Sonnenbatterie review

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Recently I heard the news that sonnenBatterie were joining Australia’s emerging Solar storage market, so I contacted Sonnen’s new Australian managing director Chris Parratt to get the scoop. The reason for my interest is that the “sonnenBatterie eco” is an AC coupled battery. This means we can connect it to any solar system – old or new. Enphase has had a crack at an AC coupled solar battery but in my view, they failed. Since reviewing Enphase, I’ve been on the lookout for an AC coupled battery that works. Today, “hot off the press”, Chris sent the spec sheets. Let’s break it down.

To be clear, the sonnenBaterie ECO is not the model that True Value Solar are importing directly from Germany, and misleading consumers by saying that sonnenBaterie is: “Fully compatible with the Bosch inverter”. The sonnenBattery as an AC coupled battery so it can be coupled with any inverter. Why would you link it to the Bosch inverter that is no longer in production?

The sonnenBatterie is a completely different solution to the Tesla PowerWall, but for the sake of benchmarking, first this post will compare the two. Next, I’ll advise what I would do if I were buying a solar system today, with batteries in mind.

Pro’s of the Sonnenbatterie

  • sonnenBatterie is German Made.
  • As an AC coupled battery it can hook up to any solar inverter, or any AC generation source. The Tesla is currently limited to the Fronius Symo hybrid and the SolarEdge.
  • It is scalable from 2kWh to 16kW of usable storage, or up to 48kWh in cascading clusters. In reality, 10-16kWh should be more than enough for an average household. The PowerWall for comparison comes in 6.4kw packs. 
  • It is warranted for 10 000 cycles or 10 years. The warranty covers all parts. Theoretically, you could cycle it 2.7 times a day, and it would be still covered by the warranty. The Tesla also come with a 10-year warranty but only 3650 cycles, and only a 4-year workmanship warranty.
  • It’s expected lifetime is 20 years. Sure that’s not a warranty, but it means if you cycle it more than once a day, it should last 20 years.
  • It’s fairly compact on the larger end. From 4kW hours to 10kWh, it uses the same enclosure: 137cm tall, 64cm wide and 22cm deep. That’s about the same size as the 6.4kWh Tesla. If you want larger than 10kWh, the enclosure is just 50cm taller.
  •  The Maximum efficiency is 93 percent. More data would be needed to compare it to Tesla’s DC coupled 92.5 percent round trip efficiency. However being AC coupled, the total system efficiency would be less than a DC coupled system.
  • It will be able to run as an “emergency power supply” in 2017 with an upgrade.

Con’s of the sonnenBatterie

  • It’s a bit lacking on its charge and discharge rate. On single phase it’s 2400W, and for three phase it’s 3300W. The Tesla Powerwall charges and discharges at 3300W. An oversized solar system will sometimes want to charge faster than 2400W, and average household would have an evening maximum demand of higher than 2400w. However, 2400w would absorb a big chunk of surplus power, especially if your solar system was designed with appropriate load shifting.
  • It’s heavy. At 116kg, the 6kwh option is even heavier than the 97kg Tesla Powerwall, but that probably speaks of its quality. Unlike the Tesla, they don’t expect you to hang it on the wall!
  • It’s IP 21 and can only operate up to 35degrees. In Queensland weather, this would limit the areas you could install it.
  • This is the big negative. The sonnenBatterie costs well over $2000 per kWh of storage capacity plus install. With far superior technologies like Redflow costing less, it’s hard to see sonnenBatterie ever becoming a cost-competitive solution.

My Advice

If you planning to install a battery ready solar system, I would advise you away from an AC couples solution purely based on Price. Since DC coupled batteries are significantly more affordable, it would be far more prudent to install a quality hybrid inverter now (such as a Fronius or Redback), and add a quality DC coupled battery when prices come down further. Whatever you do, don’t be sold on the false hope that a second rate inverter like Bosch is compatible with the sonnenBatterie. Every inverter is compatible with the sonnenBatterie, but using the Bosch inverter would be like putting a Rolls Royce engine into a Datsun.

Before you purchase solar from anyone, please do your background checks on the company. Especially if you are reading this because you have a quote from True Value Solar.
Here is a simple 5 step background check.


As a battery, the sonnenBatterie seems to be serious competition for the PowerWall. As an AC couple battery, you don’t need to purchase an expensive inverter now. It is compact and easy to install on the ground, and one unit can take up to 16kWh of storage. Its warranty is better than the PowerWall. One downside is the single phase version will only charge and discharge at 2400w, but the three-phase version meets the PowerWall’s 3300w. As with most batteries, you’ll need to choose carefully where to install it. However all said and done, batteries need to be cost effective, and AC couples solutions such as the sonnenBatterie seem to be missing the mark by a long way. Choosing a hybrid inverter today, for a DC coupled future, would be the way I would advise you to go.

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Mark Cavanagh

Mark is the Owner and Manager of MC Solar & Electrical. He’s an Electrician, accredited solar installer/designer and an electrical contractor.

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