Abstract

The two main paths to power vehicles with sunlight are to use photosynthesis to grow biomass, converting to a liquid fuel for an internal combustion engine or to generate photovoltaic electricity that powers the battery of an electric vehicle. While the environmental attributes of these two paths have been much analyzed, prior studies consider the current state of technology. Technologies for biofuel and photovoltaic paths are evolving; it is critical to consider how progress might improve environmental performance. We address this challenge by assessing the current and maximum theoretical exergy efficiencies of bioethanol and photovoltaic sun-to-wheels process chains. The maximum theoretical efficiency is an upper bound stipulated by physical laws. The current net efficiency to produce motive power from silicon photovoltaic modules is estimated at 5.4%, much higher than 0.03% efficiency for corn-based ethanol. Flat-plate photovoltaic panels also have a much higher theoretical maximum efficiency than a C4 crop plant, 48% versus 0.19%. Photovoltaic-based power will always be vastly more efficient than a terrestrial crop biofuel. Providing all mobility in the U.S. via crop biofuels would require 130% of arable land with current technology and 20% in the thermodynamic limit. Comparable values for photovoltaic-based power are 0.7% and 0.081%, respectively.

Original languageEnglish (US)
Pages (from-to)6394-6401
Number of pages8
JournalEnvironmental Science and Technology
Volume49
Issue number11
DOIs
StatePublished - Jun 2 2015

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exergy
Exergy
biofuel
Sun
ethanol
Wheels
Ethanol
Biofuels
Crops
electric vehicle
crop
crop plant
arable land
silicon
electricity
photosynthesis
thermodynamics
maize
Bioethanol
Photosynthesis

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

Cite this

Sun-to-wheels exergy efficiencies for bio-ethanol and photovoltaics. / Williams, Eric; Sekar, Ashok; Matteson, Schuyler; Rittmann, Bruce.

In: Environmental Science and Technology, Vol. 49, No. 11, 02.06.2015, p. 6394-6401.

Research output: Contribution to journalArticle

Williams, Eric ; Sekar, Ashok ; Matteson, Schuyler ; Rittmann, Bruce. / Sun-to-wheels exergy efficiencies for bio-ethanol and photovoltaics. In: Environmental Science and Technology. 2015 ; Vol. 49, No. 11. pp. 6394-6401.
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