Liquid biofuels are often touted as a partial solution to oil scarcity and climate change. But what are the realistic prospects?
There are, essentially, two types of liquid biofuel: ethanol and biodiesel. The former, produced from crops such as maize, sugar cane, sugar beet and grain sorghum, can be blended with conventional petrol in small ratios and used in existing internal combustion engines, or used in higher concentrations in modified engines. Biodiesel can be made from various oil- bearing crops, including soya beans, palm, canola and sunflower seeds. Biodiesel can be blended with conventional diesel or used alone in diesel engines.
Last year, biofuels comprised about 3% of global road transport fuels.
The US has been the world’s leading biofuel producer since 2006, when it overtook Brazil. According to BP’s data- base, in 2011 the US produced an average of 567 000 bbl/d of ethanol distilled from maize – almost half the world’s biofuel output. This ethanol industry was artificially stimulated by generous federal government subsidies. These expired at the end of last year, and the industry is now taking huge strain, especially as maize prices soar.
Brazil began developing its ethanol industry in the 1970s in response to the oil shocks. Since 1976, there has been a mandatory blending percentage for ethanol in petrol fuels, varying from 10% initially to a high of 25% in 2007. Brazil remains the second-largest biofuel producer, with 22% of the world total, averaging 265 000 bbl/d of ethanol produced from sugar cane in 2011.
The European Union was in third place, with 195 000 bbl/d, comprising mainly biodiesel, and also boosted by subsidies and blending quotas. China managed just 2.2% of global biofuels, while Africa’s production was negligible.
As with any energy source, the ultimate viability of biofuels depends on the energy return on investment (EROI) – the energy contained in the liquid fuel relative to the various energy inputs in the form of fertilisers, pesticides, machinery and diesel.
There has been a long-running debate over EROI for maize-based ethanol. A recent statistical review of studies says the ratio is effectively 1:1, meaning there is no net energy gain. By contrast, the EROI for Brazilian ethanol made from sugar cane is estimated at about 8:1, thanks to plenti- ful land, water and sunshine. The EROI of biodiesel is variously estimated at somewhere between 1.3:1 and 5:1.
So, in net energy terms, most biofuels compare unfavourably with many other energy sources, although the top performers are marginally better than unconventional hydrocarbons like tar sands and shale oil.
A second major drawback of conventional biofuels is the competition between fuel and food for land and water resources. The US is by far the world’s leading producer of maize and accounts for over 40% of global maize exports. Last year, US ethanol distilleries consumed 40% of the country’s maize crop – but contributed less than 3% of US petrol volumes. This massive diversion of US grain to feed cars has exacerbated the dramatic rise in grain prices in recent years, which have sparked food riots in dozens of countries.
Another big concern about biofuels is their potential for negative environmental impacts. In some cases, they have actually been shown to be net contributors to carbon dioxide emissions because of the farming practices employed. In Malaysia and Indonesia, for instance, virgin rainforests are being felled or burned to make way for palm oil plantations. Intensive cultivation using heavy doses of chemical fertilisers and pesticides can also degrade land and water resources.
Food security concerns have stimulated interest in nonfood feedstock crops. One example is the Jatropha plant, which yields oil-bearing fruit that can be used to produce biodiesel. Advocates argue that Jatropha can be grown on marginal dry lands, but other research indicates commercial feasibility may hinge on significant irrigation.
Some see good prospects for so-called ‘second-generation’ biofuels like cellulosic ethanol, which uses specially selected microbes – some genetically modified – to break down nonfood feedstocks like switchgrass, agricultural waste and wood chips. The problem is that there is no ecological ‘free lunch’ – for land to remain fertile, a significant proportion of the nutrients contained in the feedstock plants should be returned to the soil. While there are some promising developments, high costs have so far prohibited commercialisation, which may yet be a decade or more away.
A similar story holds for biodiesel produced from oil-rich algae, which can be grown on a diet of carbon dioxide, sunlight and water (even seawater). But, to date, the cost of algae biodiesel is several times that of ordinary diesel.
The bottom line is that we are going to need major advances in second-generation technologies that overcome the food-fuel dilemma and environmental problems associated with traditional feedstock crops. Even then, biofuels are likely to make only a modest contribution to global energy security and climate mitigation.