Install photovoltaic power storage yes or no?

What kind of funding with 40% for storage is this about?

If you want to be more independent from the grid and more self-sufficient, I would take a storage, even if it currently doesn't make much sense (costs)

A nice idea!
Unfortunately, only very few storages also work as a "UPS" when the grid is down/has disturbances, so you are not more independent than without storage.

If you choose the cost/benefit factor, when the system pays off, then I would (if it were to be a KFW40+ house) choose the storage as small as necessary and fill the roof as much as possible.

I fully agree here.

Lower Saxony Photovoltaic Funding.

What I don’t understand, please enlighten me, why should so many modules be put on the roof? You only get a few cents feed-in tariff. That’s not worth it at all anymore. And a 7kwp should always be more than enough for self-consumption?

The storage is the more sensible investment, I thought.

You do not consume the most electricity at the time when the photovoltaic system produces the most electricity, but mainly during the off-peak hours (6-9 and 16-22 o’clock). The larger the system, the more electricity you consequently generate during these off-peak hours. Ergo, you can then use your own electricity during this time. With the current system costs of about 1,000 euros per kWp, this also pays off with a 7 cent feed-in tariff (return with equity capital about 2.5-3%). The saved self-consumption is practically a bonus and increases the return accordingly.

From my own experience, I can say that 1kwp to 0.8kwh storage is very sensible.

So, 10kwp to 8kwh. Winter is basically lost anyway, and in summer the storage, no matter how big, fills up too quickly. Of course, there are also moments in summer when the photovoltaic is too small because it is cloudy, the storage is empty, and the house consumes 9kwh. Already experienced all of that.

So the topic is far too complex to give advice here.

What is certain is to fully equip the roof, and 0.8kwh per 1kwp is fundamentally sufficient.

The question of the economic efficiency of an electricity storage system fundamentally depends on the assumption of charge-discharge cycles. One can calculate it well or poorly. The discussion has become boring by now. The electricity storage system makes sense as an intelligent system that integrates existing storage and consumers. The battery storage buffers power peaks with self-generated energy during the day and lasts through the night; surpluses are directed into the e-vehicle and into the hot water storage. (The latter even extends the lifespan of the heat pump since it hardly needs to switch on in the summer anymore.) And then you can also control and switch other consumers according to solar yield - for example, the dryer or whirlpool or... There is not much left to feed into the grid, because the yield is mostly consumed on-site. Replacing expensive electricity from the supplier with cheaper own electricity is the more interesting business model than hunting for feed-in tariffs. The latter is just a nice extra.

Addition to : The rule of thumb is good. Also make sure that the system has a high charge-discharge power. Without that, it’s all nonsense in practice. We are currently switching over and then have a system with 8kWh storage and 8(!)kW charge-discharge power. Then you can even cook on the induction stove in the dark with your own electricity, and the heat pump for hot water simply stays off for months....