A Solar Powered United States of America

Version 0.91
August 3, 2002

Robert J. Bradbury
© October 2001, All Rights Reserved
This paper is still being written

Introduction

The United States of America maintains a very high standard of living with the world's 2nd highest per capita energy consumption [TG01] of ~350 million BTU/person.  It is heavily dependent on large imports of foreign oil [DOE01].  It seems logical to ask how developing technologies might be used to address this problem so it can free itself from this addiction.  If one allows for the fact that bacterial genomes can be engineered for production of energy sources then the question arises as to what energy source would you produce and how much land and other resources would be required to produce it?

The ideal energy source would of course by hydrogen gas (H2).  It burns cleanly producing no greenhouse gases.  However the country lacks a transport infrastructure for H2.  In contrast, the country already has a very large infrastructure for the transport of natural gas which is primarily composed of methane (CH4).  Provided the carbon in methane is being harvested from the atmosphere, its use as a energy source would essentially be neutral from the perspective of greenhouse gas concentrations and global warming.

Goals of this research:

  1. to eliminate U.S. Oil (& Gas) imports so we have greater freedom about where to send the U.S. military;
  2. to migrate to a sustainable energy supply, either one based on hydrogen or where any carbon released into the atmosphere is recycled;
  3. to provide a more efficient food production capability because world-wide population increases aren't going to stop soon;
  4. to get us closer to the point where the solar power collected by a family's home can supply a significant fraction of their residential and transportation energy requirements;
  5. to do all of these things at a lower cost than current solar approaches (e.g. solar cells that require building more factories and large energy investments in producing the cells themselves);
  6. to allow a "fast ramp" so this could be implemented within 10-15 years (this requires one keep the infrastructure requirements as low-tech as possible);
  7. to provide technologies that can be utilized by low-tech countries to provide increased employment & decreased energy and food costs contributing to an increased standard of living.
An essential component of this is to try and allow the use of the existing natural gas pipeline infrastructure so that we can more easily transition to a fuel-cell based power & transportation system. (At this time the problem of having to build a hydrogen distribution system is a major factor blocking the shift from a carbon based energy supply to a hydrogen based energy supply.)

This paper attempts to make the case that this can be done with "solar bioreactor ponds" and/or rooftop solar collectors that cultivate bacteria that are engineered to produce CH4 and eventually H2 (as the hydrogen transport infrastructure gets manufactured).

Available Land & Energy

The first question we have to consider when envisioning a solar pond bioreactor energy production system is "How much land is available?" This involves several considerations.  At this time, one would generally not want to utilize land that is being productively used for the production of food resources.  One would also not want to utilize land which is subject to freezing conditions for a significant fraction of the year (SRS require liquid water).   Finally, the relative ease of developing solar ponds will depend in large part on how easily the land can be converted into flat structures.  Rice paddies in mountainous terrain in Japan or China demonstrate that even very uneven terrain can be converted into a sequences of small solar ponds.  The investment in the construction of such infrastructure seems moderately high and is likely to require a number of years.  The initial initial development would utilize large areas of essentially flat terrain where the soil  can be easily dug into solar ponds by large-scale earth moving equipment or where the construction of low-rise cement walls would be preferred on rocks lacking soil cover.
 

In the United States, if we take the 7 southwestern states with the greatest solar insolation and warmest temperatures (Texas, Oaklahoma, New Mexico, Arizona, Utah, Nevada and California  [NA01]), the combined pastureland and rangeland, less any "prime" farmland comes to 222 million acres [NRCS00].  Assuming 50% of this land can be developed for solar pond bioreactors implies that 111 million acres are available for development.  Such land, 43% of which is in Texas, receives ~1600 kWh/m2 of solar energy annually.  Assuming a 2.5% energy harvesting efficiency, this provides an energy production capacity of 6.5x1019 J/yr.  This is equivalent to 3.7 times domestic oil production, 2.8 times U.S. oil imports and 1.5 times the total U.S. oil consumption.  So it is clear that if these conditions are valid, the development of solar pond bioreactors could eliminate the need for both oil imports and domestic oil production.

Discussion of the inefficiencies of methanol or biogasse production.

Yield per acre

Note advantages over photosynthetic efficiency for corn.


United States oil consumption is approximately 19.4 million barrels per day (Mmb/d) of petroleum products.  Of this amount, only ~8.1 Mmb/d are being produced domestically while ~10.7 Mmb/d are being imported [Mac01, DOE01: Figure 3.1a].  (The balance must be supplied from natural gas plant liquids or reserve stocks).  This translates to ~3.3 billion barrels per year (Gb/y).  At the current crude oil price of ~$23 per barrel this translates into a net expenditure of ~$76 billion / yr by United States citizens and corporations.  One barrel of oil contains 5.6×106 Btu (1.4×106 kcal) so the annual energy expenditure of the U.S. on produced oil is ~587 GW (GJ/sec) and on imported oil is ~775 GW.
 

We can contrast this with the energy absorption of large areas of the United States.  The state of Texas has ~131.5 million acres considered to be farmland [WA00].  Assuming a 2.5% photosynthetic conversion efficiency, that obtained by sugarcane [dosSan97], this is equal to 710 GW of energy which is approximately equal to the energy value of imported oil.

Increasing Photosynthetic Efficiency

Cyanobacteria are capable of nitrogen fixation. There are salt-water species, e.g. Aphanizomenon, Nodularia & Oscillatoria and fresh water species, e.g Anabena, Azotobacter, Azospirillum lipoferum and Beijerinckia [MAR00, Bro91].  Many of these species are also capable of forming gas vesicles.  In particular, the genes responsible for the gas vesicle production in species Halobacterium sp NRC-1 have been cloned and studied [Das94].

Methanococcus jannaschii, another organism whose genome has been sequenced [Bul96], produces methane.  Many of the organisms that fix nitrogen, do so by concentrating the nitrogenase enzyme, which is poisoned by oxygen, in a separate cell known as a heterocyst.  This cell has evolved to lack the photosystem responsible for oxygen production.  A reasonable course of genetic engineering would be to engineer into the heterocysts, the proteins responsible for hydrogen and methane production.

Thus we have an architecture where the gas vesicle allows the heterocell to float in the water, with one cell harvesting the energy from sunlight and the other cell producing ammonia, hydrogen and methane.  Further engineering of these cells to produce calcium carbonate, would allow them to coat the floor of the effectively sealing it.

The advantage of using light to produce cyanobacteria, is that they can be harvested and fed to other organisms such as blue mussels (Mytilus edulis), ghost shrimp (Palaomonetes spp.), wood shrimp (Atyopsis spp.), American flag fish (Jordanella floridae), butterfly goddeid (Ameca splendens), Milkfish (Chanos chanos), Striated surgeonfish (Ctenochaetus striatus), Lampeyes (Procatopus) and red ramshorn snails [And00, Rhu01].  Some of these species are have commercial market value.  Noncommercial species could be converted to fish food to feed commercially farmed species such as salmon.
 

Self-Replicating Systems advantages

There are a number of advantages to constructing a solar energy harvesting infrastructure based on self-replicating systems.  First, such systems are capable of self-repair.  Proteins and other moelcules that are damaged by UV radiation or free radicals are simply recycled.  Non-self-repairing systems, such as the current silicon or GaAs based solar cell arrays do not have this property and therefore decline in harvesting efficiency over time and have a limited "useful" life.  Self-repairing systems simply sacrifice a fraction of their harvested energy to self-maintenance.  Second, such systems can easily be upgraded when improvements are made in the harvesting architecture.  If R&D produces a SRS that has an increased energy harvesting efficiency (e.g. 4% instead of 2.5%), then sufficient seeds can be distributed to upgrade the entire harvesting system within a few weeks.  Strains of solar harvesting SRS could be designed with self-destruct receptors.  Each new strain of SRS would distribute molecules that activate the self-destruct sequence allowing a peaceful "takeover" of the  solar bioreactor fixed infrastructure.  (To make this foolproof a number of redundant self-destruct mechanisms may need to be designed into each solar energy harvesting SRS "version").  Third, such systems are capable of adaptation.  The programs of the SRS can be made increasingly complex such that they change their energy harvesting infrastructure based on whether they are receiving direct or diffuse sunlight (sunny vs. cloudy days) and have an "awareness" allowing them to employ seasonal energy conservation strategies.  (In the winter during colder climates solar energy harvesting ponds should store a fraction of the harvested energy  so that they can "burn" that energy to melt any snowcover that accumulates.  A solar bioreactor pond with properly programmed SRS should be able to remain snow & ice free for much of the year in all but the coldest climates.)

Increased food efficiency

(greater amounts of solar energy into bacteria and thence to shrimp or fish)
Appendix A: Photosynthetic Efficiency

One way to look at how efficient the photosynthetic process is is to look at the energy in the photons that are inputs, and the energy in the glucose that is output:

This is somewhat different from the process of photosynthesis where the overall reaction for the Calvin Cycle is:
6CO2 + 12H2O --> C6H12O6 + 6O2 + 6H2O
This is accomplished by utilizing photons to split water:
2H2O --> 4e- + 4H+ + O2
In this case, the electrons are used to produce NADPH for use in the Calvin Cycle, while the protons are used by the ATP Synthase enzyme to drive the reaction: ADP + Pi --> ATP.  The overall energy harvesting efficiency of photosynthesis is ~28% [REF].

There overal thermodynamics for photosynthesis is:

1 mole CO2
 --> 1 mole O2
(320 Kcal/mole)
 (120 Kcal/mole)

So the gross thermodynamic efficiency would be 120/320 = 38%.  But we are more interested in the efficiency of converting light energy into chemical energy.  But we must take into account the fact that not all of the energy in incident light can be utilized for photosynthesis.  Only photons with wavelengths from 400-700nm can be utilized for photosynthesis.  Thus the maximum efficiency is 12-19%. Due to the fact that ground coverage is rarely 100% only a small fraction of the available energy is converted to biomass over much of the Earth.  The following table details the typical productivity of various types of surface areas on the planet.
 

Surface Area Type Production Efficiency
Coniferous forest 0.1 - 3%
Deciduous forest 0.5-1%
Crop Land 3 - 10%
Desert 0.01 - 0.2%
Ocean 0.13%
Earth overall 0.15 - 0.18%

Looking at the thermodynamic efficiency of producing methane,

CO2 + 2H2O --> CH4 + 2O2
.....

References

Bioreactors

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