Friday, October 2, 2009

Physical Limits to Large Scale Global Biomass Generation for Replacing Fossil Fuels

This is an extract of an interesting analysis from 2006 by Helmut Burkhardt, Professor of Physics Emeritus at the Ryerson University, Toronto.

In a coarse grain global analysis the average total power used by humans is given, and compared with total solar insolation on land. The theoretically possible, and the actual overall efficiency of the conversion of solar energy by technical and biological means is determined. The resulting limitations of biomass energy for replacing fossil fuels are considered. Other problems of energy farming are analyzed. Conclusions are drawn, and future energy policies are recommended.


There is a world wide trend to switch from fossil fuels to biomass energy. While it may be useful to use biomass waste and energy farming in some locations, the large scale use of biomass to replace of fossil fuels is problematic and needs careful analysis. The first question is to see what the energy needs of humankind are.

Average Total Power Consumption

Humankind’s total primary energy consumption is some 470 EJ/a, which translates into an average total power of some 15 TW. With a world population of 6.5 billion people, we get for the average total power use is at present 2.3 kW per person.

The power consumption by sector is approximately 33% of total power for each, industry and commerce, households, and transportation; in per capita terms, the average world citizen consumes 800 W for each sector: transport, production/trade, and transportation.

Electricity is practical in many applications, and hence an essential part of total power in each sector. The average electric power used is according to the US Energy Information Administration: global average 300 W/person, in Canada 2000 W/person, and in Niger 2 W/person.

The composition of the world’s primary energy in approximate (somewhat outdated) numbers:
  • Oil 36% 5.4 TW 830 W/person
  • Coal 23% 3.9 TW 630 W/person
  • Natural gas 20% 3.0 TW 460 W/person
  • Nuclear 7% 1.1TW 160 W/person
  • Hydro 2% 0.3 TW 46 W/person
  • Biomass and wastes 11% 1.7 TW 254 W/person
  • Solar wind geothermal 1% 0.1 TW 15 W/person
Fossil fuels supply at present the bulk of world energy; as their availability is limited, and as their use contributes to global warming, they need to be replaced. Nuclear energy has problems of its own, and should also be replaced by more benign technology based on solar energy.


The replacement of fossil fuels and nuclear energy in the present world energy system by direct technical conversion of solar energy requires some 30 m2/person of solar collectors, and is technically feasible. Due to the lower efficiency of biological collection of solar energy the land area needed for bulk replacement of fossil and nuclear energy is 4000 m2/person; this is not feasible due to several reasons. There is a global shortage of biologically productive land, water, and fertilizer; furthermore, energy farming is in direct competition with food production, and contributes to further reduction of biodiversity in the Earth’s ecosystem.

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