Sunday, April 20, 2008

Does algae solve the biofuel puzzle?

The following letter was published in "The Independent" newspaper on Saturday (the 19th of April).

Sir: I endorse Richard Pike's (he is CEO of the Royal Society of Chemistry) comments (letters, 16 April) about the need to find new sources of biofuels rather than those based on growing crops. The amount of land required to produce biofuels from crops on a scale commensurate with present human activities is vast, since the useful energy-capture from sunlight represents less than 1 per cent of the sunlight absorbed by the Earth's surface.

Hence there is necessarily a conflict between growing crops for fuel and crops for food because the area of arable land available to us is limited. But growing algae to make biofuel presents potentially a different proposition, and a Texas-based company, PetroSun, has just begun production.

With their figures showing that 4.4 million gallons (US) of diesel can be produced from 1,100 acres, we may deduce that 32.6 tonnes of diesel plus 116 tonnes of (other) biomass will be produced per hectare per year. Assuming the figure of 174 W/square metre (4.18 kWh/day), this amounts to a photosynthetic efficiency of 4.7 per cent, and is better than crop-based biofuel production by a factor of 10 to 20.

It is not necessary to use arable land nor divert valuable supplies of fresh water for biofuel, since the algae grow well in saline ponds, and could be placed on any land, or on water.

Professor Chris Rhodes

Caversham, Berkshire

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