Debate over the sustainability of bioenergy has flared up again on both sides of the Atlantic, with some saying it is worse for the climate than coal. Mark Hillsdon weighs the arguments

In the forests of the south-eastern US, a chainsaw fires up, the teeth biting into the trunk of a tall, yellow pine. It teeters before crashing to the ground, where its branches are stripped and the tree – along with thousands of other – is trucked off to be used in the construction industry, furniture manufacturing and, in some cases, to generate energy, too.

Several thousand miles away in north Yorkshire, at the massive Drax power station, a delivery of wood pellets arrives, just a small part of an annual shipment of over 3 million tonnes from the US. This is now the largest biomass plant in the world, producing around a fifth of all the UK’s renewable energy.

These are the two sides of biomass, an industry which is polarising opinion and creating a sustainable dilemma. To some it is a cheap, renewable form of energy that, as an alternative to fossil fuels, has a big role to play in the battle against global warming, while also giving a shot in the arm to forest industries.

To others, it has become the “dirty” option in the green energy revolution, an inefficient fuel that destroys forests and biodiversity and which, some reports suggest, is now worse for the environment than coal.

Chatham House report

Chief among these Is February’s Chatham House report which has raised concerns and hackles in equal measure. Written by former Liberal Democrat advisor Duncan Brack, the report is damming of biomass and the negative effects it is having on the environment, concluding that: “The use of woody biomass for energy will release higher levels of emissions than coal and considerably higher levels then gas.”

The report has been welcomed by pressure groups and NGOs such as Fern and the US-based Dogwood Alliance, who have long viewed biomass as a flawed fuel. Its moisture content makes it less energy-dense than fossil fuels, they argue, which means it emits more emissions when burnt. The way this carbon is accounted for then leads to ‘missing emissions’ and it’s also causing deforestation, at a time when we need our forests to act as carbon sinks more than ever.

The good, the bad and the ugly

Hanna Aho, a forest and climate campaigner from Fern, talks about the good, the bad and ugly of biomass. The good are those feedstocks that don’t have an additional impact on forests, she says, such as residues and offcuts from sawmills, which would otherwise be burnt on site or sent to landfill.

The bad are forest thinnings, the twigs and offcuts left over from harvesting timber which should ideally be left in place, as they add carbon into the soil and play an important role in the biodiversity of the forest. But the real ire is left for the ugly, when stumps are extracted and whole trees are cut down and carted off to be turned in pellets.

Commenting on the Chatham House report, David Carr from the Southern Environmental Law Centre in the US has said: “Forests in our region … are being clear-cut to provide wood pellets for UK power plants. The process takes the carbon stored in the forest and puts it directly into the atmosphere via the smokestack at a time when carbon pollution reductions are sorely needed.”

However, it’s a practice that the biomass industry has been quick to deny. “Why on earth, if you own a forest, would you cut your asset down, which immediately stops your cash flow, then sell the raw materials to the lowest bidder?” says Benedict McAleenan of Biomass UK, an off-shoot of the Renewable Energy Association.

Instead, he says, forests are managed and a small section, perhaps 2-3%, is cut down each year. Construction and furniture are the drivers of harvesting, paying the highest prices for timber and helping to lock the trees’ carbon in place. It’s the low value twigs, misshapen branches and residues - the thinnings - that go to make the pellets, he says.

Enviva

The vast majority of the pellets burnt in the UK are produced by the US company Enviva, which runs most of its operations in the forest of south eastern America. According to the company’s chief sustainability officer Jennifer Jenkins: “The primary wood we use to make pellets is low-quality by-product of a traditional saw timber harvest that would have been cut down in order to clear the land for the landowner to replant.” Around 26% of its feedstock is secondary material from sawmills and wood industry residues, she adds.

Pellet exports from this region account for less than 0.1% of the forest inventory, continues McAleenan, compared to net forest growth of between 0.7-1%. Biomass also gives land owners a financial incentive not to turn their land over to agriculture and completely destroy the forest’s sequestrating role.

“Over the last 50-60 years the south-eastern US has seen a doubling of its forest inventories,” he maintains. “These NGOs who are saying this is a disaster, [that] we’re seeing massive deforesting, it isn’t true. We’re actually seeing growth in these forests … it’s a good environmental story.”

Carbon counting

The carbon-neutrality of biomass rests on the ability of the remaining forest, and new planted trees, to absorb the carbon caused by burning. However, as part of the EU’s Renewable Energy Directive, these “combustion” emissions are not added to the overall footprint of biomass, which only includes carbon from the supply chain. These are the ‘missing emissions’.

Add these to emissions from harvesting, processing and transporting the timber and burning wood for electricity emits around 40% more carbon pollution than coal, according to the US-based environmental organisation the National Resources Defense Council. 

“Climate change is advancing very fast right now and what increasing forest bioenergy is actually doing is putting more CO2 into the atmosphere at a time when we should be getting it out,” says Aho of Fern, adding that one can not cut down a mature tree and expect a sapling planted it its place to do the same job.

McAleenan counters this argument: “By managing the forest properly, you can remove trees, replace some and maintain its role as a carbon sink. You’ don’t have to wait for decades to replace the carbon you’ve lost from that harvest … it’s a continuous cycle of growth. We have demonstrated a 70% cut in carbon emissions compared to coal.”

Campaigners also fear there simply is not enough waste wood to fuel the industry, leaving manufacturers with little option but to cut down trees. The sustainability of feedstocks is the domain of bodies such as the Sustainable Biomass Partnership (SBP), established in 2103, somewhat controversially, by seven major European utility companies.

The programme is similar to initiatives such as the Forestry Stewardship Council, explains Melanie Wedgbury, the SBP’s head of communications, and ensures the origins of any feedstock can be traced and that it’s been sourced legally. There are also requirements around replanting.

It offers, she says, a clear system for end-users, such as Drax and Dong Energy, to be able to demonstrate compliance with the regulations. “If you want to get the subsidy that’s attached to burning biomass for energy you have to meet certain sustainability criteria,” she adds. And the subsidies are substantial, with Drax claiming more than £450m in 2015 alone.

Policy review

The EU is the world’s largest consumer of biomass, and bioenergy now accounts for 65% of all Europe’s renewable energy. However, its sustainability is currently being assessed by the European Parliament as part of its review of the Renewable Energy Directive 2009.

“Now is really the time that the EU politicians should be acting on this matter,” says Aho. “In the past 10 years there have been advances in science that people who have already invested [in biomass] have become reluctant to hear.”

A fifth of all the UK’s renewable energy is now generated by biomass, and the co-fired (using a mixture of coal and biomass at Drax will soon be joined by another at Lynemouth in Northumberland, and a purpose-built plant at MGT Teesside. Last year Drax reported that it now burns 70% renewables and 30% fossil fuels.

In Denmark, much has been made of Copenhagen’s green agenda, and biomass is currently playing an important part in the city’s carbon-free future. By 2020 its power plant BIO4 will be running completely on sustainable wood pellets, all sourced from waste wood.

Morten Kabell, the city’s mayor of technical and environmental affairs, explains that there is no national legislation concerning sustainable biomass, so the country has adopted a voluntary agreement to support the use of sustainable biomass in energy production. As a part the agreement, from 2019 at least 90% of the biomass used in Copenhagen will be certified sustainable.

“Burning biomass is not necessarily a sustainable, future-proof solution,” explains Kabell. “It doesn’t make sense to cut down millions of trees around the world just to use them in Copenhagen. Therefore we will focus on wind energy and geothermal energy in the future and the technological development of new, sustainable solutions which can make us less dependent on biomass. We need to be independent of fossil fuels and the usage of biomass is a step, not the final solution.”

There are alternatives to woody biomass, such as elephant grass and agricultural wastes, as well as manure, sludge and black liquor, a by-product of the pulp industry. New, more energy-efficient technologies such as black pellets, dubbed bio-coal, are also being developed. (See Smurfit Kappa’s Zero-waste alchemist)

“There is huge potential to have bioenergy as a central contributor to the energy system, says McAleenan. “The more that we explore the science, increase transparency and work with the NGOs, the better.”

But it seems an unlikely partnership. Aho believes more investment and subsidies should be directed away from biomass and towards solar, wind and other truly low carbon renewable energy sources. “We need to make a clear distinction between the good, the bad and the ugly,” she says, “and don’t subsidise the bad option.”

It’s an argument that looks set to smoulder.

This article is part of our briefing on the renewable energy revolution. See also:

Spotlight falls on energy storagy

Unlocking the trillions for poor countries

'We need to move faster on renewables'

Enviva  Drax  Chatham House  Sustainable Biomass Partnership. Duncan Brack  Fern  Dong Energy  Copenhagen