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Growth in biofuel production, which is meant to reduce greenhouse gas (GHG) emissions and fossil energy demand, is increasingly seen as a threat to food supply and natural habitats. Using photovoltaics (PV) to directly convert solar radiation into electricity for battery electric vehicles (BEVs) is an alternative to photosynthesis, which suffers from a very low energy conversion efficiency. Assessments need to be spatially explicit, since solar insolation and crop yields vary widely between locations. This paper therefore compares direct land use, life cycle GHG emissions and fossil fuel requirements of five different sun-to-wheels conversion pathways for every county in the contiguous U.S.: Ethanol from corn or switchgrass for internal combustion vehicles (ICVs), electricity from corn or switchgrass for BEVs, and PV electricity for BEVs. Even the most land-use efficient biomass-based pathway (i.e., switchgrass bioelectricity in U.S. counties with hypothetical crop yields of over 24 tonnes/ha) requires 29 times more land than the PV-based alternative in the same locations. PV BEV systems also have the lowest life cycle GHG emissions throughout the U.S. and the lowest fossil fuel inputs, except for locations with hypothetical switchgrass yields of 16 or more tonnes/ha. Including indirect land use effects further strengthens the case for PV.

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Residential buildings have the function of providing shelter, comfort, and a host of other amenities to their occupants, yet they are responsible for a large share of global negative environmental impacts. Understanding the need to reduce the negative impacts of buildings has led to an increase in both the quantity and popularity of green building rating schemes in recent years. Within most green building schemes, the common goal generally consists of an attempt at increasing aspects of the efficiency of resource use or environmental damage. Impact quantification is often reduced to modeled operational energy consumption, while the actual function is less simple to define or assess quantitatively. In many green building schemes, consideration of function is basically omitted from the assessment, except for the inclusion of a simple proxy metric. The dominant “function” metric that has emerged is floor area, carried over from commercial building assessments. Not only is floor area not a useful proxy for function provided by residential buildings, but placing it in the denominator of an eco-intensity metric results in a perverse ratio of two impacts. All else equal, increasing floor area gives the impression of increased efficiency, while masking the increased embodied and use-phase energy, GHG emissions, and materials use. This paper provides a review and initial inquiry into environmental assessment of residential buildings, addressing the utility of common metrics.