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 culture.

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.)

  1. 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.)

  1. 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.

  1. (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 earth.

Please give me feedback on these assumptions and assertions - and point out my arithmetic errors.



Reply to
Front Office
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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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