20th December 2004.
This is a draft (daft?) research idea,
not yet intended for wide circulation.
Biolectric research
Is this a naff name?
A radical idea needs a distinctive and
well-chosen name...
Motivation
- Energy consumption in the `developed world'
is not sustainable. Fossil fuels will soon run out,
and there will be an energy crisis.
It is essential that
-
sustainable sources of energy be developed; and
-
energy consumption be reduced.
This research proposal concerns
sustainable energy sources.
-
Sustainable power can come from only three sources:
from the sun; from tides; or from geothermal sources.
Of these sources, the sun is the most promising.
-
We can tap solar energy either at the primary source,
or in secondary or tertiary forms (wind, hydroelectricity,
waves, biomass).
Because the production of the secondary forms of solar
energy is inefficient, it's hard to imagine that
human energy needs can be met by wind, hydroelectricity, biomass,
and waves alone. (Here are my back-of-envelope
calculations.)
We must therefore develop solar energy.
How efficient are
electron systems in plants and bacteria? |
(Purple bacteria tutorial).
Efficiency:
Standard redox potential of a typical
photosystem spans about 800mV.
One photon with wavelength 500nm has energy
E = hc/l = 3.9 × 10-19 Joules = 2.4eV.
So the efficiency of the primary receptor is about 50% per photon.
|
|
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The most impressive solar electric convertors are the
chloroplasts of plants and bacteria. Photon energy
is caught in excited electrons, which are transferred
efficiently along a chain and used to charge recyclable batteries
(also known as NADPH) or to charge capacitors
(by transferring protons across a membrane).
-
Maybe a good way to make efficient solar convertors would
be to steal from the best: take working photosynthetic systems
and use natural selection to evolve them in the direction we require.
Biolectric research proposal
Create an evolutionary environment in which
bacteria are rewarded for interfacing to
external electrical hardware.
For example, put the bacteria in
a pot that contains interdigitating electrodes;
provide biochemical building blocks, but deprive the
bacteria of energy; thus the bacteria that reproduce
will be the ones that cooperate with each other to
suck electrical energy from the electrodes.
Add evolutionary pressure to retain
photosynthetic ability in the bacteria.
Now if we switch off the electrical power, and
keep putting in light, perhaps a little bit
of electricity will ooze out.
(Hopefully the bacteria will solve the problem
of guzzling electricity from our electrodes
in a way that uses their existing electron transfer chains.)
Now put in a new
feedback loop: measure the feeble electricity output,
and direct the
biochemical building blocks preferentially
to the parts of the pot that are
producing the most. (Perhaps use miniature pumps
driven by the electricity?)
Survival of the fittest will ensue.
After a few thousand or million generations, we
will have bacteria that directly generate DC electricity.
Hurrah!
The bad news:
This situation will be unstable:
bacterium that mutate so as
to stop feeding the meter will
outgrow their obedient siblings. A solar installation based
on these principles will therefore have to remain plugged in to
a feedback loop like the one above.
Initial circulation list: Graeme Mitchison, Mike Cates, Robert MacKay,
Erik Winfree, Sanjoy Mahajan, Seb Wills.
Credits: Robert suggested the idea of tapping bacteria directly,
instead of faffing around with biomass.
How Erik might be involved
Idea:
Make self-assembling structures that create the
interdigitating electrodes, and the feedback loop
machinery -- measuring the electricity output and
channeling resources there.