Experiences with Caterva Sun battery storage

Hello everyone,

I am very much in the process of acquiring a Caterva Sonne (21 KW battery storage) for my newly to be built single-family house, with which Caterva also provides balancing services on the electricity market.

Unfortunately, there are no results in the search function, so I would be interested to know if anyone here has already had experience with it or has been advised?

Thank you very much for your feedback.

Hello Dennis,

I have no experience with this system, but what do you want to hear?

Economically, it will hardly be viable, and I also don't understand what you need a 20kW storage for, especially since you first need a photovoltaic system to fill the unit for you in winter.

To me, it initially sounds interesting that you can use the electricity you produce on the roof over a year for 20 years spread over the whole year, and only the possible demand beyond that has to be drawn from the grid.

But that is pure sentimentality. With your existing air-to-water heat pump, you have a major consumer whose "operating time" you can set with a timer, for example, to midday. Just because of that, you will be able to consume 40-50% of your photovoltaic electricity yourself. Battery storage is not worthwhile, they are very expensive, and the durability is inadequately guaranteed. Not profitable. This especially applies to the one you selected, as it is massively oversized. For your 8.5 kWp photovoltaic system (by the way, a bad configuration, better to aim for around 7 or 10), a 5-6 kW storage is more appropriate. In winter, when you need a lot of electricity for your heating, the photovoltaic system does not deliver much anyway; everything goes directly to the air-to-water heat pump and household electricity, and the storage stands empty.

From my understanding, it goes well beyond a normal storage system.

Yes, it combines a fairly complex business model that requires a massive advance payment on unnecessary capacity on your part, with the promise of getting it back over decades. I wouldn't throw my money into the mouth of a startup like that, and I could imagine your bank will insist that the storage is your private pleasure (not co-financeable with a mortgage loan). But you will have to clarify that.

Honestly, I currently don't think much of current 6-7 kW storage systems, as you are still dependent on the electricity market (self-sufficiency rate about 70-80%), and therefore do not solve the problem of the difference between electricity generation (summer/day) and electricity demand (winter/night).

As I said, it's not about returns here but about sentimentality. That’s okay too. Just don’t believe you’ll fare well financially with it. That is completely excluded.

My problem is: I'm looking for the catch!

The calculation. For €27,000 you can draw electricity for a very long time. And you already achieve a respectable degree of self-sufficiency with photovoltaic and heat pump anyway. Everything purchased beyond that is completely uneconomical.

You’re looking for the catch? That was good.

From which sun is the power supposed to come if your storage is empty? Do you think the sun shines in Flensburg on December 21st like in midsummer, while your storage in Passau is empty and your photovoltaic system produces no power?

I believe that from an ecological point of view, this can be a great thing. Economically, however, it is definitely not reasonable, as the kWh will probably cost you significantly more than it would be economically viable.

What do you need 20kWh in your storage for?

Thank you for your feedback.

For me, the arguments in favor of a purchase are:

- Guaranteed 1000 EUR community premium (monthly payment) per year. Of course, knowing that Caterva is a GmbH and therefore might not exist anymore tomorrow. I don't believe that. A Siemens subsidiary that has invested a lot of money and capacity for an approval from the Federal Network Agency is pursuing a viable business model.

- A power credit amounting to the annual yield of the photovoltaic system (approx. 1000 kW/h per kWp with south orientation in my region, according to statements from various solar technicians and photovoltaic owners) regardless of the fact that I need a lot of power in winter but generate it in summer. Of course, in winter everyone's storage is "empty," but this is compensated accordingly by Caterva. Effectively, I only draw from the grid what exceeds my annual production.

All this contractually fixed for 20 years. Any repairs and maintenance of the storage system are commissioned and paid for by Caterva, as this is apparently the requirement of the Federal Network Agency and a prerequisite for granting the ancillary service license.

I think you just have to come to terms with the business model first rather than "just" seeing the 20 KW storage. For me it is clear, either this one or none.

Hello Toxicmolotov,

The concept at Caterva is completely different from other "ordinary" storage systems. The charge level is completely irrelevant. Whether summer, winter, day or night. Only the annual production quantity matters. You can use it whenever you want. Up to 10,000 kWh. For 20 years.