It seems obvious to a person or decent scientific intellect like myself that solar-electric cars are more efficient than bio-fuel cars; however, the significant part of a recent study (click here for original) that determined that electricity generated by solar is more efficient than bio-fuels for powering cars is that the analysis considered many factors of material or resource use in addition to pollution. The factors were:
• Greenhouse gas emissions
• Fossil fuel use
• The production and use life cycles of the fuel
• The production and use life cycles of the vehicle
The report was done by a team that compared 5 different approaches to power a compact passenger vehicle for 100 kilometers.
• Battery-electric vehicles (BEVs) run on electricity from solar power.
• Battery-electric vehicles run on electricity from switchgrass.
• Internal combustion vehicles (ICVs) run on switchgrass biofuel.
• Battery-electric vehicles run on electricity from corn.
• Internal combustion vehicles run on corn-based biofuel.
In terms of land-use, the report says that solar significantly out-performed all other options – it doesn’t require farm land. It performed modestly better than switchgrass in terms of greenhouse gas emissions, and significantly better than corn-based biofuel. Solar was actually equal or slightly worse than switchgrass when it came to fossil fuel requirements over the totality of the life cycle, but it still out-performed corn-based internal combustion.
The central bottleneck, as the report notes, is the low efficiency of photosynthesis. Biofuels and bioelectricity use photosynthesis to convert solar radiation into energy for transportation services. While photosynthesis has a theoretical maximum energy conversion efficiency of 33%, the overall conversion efficiency of sunlight into terrestrial biomass is typically below 1%, regardless of crop type and growing conditions. Modern, thin-film PV converts sunlight to electricity at 10%. It is believed that less than 1% of global land areas would be needed to supply all the world’s electricity needs in 2050.
Traditional corn-based biofuels are problematic because carbon emissions from agricultural production over their full life cycle largely wipe out any carbon benefits at the point of actual vehicle use. And new cropland sequesters less carbon from the atmosphere than the grassland or forest it typically displaces. Switchgrass and other cellulosic biofuel are not immune to these other flaws either.
The Devil’s Advocate
There are still a number of variables and perspectives missing from this ra-ra-ra report for solar-electric.
1) For me, a significant consideration that is missing is the commercial viability, as in what is the cost and efficiency-rating of building a new infrastructure? One would assume “less” but science is not about assumptions. This study is missing that.
2) Cost of infrastructure development is projecting and a little bit beyond the scope of this study, so that might not be fair. I propose that there is another variable that is missing: cost. Prices are conveniently left out of this study. In my novitiate opinion, price or ‘cost of goods sold’ is directly proportional to resource usage.
3) The report/study did not consider other circumstances such as region or weather and cyclical demand (daily, weekly, seasonally, yearly).
4) The report/study doesn’t consider nuclear energy generation.
In the end, we all want things to better. Better studies need to be done and questions always need to be asked. Hold their feet to the fire… even scientists!