How sustainable is biomass as a renewable energy source?

Researching the use of biomass in energy production I have found a lot of contention and passionate views on the sustainability of this energy source, particularly where large power stations including the likes of Drax are in the process of switching a significant proportion of their fuel to biomass. As always the situation is a lot more complex than it first appears…

Before we launch into the debate lets first take a look at what ‘biomass fuel’ encompasses and what makes it ‘renewable’

TreesBiomass can be extracted from a variety of sources including crop residues (straw etc.), woody biomass (sawdust etc.), urban waste (untreated wood and paper), forest residues, and short rotation (re-planted or coppiced forest). Some biomass can be directly burned to produce energy; some can be converted into another energy product like biofuel and some can be anaerobically digested to produce methane, which can then be burned to produce energy.

Biomass is considered a renewable energy source based on the concept that the plant material used can be replaced through re-growth and the carbon dioxide that is emitted from burning the harvested biomass can be absorbed by the new plant growth. Of course the Earth’s natural systems are in fact far more complex than this over-simplified idea and this is where conflicting views arise over the sustainability of using biomass as a fuel source.

Interestingly, burning biomass is actually quite an inefficient process and the carbon dioxide released often amounts to more than would be released if we were burning the equivalent in coal, oil or gas. The important difference is that fossil fuels like coal contain carbon that was sequestered thousands or millions of years earlier and when this resource is burned it cannot be replenished. This makes fossil fuels a finite resource and quite unlike managed forests and plant crops, which can be managed sustainably to provide a continuous fuel source and a system for re-absorbing carbon dioxide that is released through burning.

The ‘carbon neutral’ biomass debate

There are few who would claim that biomass is a totally carbon neutral fuel source because there is unavoidably going to be some CO2 equivalent emissions during the extraction and processing of biomass fuel. This is the case for all systems that capture renewable energy once you take into account the carbon footprint of manufacturing, transportation, installation, maintenance and disposal. However, measuring the carbon footprint of biomass is so hugely challenging (if not verging on impossible) compared to calculating the carbon footprint of manmade products like solar panels and wind turbines, due to the complex nature of our Earth’s living systems.

One area of the biomass industry that often raises heated debate is the harvesting of forests to provide wood fuel. Practices like short rotation harvesting and re-planting or coppicing are designed to be sustainable but opponents of this approach are concerned about the amount of time that it takes for the forest to become replenished and CO2 to be absorbed, as well as the potential negative impacts on biodiversity by removing carbon from the delicately balanced ecosystem of a forest.

How long before the CO2 can be completely absorbed?

If we continue looking at the management of forests as a biomass fuel source then there are contradicting views about how long it would take before the biomass is replenished and CO2 emissions are absorbed. In 2010 the Manomet study generated a lot of controversy when it suggested that it would take at least 25 to 50 years for the harvested batch of wood to be replaced by new growth. However, critics have highlighted that this theory focuses on the replenishment of individual trees and does not account for the growth of the forest as a whole.

Another important point to consider about this theory is that it is based on a study of a particular forest-type in one part of the world. The variation of growth in other types of forests will be vastly different from this sample so it is perhaps unwise to assume that this carbon calculation can be applied across the board to all managed forests or natural forests, in all climates around the globe.Fresh piled tree

In an ideal world we would take each forest on a case-by-case basis and assess the impacts of management for biomass production over a 50+ year period. Unfortunately with a lack of time and resources this is not currently possible so we must take a cautious approach when making the switch from fossil fuels to biomass as a sustainable form of energy production.

The biggest worry for many people is the potentially damaging effects of large-scale biomass energy production and in particular where it is added to existing coal-fired power stations. On such a scale it is impossible to fuel a power station without the need to import biomass from other parts of the world. Even if these are sourced from ‘sustainably’ managed forests then we still have to account for the impact of transporting this fuel around the world. Without a fully transparent system in place it is understandable why many people feel worried about what sort of negative impact these practices could have on both our ecosystems and in our atmosphere.

How can we make biomass energy more sustainable?

Biomass energy encompasses a broad range of practices and methods so it is important that we assess the viability and sustainability of using biomass on a case-by-case basis. Here are some ‘must dos’ for ensuring our biomass supply is as sustainable as possible.

  • Source locally – this is important not only for reducing transportation emissions but also for supporting local businesses
  • Research the extraction process – where has the biomass fuel come from? What has been involved in its production? How energy-intensive are the processes?
  • Make the most of waste – the best biomass systems make use of waste that would have otherwise been sent to landfill where their decomposition releases potent greenhouse gases like methane
  • Support sustainable land management – avoid energy crops that are damaging the local ecosystems or taking up valuable space for growing food. Show your support for those that encourage the healthy management of biodiversity and forests.

The benefits of biomass

Biomass energy, when implemented appropriately, has the potential to offer a cost-effective, low-carbon alternative to fossil fuels. With financial support schemes like the Renewable Heat Incentive biomass is an attractive investment opportunity for many people looking to generate their own heat on-site. When managed sustainably biomass fuel can provide an economic incentive for the careful management of woodland biodiversity. In comparison to fossil fuels, biomass is a renewable energy source that releases far less atmospheric pollutants like sulphur dioxide that contribute to the formation of acid rain.

Since we cannot easily quantify the carbon footprint of different biomass fuels, or know the full extent of their impact on our ecosystems, the global debate over the sustainability of large-scale biomass energy projects looks set to continue. Perhaps at this stage it would be wise to adopt a more cautious approach, sticking to the locally sourced and smaller scale, promoting sustainable practices where possible.

Those who are in a position to make use of a locally sourced biomass fuel can see huge cost-savings on energy bills, particularly where biomass is used as a replacement for oil or LPG. Biomass is one of the numerous energy solutions we offer and we always recommend that you check whether biomass would make a feasible energy solution for you before making the switch.