When doing preparation for a ritual, you don't have to do it all at once. So cast Energy Tap, tag aspects to add to the ritual, cast Energy Tap again, tag aspects again and so on.
Now, how you build the spell:
1) Add an aspect, unopposed. Base power is 3. +1 for making it sticky.
2) Add a second aspect. +3 power, another +1 for sticky.
3) Apply the effect to everyone in a zone. +2 power.
4) Spell has a specific requirement such as a specific time of day, an ongoing natural disaster or leyline to draw energy from or an entity helping. The book has one such factor priced at giving 2 shifts of power so -2 on the spell's cost.
Total cost is 10 for full effect unaided, 8 for 2 sticky aspects on a person or 2 fragile aspects on a zone unaided, 6 for 2 fragile aspects on a person unaided. If you do have a power source, reduce cost by 2 for every power source. So if you did the spell on a leyline, at midnight, and with one sponsor, it costs a mere 4 power for maximum effect.
The version I posted assumes one source of power and max effect. And yes, 8 shifts of power require he takes additional mental stress and consequences for casting it as well as backlash. But the point is, would you pay 2 mild consequences for +4 to your ritual if you did it directly or 2 mild consequences for +16 power by using the Energy Tap? Basically, you feed the big ritual by invoking small amounts of energy with magic instead of just your will. With you and 3 helpers you tag 8 aspects total per casting of the spell... or +16 power to your ritual. If you somehow get the full 12 helpers for a maximum circle of 13, you get to tag 26 aspects... or +52 power.
If you have a circle of 13 which are all wizards and all cast an energy tap three times for the same ritual you get to tag 338 x 3 aspects for a whopping total of +2028 power, enough to explosively rennovate a square mile of real estate. And that's why preparatory magic is terrifying.