When people think of clean energy, wind turbines and solar panels often come to mind.
But another less well-known method of generating renewable electricity is booming across the UK and environmental campaigners have raised doubts about its green credentials.
The burning of trees or plant matter – known as plant biomass – now accounts for more than a fifth (21%) of the UK’s renewable energy, second only to wind power.
The number of plant biomass power plants in the UK has more than trebled in four years, from 135 in 2014 to 429 in 2018.
Between them, they now produce enough energy to power around 7.4 million homes, analysis by the JPIMedia Data Unit has found.
Unlike other forms of green energy, biomass produces greenhouse gases. Across the country, the rise in biomass means its total greenhouse gas emissions have nearly reached the amount produced by coal.
The industry says wood is sourced from renewable forests, with new trees being planted which store carbon and help to offset the emissions produced.
But with the environment proving a key policy battleground in this year’s General Election, campaigners are calling for the practice to come under more scrutiny.
‘No better than electricity from coal’
Katja Garson, forest and climate campaigner at European campaign group Fern, said: “It is very concerning that in the global push to reduce emissions, more is not being said about the climate impacts of harvesting and burning wood.”
Critics have also raised concerns that some power plants ship wood in from overseas, saying this has an added impact on the environment.
The UK now imports 7.8 million tonnes of wood pellets a year, more than 20 times the amount imported a decade ago. Most comes from the USA and Canada, data from the Office for National Statistics shows.
Campaigners are urging the Government to rethink the £1.3 billion in annual subsidies that the biomass industry gets.
Almuth Ernsting, of the pressure group Biofuelwatch, said the Government should redirect subsidies to “genuinely low-carbon renewable energy” instead.
“For the climate, electricity from forest biomass is no better than electricity from coal,” she said.
“Both are completely incompatible with the need to rapidly reduce carbon emissions.”
‘Trees are being regrown all the time’
But Benedict McAleenan, senior advisor to the Renewable Energy Association, disputed these claims.
He said: “Pretending that biomass is somehow no better than coal means ignoring a whole host of facts.
“It particularly misunderstands the way forestry works, ignores the important role of regulations and forgets the fact that trees are being regrown all the time.
“In reality, UK rules are world-leading and prevent unsustainable practices.”
Mr McAleenan said technology being developed called Carbon Capture and Storage would allow biomass plants to “suck carbon out of the atmosphere”, reducing the emissions they produce.
He said it would not be possible for the UK to hit net zero-carbon without using bioenergy with Carbon Capture and Storage.
The Department for Business, Energy & Industrial Strategy (BEIS) said the Government has mandatory sustainability criteria for biomass sites.
A spokesperson said: “The UK boasts a thriving, diverse, low-carbon energy mix, with over half of our electricity coming from low carbon sources last year.
“Sustainable bioenergy is further boosting our energy security and keeping costs down for consumers, as we work towards our legally-binding net zero emissions goal by 2050.”
Case study: Blackburn Meadows, Sheffield
Sandwiched between the M1 motorway and a nature reserve, on the site of the demolished Tinsley cooling towers, is the Blackburn Meadows biomass power station.
Run by energy giant E.ON, the plant has been operating for the past five years and generates enough energy to power 40,000 homes in South Yorkshire.
Despite this, Sheffield City Councillor Douglas Johson, of the Green Party, is concerned the site’s carbon dioxide emissions will prevent the city from reaching its net-zero carbon goals.
“In principle, using wood to generate electricity is acceptable, provided it is genuinely waste material.
However, where wood has to be produced or wasted unnecessarily just to keep a biomass plant going, that is more of a problem,” Cllr Johnson said.
The council has an ambition for Sheffield to become a net-zero carbon city by 2030 but Cllr Johnson said the presence of the plant would make this more difficult.
Data from the National Atmospheric Emissions Inventory shows that Blackburn Meadows is one of the biggest emitters of CO2 in the local authority.
A spokesperson for E.ON said Blackburn Meadows recycles locally-sourced waste wood and said the waste “would have otherwise have gone to landfill”.
The spokesperson added: “The combined heat and power plant is a more efficient process, generating enough power for the equivalent of 40,000 homes and at the same time capturing the waste heat produced through that process for a district heating scheme providing heat to customers including Sheffield Forgemasters, the Sheffield Arena and Ice Sheffield.”