Equipment amortizations and the time value of money engineering economics must be included in engineering analysis. All the "plant energy" we have now is simply an energy transfer mechanism or energy carrier, not a fuel. And given the energy cost in producing it, all current plant energy carriers are energy negative (except for small scale fuel collection where the fuel is burnt directly to provide heat). Current analysis puts the price at around four times higher than that of oil - which is a much higher density fuel source, and thus preferable. Most uses of the nature you propose suffer from thermal inefficiencies (Carnot Cycle) and produce CO2 - which contributes to Greenhousing. We have nuclear power, we should be using it much more than we do. It is one of the smallest polluters on the planet. That way the land can be used to trap CO2 (which is what plants are really good at) in an attractive fashion. I prefer to see land in its "natural state".
I would in any case be worried about increasing the amount of low-level (i.e. unusable) heat energy on earth if we discover a cheap new source of energy without discovering a way to get some of it away from our spaceship (earth). If you want to see renewable energy, then (as you hinted) a vast space based biological or microstructure collector beaming power back to earth as laser or microwave energy is the way to go. Hopefully replacing existing CO2 sources of energy rather than increasing energy usage rates until we solve the "waste-heat" problem. In the biological system, the organisms used might produce electricity directly, or would produce Hydrogen which would be used in a fuel cell before being re-electrolysed by the organisms (closed system). In a microstructure each microstructure would act as an antenna to tune into light and like a crystal radio produce power at its terminals. It is only in space that the efficiencies of this system would make it cost competitive with current power costs.
The number you quoted is very theoretical. In (not sunny) Iowa for example 600W.m^-2 would be considered high. In sunny Arizona the peak available power is 1200W.m^-2. At 20,000 ft we get 1.72x the energy we see at the surface. So the efficiencies you quoted are way too high. Even under optimum conditions.
TheHermit < Sorry to be pouring cold water on a "nice" idea >
> -----Original Message-----
> From: email@example.com
> [mailto:firstname.lastname@example.org]On Behalf
> Of Eric Boyd
> Sent: Monday, May 17, 1999 4:52 PM
> To: Church of Virus
> Subject: virus: energy crisis?
> Hi Virians,
> I finally got around to doing something I'd been thinking about for a
> long while -- a comparison of the energy we could get from the sun to
> the energy we use.
> I start with a decided extropian stance -- I assume that genetic
> engineering is going to produce "natural gas" trees, i.e. living
> organisms which can convert the sun's energy directly into some form
> of chemical energy humans use. (could also be "gasoline trees", if
> you want). In a sense, we already have plants of this type: certain
> types of corn are used to produce an alchol that can be burned as a
> fuel. What I'm thinking of, however, is more like a "maple syrup"
> kind of operation. Each tree will be hooked up to several
> "collection" tubes (attached to specially engineered "spouts" on the
> trees themselves), and as the tree produces natural gas, it is removed
> and collected and then distributed to human users. In this way, we
> can "grow" energy in the field, with a minimum amount of effort on our
> So, with those genetically engineered organisms in mind, I began my
> analysis -- how much energy could we conceivably collect from the sun
> in that way?
> Well, the frontal area that the Earth presents to the sun's radiation
> is a circle, with the radius equal to the Earth's radius, i.e.
> Af = Pi*R^2 = 1.278 x 10^14 m^2
> where R = 6,378,000 m
> Now, only 29% of the Earth's surface is land, and only about 20% of
> *that* is suitable for argicualtral development like we're going to
> need, so that leaves
> Ap = A*0.29*0.2 = 7.412 x 10^12 m^2
> To work with.
> Now, direct sunlight striking a normal (which defines it's
> orientation: directly facing) plane carries about 1,350 watts / m^2,
> so assuming that the land above averages an incline to the plane of 20
> degrees (this is due to the fact that the land masses are primairly
> *not* on the equator), and assuming further that only one over Pi
> (=31.8%) of this land is "in the sun" at a time, we have that the
> amount of energy hitting that land is
> E = Ap * cos(20) * (1/Pi) * 1350
> = 2.993 x 10^15 watts
> Now, let's say that we can plant 10% of the usable land above with
> these new-fangled "natural gas" trees, and further that these trees
> are only 25% efficient. It follows that we can convert the
> available solar energy above into
> Etrees = E * 0.10 * 0.25
> = 7.483 x 10^13 watts = 74.8 million MW
> of useable chemical energy, continuously being "grown".
> How does this value compare to world usage?
> My data, sad to say, is a little dated, but I'll just multiply by
> large margins of safety, to be sure.
> My World Book encyclopedia says that in 1985, the USA used 74
> quadrillion BTU's of energy (from *all* sources, including nuclear and
> Now 1 BTU = 1055 joules
> Eus = 7.4 x 10^16 BTU/year * 1055 J/BTU / 365 days/year / 24 hours/day
> / 60 min/hour / 60 sec/min
> = 2.476 x 10^12 joules/sec (watts) on average.
> Now, if we assume that the US's energy consumption has doubled in the
> last 14 years, and that the US only represents 10% of current world
> energy usage, then the world now uses
> Eworld = 2.476 x 10^12 *2 * 10
> = 4.951 x 10^13 watts = 49.5 million MW
> So, since 49.5 million MW is less than 74.8 million MW, we haven't
> reached the point of unsustainabilty *yet*. Indeed, I don't think we
> will ever reach it... this Earth based scheme forgets entirely about
> space-based sources such as solar-power orbitals, or potential
> break-throughs in fusion based nuclear power, not to mention such
> energy sources as hydro-electric and geothermal.
> Conclusion: as long as we keep on the technology path, energy itself
> will not be a problem -- what will be the problem is the effect such
> large and wide scale energy production and use will have on the earth.
> Energy is violent -- and the Earth is fragile.
>  Land area = 148.847 x 10^6 square kilometers
> Ocean area = 361.254 x 10^6 square kilometers.
> 148.8 / (148.8+361.3) = 0.29, or 29%
>  Note that this value is only an educated estimate. Is it a good
>  You might think that 1/2 would be a better value -- but that would
> be forgetting that the curvature of the earth also inclines the plane
> in the longitudinal direction as well as the latitudinal direction.
> For those interested, the value of one over Pi comes from the fact
> (1) half the earth is in complete shade and
> (2) the integral of sin(x) over 0 <= x <= Pi is 2, while the area
> under the rectangle of height 1 from 0 to Pi is Pi (=3.1415). (the
> ratio of these areas relates the normal plane condition to what
> actually occurs on Earth)
> This yeilds 1/2 * 2/Pi = 1/Pi as the final fraction of interest.
>  Note that I think we can do considerably better on both of these
> counts if need be.
>  Does anybody have more current values on hand?