Sidereal Exalted, in 2nd edition Exalted, don't appear to have a clear cap on the number of dice they can add to their pools with charms.
The section on Excellencies is only moderately clear -- they can add their Essence in dice, their Essence in successes, and spend motes to reduce dice pool penalties seemingly without limit.
However, there is no explicit cap on dice pool adders anywhere in the 2nd ed Sidereals text. 1st ed Sidereals is explicit about the cap being the Sidereal Exalt's Essence score, except for Martial Arts.
I'm inclined to use the 1st ed rules here, but I'm worried that I'm missing some subtlety of the 2nd edition rules.