Biofuel from Algae - Salvation from Peak Oil?

It is nice to have an optimistic note on which to mark the start of Spring, and that could be the production of biofuels from algae. I have considered the viability of biofuels in various of these postings, and concluded that without seriously compromising food production (or eliminating it entirely) it is impossible to provide enough crop-based fuels to replace the massive quantities of oil that we currently use to run our transportation fleet of cars and planes. However, I am abruptly more upbeat about the situation potentially, having seen some truly astounding figures about the amount of biodiesel that might be obtained from farming algae, rather than from growing crops. For example, whereas the yield of biodiesel from soybean is 357 kg/hectare/year and 1,000 kg/ha/year from rapeseed, it is 79,832 kg/ha/year from algae, i.e. about 80 tonnes/ha! There are some algae that yield around 50% of their own weight of oil, and from one study it might be deduced that the yield is around 125 tonnes/ha on the basis that 200,000 hectares of land could produce 7.5 billion gallons (one quad) of biodiesel.

[Since there are 3.875 litres to the US gallon, that equals 7.5 x 10^9 x 3.875 = 2.91 x 10^10 litres. Since there are 159 litres to the barrel and 7.3 barrels to the tonne (accepted average), that amounts to: 2.91 x 10^10/(159 x 7.3) = 2.51 x 10^7 tonnes of biodiesel produced from 200,000 hectares, i.e. 2.51 x 10^7/200,000 = 125.5 tonnes/ha].

I am going to attempt some rough calculations, just to deduce some estimates of scale. In the UK we use around 57 million tonnes of oil to run all our transport - cars, planes, the whole lot. Another 16 million tonnes are used as a chemical feedstock for industry etc. However, I will look at only the fuel budget for now. Diesel engines are more efficient in their tank to wheel use of fuel than spark-ignition engines which burn gasoline (petrol), meaning that we could reduce that total by 30%, to 40 million tonnes by switching all forms of transport to run on Diesel "compression" engines. If we take the optimistic 125 tonnes/ha figure for the yield of biodiesel from algae, that implies a crop area of 40 x 10^6/125 = 320,000 hectares, or 3,200 square kilometers (km^2).
Now this is only 1.3% of the area of the UK mainland, which does look feasible, especially in comparison with values of up to five times the entire area of arable land there is, that I have deduced would be necessary to provide sufficient biofuels derived from land-based crops!
There is no need to use arable land in any case, since the algae would be grown in ponds, and these could be installed essentially anywhere, even in off-shore locations, i.e. growing the material on seawater, because salt concentration appears to assist the algal-growth.
We can make some guess as to the thickness of the algae too. One hectare = 100 m x 100 m = 10,000 m^2. Hence, 320,000 ha = 3.2 x 10^9 m^2. The volume of 40 million tonnes of biodiesel at a specific gravity of 0.84 (based on 79,832 kg = 95,000 litres; so, 80 tonnes = 95 m^3) = 4.76 x 10^7 m^3. Hence, spread over 3.2 x 10^9 m^2 gives a thickness of 4.76 x 10^7 m^3/3.2 x 10^9 m^2 = 0.015 m = 1.5 cm. So, assuming that 50% of it is "oil", that gives a thickness of around 3 cm, which seems reasonable.
How much water would be needed to fill the tanks? Let's assume they are one metre deep (with the algae floating on top of that). That's 3.2 x 10^9 m^2 x 1 m = 3.2 x 10^9 m^3. Since this amounts to 3.2 km^3 it is a significant volume of water, and if freshwater would account for about 2% of the UK's total. However, as I have indicated, seawater can be used instead, or the "ponds" could be fashioned from floating ("boon") structures off-shore. Closed ponds might be better, since that would permit a much closer control of nutrient supply, and if they were covered restrict the potential for invasion by algae with a lower oil yield.

I think that this might be the only way to provide significant amounts of "oil" post peak-oil (other than by coal-liquefaction), and large scale production should be attempted as soon as possible - well before the world's supply of naturally occurring petroleum begins to wane significantly, which gives us just a few years. The "crop" would take-up CO2 from the atmosphere, thus reducing the burden of greenhouse gas that many are worried about, and that amount of carbon would be re-emitted once the fuel was burned, but with a continual crop production working in symbiosis with the CO2 content of the atmosphere, taking it up through photosynthesis. There would be no additional CO2 emitted, other than in the production of an alcohol, methanol or maybe ethanol, which is needed to trans-esterify the initial oil into the final biofuel. This would be in a proportion of about 10% of the oil yield, and could be provided from agricultural waste, e.g. wheat grass, some minor compromise of food crops, say to grow sugar beet to ferment into ethanol, and ultimately by hydrolysis and fermentation of cellulosic material once that technology is underway, thought to be by 2015.
I have never hankered after a return to the "Stone Age", but my notion of living in localised communities remains the only means by which to survive in a fuel-poor world. If we are to produce "alternative" fuel on a large scale, doing so from algae appears to be the best bet, and from an environmental aspect it seems ideal, in that it produces fuel by absorbing a greenhouse gas without producing any more greenhouse gases during the process.
What about costs? If we assume a cost per hectare of $80,000, that would equate to $80,000 x 320,000 = $25.6 billion, or around £13 billion. Annual maintenance/operating costs have been estimated at $12,000 per hectare, which is about £2 billion. Assuming a price of $60 a barrel, that may be compared with an annual cost for 40 million tonnes of oil of $60 x 40 million x 7.3 (barrels/tonne) = $17.5 billion or about £9 billion. This would mean money that is not going out of the country to unstable regions of the world, and it would break completely our dependence on imported oil. It would also reduce the nation's CO2 emissions by probably 30%. We could even use biodiesel to substitute for coal in power stations and cut our dependence on coal imports too, while reducing CO2 emissions yet further.
Now, this approach seems to have everything to recommend it and surely it must be investigated on the large scale immediately.