Wood: A wild card for the energy transition

Wood can be produced CO₂ neutrally, used several times as a material, transported and stored in various forms, and used as heat, electricity and fuel. Last but not least, it can bridge gaps in solar and wind energy production, as it is available all year round. Researchers at the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, the Paul Scherrer Institute PSI and other institutions have calculated the energy potential of Swiss wood and further developed technologies for combustion and conversion into electricity and fuels. They also investigated how bioenergy should best be embedded in the Swiss energy system.

The authors of the "White Paper Wood" emphasise that "energy wood is of greater importance than its comparatively low potential would suggest". It summarises the results of the Federal Government's multi-year energy research programme "Biomass for Swiss Energy Future" (SCCER Biosweet), which involved up to 15 research groups and dozens of industry partners.

Unused but limited potential

Currently, wood energy accounts for about 5 per cent of the total final energy consumption in Switzerland, namely about 40 petajoules (PJ) per year. That is slightly more energy than the city of Zurich needs in a year. This share could - economically and ecologically sustainable - increase by a maximum of one third (14 petajoules), calculated the WSL bioenergy experts.

Energy wood can originate directly from the forest and open land, but it can also be residual wood from carpentry and sawmills or wood that has already been used (referred to as waste wood). The most untapped potential (5 to 10 PJ) remains in forest wood. "Wood as a valuable but limited source of energy requires efficient use," emphasises Oliver Thees from WSL, who played a leading role in the report.

The researchers suggest the following for more efficient use: From a climate protection perspective, wood should not go straight from the forest into the oven, if possible. Instead, it should first be used to make houses and furniture, chipboard or insulating materials before it is burned. This is called cascade use. At present, however, 95 per cent of the valuable energy wood is used to generate heat for heating rooms. This is not optimal, the authors warn.

Aircraft that fly with wood

For maximum energy production and CO₂ savings, wood should be used differently on a larger scale than it is today. In industry, wood can be used to generate high-temperature process heat, for example in the form of steam. Or it can be used to produce gaseous and liquid fuels - including for aircraft. The waste heat and CO₂ produced during conversion should be captured and used. This helps the CO₂ balance and compensates for other emissions, such as those from agriculture, which are unavoidable. The conversion technologies developed in the research programme improve the efficiency and CO₂ balance of such applications, but not all are ready for the market.

Furthermore, electricity can be generated from energy wood in combined heat and power plants, which would be the next best use, especially in winter, to bridge the winter electricity gap. If space heating is to be obtained from wood, this should ideally and if possible be done in large plants connected to the district heating network. These can be operated with fewer pollutants and more efficiently than a large number of small units. "We have developed new processes for converting wood into fuels and energy and brought them closer to the market, thus contributing to the success of the Swiss energy transition," says Oliver Kröcher from the Paul Scherrer Institute PSI, co-author of the report.

Stabilising the electricity grid

Because energy wood can be used in so many ways, the authors of the report call it a "wild card for shaping the energy transition". Their calculations also show that energy wood can stabilise the energy supply and the electricity grid, as wood can be stored and converted when needed to balance peak loads in the grid.

More efficient wood use will not come about by technological means alone. There is still work to be done in research, business and politics: The wood usage chains must be examined and optimised. There is a need for a basis for the practical implementation of these complex technologies. Last but not least, political measures can steer the use of wood, for example through targeted incentives for efficient combustion plants.

Text : Oliver Thees, Beate Kittl