My colleague Mackinnon Lawrence recently provided a thorough examination of the prospects for biofuels as a viable source of energy for transportation and power generation in the coming years – from both negative and positive points of view. Last week, the negative outlook was reinforced by a World Resources Institute report that found that using valuable farmland to grow crops for energy is a wasteful practice that will never supply a significant portion of the world’s energy and that will divert land more urgently needed for growing food crops.
By 2050, the report states, the amount of calories available from crops will need to expand 70% simply to keep up with increased demand for food. Since three-quarters of arable land is already used to provide human needs, “a growing quest for bioenergy exacerbates this competition for land.” Bioenergy supporters have called for biofuels to supply 20% of the world’s total energy demand by 2050 – a goal that would require about 225 exajoules from biomass each year.
“That amount, however, is roughly equivalent to the total amount of biomass people harvest today—all the crops, plant residues, and trees harvested by people for food, timber, and other uses, plus all the grass consumed by livestock around the world.”
That is simply unrealistic, especially given the anticipated growth in consumption of plants for food and other human uses such as clothing, timber, and so on. What’s more, clearing forests to burn wood pellets for energy results in a net carbon increase, once you factor in loss of the CO2 removal capacity of the standing trees. The numbers don’t add up for massive increases in biomass cultivation for energy.
There is, however, another source of renewable, bio-based energy that could be scaled up without robbing food producers of land: biomethane, often called renewable natural gas (RNG). Biomethane can come from cultivated crops, such as corn silage; but other, more promising sources include municipal waste and livestock operations. (Navigant Research’s report, Smart Waste, explores the potential for diverting municipal waste streams for energy recovery.)
One advantage of biomethane is that it is chemically indistinguishable from the methane that constitutes natural gas, which means that the infrastructure – pipelines, turbines, vehicle engines – that uses conventional gas collected underground can also run on RNG. A “poo-powered” bus, fueled entirely by gas collected through sewage treatment, went into service in the U.K. city of Bristol last November.
Not the Trees, Please
On the electricity side, the United Kingdom now has 28 biomethane-to-grid projects connected to the gas distribution network, using gas produced from the transformation of food, brewery, and van wastes – and energy crops. “These plants have the capacity to produce 1.8 billion kilowatt-hours of gas per year, enough to meet the heating and cooking needs of around 100,000 homes,” reported the Green Gas Certification Scheme, the organization advocating increased use of RNG in the United Kingdom.
In Canada, biomethane advocates are aiming “to have a fully developed RNG marketplace by 2020 that helps meet energy needs, supports growth and innovation for business, and offers a solution to issues associated with waste emissions,” according to a December, 2014 report from the Canadian Gas Association (CGA). The report found that the potential supply of energy from various biomethane sources could reach as high as 1.3 trillion cubic feet of RNG – equal to one-half of Canada’s natural gas consumption in 2012.
Such optimistic projections must be tempered, though, by the limits on sourcing biomethane from crops. More than half of the supply of biomethane projected in the CGA report would come from one source: forests.