In the system I’ve homebrewed the wizard memorizes the daily allotment of spells. But to cast a spell they must gather the spell points from the land or other source. I have a chart based on terrain that explains how many points the caster gets. I refuse to allow a caster to gather spell energy during memorization. I consider it contrary to the intent of the world. An alternate source caster Has to roll on a random chart per spell to see how close the grey is or how much shadows are present to access the black. The randomness makes it more dangerous and the black and the grey damage a living body when channelled.
Also the spell is not forgotten so a spellcaster standing in the halflings forest potentially has an nearly unlimited supply of energy. It really tempts the caster to go nuts with power my system.