Virtual People

Our bodies are solar-powered. But each of us also
accounts for a certain number of 'virtual people' who
are powered mostly by fossil fuel. The present world
population of virtual people is about 120 billion,
in terms of energy use, and it is about 60 billion
people in terms of CO2 production.
The daily human dietary energy is roughly 2,000 calories
?? or maybe a little less, but 2,000 is a comfortably
round number to work with. If it's a little on the
high side, then the implications of the following
conclusions become proportionately more extreme.
Two-thousand calories per day is roughly 100 watts, which
can be taken to represent the basic energy need (or energy
use rate, i.e., power) for each solar-powered human body.
I'm looking for comments and general feedback on the
following four items:
1. Humanity's present average energy use rate is
(according to Science magazine) 13-trillion watts. If
you divide 13 trillion watts by the world population
(~6.3-billion people), you get 2,000 watts per person.
That means that, on average, each human being uses
20 times their basic physiological energy need.
A friend of mine calls this additional energy need
'cultural energy,' since it is what powers technological
From an energy-use point of view, this means that each
living person is equivalent to, on average, 20 'virtual'
people, because the ratio of cultural energy to dietary
energy is 20 to 1.
(Cultural energy use in the US works out to about 120
times the dietary energy need. Therefore each American
is equivalent to about 120 people, from an energy-use
point of view. Across Western Europe, the ratio of
cultural energy to dietary energy is about 60 to 1.
In Japan, it's a little less, and in some parts of the
world, cultural energy is close to zero.)
2. I live at 40 degrees north latitude on the east
coast of North America, where the average day-and-night,
year-round insolation is ~100 watts/square meter.
If I could live off of sunlight directly, at 100-percent
efficiency of collection, I'd need only one square meter
of sunlight collection area to survive. (This assumes
a way to store and retrieve energy at 100-percent
efficiency for my use at night and during cloudy days
and low-light-angle winter days.)
If photosynthesis is assumed to be about 5 percent
efficient in collecting solar energy in carbohydrate
form, I'd need about 20 square meters of unshaded
land to gather enough sunlight to run my body. (NOTE:
This rock-bottom minimum does not take into account
additional body-energy needs for hauling water to my
plot of land and planting, cultivating, harvesting and
cooking my crop.)
3. I estimate that in a typical American job - one that
involves no heavy lifting, just brain power while sitting
at a desk or on an assembly line - requires about
20 watts of directed worker output for an 8-hour shift.
That 20 watts goes mostly to thinking, using a keyboard,
and talking on the phone to customers.
Therefore, if a typical employee gets, say, $20 per hour
for his or her 20 watts of directed effort then, the
employer is paying $1,000 per kilowatt-hour.
By comparison, the cost of delivered residential electric
power is $0.11 per kWh - which makes the incentive to
mechanize, or to out-source the labor, readily evident.
4. (LAST ITEM) Given that, for all humanity, the ratio
of cultural energy to dietary energy is 20 to 1, then
- IF global climate is being affected by CO2 emissions
from the burning of fossil fuel - the exhaled breaths
of 20 times as many human beings (125 billion human
beings) would, by itself, be enough to induce planetary
climate change.
I.e, 125 billion human beings would exceed the earth's
carrying capacity in terms of CO2 emissions - even
without fossil-fuel use.
However, energy production from carbohydrates produces
at least twice as much CO2 per unit of energy then
comes from the burning of fossil fuels. Therefore,
a world population of 60 billion human beings would,
on the basis of exhaled breath alone, and no fossil-
powered industry, exceed the carrying capacity of the
Please give me feedback on these assumptions and
assertions - and point out my arithmetic errors.
Reply to
Front Office
Loading thread data ...
U.K. government figures are 2000 cal / day for woemen, 2500 for men, add a juvenile population and 2000 sounds a reasonable average.
Forget the solar power.... people are organic hydro carbon powered... Plants are VERY ineficent in converting solar power into hydrocarbon fuel.
Also people do not live on calories alone...
You should start by working out the solar energy used in growing the crops needed to feed a person. ( hint, find out the calorific value of sweet corn, the yeild of an acre of field, and the solar energy on that field in a year )
Then add a factor for converting some of the sweet corn to chicken breasts and eggs.
Sudenly your energy needs to solar power a person have gone WAY up.
Then factor in the energy input to work the field and distribute the food...
5% may be right... but USABLE food carbohdrate will be a small fraction of the total plant carbohydrate production, most will go on making the plant and running that.
Good reason to go for nuclear power ?
Reply to
Jonathan Barnes
You don't have to assume. Google is at your finger tips. It took about 30 seconds to come up with a range of 1.2 to 3 acres per person to be reasonably fed.
Also, plants convert at a _gross_ rate of something like .05%, not 5%.
This also neglects inputs like farm machinery, fertilizer, and processing and delivery.
Best, Dan.
Reply to
Dan Bloomquist
Plants that produce 1kg/m2 (10 ton/ha) are 1% efficient. In the case of grains and oilseeds, 1/3 - 1/2 of that is edible.
The actual farmland per person is 0.2 ha, but the poor get by on 0.1 ha. But the wealthy nations pig out on red meat, which takes 5X the grain.
Reply to
Eric Gisin
Thanks. Can you site a reference or two on that 0.2 hectare per person, for carbohydrate energy?
Reply to
Front Office

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