Should we produce heat, electricity or biofuels from our biomass?

Given the other energy sources available in Switzerland, our biomass should be used as a priority for the simultaneous generation of electricity and heat (or even cooling). The latter should be used in remote heating networks. When this proves to be cost-effective, biomass can be used for the production of biofuel (biogas, biomethane) for gas-powered cars.

Biomass is the most versatile source of renewable energy; it can produce heat, electricity or biofuels for transport. Biomass is also starting to be used as raw material in the chemical industry as a substitute for oil, to produce bioplastics and other synthetic products (the so-called biorefinery concept). It is therefore necessary to determine which of these uses are most relevant, and to set priorities. For thousands of years, wood burning has been used exclusively for heat production, for heating and cooking. Today, we are becoming aware that the energy contained in biomass can and should be better used.

First, consider wood, which is our main biomass resource. If we burn this wood, combustion should be used as much as possible for the joint production of heat and electricity in decentralised cogeneration units supplying remote heating networks [→ Q28]. Why is this? Because this makes it possible to take full advantage of the fact that the combustion gives off heat at a very high temperature (more than 1000°C). This high temperature offers the possibility to generate electricity (through a steam turbine), while at the same time covering heat requirements. Conversely, technologies such as thermal solar panels or heat pumps provide low-temperature heat that can be used only for domestic heating and domestic hot-water production. Cogeneration therefore makes it possible to fully exploit the energy potential of biomass, particularly in units of a certain size supplying remote heating networks. However, in situations where individual wood heating is the only option, biomass should be burnt in modern high-efficiency boilers such as pellet stoves.

An alternative approach to combustion is gasification. Currently in development, it makes it possible to transform woody biomass (wood, agricultural residues, etc.) as well as wet biomass into biomethane, a gas that can be injected into the natural gas network. This process is particularly attractive because it allows great flexibility in the use of biomass while offering a very high level of energy efficiency. In particular, biomethane could be used to produce heat and electricity in individual units (micro-cogeneration), using fuel cells [→ Q27]. But it can also be used to power gas cars. This approach is interesting because it represents one of the few opportunities for our indigenous biomass to contribute to the transport sector, which is particularly difficult to decarbonise [→ Q34].

As for biogenic waste (manure, slurry, sewage sludge, etc.), nowadays it is converted into biogas by a fermentation process called anaerobic (oxygen-free) digestion. This biogas is either used to produce electricity and heat (cogeneration) in situ, or purified and injected into natural gas for the same purpose as the biomethane resulting from gasification.

On balance, Switzerland is lagging behind in the field of liquid biofuels. It does not support the production of first-generation biofuels (bioethanol and biodiesel from food crops). The 2nd generation liquid biofuel sector (from woody biomass such as wood) or 3rd generation liquid biofuels (from algae in particular) are enjoying a certain amount of international interest. It will be difficult to produce them profitably in Switzerland, but it would be possible to import them, provided that they are produced under conditions that meet strict sustainability criteria.

In practice, the best use of indigenous biomass will depend on the availability and the cost of alternative renewable options for the production of heat and electricity.

References

Office fédéral de l'environnement (OFEV) (2009)
(). Biomasse: la Suisse se fixe des objectifs stratégiques.
Office fédéral de l'énergie (OFEN) (2019)
(). Statistique globale de l’énergie 2018. OFEN.
Steubing, B and Zah, R and Waeger, P and Ludwig, C (2010)
(). Bioenergy in Switzerland: assessing the domestic sustainable biomass potential. Renewable and Sustainable Energy Reviews, 14(8). 2256–2265.
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