A joule of lower heating value from coal is thermodynamic and
economically much less valuable than a joule as electricity. Lardon
et al., for example disregard the influx of solar energy to the system
and show a range from 2.6 MJ lost to +105 MJ gained per kg of algae
biodiesel produced. These values may, for example, all become
negative if the input of solar energy is counted. However, this does
by no means invalidate all algae-based diesel concepts.
The simple mass balance approach limited for example to the
critical element carbon for liquid transportation fuels shows a necessary
but not sufficient condition of sustainability. However, it
will allow to decide early on if a given concept has any hope of
operating sustainably, and where the most serious issues reside
(for example Pfromm et al., 2010). If the carbon mass balance appears
promising, a complete mass balance will show environmental
compatibility since for example the unit operation
‘‘atmosphere” may not be enriched or depleted over time to maintain
steady state and achieve sustainability. It is acknowledged
that a unit operation such as ‘‘atmosphere” is exceptionally complex
and that our knowledge is in flux, but the mass balance approach
is amenable to handle very high levels of complexity in
an adaptable mathematical fashion.
A joule of lower heating value from coal is thermodynamic and
economically much less valuable than a joule as electricity. Lardon
et al., for example disregard the influx of solar energy to the system
and show a range from 2.6 MJ lost to +105 MJ gained per kg of algae
biodiesel produced. These values may, for example, all become
negative if the input of solar energy is counted. However, this does
by no means invalidate all algae-based diesel concepts.
The simple mass balance approach limited for example to the
critical element carbon for liquid transportation fuels shows a necessary
but not sufficient condition of sustainability. However, it
will allow to decide early on if a given concept has any hope of
operating sustainably, and where the most serious issues reside
(for example Pfromm et al., 2010). If the carbon mass balance appears
promising, a complete mass balance will show environmental
compatibility since for example the unit operation
‘‘atmosphere” may not be enriched or depleted over time to maintain
steady state and achieve sustainability. It is acknowledged
that a unit operation such as ‘‘atmosphere” is exceptionally complex
and that our knowledge is in flux, but the mass balance approach
is amenable to handle very high levels of complexity in
an adaptable mathematical fashion.
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