Légumes Perchés made his carbonic introspection

Should Légumes Perchés perched vegetables be perched less? This is, in a way, the central question posed by Constantin Nifachev, one of the co-founders of the start-up Lausanne that won the Prix SUD 2020 organized by the The weather.

Last year, as SME’s growth accelerated and mandates multiplied, he wanted to fulfill a mission that had been dear to him since the beginning of the adventure: calculating the carbon footprint of a model urban farm. “Model”, because it does not yet exist. But one of the mandates that Légumes Perchés could soon win is very similar to this typical project, confides Constantin Nifachev. “This idea corresponds to our desire: to have the most rational and virtuous impact possible”, he adds.

like a swiss house

After several months of work, he first needed to compare, before judging the result. Twelve tonnes of CO2 per year, for a farm of 1600 m² on the roof of a building, “this roughly corresponds to what each Swiss generates”. According to the Federal Department for the Environment (FOEN), in fact, pollution per inhabitant was 14 tons in 2015. “A single flight from Zurich to New York is already a ton of CO2”, he adds later, being aware that he is comparing himself here to one of the bad scholars of climate protection.

We understand that Légumes Perchés wants to be a good student. To carry out this ecological introspection, the start-up relied on the Zero Emission Group, an EPFL student association. In detail, about half of these 12 tonnes of emissions are generated by delivering and lifting the compost on roofs (5 tonnes). The concrete slab overlay and farm infrastructure (faucets, vegetable washing station, pergola, tables and chairs, etc.) are responsible for a ton of CO2. The other major emitter is inputs (4 tons), and mainly compost. The rest of the emissions are distributed between machines and other horticultural tools, pieces of seeds or even the use of a cold room.

But determining CO2 emissions is only the first half of the exercise. “The objective has always been to define how to offset these emissions, insists Constantin Nifachev. But also finding compensation methods that have a real function at the place of operation and benefits for the environment.”

The shadow of solar panels

Here, too, a model was developed. The installation of permanent ponds would make it possible to offset one ton of CO2 per year. Plant 65 trees, 1.43 tons. The 5 tons of vegetables produced locally, instead of being imported, are worth a savings of 1.25 tons. But it is thanks to the solutions offered by agrovoltaism, which combines solar panels and shade for crops on the same surface (and which is the specialty of Insolight, another SUD Prix finalist), that most compensation is possible. With approximately 70 m² of solar panels, almost 9 tonnes of CO2 emissions can be offset in this way.

Read too: Solar panels, saving the Earth or its opposite?

But this calculation does not include the social impacts of the activity of Légumes Perchés – precisely what finally convinced the Prix SUD jury to award the title – are not included. The vegetable workshops, the desire to create social bonds in the neighborhoods where their crops are grown “are qualitative elements much more difficult to measure”, recognizes Constantin Nifachev. Who promises that these benefits will be reviewed soon.

What should have been done differently? “This exercise had the potential to make us change our practices,” admits Constantin Nifachev. Perhaps in some specific cases it would be worthwhile to install the plantations between the buildings and not on the roof. But the Légumes Perchés model will not fundamentally change. Because “the answer to the big question: “Is it reasonable to occupy the roofs?” yes, he concludes. Especially when you factor in the space you don’t take up to optimize floor space.”

See too: Eureka, our video series on Swiss green solutions

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