The Life Power Stream

What's new?

Check out the calculator here to estimate your sustainable-power needs.
Look over our scaling times page, for a temporal perspective on the parable below.
The parable of the giant leaf: It takes about 100 watts to power a person's metabolism, and the average annual insolation on earth is about 250 watts per square meter. As a result, photosynthesis at 2.5% efficiency would power us entirely if we each carried around a giant leaf more than 15 feet in diameter! Our ancestors might have carried such a leaf, were it not the subject of the most abiding agreement in the natural history of metazoan inventions. To wit: "I'll plant myself and hold our leaves, while in return you eat my fruit and spread the seeds." Can you name a multi-celled organism who has NOT benefited from such a deal? Of course, there may be a few who've not been keeping their side of the bargain...
...speaking of which, what have you done lately to take care of the organisms that hold your giant leaf skyward?

An updated PDF table for comparison of various energies, in various units.
Consider defining a Person-Day [pday] of energy as 2100 [Calories], and a Person-Unit-of-Power [pup] as 1 [pday/day] ~ 1/7 [horsepower]. This helps lift the fog put up by too many apparently unrelated energy units, clarifying for example that... a 100W light bulb (left on continuously) uses as much of life's power stream as a single human being. Considering that a 5 [Calorie] candy (e.g. an M&M®) provides enough energy to do perhaps 50 pushups, 2100 [Calories] per day is quite a bit of energy! Use of a fluorescent light with equivalent output can cut the energy cost of lighting by perhaps a factor of four, while LED's not yet available for residential use in developed countries may do much better than that in days ahead. On the subject of transportation energy, if your car gets 30 miles to the gallon, it thermalizes as much of life's power stream as one human being for every 1000 miles per year that it travels. Thus driving 25,000 miles per year thermalizes the available work need to keep 25 people alive. In most cases this energy was initially captured from solar photons by ancient plants. These in turn were converted to fossil fuel reservoirs, perhaps half of which have been thermalized in modern times. Hybrid vehicles available on the market today can reduce the energy cost per mile by a factor of 2 or 3, as of course can traveling more than one person to a vehicle. (The volume of CO2 that a car puts out while running is also an amazing number, which however escapes me for the moment.) In the meantime, the stream of power that life on earth is managing to trap from incoming sunlight seems to be decreasing in size from a peak in the last century, somewhere near 10^15 watts. This, of course, is the energy source from which those fossil fuels were originally made. The CO₂ created in their burning might (or might not) stimulate further biological production on a planet whose temperature and water level have increased (hopefully not by too much). These numbers, and those below, are a subset of those that you might enjoy thinking about, as you consider the move toward sustainable lifestyles and development in the days ahead.
Bloomfeld in his book for our How Things Work course refers to "available work" as "ordered energy" to distinguish it from thermal energy at ambient temperature (so-called "dis-ordered energy"). Bravo! Of course energy in one form or another is automatically conserved, but available work is what we're talking about here.
Where can we find out details on state by state "appetites" in the US for energy in the form of available work? This is a timely question. If you have ideas about this, send us a note.

By combining biological energetics with physical science units, one can show that the steady-state rate at which available work is captured by living things is a limited, but objective, indicator of the state of life on our planet. Its role might be similar to that played by the GDP (Gross Domestic Product) when it functions as an indicator of the state of an economy*. Of course, the life power stream involves our role in a budget that is balanced not by us, but by the laws of physics.

Concerning the resource impact of a given consumable, it allows us to calculate a single number in units of power stream time. For example, a hotdog without mustard or bun probably requires more than 50 nanoseconds of the full powerstream presently in use by life on our planet. Although any single number will have both advantages and pitfalls, in principle this is a number which tells us something tangible in a global context, even when it is not the most important thing to know.

* Some think that coins, currency, and the financial systems that have developed therefrom are in essence ritualized forms, in nature, of available work. After all, they only make sense if they obey a conservation law, and cannot be inexpensively replicated (e.g. by xeroxing) at will.

Other resources of possible interest: What does quantum mechanics look like in complex color? Comparing energies: Does food, gasoline, or electricity buy more for less? How about constant acceleration at anyspeed? deBroglie's electrons and some remarkable TEM facts. Try focussing a high-res electron microscope image on-line! Is statistical physics a dead subject, or is there another paradigm change afoot?

This page is copyright (1996-2005) by P. Fraundorf & R. L. Fraundorf

Dept. of Physics & Astronomy, University of Missouri-StL, St. Louis MO 63121-4499

Phone: (314)516-5044, Fax:(314)516-6152

For source, cite URL at http://newton.umsl.edu/infophys/lsp.html

First Posting: August 1996. Version release date: 12 Apr 2005.

Whole-site page requests est. around 2000/day hence more than 500,000/year.

Requests for a "stat-counter linked subset of pages" since 4/7/2005: .

Physical energy, variously measured in joules, BTU's, Calories (kcal), megatons, ergs, kilowatt-hours and electron volts, is involved in many aspects of life on our planet. For example, plants and animals need energy to live and work, houses need energy for heating and for appliances, and cars need energy for locomotion. As you might guess from the list of unit names above, the inter-relationship between these various aspects is obscured by the specialized jargon for dealing with energy that has evolved independently in each. A table of common energies in various units might also be used to illustrate this point.

Physical power, defined as energy per unit time, is variously measured in watts (joules per second) and horsepower. Electric companies, used to delivering energy per unit time, have even chosen power multiplied by time (kilowatt-hours) for their unit of energy.

One approximate constant for life on our planet is also a power: the flux of solar energy per unit time incident on our planet in the form of electromagnetic radiation from the sun. This solar constant between 10¹⁷ and 10¹⁸ watts, has been and continues to be the major ongoing (i.e. steady-state) source of energy put to use by life on our planet.

If we consider only the arable land on earth (about a quarter of that 25% of the earth's surface area which is not ocean), and figure that plant life on that land converts about a 40th of the incident energy to calories in biomass (after the plant respiration losses requisite to that capture, cf. E. P. Odum, Fundamentals of Ecology, Saunders 1971), then the steady-state energy per unit time captured by life on our planet (the life power stream or "LPS" mentioned above, dominated by Odum's net primary productivity) is around 7×10¹⁷×(1/4)×(1/4)×(1/40)=10¹⁵ watts. Experts who've considered land and sea-based biomes more carefully, namely Vitousek et al. in Biosciences 36-6 (1986) 368-373, find a global photosynthetic productivity closer to 1.5×10¹⁴ watts, with about 60% of that land based. Until we have time to take this into account, our initial LPS value of 10¹⁵ watts will serve to illustrate its nature and some applications in the Tables below.

One thing to note quickly: Independent of its impact on species diversity and quality of life, conversion of a garden to a parking lot, or a rainforest to a desert, decreases the LPS by the fractional loss of ecological net primary productivity which ensues as a result. Although LPS indicators, like GNP indicators, are by no means everything, they therefore are an objective measure of a real feature of the state of life on our planet.

Some Rates of Energy Capture & Use

Rates at which energy is being used can be expressed in terms of the LPS for comparison. We've listed only a couple of entries so far. A look at the 1993 World Almanac (Scripps Howard Publishing) shows that the energy production/consumption they refer to is not that which goes directly through living things, but which is mined from the earth as fossil fuels and/or generated by hydroelectric or nuclear power plants. Except for the hydroelectric component, these are not part of the steady-state resource considered in the LPS, since they tap the "standing crop" of energy resources already in place on our planet. The authors seem unaware that the real primary producers of energy for life on earth are plants. Even though the energies they do consider are mostly from past accumulations rather than new acquisitions, the listed rates of fuel/electricity discovery and use still seem to constitute only a small fraction (e.g. a percent or so) of the primary energy production associated with the earth's biological LPS.

Some Rates of Energy Capture & Use
User	Power	LPS fraction
one human being or a 100 watt bulb	100 watts	10^-13
Guri (Raul Leoni) Hydro Plant, Venezuela	10¹⁰ watts	10^-5
World Nuclear Power	3×10¹¹ watts	0.0003
1990 Fuel/Electricity Consumption Worldwide	10¹³ watts	0.01

Although our fuel/electricity sources are modest in comparison, our species is also a major consumer and modifier of the terrestrial photosynthetic productivity which comprises most of life's steady state power. For example, as was mentioned at a recent AABGA meeting in St. Louis, the 1986 article in Bioscience cited above estimates that humans are either consuming, wasting, or diverting about 40% of the land-based component of that photosynthetic productivity!

Suggestion of other quantities to list, and better researched and documented values for the ones already listed, in the tables here as well as in the text, would be of interest. We would be happy to link to and/or credit the original sources for improved values, if you are able to provide them to the e-mail address below.

Some Amounts of Energy

Lastly, we note here that specific quantities of energy can be measured in terms of the time the present-day LPS would require to generate that energy. In other words, how long would a given resource allocation exclusively tie up the full machinery of life on earth?

The answer is not always obtained with a simple energy units conversion. Some forms of energy require a larger investment by the machinery of life on our planet than do others. For example, I gather from reading Odum (above) that animal biomass requires something like 100 times the primary production that one might infer from its caloric value alone. This is because a cow, for example, requires much more than its weight in grain to reach maturity. A carnivore's LPS need is accordingly larger than a vegetarian's, by the corresponding factor.

Some Amounts of Energy
Quantity	Energy	LPS time
a human or a 100 watt bulb for 1 hour	360000 joules	0.35 nanoseconds
Food energy in an apple (120kcal)	500000 joules	0.5 nanoseconds
Vegetarian's daily requirement (2100kcal)	9000000 joules	8 nanoseconds
Combustion energy in a gallon of gas	10^8 joules	100 nanoseconds
Carnivore's daily LPS needs (2100kcal*100)	9x10^8 joules	800 nanoseconds
Earth's gravity well for a person	4x10^9 joules	4 microseconds
Energy thermalized in 1 megaton explosion	4x10^15 joules	4 seconds
US daily fuel/electricity consumption	2x10^17 joules	4 minutes
Fossil fuel left on earth	2x10^23 joules	6 years

Again, better-documented values for the entries here, and suggestion for other things to list, would be most welcome. For example, better values for the LPS and fossil-fuel resources needed for various consumables (including hamburgers, french fries, and gasoline for example) might provide the basis for a "used-resource" labelling program for consumables to increase consumer awareness of their impact on the world in which we live!

Note: A nanosecond (one billionth of a second) is the time it takes light to travel approximately one foot.

Some related links...

Availability, exergy, and all that... by Mark Simpson and James Kay.

Yahoo's Science/Energy Page.

The New Bottom Line, on Sweden's Next Step Program.

Technocracy Pages (formerly here), on the U.S. Depression Era Movement for Energy Accountability.

Availability, emergy, and all that... by Thomas Wayburn

Send comments, your answers to problems posed, and/or complaints, to philf@newton.umsl.edu. This page contains original material, so if you choose to echo in your work, in print, or on the web, a citation would be cool. (Thanks. /philf :)