[extropy-chat] Nuke 'em

Eugen Leitl eugen at leitl.org
Sun Oct 23 21:01:39 UTC 2005

On Sun, Oct 23, 2005 at 12:13:07PM -0700, Damien Sullivan wrote:

> A while back I read _Why Big Fierce Animals Are Rare_ by Paul Colinvaux, an
> ecologist.  IIRC he said something like most plants get 8% in their growth
> phase under optimal conditions.  They're all using the same chloroplasts,

No, actually they aren't: http://www.biologie.uni-hamburg.de/b-online/e24/24b.htm
E.g. Miscanthus is a C4 perennial grass.

> after all.  Algae are just always in the growth phase.

Problem with algae is that they don't grow on the field, and produce
dry biomass. I can't emphasize enough this simple fact.
> More to the point, he said plants' energy efficiency in dim light is often
> much higher, such as 20%.  This could be "evolved assuming shade" but could

I don't see why everyone is hypnotised by efficiency. It's just a yet
another factor in the total life cycle computation. A dirt cheap 3% efficient
polymer photovoltaics film can be much cheaper than fossil fuel sources,
something you can't expect from a 35% efficient InGaP/GaAs/Ge.

> also be a sign that energy isn't the limiting factor.  And here's a question:
> to make a plant growing at high noon grow faster, do you increase the
> intensity of light, or increase its CO2 concentration?

Mu. I would not want a plant in the cycle in the first place.
> And what are the thermodynamics of getting CO2 from 300 ppm to 100,000 ppm or
> whatever the C concentration in biomass would be?

Plants are nanotechnology, so it works for them. Unfortunately, trees have
no power sockets in them, nor do they grow on demand whatever you just
ordered online.
> > they are losing the energy in the green photons (which is significant).
> OTOH, we might expect on evolutionary grounds that if most photosynthesizers
> aren't using all the photons then there isn't much gain for them to do so.

On evolutionary grounds, we can expect that critters are caught in a local
minimum. Can you imagine an evolutionary process resulting in nonprotic 
photochemistry? Why are plants not velvet black in the first place?
> > Ultimately the problem is that the standard photosynthetic harvesting
> > apparatus is not using the full energy of each photon.  Its delivering
> Which is why a solar heat engine can produce electricity better than a
> photovoltaic, at least in direct light.

Uh, I'd like to see your Stirling beat 35% efficient (theoretical
plateau around 55%) solar cell.
If you cheat using mirrors, you need to include production, maintenance, 
cleaning and tracking. Then the Carnot efficiency doesn't look so good.

In comparison, rectenna arrays in solar spectrum range can be quantitatively
efficient http://www.nrel.gov/docs/fy03osti/33263.pdf leaving any Carnot
process based device smoking in the dust.
> > If you study the light absorption frequencies of various photoplankton
> > you will discover they are very precisely tuned for the light energy
> > which reaches the water depth they inhabit.  Land plants are not so clever.
> Any references to read more in?

Eugen* Leitl <a href="http://leitl.org">leitl</a>
ICBM: 48.07100, 11.36820            http://www.leitl.org
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