. . . . but electricity doesn't work like that. There is no "left over" electricity. Adding anything inline as you suggest will only divide the voltage amongst the appliance and this "waste energy" device. Think of it a little like this. You have a 100 watt lightbulb, and you think, "Hey, if I cut the neutral, and stick another 100 watt bulb inline to catch the exiting power, I'll get twice the light." But what you get is two bulbs lit at half their intensity.

Now, you might be able to capture some energy from EMF generated by the flow of electricity. Unfortunately, in the home, currents and voltages never get high enough to make much use of. One could build a large coil under high tension power lines to capture EMF and convert it to electricity. At first, it appears this really is free power. Heck, everyone should be doing this, right? But, it's not. If one were to do this, it actually creates a "drag" on the power flowing though the wire, an inductive resistance if you will, which is actually robbing power from the power company. Hence why it's illegal to do such a thing.

What you should research is "POWER FACTOR." This is what really means a hill of beans when talking about the nitty gritty of waste energy, because if you can increase your power factor, you get more out of each watt you are charged for. You'll be happy to know though, that your iron (or most any resistive heat device) operates at maximum power factor. Motors and electronics, not so good. There are ways to increase power factor efficiency, but it's tricky, and the payoff is hardly worth the effort. (considering today's low Kwh rates) If you are just curios how well a certain appliance rates on power factor, there is a gizmo on the market that can tell you that value at a glance. It's called the Kill-a-Watt.

You're right that you take electricity from the power plant and it runs through your stuff and then back to the power plant. In that respect I understand how you might think it would be nice to keep the "excess" electricity.

But in reality you send back ALL of the electricty to the power plant. You dont actually "use up" electricity. YOu pay them to push the electrons through your house, the come in, the run through your stuff which powers your stuff, and then all those electrons go back out of your stuff and back to the power plant.

I should add that technically not 100% of the electrons actually make it back, but this is an analogy not a textbook on physics.