Alternative Fuels

Posted by: Nic





In keeping with my current job, the purpose of this post is to examine fuel usage in North Carolina and look at the ability of different alternative fuel options to meet the demand.



A summary of fuel use in North Carolina in 2006 is provided below. For comparison I have included fuel usage for Western Australia (us being from there, and all). I am getting ahead of myself, but what is interesting is that the per capita gasoline use in North Carolina is twice that of Western Australia, even though Western Australia could be considered a highly urbanized and car-dependent society.



I am going to look at three alterantive fuel sources - Canola for biodiesel, and winter wheat, switchgrass and poplar for ethanol.

Canola for Biodiesel

Currently about 170 thousand hectares of land are used for winter wheat production in North Carolina. This land could be used for Canola production and the oil from this used for biodiesel.

Assuming a Canola yield of around 2 T/ha and a recoverable oil yield of 45 % 150 ML of oil could be produced annually. Assuming a 100 % conversion efficiency of this oil to biodiesel this would only meet 3% of North Carolina’s annual diesel requirement.

Wheat for ethanol

The winter wheat production could instead be used to produce ethanol.

North Carolina’s winter wheat yield in 2006 was about 680 thousand tonnes. Assuming a starch content of about 65 % and a starch to ethanol conversion of 75 % this would produce about 300 ML of ethanol a year. Now, ethanol has a lower energy density than gasoline so this is equivalent to about 250 ML of petrol. So this would meet about 1.6 % of North Carolina’s gasoline needs.

Switchgrass for ethanol

Switchgrass (Panicum virgatum) is a fast growing perennial bunch grass which can yield about 10 T/ha annually.

North Carolina has about 8 hundred thousand hectares of pastoral land so let’s assume 50 % of this is turned over to Switchgrass production. Work shows that the ethanol production from Switchgrass is about 280 L/dry Tonne (this figure is rubbery though and technology change could increase it). This works out as 1200 ML of potential ethanol production (equivalent to about 1000 ML of petrol) or about 7.5 % of North Carolina’s gasoline needs

Short rotation woody crops for ethanol

The option exists to use woody biomass to make ethanol. We could use forest material in North Carolina but instead let’s assume we are using short rotation Poplars grown on 50 % of the pastoral land. Poplars can get about 17 T/ha which equates to about the equivalent of 1800 ML of gasoline or 13 % of North Carolina’s gasoline needs.

Energy yield per hectare

If you look at energy yield per hectare Switchgrass yields about twice the quantity of ethanol per land area that winter wheat does and Poplar nearly four times. So woody crops are more efficient for fuel production than grains.

Summary

The diagram below summarizes how much of North Carolinas gasoline usage could be off-set using these various alternative fuel sources.

What these simple calculations show is that common biofuel feedstocks can not meet the gasoline and diesel requirements of North Carolina.

I am not implying that biofuels should not be considered, as the third pie-chart shows, with increased energy efficiency biofuels could provide a large portion of energy requirments. What this tell us is that current energy use in North Carolina is simply unsustainable and people will need to adopt lower energy use. By my estimates people will need to use 1/8th the energy they currently do in order to reach a sustainable energy consumption.

References

Fuel useage statistics for North Carolina from the Energy Information Administration (http://www.eia.doe.gov/ ).

Western Australia fuel usage statistics from http://www.abareconomics.com/ and http://www.abs.gov.au/.