- Jan 21, 2020
- 4 min read

Biomass Energy - Angel or Devil?

Updated: Feb 7, 2020

The conversion to biomass energy has been a large part of reducing reliance on fossil fuels. But is this renewable energy source really as green as we first thought?

In May 2019 the UK went 2 weeks without using any coal to generate electricity. To put this in perspective, the last time this happened, Queen Victoria was on the throne.

But whilst Biomass Power Plants reduce the dependence on coal, their smokestacks are still emitting carbon dioxide, possibly more than the coal fired power plants they have replaced.

The logic behind biomass energy is simple.

Trees and plants absorb carbon dioxide from the air, they use photosynthesis to isolate the carbon and then use it to build tree trunks, bark and leaves
When the plant dies, it rots down and much of the carbon is released back into the atmosphere as carbon dioxide.
We intercept this carbon cycle, using the stored energy productively rather than letting it be released to nature

As it stands, around half the EU’s renewable energy is based on biomass, and this figure is likely to rise.

“The benefit of biomass is that it can be implemented rapidly and uses the current energy infrastructure,”

says Niclas Scott Bentsen, an expert on energy systems based at the University of Copenhagen in Denmark.

Drax - A Massive Operation

In the UK, the Drax Group has led the way on the above process.

Over the last decade, the Drax coal-fired power station in North Yorkshire, which produces around 5% of Britain’s electricity, has had four of its six generating units converted to run on biomass. Today, Drax generates around 12% of the UK’s renewable electricity – enough for four million households.

Shipments of wood pellets arrive in UK Ports almost daily, each carrying around 62,000 tonnes of wood pellets (enough to keep the boilers going for two and a half days).

Unloading the ship takes three days and requires 37 freight train journeys. These pellets then end up at Drax in one of four “Albert Hall-sized storage domes."

Surprisingly, it seems that the transportation of the pellets throughout this process only contribute to a very small proportion of the supply chain emissions.

In just under two hours an entire freight-train’s worth of wood pellets goes up in smoke, and whilst it may seem that this is contributing to deforestation, it is actually incentivising landowners to maintain and improve their forests to use for biomass, rather than using the land for other ventures.

According to Drax, moving from coal to biomass has greatly decreased the plant’s CO2 emissions by over 80% since 2012.

These calculations rest on a couple of key assumptions:

The carbon released when wood pellets are burned is recaptured instantly by new growth
The biomass being burned is waste that would have released carbon dioxide naturally when it rotted down.

But are those assumptions correct?

Carbon Debt Payback

Biomass supporters claim that when forests are harvested sustainably, and the timber industry thinnings are used as fuel, the smokestack emissions are cancelled out by the carbon absorbed by forest regrowth.

However, some scientists say that this carbon accounting simply doesn’t add up.

“Wood bioenergy can only reduce atmospheric CO2 gradually over time, and only if harvesting the wood to supply the biofuel induces additional growth of the forests that would not have occurred otherwise,”

says John Sterman, an expert on complex systems at Massachusetts Institute of Technology (MIT) in the US.

The time needed for the regrowth to mop up the additional CO2 is known as the “carbon debt payback” time. This is regularly disputed.

Even if biomass energy isn’t 100% carbon neutral, there may still be a place for it in the energy mix.

Currently, around two-thirds of renewable energy in Denmark is provided by biomass. It plays a critical role in district heating, particularly when the wind fails to blow.

In 2018 it was calculated that the carbon debt and payback time for a Combined Heat & Power Generation Plant in Denmark was paid back after just one year, and that after 12 years greenhouse-gas emissions were halved relative to continued coal combustion.

These numbers are vastly different to the 40+ years of payback time which were estimated for the process used by plants similar to Drax.

In this Danish study, the plant burns wood chips rather than pellets, which reduces processing energy.
The wood is sourced locally from mixed forests in a cold temperate region, which have different growing characteristics from trees in warm temperate regions.
The energy it produces is maximized, producing both heat for local houses and electricity.

Getting More out of Biomass

Simon McQueen Mason, a biologist from the University of York, UK, thinks that just burning biomass is missing a trick.

“Just using it to generate heat and electricity seems like a waste of a really good resource.”

Instead, McQueen Mason is investigating ways of making gas and liquid fuel from biomass.

The intention is to get micro-organisms and bacteria to munch their way through wood material, and then in turn, collect the resulting gas and liquid produced as the bugs digest the biomass.

Pilot plants using sugar cane residue are already proving promising and could provide a solution, but currently burning it is providing governments with a quick-fix way to reduce emissions.

Despite the smoke coming out of the boiler chimney at Drax, the EU’s classification of biomass as a renewable form of energy enables the UK to ignore the carbon dioxide being produced here, on the assumption that it will be mopped up by the trees on the other side of the ocean.

Making use of this form of carbon “loan” has played a key role in reducing reported emissions across the EU.

Even if living trees can soak up these carbon-dioxide emissions, there is a danger due to the fact that regrowth is not a certainty. The forest land may be converted to other uses (e.g. Pasture, agricultural land or development).

This does not even take into account the risks from forest wildfire, insect damage, disease and other ecological stresses, including climate change itself which may limit or prevent regrowth.

This could result in the biomass carbon debt never being re-paid.