Solar_Registry is a class for storing singleton objects which are used usually for things like SQL objects and the response and request objects. Now what's interesting, is that in the new version of Solar a new configuration key registry_set was added for the Solar arch-class. You can use it to tell Solar to automatically add objects to the registry when it starts up.

He compares the two methods - manual loading and the automatic version and includes a "real world" example of loading up an SMTP object.