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Strawman tactic
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Posted by Reality (more from Reality) on Fri, 15 Jun 2012 03:46:58 Share Post by Email
In Reply to: Re: conversion is quite efficient....., Mark from Toronto, Thu, 14 Jun 2012 21:12:09
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I gave 3 reasons why the kinetic energy available for recapture is 50% or less, what makes you assume I think 2 of the 3 are not contributing factors? The passive wheels take a cut into the energy available because they have brake pads there. If you are driving hilly route, rear wheel braking while going down the hill has to be non-trivial in brake force distribution because otherwise front wheel braking alone would spin the car in many situations.

Sure, I believe you drive up and down the hill, stop-and-go all the time, and never use more than 25% of your vehicle braking capacity, and hardly ever needing to coming to a full stop (regenerative braking can't do full stop on its own). Pigs fly too, and I was born yesterday.

Drive motors have to deal with even wider rpm range than the alternator, which is strapped directly to the ICE engine. That means, regeneration efficiency is probably comparable to and likely lower than alternators.

The 33-50% regeneration quoted for Prius further supports my contention. That's the first ratio, percentage of mechanical energy available for regeneration before it is turned into electricity, before it is stored in chemical energy, before converted back to electricity, before driving wheels again. In my earlier analysis, I assumed the upper limit 50% for this stage.

Where is your earlier assertion about 85% efficiency for the overall system coming from? Overall efficiency is the product (multiplication) of all stages, not average of all stages.

Regenerative braking technology is certainly not in its infancy. It has been used on railways since the 1930's. There, the percentage of energy available for recapture is much higher because the wheel friction on road surface is much less, and trains literally rarely have to come to an unscheduled full stop. Regenerative braking there is used to control trains going down hill for tens of miles (after having climbed for tens of miles). The energy captured there is often fed directly into the local electric grid because the trains run on fixed routes and are wired into the grid.

5kW gas turbine is still 5kW, or about 7hp. That makes for a car that can sustain a top speed of about 30mph, if that.




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