The easiest method to collect the Energy Tank is to charge a shinespark, then jump off the ledge towards the center of the room, and spark up. The fastest way is to charge the spark while you open the red door, but you could alternatively open the door, then charge the spark through the room transition.

If you end up standing on the Energy Tank's platform after collecting it, you can run off the ledge to the right, angle down, and fire to expose the missiles, and you'll collect them. You'll likely need to stand left of the center of the platform to get enough run speed for this.