Is preparing for photovoltaics in new construction sensible?

The net payments of the EVU are added to the taxable income. The sales tax is initially paid monthly to the tax office. Later quarterly or annually. The VAT paid to the installer for the system is refunded as input tax deduction by the tax office. Deadlines for submitting the invoices must be observed here. One also then receives a second tax number as a small business owner. Then one still pays VAT on own consumption for the first few years. However, I have not yet researched to what extent the system can be depreciated in a profit-reducing manner. Mine has only been in operation since the beginning of the year. Ergo: the possibilities of various large corporations to simply no longer have to transfer anything to the tax office do not exist for us small business owners. But as a rule, the photovoltaic system amortizes itself at around €1,000 net / kWp after 11-12 years. The bigger the better!

But as a rule, the photovoltaic system has paid for itself after about 1,000 € net / kWp in 11-12 years. The bigger, the better!

Thanks also for your explanations!

To what extent the system can be depreciated in a way that reduces profits, I have not yet researched.

With the declining feed-in tariff, this is no longer quite so easy. For income taxes, one must be able to provide a so-called total surplus forecast for a profit-reducing consideration of their commercial activity. Simplified, this is often referred to as "hobby activity." Currently, there are various tricks for how to manage this from an income tax perspective, despite high depreciation of the system, but this would go beyond the scope here, and a forum should not and may not replace legal advice. It should be mentioned here that the tax authorities have increasingly focused on this issue after it was neglected for years.

In contrast, no such forecast must be achieved for VAT. There is currently even a bonus here, in that you can have the full input tax amount for the battery storage reimbursed, even though the storage is 100 percent privately used. The prerequisite is that the purchase is related to the photovoltaic system.

Details should be clarified with a trusted tax advisor, at least for the year the system goes into operation. The following years can then also be managed on your own. As a small tip, if the system has less than 10 kilowatts of power, it is exempt from trade tax. So don’t let your tax advisor “sell” you a trade tax return (in particular, you are also far from the exemption amount).

As a small hint, if the system has less than 10 kilowatts of capacity, it is exempt from trade tax. So don't let your tax advisor "push" a trade tax return on you (especially since you are also far from the exemption amount).

Does the 10 kWp limit still apply here currently or was that only the case until the end of 2020?

Does the limit of 10 kWp still apply here currently or was that only the case until the end of 2020?

You are probably confusing two things here.

The removed limit refers to the Renewable Energy Act surcharge on self-consumption.
So far, only systems up to a size of 10 kWp were exempt.
Now the exemption applies up to 30 kWp.

The size I mentioned relates to trade tax.
The following exemption provision was added to the law in Par. 3 No. 32 GewStG:

"if their activity is exclusively limited to the generation and marketing of electricity from a solar system installed on, at, or in a building with an installed capacity of up to 10 kilowatts."

Thus, this now definitely circumvents the compulsory membership of traders in the Chamber of Industry and Commerce (IHK).

The 10 kWp are irrelevant for trade tax as they are well below the mentioned exemption amount. The 10 kWp are relevant insofar as with larger systems there is a cap of 70% of the feed-in; the system is strictly throttled to 70% of its nominal capacity. Furthermore, you receive a slightly lower remuneration for the feed-in exceeding 10 kWp.

Photovoltaics was one of the few services where I was able to get sufficiently many offers. Most wanted to sell me 9.85 kWp with a 10 kWh storage. Best with a cloud included. Together then for around 22-24k net. That is nonsense. Energy is produced on the roof and not in the basement. I then installed a system with 27 kWp capacity without storage for 24k. 17 kWp S/W, 6 kWp S/O and the rest N/O. Today I would go full 30 kWp. On a cloudy winter day I can easily supply the heat pump with it from 8:30 to 4 pm. In the afternoon, when my 17 kWp on S/W are in the light, I raise the flow temperature a bit and buffer into the screed.