By James Crooks

It is easy to get lost in the currents of the ever-changing world of energy. Between being bombarded with prices for kilowatt hours, the latest efficiency data for solar-energy panels and the pros and cons of the new nuclear micro-reactors, it is understandable that a few things might fall through the cracks. A renewable source of energy that has enjoyed significant growth since the establishment of the Kyoto Protocols in 1997 is that of biomass. In 2017, biomass contributed 119.301 kilotonnes of oil equivalent energy across the EU – double that used in the year 2000 – representing nearly 60% of the total renewable energy produced across the EU and more than wind and solar combined. But what exactly is ‘biomass’? And how can burning fuel and releasing carbon dioxide claim to be carbon-neutral or even carbon negative?

Figure 1: Ameresco Biomass Cogeneration Facility at SRS. Photo: Savannah River Site

How Biomass Works

As a source of energy, biomass refers to the use of biological material – plants or animal products – which is burned to create heat, which in turn is used to create electricity. These biological materials may be grown specifically for the purpose of energy production or be by-products of other human activities such as agriculture or forest management. Biomass also includes so-called first- and second-generation fuels which are derived from biological material such as bio-ethanol, bio-oils, or even bio-fuel cells.

Figure 2: Biomass (left) and bio-oil (right). Photo: Pacific Northwest National Laboratory – PNNL

Given this definition, most of human history has been fuelled with energy from biomass (e.g. wood) or biomass-derived fuels (e.g. charcoal). With that in mind, when was the last time you looked at a campfire or wood-fired stove and thought: “Now there’s a clean and renewable source of energy!”? We know that burning wood and other carbon-based fuels releases carbon dioxide into the atmosphere. How is it, then, that biomass projects can claim to be “renewable” and “clean”?

Both of these claims – renewability and cleanliness – come down to the fuel itself. Because biomass projects rely predominantly on the direct or indirect results of biological processes – trees or crops which can be deliberately planted and harvested – the supply of fuel is considered to be renewable according to the legal standards set up by the UN in the Kyoto Protocols. Moreover, many of the fuels used in biomass projects are themselves carbon negative. Plants take in carbon dioxide from the atmosphere during photosynthesis and because some of this carbon is then sequestered into the soil, at the time of harvesting the plant contains less carbon than it took out of the atmosphere during its life-span. Therefore, even after the plant material is burned in biomass plants or boilers, the total resultant carbon dioxide emission is lower than the amount of carbon dioxide absorbed by the fuels during their lifetime. As such, although it is true that biomass power plants do emit carbon dioxide in order to convert fuel into energy (via heat), it can be said that a biomass project is carbon neutral or even negative across its life cycle.

Not All Biomass Projects

All of this works well in theory. As long as each biomass project carefully sources its fuel in order to maintain at least carbon neutrality (taking into consideration also emissions involved in transport and processing), and does not outstrip the growth-rate of its fuel source, each biomass project should fairly be considered to be a renewable and environmentally friendly source of energy.

However, even in these cases, it is important to be wary of the details. Although a project might be completely carbon neutral or negative across its life cycle, it is nevertheless important to bear in mind the localised impact of the emissions of biomass plants. Recent studies have highlighted the health impacts of pollution on local populations. These have shown that atmospheric pollution is the leading environmental cause of premature deaths in the EU. Emissions from biomass plants undeniably contribute to local air pollution even if they are deemed to be carbon neutral.

Figure 3: Wood harvested for biomass plant in Benin Photo: Geres – Acting for climate solidarity

Further criticism of biomass plants has come from conservation groups concerned with the impact that demand for fuel is having on forestry practices. The demand for wood pellets to serve the growing biomass industry has led to the clearing of mixed forests; these mixed forests are often then replaced with fast-growing monocultures (usually pine) to be harvested in the future. These practices have major impacts on the overall biodiversity of the affected areas, with tropical and sub-tropical forests the most vulnerable to exploitation. This is because ‘developed’ countries such as the UK outstrip their ability to supply their own power plants.

Moreover, as recent studies have highlighted, carbon emissions from the change in land-use are often not taken into account when establishing the carbon neutrality of biomass projects. Searchinger et al. point out that unless the new use of the land increases the potential of an area for the absorption of carbon from the atmosphere, the area itself becomes a net loss in carbon absorption: “[this] remains true even if limited harvest rates leave the carbon stocks of regrowing forests unchanged, because those stocks would otherwise increase and contribute to the terrestrial carbon sink”. Other critics of the field have estimated that it could take between 50 and 100 years for even well set up projects to offset the carbon released during both energy production as well as the initial disruption of the carbon sink.

Biomass in the Future

The need for renewable and carbon-neutral energy is immediate. With the impacts of climate change already being felt by populations all over the world, it is imperative that we find alternatives to the fossil fuels that have dominated the energy market for much of modern history. Despite the caveats listed above, biomass energy can remain a viable means of reducing the impact we have on the environment. With nuclear power out of favour, wind, solar and other renewable energy sources alone cannot yet support the energy demands of the 21st century world. Biomass represents a reliable energy source with more redeeming features than traditional carbon-based fuels. Furthermore, because of the relative ease of converting coal plants to biomass power plants and thus reducing the immediate need for investment in infrastructure, it should be seen as a strong short-term solution to fill the energy gap.

Those caveats, however, cannot be ignored wholesale. It is vital that biomass projects and their suppliers are carefully managed, monitored and held accountable for the overall emissions and impacts of their plants. Biodiversity – especially in vulnerable areas – should not be sacrificed. The use of biomass plants should not outstrip our own ability to supply and regenerate the required fuel in a carbon-neutral and environmentally-friendly manner. Many biomass projects already emphasise this, preaching forestry management rather than harvesting and replacement. This must become an industry standard. Governing bodies have a significant role to play in this; the EU need to take a stronger stance in their upcoming review of the sector, scheduled for the end of 2020 than the non-binding recommendations introduced in 2014.    

Ensuring these and similar measures are put in place would place a finite cap on the use of biomass as an energy source going forward; on the other hand, without such restrictions, then we will be left with the same emissions problem we face now, simply from a different source.