David Pimentel, professor of ecology and agriculture at Cornell University claims there is no energy benefit to using plant biomass for liquid fuel.

“The United States desperately needs a liquid fuel replacement for oil in the near future but producing ethanol or biodiesel from plant biomass is going down the wrong road, because you use more energy to produce these fuels than you get out from the combustion of these products,” he said.

Pimentel and Tad W. Patzek, professor of civil and environmental engineering at Berkeley, conducted a study of the energy input-yield ratios of producing ethanol from corn, switch grass and wood biomass as well as for producing biodiesel from soybean and sunflower plants.

They assessed inputs such as energy used in production of pesticides and fertilisers, running farm machinery and irrigating, grinding and transporting the crop, and in fermenting/distilling the ethanol from the water mix.

Their study found that, for ethanol production, corn needed 29% more fossil energy than the fuel produced, that switch grass needed 45% more and that wood biomass required 57% more than it produced.

For biodiesel production they found that soybean plants needed 27% more energy than it produced and that sunflower plants needed 118% more.

Countries worldwide are mandating the introduction of biofuels as an environmentally friendly and sustainable alternative to traditional fuels which can help meet Kyoto needs.

In the EU, at least 2% of the energy content of all petrol and diesel is required to come from renewable sources and the ever rising price of crude oil is increasing its market awareness further.

However, this study could seriously harm the burgeoning industry if its findings are accepted. This is unlikely though, given that so many other studies have found quite the opposite.

A previous study by the US Department of Agriculture and the US Dept of Energy (see Lifecycle study of biodiesel) found that biodiesel actually generated 3.2 units of fuel for every unit of fossil fuel consumed in its life cycle.

It also found that biodiesel reduces net emissions of CO2 by 78.45% compared to petroleum diesel and significantly reduced emissions of particulate matter.

A study by North Energy Associates and Sheffield Hallam University’s former resources research unit found that, in producing bio-ethanol from wheat straw, the bio-ethanol produced contained five times more energy than the fossil fuel used in its production.

Philip Wood, CEO of D1 Oils – one of the few truly global biodiesel companies – told edie that the energy content of biofuels was largely dependent on the crop used to produce it.

“It all depends on the feedstock and on the method of planting and harvesting,” he said.

The company has in the past cast doubt on rapeseed and other EU preferred crops (see edie library) to meet energy requirements. Instead, D1 uses seeds from the Jatropha tree – a hardy scrub plant which grows on marginalised land. It not only produces a far higher oil yield but is also far less intensive in its use of fossil fuels.

The fertilisers and composts used are generally organic rather than chemical and the tree lasts for about 30 years to save on energy intensive planting each year. In addition, most harvesting is manual, saving on fuel usage.

“Our modular refinery – the D1 20 – also requires very little energy to operate. In fact it can run on the biodiesel it produces,” Wood added.

While he may have cast doubt over the production and use of biodiesel, the Cornell study’s author remains an advocate of biomass for thermal energy and renewables such as solar, wind and hydrogen conversion.

However, despite the various studies to the contrary, on liquid biofuel, Pimentel remains adamant: “Ethanol production in the United States does not benefit the nation’s energy security, its agriculture, economy or the environment.”

By David Hopkins.

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