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in terms of gross available energy. But comparisons with other sources of primary
energy cannot be done with a high degree of accuracy because there is still a fairly
large uncertainty concerning the global annual rate of phytomass combustion; there
are also major disparities in average conversion efi ciencies of phytomass and fossil
fuels. Biofuels contributed about 9% of the world's total fuel supply in the year
2000. But as the overall conversion efi ciency of fossil fuels is now about 40%, the
combustion of 340 EJ of fossil fuels produced nearly 140 EJ of useful energy. Even
if we assume a conversion efi ciency of 20%, the world's biofuels yielded less than
10 EJ of useful energy, or less than 6% of the useful energy contributed by fossil
fuels.
The demand for wood and crop residues for household cooking and heating
would be even higher if it were not for improved stoves. Schumacher (1973) was
an early proponent of their diffusion, but most of the designs introduced during the
1970s proved impractical: usually too expensive, inconvenient to use, difi cult to
repair, and short-lived (Kammen 1995). The most important change came with
China's National Improved Stove Programme, launched in 1982 and originally
intended to provide 25 million units within i ve years. The program far surpassed
its initial expectations. By the end of 1997 about 180 million stoves had been
adopted by nearly 75% of China's rural households (Wang and Ding 1998). Because
these stoves are typically 25%-30% efi cient, they were credited with saving close
to 2 EJ a year (Luo 1998).
While the traditional biofuels retain their importance in rural areas of many low-
income countries, their use is now marginal in all but a few afl uent nations. After
their displacement by fossil fuels they began to make a slight comeback following
the rise in oil prices during the early 1970s, but their share for all OECD countries
was only 4.3% in 2009, compared to 3% in 1973 (IEA 2010). The highest national
shares of combustible renewables in the total primary energy supply are now in
Sweden and Finland (in both countries about 20%, mostly wood-processing and
logging wastes used by industry) while the contributions are below 7% in Germany,
5% in France, less than 4% in the United States, and less than 1.5% in Japan.
Given the high rates of urbanization and a nearly universal urban access to
natural gas and electricity, the household use of biofuels in afl uent countries will
remain minuscule. But many proponents of renewable energy have argued that
biofuels could make a major difference is in supplying liquids for road transport.
This is an old proposition: Henry Ford favored ethanol a century ago, and his
famous Model T could, like the Brazilian l ex vehicles today, run on gasoline,
ethanol, or a mix of the two fuels (Solomon, Barnes, and Halvorsen 2007). Brazil
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