations and have to perform in extreme conditions, including high summer temperatures. This is where the Fronius active cooling system really shines enabling continuous operation with minimal power derating in high ambient temperatures up to 50 degC.

See the Fronius Symo Solar Inverter Specification sheet here.

Key features

  • Unique Snap-in design for easy installation & service

  • High input current (ECO 27) = 47.7A (Isc max 71.6A)

  • Integrated DC isolator and DC string fusing.

  • Fan forced active cooling system.

  • External relay control - Digital output.

Fronius Symo integrated string fusing.jpg

The Fronius ECO series are highly sought after for larger scale commercial systems due to the high performance, reliability, advanced communication options, and unique features such as the integrated string fusing. The integrated all-pole string fusing (fuses optional) mean string combiner boxes are no longer required making installation quicker and easier.

See the Fronius ECO Solar Inverter Specification sheet here.

Limited Home Energy Storage Options

The one rapidly growing segment where Fronius has been severely lacking is battery storage. While most rival manufacturers have developed a range of battery storage (hybrid) options, Fronius have only one inverter available, the Symo Hybrid which as explained below, has a number of limitations.

Fronius Symo Hybrid

Residential 3-phase hybrid energy storage inverter

Fronius Symo hybrid solar inverter.jpg

The Fronius hybrid inverter option has not gained much traction due to only being available in 3-phase form. Most homes outside Europe are single phase so the Symo hybrid is simply not compatible. The inverter application was further limited due to the single MPPT input, generally meaning only one panel orientation could be used. The lack of sales was not only due to the inverter limitations but for many years the only battery option available was the rather expensive Fronius battery. Although, this was helped when the more affordable and popular LG Chem RESUH battery battery was added to the list in mid 2018.

Off-Grid With The Fronius Primo

Surprisingly the Fronius Primo inverter has become a key feature in many off-grid solar or stand-alone power systems. The Primo is a solar inverter, not a battery inverter, but it can be coupled with a compatible multi-mode (battery) inverter to form an advanced AC coupled energy storage system.

*Fronius Primo solar inverter AC coupled with the popular  Selectronic SP PRO  off-grid inverter/charger

*Fronius Primo solar inverter AC coupled with the popular Selectronic SP PRO off-grid inverter/charger

AC coupling for off-grid power systems has become the configuration of choice over recent years. The flexibility and simplicity of AC coupling allowed off-grid systems to become much larger and more powerful. Several years ago, Fronius made the clever move of teaming up with two of the leading off-grid multi-mode inverter manufacturers, Selectronic and Victron Energy, to allow the Primo inverters to operate in both on-grid or off-grid systems.

*NOTE: The Fronius Primo inverter must be ‘Selectronic certified’ to function in a ‘managed’ AC coupled off-grid system. Selectronic certified or ‘Scert’ single phase inverters are slightly modified to enable high precision battery charge control. However, Victron AC coupled off-grid systems use a standard Primo or Symo inverter and enable off-grid charge control using frequency shifting. This is adequate but not as precise and can affect some sensitive electronic appliances.

New GEN24 Plus Hybrid Inverters

New generation Fronius hybrid (Symo) inverter due in October 2020

Fronius Gen24 solar inverter range.jpg

Fronius designed and engineered an entirely new hybrid Inverter platform known as the GEN24 Plus. It’s been a long wait, but the Symo 3-phase version is finally due to be released in October 2020, while the Primo is due early 2021. The GEN24 plus range is built around Fronius’s vision of ’24 hours of sun’, referring to the use of solar combined with energy storage to deliver power both day and night for maximum self-sufficiency.

GEN24 Plus Inverter Features

Some of the standout features of the new inverter range include the extremely wide PV operating (MPPT) voltage range which starts from a very low 65V for the Primo and 80V for the Symo. This means strings can be as small as 3 panels.

  • Very wide MPPT voltage range - 65V to 530V

  • Dual MPPT trackers - 22A / 11A - Parallel strings ok

  • Very high battery efficiency - 94% round-trip with BYD

  • Basic grid backup with or without a battery - PV point (3kVA)

  • Full backup power with battery (22A) & external contactor

  • Over-sizing solar array up to 150%

  • Advanced active cooling system with front heat shield

  • Arc fault detection (US only)

The most obvious physical feature is the unique front-mounted fan giving it a surprisingly retro look. Although, there is much more behind the front cover as it hides an extremely sophisticated thermal management system with a cleverly designed spiral heat-sink. This active cooling system described in more detail below helps improve both performance and reliability. But it doesn’t stop there; the GEN24 Plus will also feature integrated grid backup and 4 digital inputs/outputs to take full advantage of smart home controls. The one apparent deficiency is the lack of a display or buttons. Although, this has become an industry norm as inverters transition to app based setup and monitoring.

GEN24 Plus Battery options

The GEN24 plus inverters will initially only be compatible with the higher voltage battery systems from BYD (Premium HVS & HVM models). However, the popular LG Chem RESU batteries will also be certified at a later stage.

The GEN24 will initially only be compatible with the BYD HVM & HVS batteries. LG Chem compatibility TBA

The GEN24 will initially only be compatible with the BYD HVM & HVS batteries. LG Chem compatibility TBA

Quick installation and setup

Like the snap-in inverter range, the new Gen24 plus inverters have an enclosed cable/terminal connection area which makes installation much neater and easier for installer -  Click to enlarge

Like the snap-in inverter range, the new Gen24 plus inverters have an enclosed cable/terminal connection area which makes installation much neater and easier for installer - Click to enlarge

Throughout the long development process, Fronius was actively gathering feedback from solar installers about features which would make the installation and commissioning process quick and easy. This led to several innovative design features and a new mobile App which will no doubt make the new GEN24 plus series some of the easiest inverters to install and setup.

  • Fast 3-Step commissioning with new Fronius App

  • Easy auto Wifi connection using one touch WPS button

  • Fast cover removal - access via 180 locking screws

  • No tool, spring clip internal cable connections

  • Rear access & large internal cable area for neat installs

  • Easy inverter breakdown and exchange of parts

Active Cooling

Is active cooling the secret to long term reliability?

Like the current snap-in inverters, the new Gen24 Plus hybrid inverters use an active cooling system.

Like the current snap-in inverters, the new Gen24 Plus hybrid inverters use an active cooling system.

Unlike the majority of manufacturers, Fronius only design inverters with active or fan-forced cooling. Most inverters available today are transformerless and utilise large rear-mounted heat sinks which use natural convection to cool the inverter. This simple design, known as passive cooling, doesn’t rely on any moving parts such as fans which can fail over time. However, relying on passive cooling alone can be problematic, especially in higher temperatures or locations with low natural air circulation. While mounting a solar inverter in locations exposed to the sun should be avoided, it is sometimes not possible and this is where many ‘cheap’ inverters relying on passive cooling alone can fail. Mounting in exposed positions with full sun (especially during the afternoon), heats the inverter to extreme levels and can cause severe power derating, thermal shutdown, and early failure

Fronius only use fan-forced active cooling which extracts heat at a more constant rate. As highlighted in the chart below, this can increase performance with less power ‘derating’ in high ambient temperatures. Power electronics have a maximum operating temperature after which the power transfer needs to be reduced to prevent overheating and potential damage. This is where active cooling can dramatically improve reliability. Fans can also fail; however, modern brushless DC fans have a very long lifespan. If a fan replacement is required, then it is easier to replace a fan rather a blown transistor or capacitor which may be impossible.

Image credit Fronius -  Click to enlarge

Image credit Fronius - Click to enlarge

Adequate cooling is essential for increasing the life of any electronic product. It is particularly crucial for solar inverters that use sophisticated power electronics to transfer thousands of watts of power in extreme environments. Modern inverters use solid-state transistors (semiconductors) to convert the DC power from solar to AC power. High temperatures will reduce the efficiency, performance, and life of transistors and most other electrical components.

The new generation Fronius Symo hybrid solar inverter with the front cover removed, revealing the advanced spiral heat sink design.

The new generation Fronius Symo hybrid solar inverter with the front cover removed, revealing the advanced spiral heat sink design.

Based on the long development time and vigorous testing, we are confident the Fronius engineers have designed the new GEN24 inverters to be extremely reliable, efficient and offer high performance in all conditions. Looking at the GEN24 Plus specification sheet, it appears the new inverters may have high tolerance to being located in exposed locations with little protection. However, this it is yet to be verified in real-world conditions.

Fan Noise

Naturally using fans for cooling creates some level of noise. As the inverter internal temperature increases, so to does the fan speed and associated fan noise. For most installations, the relatively low fan noise, which is reported to reach a maximum of 65 dB(A) is not an issue. However, if installed outside in specific locations, such as outside a bedroom window, the noise may be problematic as the fan can start cooling early in the morning soon after sunrise. In this situation, a long sleep-in on a hot summer morning might be more difficult with the window open. (Protip :)

Service & Warranty

In regards to service, Fronius has ranked very highly for many years due to the low failure rates and great service. If a failure occurs, they usually ship replacement units in 3-5 business days. Fronius inverters are available with either 5 or 10 year warranties, depending on the location or country.

Monitoring – Solar Web

The smart meter. Required for both solar & energy consumption monitoring. (single phase meter shown)

The smart meter. Required for both solar & energy consumption monitoring. (single phase meter shown)

Wifi monitoring comes standard with all inverters via the Fronius Solar.Web. The addition of the Fronius smart meter enables monitoring of energy generation and consumption, and can be used as a complete home energy monitoring system. A free solarweb smart phone app is also available for android of iOS.

There is also the option of adding the Fronius Ohmpilot which is designed to automatically use excess solar energy to heat water.

Fronius Solar. Web portal - Image credit Fronius

Fronius Solar. Web portal - Image credit Fronius


From reading this review, it’s obvious why Fronius is widely considered a leading solar inverter manufacturer. When you sum it up, the reasons are pretty simple - high build quality, proven performance and reliability from an experienced manufacturer. The only real problem is getting hold of one is now rather difficult due to the limited supply and high demand.

The decision to engineer active cooling into all inverter platforms seems to have paid off by providing a higher level of performance and reliability, especially in extreme environments. The clever snap-in design, advanced communications, and features such the integrated DC isolator and string fusing won over many installers. This, together with a high level of service and support, means any issues have been promptly addressed. In an industry plagued by cheap, unreliable inverters, this kind of service and reliability is essential.

Fronius GEN plus PRIMO solar inverter.jpg

Energy storage, on the other hand, is the one area where Fronius has been lacking. Until recently the Austrian manufacturer had only really dabbled in the hybrid space, but this is about to change with the new GEN24 plus inverters due to be released in late 2020. The rapid evolution of hybrid inverter technology over the last 3-4 years has seen many manufacturers rush out inferior and problematic products with multiple issues. In some ways, this may have benefited Fronius who don’t appear to rush through development. The slow and steady approach to designing new inverters may result in Fronius also becoming the dominant player in the hybrid energy storage space. Looking forward to testing out the new GEN24 plus inverters in 2020.

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