Kinda like when you draft someone on a highway, you are stealing their gas.
A radio station transmitter does not suffer greater costs when more radios are tuned in. It just blasts that energy out in all directions, and your radio picks up a bit of it. This gizmo just collects that energy and routes it for other uses.
More kinda like when you drive on a highway, you heat up the road. Clever people have embedded water pipes in sections of freeways and gathered that waste heat & put it to good use.
When your drafting on a highway you are raising the pressure behind the lead car reducing that cars drag also.
While this may be the case, it doesn't appear to be slam dunk analysis.
Some claim a truck being drafted by a car would have a slight increase in mileage. Others (I tend to agree) say any increase in fuel cost for the truck would be so small as to be impossible to measure.
Some claim a zero sum for the truck, but a true zero sum in nature is extremely unlikely.
If you have a definitive link on the point, I'd be interested to see it. Actual experiments, not jackleg engineers like me bloviating.
http://ask.metafilter.com/58487/Does-a-truck-work-extra-to-pull-a-drafting-car
Exactly. Ask ANY pro bicyclist how VALUABLE drafting is.