Evaluation of Photovoltaic Offer and Components

Our offered system has less power but a larger storage. We had 12.45 kWp, 10 kW inverter, and 12.8 kW storage. It was about 25.6k net, after deducting discounts. The electrician who does the house electrics is also ours.

I don't find it that expensive for the current times. The days of bargain prices have long passed. The new distribution box along with wiring and a completely new grounding system and the scaffolding setup already consume quite a bit. At first, it's nice to have fairly powerful modules, and you have to consider the storage or base it on the costs involved. I don't think it will get significantly cheaper. Additionally, there is the advantage of having a contact person within reach.

I didn't find it that expensive either. More like in the middle range.

With the offer, I would take another look at what the storage costs price-wise, and how long the warranty on it lasts.
Storage systems are often massively overestimated.
Calculate with 170 cycles per year, or optimistically with 200. If I assume 200 cycles and want to do it correctly, I still have to consider the losses (5% each way? Depends on the storage as far as I know). Let's just ignore that for simplicity.
So let's say 200 x 6 kWh savings per year. Calculate with the current price cap of 0.4 = 480€ savings for electricity you don't have to buy from the grid. Minus the lost feed-in tariff of about 0.08€ for the 1200 kWh -> 480 - 96 = 384€ per year.

If your storage has a 10-year warranty, it should not cost more than 3840€ so that you don't make a loss if the unit completely fails shortly after the warranty expires. With 5 years, even only half.
And in this calculation, two things have already been optimistically calculated for simplicity: the number of full cycles per year, and ignoring the losses during charging and discharging. Also, I have left out the fact that storage loses capacity over time.

If electricity gets significantly more expensive in the future than it is now, but the feed-in tariff stagnates, the calculation would look completely different. But who has a crystal ball.

If you now also calculate against the fact that the money you invest in the economically shaky storage system could be put into additional photovoltaic modules (assuming you have the space), the storage performs even worse. The photovoltaic system almost certainly pays for itself before the warranty expires. The fuller the roof, the better.

I don't want to start another storage discussion here. But the statement "fill the roof and feed in as much as possible" has long been obsolete given the electricity purchase costs in relation to the feed-in tariff.

To put it more simply. You install a photovoltaic system on your house roof. And after about 3 weeks at the latest, you regret not having installed a storage system. If it even takes that long. When I look at my app in the evening and see zero grid consumption, it feels really good. Without storage, there is probably 10 kWh electricity consumption.

The feed-in only interests me marginally. Because then I get 80 cents feed-in tariff and have 4.80 euros electricity costs.
There are still 4 euros left that I have to pay to the energy supplier. Despite the photovoltaic system.

With my storage system, I pay zero euros to my energy supplier. And I don't have to worry if the sun doesn't shine tomorrow.
The storage system takes care of that.

With a ratio of 6:1 between tariff and electricity costs, every storage system pays off.

And believe me, it's extremely annoying when your meter keeps running despite the photovoltaic system. Aside from when you are at work, the sun is shining, and you can't operate your power guzzlers. I can also wash clothes or turn on the oven in the evening without noticeable grid consumption.

With a ratio of 6:1 between compensation and electricity costs, every storage system pays off.

That is just one factor. The much bigger one is the purchase price. And of course the time how long the battery lasts, but that is hard to determine at the time of purchase.

There are still 4 euros left that I have to pay the energy supplier. Despite the photovoltaic system.

For that, you have paid the battery seller, and immediately in advance for (hopefully) many years - maybe at the end of the battery's lifetime you are in the plus or not.

PS: I have a battery myself and appreciate it very much. However, I bought it at different price times and at that time claimed both VAT and subsidies.