>> But *if* [[and it's moot depending on various assumptions in each
>> setting]] there's an overall energy loss, then using the output to
>> drive itself increases the loss per unit of output.

> So what's really messing up the equation is the external fossil 
> energy
> needed to get at the biofuel.

It's not that it's *fossil* energy per se that neds inputting - it's 
the fact (apparently) that overall the net process loses energy. If 
you consider biofuel to be an energy transport medium (as hydrogen is) 
and IF you have sources of energy elsewhere that are net energy 
positive but not accessible, then the biofuel may be viable (eg a 
methanol operated car may use solar energy produced in the Simpson (or 
Sahara) desert.. If though you are looking at the biofuel as being an 
energy "source" in its own rigjht there appear to be 'problems'.

'> That puts forward the case for nuclear
> (fission now, hopefully fusion in the future), hydro, wind, solar 
> etc to
> do that.

The arguments are that all of these (except for fusion) are in fact 
net energy negative and/or not renewable. eg Nuclear fission is 
relatively exhaustible UNLESS you go to fast breeder technology with 
(amongst other things) Plutonium as an output. Some like this option. 
It seems to me (although the nay sayers say nay) that systems that you 
mention which are essentially solar (wind, photo voltaic, solar 
thermal) can have their net returns improved with improved technology. 
For force based systems (wind. some thermal) this would largely have 
to be done by increasing system lifetimes, reducing cost or producing 
raw materials more efficiently. Actual energy conversion efficinies 
are already reasonably high (eg wind turbines). Hydro is arguably 
already near peak capability already both in terms of efficiency of 
conversion and lifetime costs. PV still has efficiency gains possible 
and new and 'cheaper' materials.

> And also reducing the demand for fuel in the first place ...

And that's another story.


    Russell. 

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