The exported electricity is going back to the national grid via ESB Networks. You do not need to put an agreement in place with your supplier. In theory there is nothing you need to do. In practice, we would recommend contacting your supplier with your MPRN and just confirming that they have updated their systems to record that you have installed solar power. Once this is done they will have their own processes for making payment per your existing contract with them. Each supplier has a slightly different process but essentially it will appear as a line item on your bill.