Photovoltaics at any cost - current situation and offers

I would be interested in the calculation that makes the storage a good investment in summer, especially with 7 kWh for almost 7,000 EUR?
It fills up in summer in no time. And then? Does one consume an average of 7 kWh at night in summer? Because if I fill the storage fully once at the beginning of June and then only draw 1-2 kWh at night, then that makes no sense.
About 2/3 of the photovoltaic energy is "generated" in the 6 warm months. In the 3 mild and especially the 3 cold months of the year, the photovoltaics are at best enough to cover the daily demand, usually not even that in the cold months.

Or you install an air conditioning system to consume your own electricity in summer. But then you no longer need the storage.

You can take a look at the load profile of a heat pump-heated house anytime. You need the most electricity exactly when photovoltaics deliver almost nothing anymore.

In my small semi-detached house with 2 units, ground-source heat pump, and 4 kWh battery, I have a withdrawal (in the period where nothing is generated) (average) of about 5-6 kWh. My battery is therefore a bit too small to be optimal for this case.
In the bad season, however, the battery sometimes deactivates completely! to avoid "unfavorable" cycles.

You can certainly take a look at the load profile of a heat pump-heated house. You need the most electricity exactly when the photovoltaic system hardly produces anything anymore.

Yes, that's true. Often, only 150 cycles remain. If you exclude the special cases (DIY battery, it fell from the truck of a brother-in-law’s acquaintance, and other jokes), it is practically impossible to calculate a battery economically (!) profitable. Especially not when considering current electricity prices. It gets particularly difficult with heat pumps. Because with a heat pump, you have the option to schedule hot water production during the day, or in winter you use the photovoltaic yield directly anyway, and in the transitional period you can even increase this by planning a daytime increase. This results in fewer cycles per year for the storage – the payback period extends. Usually to a number of years in which you no longer trust the battery to hold out. But it always remains a calculation with many unknowns. Just the losses during storage and retrieval alone cause a lot of head-scratching. However, I have been reading a lot lately, also in the specialist forum. My conclusion is, if I had invested the money for the battery in more modules, it would certainly have been more economical. But economic efficiency was not the only deciding factor.

I have in my small semi-detached house with 2 residential units, a brine-water heat pump and a 4kWh battery an extraction (in the period where nothing is generated) (average) of about 5-6kWh. My battery is therefore somewhat too small to be optimal for this case.
In the bad season, however, the battery sometimes completely deactivates! to avoid running "unfavorable" cycles.

Would you like to explain that in more detail? So what do you mean by 5-6kWh from a 4kWh storage?
Is that per day, per week, per month? What does a period where "nothing" is generated mean?
How large is your photovoltaic system?

Battery DIY

Do you have more info here regarding legality or practical issues?

Do you have more info regarding the legality or practical problems?

No, I've only read several times that it is done. But you can find information about it on the internet. This site is not the only one that gathers people interested in a particular topic for exchange. And there is also one that deals specifically with the topic of this thread. You can find quite a bit related to your question there as well.

Do you have more info here regarding the legality or practical problems?

The same practical problems you have when driving a homemade car. Nobody accepts it, nobody insures it, and if something happens, you are left alone with the damage and consequences.