Waiving feed-in tariff, always feasible? Storage price?

Your problem was the tax return, wasn't it?!
You don't have to give up the feed-in tariff. You can receive it without having to submit a VAT return.

Regarding the battery, you were already informed that it is economically a total loss at that price for the size. Or do you want it more for ideological reasons and don't care that you're burning money with it?

Cloud can be quite nice. I use a cloud plan. But for that, you have to feed in again; otherwise, cloud usage cannot be charged.

Thanks for your numerous answers! So to sum up: I can voluntarily waive the feed-in tariff. I assume I report this to the municipal utilities. Then I give away my surplus. Do you have an opinion on: storing surplus in a battery or cloud? There are different opinions about this.... I find the idea of the cloud very attractive. But I am an absolute layperson in this field.

You’re overcomplicating things. You register hobby activity (this concerns income tax). You register small business regulation (you have nothing to do with VAT, you get the feed-in tariff). This gives you the minimal effort you can’t avoid anyway. These are 2 forms you have to fill out, nothing rocket science.