What must each BA agree on with adjacent BAs regarding their Composite Confirmed Interchanges?

Each Balancing Authority (BA) must agree with adjacent BAs that their Composite Confirmed Interchanges are identical in magnitude and opposite in sign. This ensures that for every unit of power interchanged, there is a corresponding and equal negative interchange, maintaining the balance of power flow between BAs.

When one BA exports electricity to another, the importing BA's confirmed interchange must reflect an equivalent import in its records. This alignment is crucial for system reliability and stability, as it ensures that power flows are accounted for accurately across the entire interconnected grid. By doing so, BAs can effectively prevent mismatches that could lead to operational issues or stability concerns.

In contrast, the other choices do not correctly capture the requirement for confirming interchanges. Maximal capacity refers to the highest possible limit of power transmission but does not address the balance needed between interchanged values. Variable generation output could lead to inconsistencies and does not ensure that the interchanges match in signed numbers. Lastly, equal overall load does not specifically pertain to interchanges but rather to the overall demands across the system, which is a separate aspect of management for BAs.