Sorry for the downer, KS, I was having a very boring day.
This is much more interesting to think about.
I got out an old book that I keep because the ideas in it just always seem new. J.E. Gordon, "Structures" for anyone who is interested by the stuff below. This guy understood the design and construction of - everything. He invented honeycomb panels, and while he seems too modest to admit it, I think he played a major role in the development of structural fiberglass materials. In the book he wrote something that I will remember forever about choosing materials, and the relative merits of "old" materials versus "new" materials.
The book lists the relative "structural efficiency" of many common materials. Here are a few examples below. I've ordered them by "newness". Starting with carbon fiber, only about 50 years old, and end with concrete, used extensively by the Romans.
| Material | Stiffness (E)
Young's modulus
(GPa) | Density (rho)
(gram/cc) | Structural
Efficiency
E / rho | Cost of
production
(tons of oil, per ton) | Economic
Efficiency
E / rho / cost |
| Carbon-fiber | 200 | 2.0 | 100 | 100 | 1.0 |
| Aluminum | 73 | 2.8 | 26 | 6.0 | 4.3 |
| Steel | 210 | 7.8 | 27 | 1.5 | 18 |
| Spruce | 14 | 0.5 | 28 | 0.03 | 933 |
| Concrete | 15 | 2.5 | 6 | 0.1 | 60 |
I like to get out this table when I feel like shaking peoples beliefs about how "good" the "modern" materials of today are. Every material can be chosen for its strength, or its lightness, or its cost, but often it's hard to picture how the factors relate to each other. So why not try a simple division of one into the other?
Carbon fiber starts out looking like a winner, but finishes badly as the worst in the list. Why? There is an enormous amount of energy invested in making it before it can be used. Not only in the chemical factory but also at the shop using it, considering the storage (refrigerated) processing (climate control) waste (about 33%) and so on.
Metals are a bit better and it looks like they will be the dominant material of everyday technology for a very long time to come.
But standing above them all is wood. For some reason, simple, humble wood can stand its ground, considering both the energy budget and the structural efficiency of its competitors. The more the cost of oil goes up, the better wood looks.
I could have included plastic or fiberglass or silicon/boron fiber composites but the conclusion is about the same. Perhaps for fun I could try to add carbon nanotubes (invented after JE Gordon's book was published) to the list, but I'm sure the cost would be staggering.
Gordon doesn't get into the recycling of the materials, a factor that gives metals an advantage, and makes carbon composite look even worse. Wood comes out even in that regard because it can either be burned or sometimes re-used, but nature will always put the resulting waste to use.
The "invested energy" in any product can be an important consideration in its "greenness". For instance, a wall made with steel studs, compared to the same thickness wall made with wood studs, compared to another wall made with structurally insulated panels (SIP)'s all have very different amounts of energy invested in their production, which would be taken into account in the evaluation of a LEED building for example.
We can do the same with our wind turbines. Not all of us are greenie-weenies, but many of us do recognize the value of keeping our footprint on the earth as small as we can. If we intend to build our DIY wind turbines with materials that have enormous amounts of energy embodied in their materials, and from them gain only a few kiloWatt-hours, then can we really say we are "saving energy" or "producing it ourselves"?
I realize, this is way more than you asked for, Yianie.
{professor know-it-all = /end}
