From pv magazine France
French cooperative Céléwatt has started construction on a small-sized solar park in Carayac, a commune in the Lot department in southwestern France.
The 250 kW ground-mounted array, scheduled for completion in 2021, is built entirely on mounting structures made of raw oak wood. “Our original idea was to promote local employment and natural resources,” Bertrand Delpeuch, the president of Céléwatt, told pv magazine. “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 in 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 30km from here, this saves the extraction of 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 solar plant with untreated, unprocessed wooden support.”
The project constraints are numerous, as the wood is not milled in a sawmill and the developer 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 power to French energy cooperative Enercoop at a price of €0.08/kWh.
The first prototype comprises fixed connections and metal brackets at right angles. “It did not work,” said Saintignan. “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 PV panels are fixed on an omega purlin, which has the ability to deform and dampen the natural movements of the wood.
To maximize the mechanical characteristics of the rough wood, the 600 oaks are cut out of the growing season, and to avoid any discontinuity in the fibers. As the trees are small in cross section, they were skidded over the shoulder by a local company, Le petit oak noir. “We have succeeded in employing several companies in the region,” Delpeuch added.
Céléwatt claims that everything has also been done to optimize the duration over time. “This is a very resistant and endogenous wood species, which will not fear weather fluctuations,” continued Saintignan. “The structure is made to adapt to the movement of the wood.”
While the risk of fungal colonization has been minimized, simple parts replacement solutions have also been provided. The stability of the panels will be checked every three years with visual inspection 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 outlet, marketed under the “Mécowood” brand, which the company would like to promote in other projects. “This raw wood table can have many other applications, such as the integration of solar panels in a wood storage shed or a heat pump … The possibilities are numerous,” assured Saintignan.
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All of this will have to be replaced too soon. Not a good idea, in my opinion.
oak structures may last for hundreds of years. I just finished a 43kW plant made from oak🤭 also a test project..
Solar panels last 25 to 30 years. Oak should last this long – although the hundreds of years this article talks about is unrealistic. Oak can last that long when kept dry and indoors bit not outdoors exposed to the elements. It should be a decent match to the use though.
I am sudre they have looked into the replacement requirements, and that the price over all for a few decades will be cheaper doing it this way. By that time, there will probably be increased output from new solar panels and they would be replaced anyway.
Cedar is the only product that lasts on or below grade. ( Fence posts)
Check out Anar solar. They use a whole new approach. A simple useful system.
Cyprus pine in Australia is grown in plantations and very durable.
By coincidence, I’ve installed my last two solar arrays on logs cut on my property. These are pine logs so probably won’t be as durable as the oak but it’s very easy to inspect and replace pieces. The first array has been in service for 3 years and has held up well to the deep snow we get here. The logs are growing some fungus but are otherwise in good shape.
Thanks for sharing. Do you see a significant cost benefit considering the full life cycle of the panels? Or would it cost pretty much the same as the steel structures, but it would be more environmental friendly? I think if there is a sizable monetary difference, we can see better adoption of this idea.
These poles presumably come from managed oak forests. I used to live quite close to one in northern Alsace near Haguenau. The management plan would normally provide for thinning at about 15 years (what you see) and 40 (12″ logs for firewood) with the final cut for structural timber at 100 years or more. These early thinnings are more or less waste. Good thinking!
Note that the feet of he oak struts are bolted to galvanised steel bases. No wood is underground, which is where it’s most likely to rot.
How is electric grounding of panels accomplished? Any reports of lightning damage?
Maybe also good for mushroom growing? Do not forget to use wood from coppicing woods.
The world’s electricity is supported by power poles made mostly of wood. They last for several decades, but they’re soaked in creosote. It’s just a good way of using what nature provides. Thanks for the informative article.
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