I've tried going through an osan fight without letting my sigils tick, while using e lix. At 12k ish energy the regen doesn't come close to covering my e consumption and I have to sigil several times (4165 e per tick). 246 energy from firebolt, 619 from firestorm, 490 from shards, 348 from attune, and 246 from lure.
I haven't bothered calculating, but I'd imagine I use about 20-25k energy per 3 minute period. It was much easier to keep my dps druid's energy up because there was sufficient time inbetween casts to sigil
Level 220 mage- InnerCircle of Rhiannon
Necro, proteus, unox kills http://www.celticheroes.net/profile.php?hero=runvs