[Greenbuilding] re OT What car?/Reuben

[tom]

On May 5, 2008, at 6:12 AM, "Donald Eyermann" <zeroenergy at cox.net>  
wrote:

> And if recharged by
> the sun....how do you quantify an efficiency rating when you're not  
> using a
> man made fuel commodity?

You use Howard Odum's 'emergy' systems analysis.

Energy Basis for Man and Nature, Odum, H. T.  1976.

It is a shame, and to our peril, that more people are not aware of  
Odum's work- his emergy system analysis is the most complete  
accounting of energy use/flows, etc. that I've ever encountered.   
There is nowhere to 'hide' in it.

The amount of energy the earth (or a given location on the earth)  
receives from the sun is a measurable quantity- start from that and  
you can quantify an efficiency rating.

> We live on a planet with inexhaustible geothermal energy orbiting  
> about a
> star that emits unlimited energy every day.

Alas, neither of these points is true.  It may be abundant, and we  
may never have the capacity to use it all up, but in the long-view of  
geological or solar-system lifespan everything has a limit, including  
geothermal energy.  And our sun does not emit unlimited energy every  
day- a star is basically a nuclear fusion reactor and that process  
produces a measurable amount of energy per given time period, etc.   
And a star has a life-span, it is not eternal.  Additionally there is  
a specific, limited average amount of that energy from the sun that  
we receive on the earth, and of that amount there is a much smaller  
amount that we are able to harness and use.  We can incrementally eke  
out slight improvements in the efficiency of harnessing the sun's  
energy and transforming it into forms of greater use to us, but it is  
an extreme of hubris to not just hope for, but to actually expect  
that we will achieve an efficiency through technology greater than  
the millions-year evolution of photosynthesis.  When a true, full  
energy accounting is taken (every single input, nothing hidden or  
'externalized'), nothing we have ever devised comes close to the  
efficiency of a tree at capturing the energy from the sun (and  
converting it into forms useful to other forms of life on earth).