Help with photovoltaic decision

I can only say something about the Fronius inverter - it has been running without any issues for 4 years now. Even during the power outage last Monday, it dutifully did its job and kept the house - including the heat pump - running smoothly... but it was pretty creepy when everything outside was dark and the neighbor suddenly knocked on our door because she had seen light.

I can't say anything about the size of the system - for example, with us, only space for 3.2 kWp was reasonable.

Regarding the use of a battery, I can only answer personally that I would never install without one again - yes, of course, efficiency, costs, blah blah blah. To me, the security it provides in an emergency is worth every penny. And I have mentally stored the expression of the other neighbor, who also stood at the door the following day and sheepishly admitted that it was a foolish decision not to buy one and instead choose the better equipment for the new family car, very well.

Therefore, I also recommend the installation of an off-grid controller.

The security purchased with it is worth every penny in an emergency.

If that matters: not every storage system can do this, and the solutions differ between emergency power (a functioning socket on the device, e.g., for a freezer) and backup power (supplying the household from the battery; for this, the "black start capability" of the system is important). Since many people have not the slightest clue about energy, such systems are often sold inappropriately. Also, few know that in backup power mode, the discharge capacity determines which devices work and which do not. And many also do not know how long that can last. Nor do they know that only a few systems recharge the storage from the sun during a power outage, and that in winter the storage must be managed so that it is not empty during a power outage... I hardly know any topic that fosters such skewed expectations.

Currently, there is a discussion in politics about whether to charge electricity producers a fee as a network charge. In other words, this would affect everyone who feeds in. To what extent politics will agree to this and from which system size/feed-in quantity it counts is still unclear. However, if you listen to the discussions, I would actually opt for an oversized storage system. Provided it can be implemented cost-effectively.

If you listen to the discussions, I would actually go for an oversized storage. Provided that it can be realized cheaply.

These discussions are really investor-friendly again. After the last change in February, the photovoltaic system can be switched off in case of feed-in surpluses, so that in the worst case the self-used electricity is drawn from the grid again. At other times, the remuneration for the fed-in energy is also charged with grid fees. The normal power plants, on the other hand, remain exempt from this.

Or the self-consumer is charged with a higher basic fee. Then you have double costs due to too large a storage and higher basic fees.

That really makes investing fun when the framework conditions change monthly.

Or you simply take an AC storage (e.g. Zendure, Anker etc.) and install it yourself. Slightly more conversion losses (about 20 percent) and only 800W output allowed, but only a fraction of the installation costs... should pay off quickly.

The security purchased with it is worth every penny in an emergency.

I'm not getting any younger either, but I can't remember a power outage lasting longer than 5 minutes.

instead take the better equipment in the new family car,

The equipment that I can use 24/7/365 and actually do would be worth every penny to me. The world is just that different.