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New Concept Tire Could Recharge Car Battery
randomErr writes Goodyear Tire showed off its new BH03 tire that can partially recharge your electric car while driving. At the 2015 Geneva International Motor Show a new concept tire was displayed that uses heat generated while driving and converts the thermal energy to electrical power. The triple inner tube design changes pressure to maximize electrical output while adjusting to the road conditions.
A theory that ignores friction isn't especially interesting in this context.
Rolling friction is a pretty small contributor to energy loss for a moving car. Of this initially small amount of lost energy, some heats the road, and some heats the tire. As someone else observed below, the change in tire temperature is typically around 30 F, or 15-20 C, much less than a 10% change in absolute temperature. That means that a perfectly efficient heat engine could reclaim at most 10% of the thermal energy from the warm tires. In practice, the efficiency would be lower still.
Here's an infographic breaking down energy loss for an internal-combustion vehicle. Even if we assume that the electric vehicle has zero engine loss, rolling friction still represents at most maybe 20% of your energy loss. That means that you'd be reclaiming less than 2% of your total lost energy. In practice, considering the efficiency of the recapturing engine, it would probably be well under 1%; considering the added weight and mechanical loads of the recapture equipment, you might well end up losing net efficiency.
I'm not an engineer, but I have a basic understanding of thermodynamics. This story appears to be pitched at people who don't. If the engineers behind this want to convince people who know anything about physics or engineering, they're going to need something a lot better than this press release.
This is actually relevant to the OP because the biggest bang for the buck in capturing wasted energy in modern electric cars like the Tesla is the inability to do full regenerative braking in the winter when the battery is too cold to receive the full charge rate. When the temperature is low regen braking in the Tesla is limited (ranging from almost nothing up to the full 60kW) based on how cold the battery is. The car actually makes strategic decisions about when to spend power to *heat* the battery because the energy put into warming the (large) battery mass will at some point be more than outweighed by the gains in regen braking recouped energy.
It must be very frustrating for the Tesla engineers to have a 60kW "free" energy source and limit it because the batteries can't take the charge rate. It seems naively like that energy could be put directly into heating the battery, but I'm sure there are a lot of engineering issues (you probably can't just dump 60kW into a point heating source, etc.)
So, solving *that* problem would probably make Teslas 20% more efficient than they are now in the winter... and that would add up to a *lot* of energy.
The Geneva Motor Show has always been full of stuff that looks cool but can't possibly work. "Concepts" which are nothing more than bad sculpture. It is neither engineering nor art.