Photovoltaics - Questions about Tax/Business

You do not have to register a business in any of the cases. This has already been mentioned. You might mean the start of the entrepreneurial activity. You must notify the tax office of this by form.

The most financially sensible thing you can do: fully install the roof system, feed surpluses directly into the grid, and waive the small business regulation for 5 years so that you are entitled to input tax deduction and get the VAT of the investment back.

In the forum mentioned multiple times by others, you are also better off tax-wise than on the blog of a cloud provider with their own interests. Have you checked taxes there? Search a bit but you will find everything you need to know there. I am not an expert, but some of what is stated in your source is outdated (calculation of self costs) or not correct that way. They also seem to regularly deal with loss-making systems there and sell such a bad investment as a tax saving model.

Furthermore, the cloud story is not clearly clarified from a tax perspective even among experts, which for you might mean additional unnecessary costs for advice, on top of the losses from storage and possibly from the cloud contract, which reduce your profit. The profit comes exclusively from the modules on the roof. More modules, more profit; storage and gimmicks, less profit.

If you have already signed something, check if you can get out again.

Thank you for the reply. I read through the FAQ in the other forum but haven’t gotten through all the linked content yet. I had a phone call with Sonnen because there was a statement that the entire self-consumption (including the self-produced electricity) counts towards the allowance. Only when I specifically asked about it on the phone was this confirmed to me. Now the offer isn’t as attractive as before, and I have to calculate carefully whether it’s worthwhile. Because the topic of taxes also came up, the advisor sent me the link. Of course, the post is from Sonnen, but it helped me a bit to better understand the topic. I will continue to inform myself further in the other forum, but now I understand quite a bit right away.

Whether the tariff from Sonnen is still worthwhile, I have to see. Most electricity is produced in the summer months, but consumption is lowest then since the heating only produces hot water and not much light is needed. In winter, when photovoltaic hardly generates any electricity, I need more.
According to the databases, one can roughly estimate that the consumption in summer will be 2,100 kWh (air-to-water heat pump 600 kWh + 1,500 kWh general electricity). Thus, about 4,500 kWh of the allowance remains. In winter, consumption is probably about 5,900 kWh (3,400 kWh for air-to-water heat pump and 2,500 kWh general electricity). So I would have to pay for 1,400 kWh additionally. Without Sonnen, I would have to draw 5,900 kWh, or am I wrong?

What could naturally upset my calculations here is if, for example, I use an air conditioner in summer or at some point in the future charge my car. But then I can just cancel the tariff. My current questions are:

1. Is the Sonnen Community still worthwhile? Is it maybe worth a try and cancels if necessary?
2. If (1) no, then the question about the battery. It is pointed out that it is not worthwhile. So I will read up on it.

I see the whole thing much more critically now and therefore wanted to thank you here for all the information and tips! Since I haven’t signed anything yet, I have to keep informing myself.

Just a simple calculation with the SonnenFLat 6750. Without taxes, simply with your numbers (which I find exaggeratedly high) and my system (10kWp, south orientation, WestSaxony).

Without SonnenFlat:

8100kWh consumption, realistically about 30% self-produced, means 5670 kWh from the grid and 2430 kWh self-consumption.
The system produces about 10,000 kWh per year with 0.10 cent feed-in tariff, minus the self-consumption
7570 kWh feed-in.

5670kWh * 28Cent/kWh = ~1600€ electricity bill
2430kWh * 28Cent/kWh = ~ 680€ saved through self-consumption
7570kWh * 10Cent/kWh = ~ 750€ feed-in tariff

Deficit just under 170€

Sonnenflat

With Sonnen you then have 6750 free, so you still have to pay for 1350kWh at 23 cents from the sun tariff

Deficit just under 310.50 € + 12*20€ (membership fee) = 550€

The deficit above must of course be €850 and not €170. This leaves an advantage of €300 for the Sonnenflat. However, this does not take into account the investment you additionally have to make for the battery storage.

I would leave it and stick to the principle keep it simple.

Thank you for the list. My assumption was similar, although I did not consider the realistic consumption of 30%, but tried to reach the goal based on consumption databases and assumptions.

In my opinion, the 300€ do not take the following things into account (+ for positive / - for negative)
+ Rising electricity costs
+ Increased depreciation (approx. 1,000€ instead of 500€)
- Taxes
- Increased consumption due to an air conditioner in summer. Assuming I operate the air conditioner with the self-produced electricity, so that the 30% might maybe rise to 40-50%, then the "flat" becomes completely unattractive.

From a purely economic perspective, the risk that there will be no advantage is relatively high. But I have also read that the ecological aspect must be taken into account. If you have a storage system, you use self-produced electricity at night, even if it is more expensive. But then you do not use coal power. I am not saying now that everyone should consider this and therefore get a storage system. But it is an argument on the pro-storage side. We just do not yet know how highly we should rate it, because such a battery is not exactly the best ecological choice either.

The fact is, and I thank you all for this, that the Sonnenflat is not as lucrative as previously assumed. You have really pointed out very important things to us, and where we definitely wanted a storage system with the Sonnenflat in the past, it no longer looks like that. As I said, thanks again for the "help" and the time taken!

From a purely economic perspective, the risk is relatively high that no advantage will arise. However, I have also read that the ecological aspect must be taken into account.

Counterargument: You take away the other person's surplus solar power during the day and store it in your battery with energy losses (and financial losses) to use it yourself at night. But does your higher self-sufficiency currently have an ecological benefit? I think not at the moment, as long as the photovoltaic electricity is also consumed during the day and wind power or similar does not have to be reduced because of it. The battery also has to be manufactured and later replaced. This is purely about the battery, not about the flat rate. The latter does not change the physics. Admittedly, I have not dealt further with the ecological aspect of batteries. More modules are certainly always sensible. Thanks for the feedback on the considerations about the solar flat rate.