WSL is studying the energy potential of biomass at the Swiss Competence Centers for Energy Research (SCCER), and devotes its attention to both woody and non-woody biomass.
It’s peaceful here at this park in the heart of Zurich. Young people sit in groups on the lawn, enjoying the morning sunshine on Platzspitz. Just across from them, a Grün Stadt Zürich employee makes his rounds on a ride-on mower. It’s something he and his colleagues across all of Zurich’s green spaces do on a regular basis, so that the sun-worshipers can continue to enjoy the lawns. An enormous quantity of grass is heaped together every year – but what happens to this biomass?
As part of his study at WSL, geographer and development planner Georg Müller has set himself the task of finding out how much of this landscape maintenance green waste is accumulated in the canton of Zurich, and how much of it is put to use. He not only investigated grass cuttings from parks and other public green spaces in urban areas, but also non-ligneous cuttings from maintenance of nature reserves, roads and railway lines. What interested him the most in all of this was how much of this plant waste could be converted into energy.
“In the context of energy transition, renewable energy sources are playing an increasingly important role. In this respect, biomass has a part to play, too,” says Müller. In fact, all biomass can be converted into energy. It can either be burnt to produce warmth or fermented to produce biogas. Biogas production is based on putrefaction processes that occur naturally in moorland and lake beds: microorganisms break down organic substances under airtight conditions and create biogas. This can be collected in a reactor and converted into electricity at a power station, or fed into a natural gas grid after processing. Even the grass cuttings from Platzspitz make their way to the municipal biogas plant every week.
Power for 5,000 households
Of course, landscape maintenance green waste constitutes only a small part of the biomass that can be used for energy purposes. Nevertheless, this kind of energy creation has been on the agenda for some time now in other countries – Germany even subsidizes it with funds from the public purse. In Switzerland, however, the use of herbaceous biomass for energy purposes seems less of a priority. Müller wants to use his work to change this – but that is not his only motivation: “If we use the biomass energy that results from the maintenance of conservation areas, we can combine the concerns of nature conservation and climate protection.” From a climate protection standpoint, the conversion of biomass into energy means that no additional CO2 is emitted into the air. And when it comes to nature conservation, regular mowing and the removal of cuttings help to promote the diversity of the plant and animal world; for example, in hay meadows.
In order to find out how much green waste is available in the canton of Zurich, and how much energy might be obtained from it, Müller relied on existing databases, such as area inventories of various habitat types. Where no data was available, he carried out interviews with the specialists who maintain the various green spaces. In order to make statements that go beyond the canton of Zurich, he also made projections for the whole of Switzerland. From this it emerged that if green waste from the whole of Switzerland was converted into energy, it would cover the electricity needs of about 25,000 households. Nonetheless, Müller is keen to qualify this: “Farmers today use roughly 40 % to 50 % of green waste as animal feed or straw, particularly cuttings from nature conservation areas. Using this to source energy would not make much sense, since it’s already being used for sustainable purposes.”
The same goes for grass cuttings that are used as mulch – as is the case in a number of parks. This can be ecologically and economically beneficial, and allows a more sparing use of fertilizer. Müller has left these areas out of consideration, calculating only the potential sustainable energy available for use (see infographic for definitions of potential). The projected figure for this stands at about 90,000 gigajoules for the whole of Switzerland, enough to cover the electricity requirements of roughly 5,000 households. Müller sees the greatest potential in biomass growing alongside motorways and cantonal roads. Maintenance services remove this after mowing or mulching for safety reasons, as the material can blow onto the road or clog the drains.
Biomass to become more important
Even if green waste makes only a small contribution to energy transition, Müller is convinced it will become a more significant energy source in future, a statement with which Oliver Thees can only concur. He’s in charge of WSL’s Forest Production Systems research group. Together with Vanessa Burg, Matthias Erni and Renato Lemm, he investigates the potential future role of biomass in the Swiss energy system under the auspices of the BIOSWEET competence center. As part of the Energy Strategy 2050 plan, the Commission for Technology and Innovation (CTI) and the Swiss National Science Foundation (SNSF) have established eight competence centers for energy research – the Swiss Competence Centers for Energy Research (SCCER). SCCER BIOSWEET (BIOmass for SWiss EnErgy fuTure) is one of these.
The vision of Thees and the other researchers from across nine institutions is to double the energy supply derived from biomass by 2050. Most of the institutions within SCCER BIOSWEET focus on technology research; they investigate how biomass can be more efficiently converted into electricity, biogas or liquid fuels in future. Thees and his WSL team are taking a closer look at biomass resources and their availability. First, there is woody biomass, which includes not only forest wood – treetops, branches and thin trunks that are not used for industrial purposes – but also wood from tree and shrub maintenance in urban areas, and road and embankment (‘wood from landscape maintenance’). It can all be used to source energy. Wood from building renovation (‘waste wood’) or production waste from sawmills and carpenters (‘industrial wood residues) can also be added to this list. Second, there is non-woody biomass, which includes the landscaping green waste mentioned above, animal manure, agricultural crop residues, biogenic waste from households, gardens and industry, and sewage sludge. Since all types of biomass are very different in terms of quantity and energy content, the first thing to do is to establish a comparable basis. For all types, the research team calculated how many tonnes per year of the dried substance are theoretically available and how much could be sustainably used. They then worked from there to calculate the future energy potential, broken down into every region in Switzerland. “Compilation of this information allows us first of all to compare the different types of biomass, and to determine where the most energy can be sourced, both now and in the future,” Thees explains. It should also provide an important decision-making basis for politicians and operators of biomass power plants.
The first phase of the research project comes to a close at the end of 2016, by which point the data for all biomass types will be available. In the second phase, the team will define a variety of energy scenarios and simulate how these might develop by 2050 on the basis of the SCCER BIOSWEET project data. A preliminary study, however, has made it possible to draw some initial conclusions. During the research project Renewable Energies Aargau (see also Diagonal 2/15), one of Thees’ colleagues investigated the different biomass types in canton Aargau, just as SCCER BIOSWEET is now doing for the whole of Switzerland. The project showed that the types of biomass that demonstrated the greatest potential for energy use were animal manure and forest wood (see infographic). Comparison with other renewable energy sources in Aargau showed that the contribution of biomass to the renewable energy supply would nonetheless remain modest. For Thees, though, this is not a reason to sit back and give up: “In contrast to solar or wind energy, biomass energy is storable, which makes it an effective long-term solution to balance out fluctuating supplies of solar and wind energy. It’s also the only energy source to produce heat, power and fuel. I’m convinced that biomass will play an increasingly significant role in the overall energy system in future, even if only in small quantities.” (Christine Huovinen, Diagonal 2/16)