Can algae save the world?

Yet another story today about how genetically engineered algae can produce much more crude oil per acre than biofuels. But how do the numbers stack up?

A liquid fuel made from plants that is chemically identical to crude oil but which does not contribute to climate change when it is burned or, unlike other biofuels, need agricultural land to produce sounds too good to be true. But a company in San Diego claims to have developed exactly that – a sustainable version of oil it calls “green crude”.

Sapphire Energy uses single-celled organisms such as algae to produce a chemical mixture from which it is possible to extract fuels for cars or airplanes. When it is burned, the fuel only releases into the air the carbon dioxide absorbed by the algae during its growth, making the whole process carbon neutral.

1 (US) gallon of oil delivers around 43 KW of energy (depending on the grade). 1 barrel of oil is 42 US gallons, so delivers approximately 1806 KW – let’s call it 1800 KW. So, how much algae do we need to store that much energy?

The sun delivers around 342W per day per square metre. Let’s assume our production site is chosen to get enough sunny days and hours to gather a significant fraction of that onto the algal tanks, say 250Wpd.

Assume algae engineered to high conversion efficiency through photosynthesis into growing more algae, say (to make our sums easy), 180Wpd. The company described in the Guardianarticle referred to above, Sapphire Energy, claim their GM algae can get 40% of that into crude (and 60% into other useful chemicals).

So, we need 25,000 sq.m of algae tanks to produce a barrel of oil equivalent per day. Assume infrastructure around the tanks adds around 10% overhead (may be more, but there’ll be a lot of incentive to work on getting this right). Assume that the need for energy input to the process (running the place, and making the oil out of the algae) is also fairly efficient, taking out another, say, 20%, raising that to 32,500sq.m per daily barrel.

World oil production is 88mbd and demand is rising above that.

So, replacing 1% of world oil demand needs approximately 29,000 sq.km of tanks etc (but at least would produce income of around $120 million per day to pay for all that). Replacing 10% needs 290,000 sq.km.

So, covering the whole of the Mojave desert can produce just under 2% of the world’s oil (or 8% of US consumption).

Fuelling US consumption from this would require approx 725,000sq.km = just under 10% of the land area of the continental US (assume Alaska isn’t available for this) – or a little more than the whole of Texas, to give a comparator. Since some of this would have to be land with more regular cloud cover, that would have to go up by a significant amount.

Er – and introducing an area of 700,000sq.km of open warm still water into the equation will increase cloud cover and rainfall (not to mention mosquitoes – you can’t cover the tanks, and insecticides would alter the chemical composition of the output: you could probably stir them, but that will use energy, and cut the net gain.). 

An alternative estimate is in the article:

Yusuf Chisti at Massey University in New Zealand estimates that algae could produce almost 100,000 litres of biodiesel a year per hectare of land, compared to 6,000 litres a hectare for oil palm, currently the most productive biofuel. 

100,000 litres is 26,417 US gallons, which is 1.1 million KW, which is 113KW per sq.m, which is 311W per sq.m per day, and is seriously overoptimistic, since it pretty much turns the sun’s energy into oil at near 100% efficiency and the company only claims that 40% of the harvest is oil. My numbers get just on 18,000 litres from a hectare – still three times as good as biodiesel (though I suspect that biodiesel number needs netting off for the oil used to produce it, as well).

So – even with a following wind and a lot of work on getting the processes as efficient as possible, not a laydown slam, but not impossible, either. And at least it is better than biodiesel ..