24.08.2022 | When silo bales store energy for the winter

Garden waste in summer slumber

Jeanette Schranz

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Axpo knows how to make energy from organic waste throughout the year. With a clever storage option using silo bales, surplus garden waste, vegetable peelings and food scraps can be stored during the summer months and transformed into energy when demand is high.

Logically more garden waste is produced during the warmer months than in winter. Trees, bushes and fields sprout as soon as the first warm days occur and continue growing until the fall when leaves drop. Axpo produces around 75 GWh of renewable electricity per year in its fermentation plants using green waste, scraps and food waste. This corresponds to the annual electricity consumption of around 17,000 households - roughly the size of the city of Olten.

Smart energy storage system

Silage film is utilised to store organic waste in the summer when quantities exceed the capacity of the fermentation plants. The surplus garden waste is shredded and packed in silo bales. The silage film works as a biological energy storage system and prevents the valuable substances in garden waste from escaping and maintains the energy content. The bales are then stored at the fermentation plants and the garden waste falls into a summer slumber.

The silo bales are then unpacked and processed at the plants during the winter months when demand is higher. The aim is to achieve maximum utilisation of the plants throughout the year.

Twice recycled, twice as good

Nine of the 15 Axpo fermentation plants store energetic garden waste in silo bales for the winter. The silage foil is made of high-quality polyethylene and is recyclable. InnoRecycling AG is an Axpo business partner and handles the proper recycling of the foil. Without the storage of organic waste in bales during the summer, climate-relevant gases such as methane and nitrous oxide would be released into the atmosphere. Both gases exhibit high greenhouse gas potential and contribute to global warming. Conserving the green waste in silo bales prevents this.

 The natural recycling circuit

To enlarge the graphic

Over 300 cities, towns and companies in Switzerland regularly supply Axpo with organic waste. This waste is used as the raw material and energy source for the fermentation plants. Axpo knows how to produce biogas, heat, organic fertiliser, electricity and animal bedding (naturbett-einstreu.ch) from garden waste, vegetable peelings and food scraps.
The sustainable products fit seamlessly into the natural recycling circuit by returning nutrients back to nature.

The different recycling processes support CO2 reduction and an improved climate footprint. The energy produced, the high quality fertiliser, and the various compost products carry the seal of quality for organically produced products and are certified for use in organic farming.

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