Biomass energy: definition and principle
Biomass is renewable energy produced from organic matter of plant or animal origin, including agricultural, forestry, industrial and household waste. This energy resource comes from the sun, which enables photosynthesis and plant growth, and can be regenerated through sustainable land and forest management practices. Biomass is considered a carbon-neutral energy source, as the CO2 emitted during its combustion is offset by the amount of CO2 absorbed by plants during their growth. It can even be carbon-negative, i.e. absorb carbon over its life cycle, if the carbon from its combustion is captured.
The different types of biomass energy
Wood as energy
Wood is mankind’s oldest source of energy. It is used in a variety of ways to produce energy, notably in the form of logs, pellets or wood chips. It is commonly used for domestic heating, with wood-burning stoves and boilers offering an environmentally-friendly alternative to fossil fuels. Wood is also used in biomass power plants to produce electricity and heat.
One of the main advantages of wood as a renewable energy source is its local availability. Countries with vast forest resources, such as Finland, Sweden or Canada, can take advantage of this resource to reduce their dependence on imported fossil fuels. In addition, the development of the wood energy industry can stimulate the local economy and create jobs in the forestry and energy sectors.
Methanization is a biological process that transforms organic waste into biogas, a mixture composed mainly of methane and carbon dioxide. It is both ecologically and economically advantageous, as it enables the production of a renewable energy source from organic waste. Not all organic matter can be methanized. The most interesting wastes are: livestock effluents (slurry and manure), crop wastes, certain “methanogenic” crops such as corn, and sewage sludge. Others can come from industry, especially the food industry.
Biogas from methanization can be used to produce electricity, heat or be purified for injection into the natural gas network. Methanization also contributes to the sustainable management of organic waste from agriculture, industry and households, and produces a digestate that can be used as fertilizer.
However, anaerobic digestion presents challenges such as the need for a constant supply of substrates, the management of odour nuisance, competition with land use for food production and the environmental risks associated with gas or liquid leaks. In addition, biogas yields can vary according to substrate composition and operating conditions.
Biofuels are fuels produced from organic matter or waste, offering a renewable alternative to fossil fuels. They are generally classified into different generations, reflecting the types of raw materials used and production technologies. First-generation biofuels are produced from food crops, such as bioethanol (biogasoline) from corn or sugarcane, and biodiesel from vegetable oils. Second- and third-generation biofuels are made from non-food raw materials, such as crop residues, algae and agricultural, industrial and municipal waste.
The appeal of biofuels lies in their potential to reduce greenhouse gas emissions, improve energy security by diversifying energy sources, and stimulate rural development and the circular economy. However, biofuels also present challenges, such as competition with agricultural land for food production, the environmental impacts associated with feedstock production and processing, and the need to improve production technologies to increase efficiency and sustainability.
An ancient practice is to use manure as fuel. New types of biomass are being developed:
- Biomass thermolysis is another mode of decarbonized energy production. It involves heating organic matter to evaporate the gases it contains into a hydrogen-rich syngas, leaving only the solid carbon (biochar). This method would be an energy grail, being carbon-negative without carbon capture.
- Miscanthus or elephant grass
The ecological impact of biomass energy: low-carbon or not?
There is much debate about the impact of biofuels:
Biofuels come in many forms, including ones that are nearly identical to fossil fuels but sourced from biogenic sources. Solid biomass, either direct from wood chips, lignin or processed pellets, is the mostcommonly used renewable fuel in industry today and is occasionally used in cement kilns and boilers. Biomethane, biomethanol, and bioethanol are all commercially made today using fermentation and anaerobic digestion techniques and are mostly ‘drop-in’ compatible with fossil fuel equivalents. In principle they cycle carbon in and out of the atmosphere, but their lifecycle GHG intensities are typically not GHG neutral due to land-use changes, soil carbon depletion, fertiliser use, and other dynamics (Hepburn et al. 2019), and are highly case specific.IPCC, WGIII, Industry, p.1182
Advantages and disadvantages of biomass
The main advantage of biomass is that it behaves like fossil fuels:
- As sources of heat or electricity, they are scalable and can adapt to intermittency.
- In the case of biofuels, it is possible to use them in airplanes or combustion-powered cars.
However, they have several disadvantages, depending on the type of biomass.
- Wood combustion releases fine particles, which can be a health problem, especially in homes.
- Methanization and, above all, biofuels can compete with food crops.
- Exploited forests are not infinitely extensible, and they are of less interest in terms of biodiversity than non-exploited forests.
In short, the main problem with biomass is the space it takes up.