This is complicated legalese. "For your own use" doesn't technical exist, you are outputting your solar production into the main grid - and this is capped at 800W for grid (and house installation) safety and stability issues. You need a meter that can run backwards, but you have the right to demand from your electricity provider that they install one.
Bypassing the grid and using your own storage infrastructure is AFAIK not allowed in Germany (there are heavy taxes on electricity, that you would be omitting - similar as to how you technically are not allowed to make your own Schnaps at home due to taxing).
Last I read them, electricity tax was only applicable for sale and certain situations that involve transferring power across parcel/plot boundaries.
An entity is allowed to generate it's own local solar power for own local consumption, and for that it's perfectly fine to rent/lease the equipment/panels but you can't just tax-free buy electricity itself outside some limited situations that are to allow e.g. an apartment tower to use solar panels as cladding to then sell the power to the tenants instead of forcing every tenant to lease their own electrically independent section of the facade.
Bypassing the grid and using your own storage infrastructure is AFAIK not allowed in Germany (there are heavy taxes on electricity, that you would be omitting - similar as to how you technically are not allowed to make your own Schnaps at home due to taxing).