What does sustainable biomass actually mean?

There’s no doubt that burning wood to make electricity produces less carbon emissions than burning coal – but does that make the process sustainable? It’s a controversial area, but here Nick Cottam sifts through the arguments of those on each side.

On Friday 13 March 2020, shortly before the UK entered a prolonged period of COVID lockdown, the Zheng Zhi bulk carrier vessel docked at the Humber International Terminal in the Port of Immingham. Housed in this enormous ship’s hold were just under 64,000 tonnes of wood pellets from the US port of Baton Rouge in Louisiana, the largest ever biomass shipment, bound for the Drax Power Station in Selby, Yorkshire.

As the Zheng Zhi nosed its way into Immingham, applause, praise and indeed some degree of controversy were already echoing around the port and beyond. Biomass from plants, animal waste, charcoal and in this case, wood residue, currently contributes around 40% of the UK’s renewable energy. When burnt to generate electricity at Drax and other power plants around the UK it also produces several million tonnes of greenhouse gas emissions every year.

However, despite its emissions, bioenergy is clearly cleaner and less polluting than the coal it is replacing, claim advocates. Not true, argue opponents. Bioenergy, they claim, is an expensive political stop gap which is itself doing significant damage to the environment.

Targeting net zero

Whichever way you look at it, the introduction of biomass and its resulting bioenergy has been an effective short-term political fix as part of efforts to phase out coal and move towards net zero carbon emissions targets, both in the UK and elsewhere. Alongside the mighty Drax Power Station which over the past 10 years has converted four of its six generating units to biomass, there are now over 1,770 biomass power plants operating in the UK which, between them, have become an important part the energy mix.

‘Bioenergy from biomass and waste already plays a significant role in delivering low carbon heat, power and transport fuels in the UK,’ notes Hannah Evans of the Energy Systems Catapult, the UK energy technology R&D centre: ‘Our research in this area aims to highlight the importance of developing the bioenergy sector to deliver cost-effective emissions reductions.’

Like diesel for motor vehicles, bioenergy has been seen as a good political fix and a quick win in the drive to balance energy security with cutting carbon emissions. Just as coal has become the number one persona non grata in the low carbon energy mix, so biomass is seen by many, including our political leaders, as an acceptable substitute. There’s plenty of timber residues in the world, runs the argument, so why not burn it?

What’s more, say advocates, providing the wood you burn comes from sustainably managed forests, there’s a convenient carbon offset built into the arrangement. The trees are replaced, the forests keep growing and while carbon emissions result from the burning of biomass, plenty of carbon is being taken out of the atmosphere by all those growing trees.

Rising greenhouse gas emissions

However, opponents such as the US-based Natural Resources Defense Council (NRDC) and the UK and US-based Biofuelwatch argue that trees simply can’t grow fast enough to absorb enough carbon to counter carbon emissions from bioenergy generation. In the UK, for example, greenhouse gas emissions from bioenergy rose from 4mn tonnes a year in 2010 to 15mn tonnes a year in 2017, but emissions from coal reduced by 20mn tonnes over the same period.

So what happens to bioenergy in the medium and long term when the coal has been phased out? Needless to say, biomass sensitivities have heightened as demand for the fuel increases, driven by generous government subsidies.

Over the past decade, Europe has significantly increased its use of renewable energy and about 50% of this has come from burning biomass. Like the UK, other countries are exhausting their home-grown residues of timber and turning to imports, some of them involving long haul shipments like the Zheng Zhi.

According to climate expert Phillip Williamson of the University of East Anglia: ‘Replacing fossil fuels with biomass energy seems like a good idea, both nationally and at the global scale. But such policies haven’t been properly thought through and risk making matters worse, not better.’ He adds that: ‘even if further carbon dioxide releases can be prevented, the scale of bioenergy required seems likely to have serious land use implications, either at the expense of food production or resulting in natural habitat loss.’

Perhaps inevitably, carbon capture and storage is put forward as a viable mechanism to reduce carbon emissions from bioenergy. National Grid has stated that using carbon capture to trap bioenergy power plant emissions would mean that the electricity produced by bioenergy would save 62mn tonnes of carbon dioxide by 2050, the equivalent to about 13% of the UK’s total greenhouse gas emissions in 2019.

According to the latest 2020 Outlook Report by the International Energy Agency, renewable energy capacity is set to expand by 50% between 2019 and 2024 and bioenergy will continue to be an important part of the mix. While solar PV is expected to lead the charge, accounting for almost 60% of the expected growth, bioenergy is on a par with offshore wind, with the greatest expansions in China, India and the EU.

Generous subsidies

Bioenergy growth in the UK has been backed by taxpayer largesse to the tune of millions of pounds. In 2016, according to the campaign group Biofuelwatch, energy companies received around £890mn in UK subsidies for generating electricity from bioenergy, and the vast majority of that came from burning wood.

While new rules in the UK were introduced in 2018 to stop subsidies for new bioenergy power plants, the rules do not apply to existing facilities. This means that Drax Power Station, for example, the UK’s largest bioenergy burner, will continue to receive subsidies of around £2mn a day.

While Drax has its critics, the station continues to be an integral part of the UK energy mix and claims to take sustainability, including sustainable biomass sourcing, very seriously indeed. On 26 May 2020, for example, Drax supplied just under 14% of the UK’s electricity, delivering a consistent and responsive load unaffected by variations in weather or other technical factors.

What’s more, says Drax Group Media Manager Selina Williams, all the wood burnt is sustainable: ‘We get two-thirds of our wood chips from managed forests in the south of the US, but none of this is virgin timber. This is residue timber that can’t be used anywhere else and all of it comes from growing forests.’

Drax and others on the side of bioenergy make the point forcefully that they are using timber that has locked up carbon, helping to offset carbon emissions when the timber is burnt for energy. ‘We never cause deforestation, forest decline or carbon debt,’ adds Williams. ‘We’re independently audited and our biomass complies with and in many cases goes beyond stringent standards set by Ofgem and the EU.’

Sustainable sourcing

While opponents such as NRDC highlight forest decline and the time taken for new trees to absorb significant amounts of carbon, Williams insists that Drax will only source from forests that are growing at a greater rate than the material that is harvested. ‘The forests we source in the US South have doubled in growth since the 1950s,’ she adds.

While it’s clear that the sourcing of residue timber for bioenergy – doesn’t drive the forestry industry, there is little doubt that the growing demand for biomass has had an impact and, in the view of many, changes the economics.

The ‘Cut Carbon not Forests’ campaign is among the more vociferous opponents to the growth in bioenergy generation. ‘The climate emergency requires us to build a genuinely clean energy economy and end wasteful subsidies for dirty biomass energy,’ said Almuth Ernsting, Co-Director of Biofuelwatch, which is part of the campaign. ‘Cutting down trees, shipping them from forests overseas and burning them in power plants was never compatible with the need to keep global warming to 1.5°C,’ she adds.

Without further reform, argues the campaign, UK energy bill payers will spend £13bn in direct support to large biomass power plants between now and 2027. Drax, it says, will account for £10bn of this money, as well as being exempt from paying carbon taxes. The campaign argues that climate change and biodiversity are inextricably linked, the priority being to keep forests standing where at all possible.

To understand the polarity of arguments for and against the growth in timber for biomass you only have to compare contrasting images published by the NRDC and by Drax. The former presents blighted areas of cleared forest, while the latter shows responsible forestry management in its latest sustainability report. In the case of Drax, it’s all about responsible sourcing and in the US South, notes the company, forest harvest statistics show that biomass accounts for just 3% of the material harvested.

Supporting woodland management

Other smaller UK bioenergy operators also highlight their approach to climate change and the responsible sourcing of timber. For example the Kent Renewable Energy biomass plant at Dover, which opened in 2018, claims to be saving over 100,000 tonnes of carbon dioxide a year. As part of this process the company says it is playing a part in ‘reinvigorating the woodlands of south-east England’, and supporting local coppicing, which is leading to a higher proportion of the region’s 320,000 ha acres of woodland being actively managed.

‘Unmanaged woodlands represent a huge opportunity in terms of carbon balances, biodiversity management, employment opportunities and productive potential,’ notes the company. ‘By providing a significant local market for low-grade wood, our power plant is re-vitalising local forestry.’

In contrast to Drax, the Kent plant is tapping into home-grown timber, not all of it residue, and making a virtue of promoting local forestry and all its various offshoots. The 27 MW plant highlights its capacity to supply electricity to 50,000 homes – more load, more coppicing but undoubtedly some impact on biodiversity. Whether this counts as sustainable bioenergy remains open to debate.