Ethanol, for instance, is an alcoholic biofuel easily distilled from sugary or starchy plants. It has been used to power cars since Ford’s Model T and, blended into conventional petrol, constitutes about 10% of the fuel burned by America’s vehicles today. Biodiesel made from vegetable fats is similarly mixed (at a lower proportion of 5%) into conventional diesel in Europe. But these “first generation” biofuels have drawbacks. They are made from plants rich in sugar, starch or oil that might otherwise be eaten by people or livestock. Ethanol production already consumes 40% of America’s maize (corn) harvest and a single new ethanol plant in Hull is about to become Britain’s largest buyer of wheat, using 1.1m tonnes a year. Ethanol and biodiesel also have limitations as vehicle fuels, performing poorly in cold weather and capable of damaging unmodified engines.

In an effort to overcome these limitations, dozens of start-up companies emerged over the past decade with the aim of developing second-generation biofuels. They hoped to avoid the “food versus fuel” debate by making fuel from biomass feedstocks with no nutritional value, such as agricultural waste or fast-growing trees and grasses grown on otherwise unproductive land. Other firms planned to make “drop in” biofuels that could replace conventional fossil fuels directly, rather than having to be blended in…..

Even if second-generation processes can be economically scaled up, however, that might in turn highlight a further problem. To make a significant dent in the 2,500m litres of conventional oil that American refineries churn through each day, biofuel factories would have to be able to get hold of a staggering quantity of feedstock. Mr Ghisolfi of Beta Renewables points out that a factory with an annual output of 140m litres needs 350,000 tonnes of biomass a year to operate. “There are only certain areas, in Brazil and some parts of the US and Asia, where you can locate this much biomass within a close radius,” says Mr Ghisolfi. “I am sceptical of scaling to ten times that size, because getting 3.5m tonnes of biomass to a single collection point is going to be a very big undertaking.”

Billions of tonnes of agricultural waste are produced worldwide each year, but such material is thinly spread, making it expensive to collect and transport. Moreover, farms use such waste to condition the soil, feed animals or burn for power. Diverting existing sources of wood to make biofuels will annoy builders and paper-makers, and planting fuel crops on undeveloped land is hardly without controversy: one man’s wasteland is another’s pristine ecosystem. Dozens of environmental groups have protested against the EPA’s recent decision to permit plantations of fast-growing giant reed for biofuels, calling it a noxious and highly invasive weed. Just as the food-versus-fuel argument has proved controversial for today’s biofuels, flora-versus-fuel could be an equally tough struggle for tomorrow’s.

Biofuels: What happened to biofuels?, Economist Technology Quarterly, Sept. 7, 2013