Can I have multiple suppliers on one connection at the same time?
Per connection (EAN) one main supplier for delivery. For feed-in you can since 2024 choose a separate provider — the "decoupling" of supplier/feed-in buyer.
The Energy Act 2024 introduces "decoupling": your consumption supplier (where you BUY power) no longer needs to be the same as your feed-in buyer (where you SELL solar power). From 2024 you can choose different parties for delivery and feed-in — useful if your supply contract is cheap but you can get a better feed-in tariff elsewhere. Per EAN there remains one MAIN supplier for delivery administration and billing, but you can split contracts. Practically: ask both parties for their "decoupling" offer and watch for connection fees + admin charges.