• Wayne Williams/CEO

How many miles can a car travel on an acre of ethanol in a year vs a similar sized electric car trav

How many miles can a car travel on an acre of ethanol in a year vs a similar sized electric car travel on an acre of solar in a year?

By 2040, the number of electric cars in the world could reach 150 million, or even, if more ambitious targets for emissions reductions are adopted, 715 million. The bio-fuel industry is not giving up without a fight. At the recent UN climate talks in Morocco, a consortium of 20 countries launched Bio future, a platform designed to encourage the use of low-carbon bio-fuels, including the second generation of sugarcane cellulose-based bio-fuel. Today much has changed, bio ethanol is available throughout Europe at many filling stations, and research is progressing rapidly to make bio-diesel a carbon-neutral and sustainable alternative. Add to this a revolution in electricity generation, from coal to renewables, and you can imagine a world where green energy can not only reduce regional pollution from our communities, but potentially remove them completely from the equation. Scanning the bio-fuels literature leaves you with the feeling that while there are many possible alternatives from genetically modified crops such as canola (oil seed rape) to algae or modified bacterial strains that can synthesize diesel fuel, none can compete on the fuel market and be widely deployed without first overcoming several major hurdles. Bio-ethanol production is well documented with regional successes such as the production of sugarcane-to-ethanol in Brazil, but it is more difficult to envisage a more global approach. Oils from terrestrial plants such as soy and palm can be used to generate bio-diesel, but this solution does not look feasible either due to the enormous amount of agricultural land that would be needed. Algae can be a viable alternative, not least because they can be grown without the use of valuable agricultural land, e.g. by growing marine microalgae in salt water, but all of these approaches, although ultimately carbon neutral, produce local emissions that affect the health of people.

Let's analyze the statistics. Take the example of a typical bio-diesel-fueled family car. Assuming an output of approximately 60 miles per gallon (3.9 L/100 km) and a total of 12,000 miles (19,312 km) per year, this car can use 200 gallons (757L) of bio-diesel per year.

If the bio-diesel was produced from Canola, fueling a single car for 12 months would take two acres (0.81 hectares) of agricultural land a year (an acre of Canola, according to the U.S. Department of Agriculture, can produce about

100 gallons of bio-diesel a year). If algae were used, literature suggests a potential of 14,000 gallons per acre, suggesting that 70 cars could be kept on the road a year per acre of land, but the estimated cost would be between US$300–$2,600, compared with $40–$80 (2009) for petroleum. Take the electric mini E, which consumes an average of 22 kWh per 100 miles, or the Tesla Model S, which consumes 28 kWh per 100 miles. The Tesla covering 12,000 miles (19,312 km) would require 3,360 kWh of electricity, or 3.36 MWh/ year.. If this electricity came from a field of 2-axis CPV solar panels, those two acres needed to support a single Canola bio-diesel-fueled car could provide enough power for 212 Model S Tesla's and even when compared with a single acre of Algae-based bio-diesel, which could support 70 cars, the same space covered with 2-axis CPV solar panels would support 106 Tesla's or 135 mini Es. These are figures and one can disagree about the exact acreage and efficiency of solar panels at different locations, but the argument is that however you quantify it, solar electricity is a more efficient fuel than bio-diesel and although bio-diesel is perhaps carbon-neutral at the point of use, local emissions are present. An acre of desert PV will easily yield 300,000 kWh (150 kW per acre x 2,000 hours of direct normal sun) and a million miles per year for an EV. Since 2,500 to 3,000 hours are available in many places, the figure jumps to between 375,000 and 450,000 kWh per year, yielding between 1.25 million and 1.5 million per miles per year. In other words, the output from (more expensive) ethanol is little more than a rounding error compared to the output from PV. The choice is between a million miles per acre per year, costing 2 to 4 cents each from the sun, or 10,000 miles per year costing 12 to 20 cents from a cornfield that would be better served making food.

Wayne Williams

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