Yeah, checking wikipedia the efficiency of TEGs are ~5-8% so I guess that is why this idea isn't used. It would be hard to justify the cost / weight at that limit.
There's got to be more to it than that. I would suspect that energy recovered over the service life isn't enough to more than break even.
If up front cost and/or weight/packaging were the issue you'd see them employed at least occasionally in marine/rail/off highway/stationary industrial applications where physical trade-offs aren't as big of an issue and the up front cost is can be more easily amortized over the long service life of the equipment it's tacked on to.
If up front cost and/or weight/packaging were the issue you'd see them employed at least occasionally in marine/rail/off highway/stationary industrial applications where physical trade-offs aren't as big of an issue and the up front cost is can be more easily amortized over the long service life of the equipment it's tacked on to.