Sun to Wheel

Biofuels may provide a transition to zero emission fuels but over-harvesting forests and/or agricultural
lands led to the decline of most civilizations over the last 7000 years. Maintaining production on
diminishing soil resources now requires ever increasing amounts of fossil nutrients and fuels. As we
bump up against the finite limits of fossil nutrients and fuels, feeding a growing population will not be
possible much less a growing number of internal combustion engines (ICE).
Ultimately all energy on the Earth comes from the Sun so fuel efficiencies should be measured from the
Sun. Fossil fuels are inherently very inefficient because of the millions of years of solar energy it took to
produce them. Photosynthesis is about 1% efficient at producing carbohydrate energy from solar energy.
The efficiency of producing liquid fuel from carbohydrates varies widely depending on the process and
the distance to the use. Then there is the efficiency of the ICE which yields an overall efficiency for
biofuels from Sun to drive shaft of 0.01- 0.03%.
Producing electricity from solar energy using photovoltaics (PV) is from 5-20% efficient and solar thermal
generation can reach over 35% efficiency without counting the cogeneration possibilities. Current battery
charge/discharge efficiency varies from 80-95%. Electric motors are over 90% efficient including line and
motor controller losses. Total efficiency from Sun to electric motor drive shaft is between 3-30%. This
gives solar charged electric vehicles an advantage 10 to 300 times greater then burning biofuels.
The obvious question is: Why aren’t we all driving zero emission battery electric vehicles?
Of course for EVs to be clean the electricity used to charge their batteries must be generated from zero
emission renewable sources. If EVs are charged with power generated from fossil fuels or radioactive
material the cost of our mobility will be passed on to future generations in the form of poor air quality,
depleted resources, climate change and radioactive waste.