• Last year bioenergy-based sources of electricity generated almost 34TWh, nearly 25% of all UK renewable power, DESNZ says.
• Long-term policy incentives for the technology remain uncertain, sparking action from the anaerobic digestion industry association (ADBA).
• As the industry innovates, demand for advisory services to make plants more sustainable, and bring negative emissions technologies to market, is expected to stay strong.

Since 2002, the UK government has given over £20bn in subsidies for energy from biomass, the National Audit Office (NAO) found last year.

At around £0.9bn/year, this compares in scale to the funding for offshore wind, announced in the most recent round of contracts for difference funding, for example.

But in the UK’s Clean Power 2030 plan, energy from biomass takes a relative back seat in terms of its expected portion of the eventual clean electricity grid.

And policy support for electricity and heat from biomass technologies, has now closed to new plants in many cases.

However, unsubsidised plants are emerging as the cost of carbon increases.

Future Biogas, a biogas producer, said in February it is developing such a plant in partnership with AstraZeneca, to provide heat for the pharmaceutical company’s R&D and manufacturing in Lincolnshire.

In March, a proposed transformation of Grangemouth refinery into a hub that includes bioethanol and biomethane production was put forward, showing there is support for bioenergy.

Pressure to decarbonise the economy is also bringing attention to bioenergy’s potential for negative emissions, when carbon dioxide is captured alongside energy production. Future Biogas’ new plant in Lincolnshire is set to include carbon capture, for instance.

As Lewis Farrar, senior process engineer at SLR Consulting, puts it in a recent article on the subject: “If the world is going to get serious about its climate targets, it needs carbon-negative technologies.”

Government funding for bioenergy

Following years of policy incentives, bioenergy-based sources of electricity generated almost 34TWh last year, nearly 25% of all UK renewable power, DESNZ says.

Ofgem, administrators of the non-domestic renewable heat incentive (NDRHI), says it has paid almost £5bn in support across 22,812 heating plants, around 80% of which produce energy from biomass. The scheme has generated 78TWh of heat since its inception in 2011.

But funding schemes that support renewable electricity production, like the Feed in Tariff (FiT) and renewables obligation certificates (ROCs), are closed to new applicants, with payments ending for existing recipients within twenty years.

To support bioenergy for heat and the gas grid, the NDRHI and Green Gas Support Scheme (GGSS) were set up. But the former closed to new applicants in 2021; and the latter expected to do the same in 2028.

The NDRHI funds applicants for up to 20 years; GGSS for 15 years.

In its Clean Power 2030 report, the government explains it is “considering whether there is a strong value-for-money case to provide future support for these generators”. It adds that this “would be subject to robust sustainability criteria”.

In a report last year, the NAO said the government’s current arrangements are not sufficient to give it confidence the industry is meeting sustainability standards.

There are also claims that some energy from specific solid biomass power plants in the UK comes from burning wood from ancient forests in North America, while government subsidies fund it.

Anaerobic digestion (AD)

Anaerobic digestion (AD) is one of the more compelling sustainability cases, when it comes to generating energy from biomass.

This takes in organic waste like animal manure, sewage sludge and food waste as feedstocks. Microorganisms then break them down, in an oxygen starved atmosphere, producing a predominantly methane and carbon dioxide gas blend, known as biogas.

The gas can be burned to create heat in a boiler, or heat and electricity in a combined heat and power (CHP) engine.

If cleaned up into a pure stream of methane, referred to as biomethane owing to its biogenic origin, it can be injected straight into the natural gas grid.

The solid byproduct of AD, digestate, is a nutrient-rich material that can be used as fertiliser. It can replace artificial alternatives and promote sustainable farming.

In a research paper, academics from Aberdeen University calculated that up to 24% of the UK’s electricity demand could be met by anaerobic digestion, though they acknowledge this is theoretical.

In December, the Anaerobic Digestion and Bioresources Association (ADBA) published a report on the technology’s role in UK net-zero targets. It makes the case for a 100TWh “green gas potential” by 2050 in the country.

This is multiple times higher than the 30 to 40TWh the government put forward as a 2050 target, in its 2023 biomass strategy.

For context, it is projected the UK’s total annual electricity demand will be 692TWh in 2050, according to the Climate Change Committee’s seventh carbon budget.

In March, the ADBA sent an open letter to chancellor of the exchequer, Rachel Reeves, voicing concerns.

The letter explains that in the last year, several anaerobic digestion (AD) plants have closed. And “the lack of action to support our clean power sector” is making it hard to meet targets.

The association adds the UK is at risk of losing 2TWh of renewable electricity from AD by 2030. And it calls for AD and biogas to get “equal treatment with other renewables under the UK Emissions Trading Scheme”.

Making AD sustainable

Because biogas and biomethane end in combustion, carbon dioxide is released along with the energy. But the process can be considered renewable in context.

As the researchers at Aberdeen University say in their paper, biomass is generated at a finite rate. So it is renewable when it is “consumed at the same rate at which it is generated”.

Sewage sludge and food waste, for instance, if left to decay rather than being sent to an AD plant, would release harmful methane gas to the atmosphere. And they come from plants that sucked up carbon when they were growing.

This makes AD a waste management process, as well as a source of energy.

Other feedstocks, like energy crops, can be harder to make sustainable, but there are methods to do so.

For example, recipients of subsidies can use energy crops in some cases if they can evidence certain sustainability requirements.

Farrar explains SLR works with clients to ensure their feedstock is sustainably sourced and complies with regulations.

The company also provides environmental impact assessments (EIAs) as well as lifecycle assessments (LCAs).

LCAs measure carbon emissions across the entire AD process to confirm it delivers a net carbon reduction compared with fossil fuels.

It is also important to find carbon hotspots so that further savings can be made, he says.

SLR has experience in, and has managed, every step in the process of AD projects, from initial feasibility studies and technology provider selection, to planning and permitting, serving as the owner’s engineer, and overseeing commissioning and plant handover.

Because it has multidisciplinary experts, Farrar explains, the company also helps clients understand and manage broader environmental impacts. For instance, odour control from handling organic feedstocks, or minimising methane leakages.

While the aim is to advise operators to source waste feedstocks where practical, he notes that the company’s specialists can help prevent issues like soil erosion and nutrient depletion that can be risks during the cultivation of energy crops.

Bringing negative emissions to market

When AD uses feedstocks that are sourced sustainably, the resulting biogas or biomethane is generally considered as renewable and low carbon, as described.

Therefore, if carbon dioxide as a byproduct is captured and stored or used, the energy generation can have net negative emissions. This is known as bioenergy with carbon capture and storage (BECCS).

Farrar says the UK has over 130 biomethane plants with the potential to capture 1m tonnes/year of biogenic carbon dioxide.

He notes this is more than the country’s annual industrial demand for the chemical, for uses like carbonated drinks, medical applications, and fire extinguishers, at 600,000 tonnes. Using biogenic carbon dioxide would replace its fossil fuel-derived equivalent.

Some 10% of AD-derived biogenic carbon dioxide is currently captured, he says. But demand for this is expected to grow, particularly for uses like sustainable aviation fuels (SAF) and gas to cure concrete. The carbon dioxide can also be stored underground.

The UK government hopes to improve the rate of greenhouse-gas removals (GGR) across a range of technologies. It has a target of 5m tonnes/year of engineered GGRs by 2030, and 23m tonnes/year from 2035, Farrar says.

This is increasing demand for related advisory services.

Farrar says uncertainty is holding back demand for BECCS. The carbon pricing environment is ever-changing, which impacts the revenue streams it could generate. The UK’s carbon dioxide transport and storage infrastructure is nascent.

Firms like SLR are called upon at the feasibility stage to assess the market for captured carbon dioxide to help create business cases for BECCS projects.

Farrar and his colleagues support clients on both the commercial and technical sides of retrofitting carbon capture to AD and energy-from-waste plants, for instance.

He adds that public perception of the technology can be another barrier, as can securing planning permissions and permits.

Accurately quantifying the true emissions savings, ensuring things like carbon leakage and land use changes are accounted for, is another essential piece of making the technology successful.

But there are BECCS projects gaining traction.

In October, Evero, a biomass energy company, announced its two plants have passed a “delivery assessment”. These form part of the HyNet industrial cluster in Northwest England.