Solar-powered cars versus biofuels
Which approach makes sense as we manage the planet’s ever diminishing resources and plan for the future?
In an earlier life as a genetic engineer, I dreamt of biofuels as a sustainable alternative to fossil-fuels to power cars. I had no aspirations, at that time, of ever owning an electric vehicle, since in the UK you could only really satisfied that urge if you were happy to drive a milk float!
Today, much has changed, bioethanol is available at many filling stations across Europe and research is progressing rapidly to make biodiesel a carbon-neutral and sustainable alternative.
On the electric vehicle front, things have also changed. There are numerous electric vehicles to choose from, many of which look sleek and sporty, like the Tesla Model S, providing both the speed and range to make them a realistic proposition.
Add to this a renaissance in power generation, from coal to renewables, and you can imagine a world in which clean electricity can not only remove local emissions from our cities, but potentially remove them from the whole equation altogether.
So which approach really makes sense as we manage the planet’s ever diminishing resources and plan for the future?
Scanning the literature on biofuels leaves you with a sense that although there are many possible alternatives from genetically modified crops, like Canola (oilseed rape), through to algae or modified bacterial strains that can synthesize diesel fuel, none can compete in the fuel market and be broadly deployed, without first overcoming several major hurdles.
The production of bioethanol is well documented with regional successes such as sugarcane-to-ethanol production in Brazil, but a more global approach is harder to envisage. Oils from terrestrial plants like, soy and palm can be used to produce biodiesel, but owing to the enormous amount of agricultural land that would be required, this approach doesn’t look feasible either.
Algae may provide a viable alternative, not least because they can be grown without utilizing valuable agricultural land e.g. by growing marine microalgae in salt water, but all these approaches, although ultimately carbon neutral, produce local emissions, which affect people’s health.
Let’s look at the numbers.
Take the example of a typical family car, fueled by biodiesel. Assuming an efficiency of about 60 miles per gallon (3.9 L/100 km) and a total of 12,000 miles (19,312 km) a year, that car will have an annual consumption of 200 gallons (757L) of biodiesel. If the biodiesel was produced from Canola, it would take two acres (0.81 hectares) of agricultural land a year to fuel a single car for 12 months, (an acre of Canola can generate about 100 gallons of biodiesel a year according to the US Department of Agriculture). If algae was used, literature suggest a potential of 14,000 gallons per acre (1), which would mean 70 cars could be kept on the road a year per acre of land, but the estimated costs of a barrel of algae-based fuel using current technology would be between US$300–$2,600, compared with $40–$80 (2009) for petroleum [2–5].
At the start of my journey, I was committed to biofuel, I even bought a car that could run on bioethanol (328 gallons per acre for current corn-based ethanol production (1), which means 1.6 cars kept on the road per year per acre of land if you ignore the lower calorific value of ethanol compared to diesel).
This year I’ve gone electric and here’s why…
Take the electric mini E, which consumes an average of 22 kWh per 100 miles (6), or the Tesla Model S, which consumes 28 kWh per 100 miles (7). 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 (8) solar panels, those two acres needed to support a single Canola biodiesel-fueled car could provide enough power for 212 Model S Teslas (9) and even when compared with a single acre of Algae-based biodiesel, which could support 70 cars, the same space covered with 2-axis CPV (8) solar panels would support 106 Teslas or 135 mini Es.
These are estimates and one can argue over the exact acreage and the productivity of solar panels in different locations, but the point is that however you calculate it, solar-electricity is a more efficient fuel than biodiesel and although biodiesel maybe carbon neutral at the point of use there are local emissions, which will affect the health of our ever growing urban populations.
By 2035, the International Energy Agency predicts that 1.7 billion cars will be on the roads. If these were all powered by Canola biofuel, we’d need to allocate 3.4 billion acres of arable land to biofuel production and even if we were able to overcome many of the challenges associated with scaling up algal biodiesel production, we’d need 24.3 million acres of space. For electric vehicles, just 16 to 17 million acres would suffice, and we wouldn’t need to compete with food production: solar plants work best in deserts and arid areas, with cloudless skies, where crops don’t grow.
With the human population rising exponentially, why would we use agricultural land to produce fuel in place of food? The Sahara desert alone covers about 2,223,950,000 acres (9,000,000 square kilometers). Ambitions to cover areas of desert with solar panels may lack political will, but the technology is available now to achieve it. In the absence of political will to realize this solution, perhaps the answer lies in individuals installing residential rooftop PV.
In the US the average total daily drive for urban-based cars is about 36 miles, while rural-based cars on average travel around 49 miles, which means for a Tesla you would need roughly 14kWh of energy a day. Even in the UK, not known for its cloudless skies, the annual insolation is in the range of 750 – 1,100 kWh/m² with London receiving 0.52 and 4.74 kWh/m² per day in December and July, respectively (10), so with an average sized residential rooftop PV installation of say 50m2 it would be easy to power your daily car travel.
For me, the answer is clear, what do you think?
1. Neltner, Brian. “Algae Based Biodiesel.” Algae Based Biodiesel: 29 Apr. 2008. Web. 26 Jan 2017
2. Dismukes GC, Carrieri D, Bennette N, Ananyev GM, Posewitz MC. Aquatic phototrophs: efficient alternatives to land-based crops for biofuels. Curr Opin Biotechnol. 2008;19(3):235–240. [PubMed]
3. Borowitzka MA. Algal biotechnology products and processes – matching science and economics. J Applied Phycology. 1992; 4:267–279. (LINK)
4. Chisti Y. Biodiesel from microalgae. Biotechnol Adv. 2007;25(3):294–306. [PubMed]
5. Alabi AO, Tampier M, Bibeau E. Microalgae Technogies and Processes for Biofuels/Bioenergy Production in British Columbia. The BC Innovation Council; BC, Canada: 2009.(LINK)
6. http://www.myelectriccar.com.au/images/MINI-E-spec-sheet.pdf
7. Tesla Motors set a goal to deliver a range greater than 300 miles with the 85 kWh Model S battery (ie, 0.28kWh/mile) http://www.teslamotors.com/blog/model-s-efficiency-and-range
8. According to the National Renewable Energy Laboratory NREL, it takes 2.8 acres of land to generate 1GWh/year using 2-axis CPV solar panels http://www.renewableenergyworld.com/rea/news/article/2013/08/calculating-solar-energys-land-use-footprint
9. Two acres could fuel nearly 212 Tesla Model S cars a year on the road. ie, 1,000,000 kWh/ 2.8 x 2 = 714,285.7 kWh / 2 acres, then 714,285.7 / 3360 kWh = 212.6 cars / year.
10. http://contemporaryenergy.co.uk/insolation-map/
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