It seems nowadays that a new solar battery is launched every month, and more and more new brands are entering the market. However, it’s not common to see an 80-year-old, highly respected brand launch its first advanced solar battery. This is what makes us sit up and take notice of the Fronius Reserva – the Austrian giant’s re-entry into the battery arena.
Let me be honest right at the outset – I did not find myself oohing or ahhing reading about the Reserva. It is a great product, but it is like a Honda Civic: we respect it for its reliability, but c’mon – who has ever had a Honda Civic poster in their bedroom? But then again, a Civic is often what many of us really need. Alright, enough musings, let’s go talk about what the Reserva has in store.
Specs
The Reserva uses LFP (lithium iron phosphate) chemistry, promising longer life and better safety. It is also a high-voltage battery that supports three-phase connections.
The battery features a modular design with 2-5 stacks, resulting in capacities of 6.3 to 15.8 kWh. These towers can also be connected in parallel to get up to 63 kWh in storage capacity. A dedicated DC connector on each stack eliminates the need for combiner boxes, saving your money and your installer’s time. Here’s a chart showing the four basic models of the Reserva:
Fronius Reserva variants and specs
Fronius decided to go with a DC-coupled design for the Reserva, which means you can expect slightly better efficiency, but also a complex and a tiny bit more expensive installation. The battery comes with a 10-year warranty, at the end of which Fronius promises at least 80% of the rated capacity – not bad at all.
The battery has an IP65 rating, which means you can install it outdoor-ish, though we aren’t very comfortable with the idea of installing it fully outdoors for a decade or more. This is an important upgrade over Fronius’ previous solar battery, which had an ‘indoor-only’ design.
Features
The Fronius Reserva offers everything that a typical solar battery on the market today does. Let’s go over its key features.
Companion App
The new Fronius battery works with the company’s Solar.web app, displaying both real-time and historical data. The app creates a digital ecosystem for all your Fronius products, giving you a bird's-eye view of the battery, solar panels, inverter, and even the EV charger, if compatible.
Fronius Solar.Web App
Reliable Support
One of the key features of the Reserva does not lie on or in the battery itself, but comes as a benefit of going with a reputable brand. Fronius offers what it calls ‘fastest service on the market’. It claims that its technical support team can offer ‘comprehensive troubleshooting’, as it has access to all the relevant data of your battery’s performance.
Data Security
Speaking of data, Fronius has stressed more than once that all the customer data that it receives is stored on European servers. What they really want to stress is that the data isn’t stored in a country without strict laws about data security, or a country with some history of acquiring people’s data for political purposes without their consent. Nice!
Black Start Capability
The Reserva supports blackout protection and black start capability – meaning it can restart without relying on the grid – although this is not an industry-first. However, you need to install a Fronius Backup Controller and a Backup Switch to enable automatic backup power switching. This means about $1,000 more in your total purchase costs.
An area the Reserva could improve is its response time when switching to backup power. The Tesla Powerwall, for example, switches instantly to backup power in the event of a power cut, and you can barely recognize it happening. The Reserva, on the other hand, takes up to 30 seconds.
For households, this is not such a big deal, but for businesses that rely on a consistent power supply, this can be an important factor to consider.
Drawbacks
Lack of Some Advanced Features
The Fronius Reserva does not offer built-in fire suppression, something that brands like Sigenergy or Alpha ESS already offer. Essentially, this is just an integrated little fire extinguisher that goes off when the device senses a fire. We can trust Fronius to make a device that wouldn’t catch fire, but it's always good to have added protection.
The Reserva also lacks module level balancing – a BMS (battery management system) feature that equalizes individual cell voltages in a battery/module to ensure optimum charging-discharging and maximised capacity.
Agreed, these are somewhat modern, advanced features that not all brands offer. But in a few years, when these become standard, you may look back and wonder if you should have chosen a battery with these features as standard.
Limited Compatibility
Another important limitation of the Reserva is that it only works with Fronius’ Gen24 Plus inverters (the Symo and Primo models). While Fronius inverters work with several battery brands, the battery itself does not support connection with a different inverter brand.
Design
Sometime in the past couple of decades, batteries’ looks started becoming important. Several customers started placing their batteries in their entrance lobbies, and they wanted something that would look aesthetically pleasing, unlike older lead-acid batteries that resembled something from an evil scientist’s lair.
The Fronius Reserva pays just enough attention to aesthetics, adopting a sleek, plain white tower design that most modern batteries now use.
Fronius Reserva’s tower design
It has multiple battery modules stacked vertically, with the topmost module having the branding and a status display. The status display is somewhat disappointing, as it really is just five tiny LED lights that light up to show the state of charge. For the kind of price that Fronius charges, it would be nice to have an informative display screen. That said, the Solar.web app is quite sufficient, and the lack of a display screen on the battery itself is not such a deal-breaker.
Another thoughtful aspect of the Reserva’s design is its long cable. The 30 m cable length between the battery and inverter offers notable flexibility for installations.
Pricing
Fronius is by no means an inexpensive brand, and that reflects in the Reserva’s pricing. Although not ridiculously expensive, the battery does cost upwards of $1,000 per kWh of capacity. This is in line with the Tesla Powerwall 3, but a bit pricier than some of the other options on the market.
Should You Buy It?
Like any other product, there is no general answer to whether the Fronius Reserva is a good option for everyone in general. The Reserva is a good battery if you already have a system with a Fronius inverter, or you are in the process of installing one. If you are going with a different inverter brand, there are still plenty of great alternatives on the market.
There are a few reasons to choose a different battery over the Reserva, but the strongest reason to go with the Reserva might be Fronius’ reliability of technology and (especially) service.
Final Thoughts
The global solar battery market is projected to triple in size, from just $6.39 billion in 2025 to $19.10 billion in 2032. As such, it would only be a surprise if big brands like Fronius don’t enter this market. The Reserva battery is the brand’s second attempt at offering a solar battery. The first one, unimaginatively named the ‘Fronius Solar Battery’, was quite unimpressive.
The latest battery offers nearly all modern features, even though it cannot claim to be the most innovative battery on the market. With its slower-than-ideal response time and limited compatibility, it may not be an immediate choice for buyers. But homeowners who are opting for a Fronius inverter and want a complete ecosystem from a reputable brand can find the Reserva to be perfect for their needs.
If you’re wondering whether the Reserva is a good fit for you, it’s always a good idea to speak with an installer, get multiple quotes, and make an informed decision.
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