From the answers to the following question (1), I gather that it is theoretically possible to operate an alternator / dynamo / generator:

1. Without permanent magnets.
2. With an external energy source for the electromagnet which substitute themselves to the permanent magnets.
3. Even without an external energy source, provided that the current needed for the electromagnets can be tapped from the energy provided by te device itself (via either a temporary storage (battery or capacitor) or via the use of the residual magnetism of the electromagnets's cores).

***My question is:***

Is there a way to derive theoretically the proportion of the current (or of the power) produced by the alternator which is lost (has to be re-injected) in order to supply the electromagnets of the device with power?

In other words, at what costs in terms of percentage of the output does the choice of operating an alternator without electromagnet come?

(1) [Source of initial magnetic field in an alternator](https://electronics.stackexchange.com/questions/519621/source-of-initial-magnetic-field-in-an-alternator?newreg=416f0496f38c47749932c06dc2e76676)