davep wrote:I don't necessarily agree about that, as a liquid fuel that can fuel a tractor is far more useful than the same amount of energy stored in plants, for example.
My point is that you have a more efficient energy transfer if the same biomass is burned to generate electricity and run in an electric tractor than if it's distilled and burned in an ICE tractor.
The system can get very efficient with reverse flow heat exchangers and suchlike,
That stuff never happens in the real world and real vehicles...
but the main point is that you still have as much protein and minerals as you had before. All that is taken out is carbohydrates that are gleaned from photosynthesis. This is important in that it doesn't in itself actually deplete the soil
Only if you dump the stuff back onto the fields, which means more fuel being burned to spread it.
and the distillers grains can still be used on farm. Also, the CO2 can be used for algae to feed a fish farm, or to bump up production in greenhouses etc. I agree that there would be little point in making ethanol if it wasn't part of an integrated farm where the 'wastes' were used as inputs to other processes.
I suppose if you have a crop which you plant anyway to feed your livestock, and you distill it first to get the ethanol, it might make some sense, but it's really more efficient to just feed your livestock on grasses that you don't have to plant in the first place. Corn fed livestock is pretty inefficient. I just think they are trying to paint a prettier picture for ethanol than really exists when you look at all aspects of it.