9.2 kWP system - size of the battery storage?

Good morning everyone,

two weeks ago, our electrician installed a 9.2 kWP system on the roof. Orientation is south with a roof pitch of 35° without shading from neighboring buildings. We will also install a battery storage system. The plan was to install the 9.8 kW battery from Varta (S4). Unfortunately, this is no longer available and has also been discontinued. The successor series (S5) unfortunately only offers 6 kW or 12 kW. To be honest, the former is too small for us. The 12 kW battery, on the other hand, seems too large and is also more expensive than the originally planned battery mentioned above. I am concerned that the 12 kW will not benefit me in the weaker months or that I will not be able to fully charge it. What is your assessment? In summer or the stronger months, however, it is probably much better if you can store twice as much?

Best regards

Let's take a step back: Why do you want a storage?

Let's take a step back: Why do you want a storage system?

Because we want to use as much electricity as possible ourselves. This includes heating and hot water preparation via the geothermal heat pump, household electricity (family of four) also during off-peak times, as well as the wall box for the electric car.

You are aware that this will cost you (significantly) more than simply buying electricity? As a rule of thumb, you can currently say that one kWh from the storage costs about 50 cents.

I have a 13 kWp system and a 7.5 kWh storage. I get along great with it. From March onwards, I supply myself almost completely independently. Choose the storage size according to your monthly consumption. The storage should also cover your household consumption at night during the summer months. Nothing more. Better to have more on the roof, that way your system pays off faster. More storage won’t help you much in summer anyway. ;) And then it costs too much in relation.

Yes. Our primary concern here is the degree of self-sufficiency we can or want to achieve, as was the case with the chosen heat pump. Additionally, the battery had an emergency power function. Whether one needs that or not is debatable. We will definitely take a storage system. The question with the system size is the capacity of the battery.

But since we're already calculating: If I cautiously assume that the battery can be used for 12.5 years and provides me with 6 kWh of additional storage capacity on 200 days each year at a gross cost of about €4,000, it is at least not more expensive over the service life than drawing from the grid? --> 200 x 6 x 0.35 x 12.5 --> and I don’t think electricity will still be available for €0.35/kWh in 5-10 years.