Okay, so they're tapping into the ley lines to power their magic, but it requires energy to tap into energy? 

So does this require a ritual, say dancing, to draw in that power from the ley lines, perhaps to fill a reservoir  that can then be tapped to power the spells? Is this like an external reservoir, say an altar or large stone, or a gemstone one might wear, or some internal space one can use? Some call it a core?