The 250 kW ground-mounted generator, scheduled for completion in 2021, is built entirely on raw oak timber mounting structures. “Our original idea was to promote local employment and natural resources,” said Bertrand Delpeuch, President of Céléwatt. magazine pv. “As we had no room for maneuver on the origin of our 746 monocrystalline panels, which are delivered to us from China by the company Talesun, we decided to focus on the poles.
This region of the Lot department is indeed rich in oak forests. This straight and solid wood, about 15cm in diameter, is traditionally used as a bouchot (breeding support) for the culture of mussels in Charente-Maritime. “Replacing the galvanized steel supports of the solar park with raw wood from forests about 30 km from here saves the extraction of the ore and its transport from China, then its transformation, which is carried out in Portugal, ”Delpeuch explained.
Céléwatt called on the engineering company Mécojit in Capdenac-Gare, with which it had already built another solar park. “It was a real gamble at the start,” recalls Olivier Saintignan, project manager at Mécojit. “To our knowledge, this is the first example of a playpen with untreated and untreated wood support.”
The project constraints are numerous, because the wood is not machined in a sawmill and the promoter must take into account its different sections and imperfections. “Then you have to mount the structure on uneven ground,” said the engineer.
The project is being built without public support and will sell electricity to the French energy cooperative Enercoop at a price of € 0.08 / kWh.
The first prototype includes fixed connections and metal brackets at right angles. “It didn’t work,” Saintignan said. “The pivot links had to be able to move together to adjust the heights and create a plane. Finally, the connections by bolting and the bores, are made directly in the field and the assembly is made by bolted threaded rod, which allows movement between the parts. The photovoltaic panels are fixed on an omega tip, which has the capacity to deform and to dampen the natural movements of the wood.
To maximize the mechanical characteristics of the raw wood, the 600 oak trees are cut during the growing season, and to avoid any discontinuity in the fibers. As the trees are small, they were skidded over the shoulder by a local company, The Little Black Oak. “We have managed to employ several companies in the region,” added Delpeuch.
Watt cible affirms that everything has also been done to optimize the duration over time. “It is a very resistant and endogenous wood species, which will not fear climatic fluctuations,” Saintignan continued. “The structure is made to adapt to the movement of the wood.”
Although the risk of fungal colonization has been minimized, simple parts replacement solutions have also been proposed. The stability of the panels will be checked every three years with a visual check of the resistance of the wood, and a general overhaul will be carried out during the ten-year maintenance.
For Mécojit, what was initially a gamble has become a new point of sale, marketed under the “Mécowood” brand, which the company wishes to promote in other projects. “This raw wood table can have many other applications, such as the integration of solar panels in a wood shed or a heat pump … The possibilities are numerous”, assured Saintignan.
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