A laboratory of solar energy gives Lyon its moment in the sun

What’s remarkable about Tahar Diab’s big yellow house with pool in Rognac, a town near Marseille, is the view from above. His tiled roofs are covered with 16 solar panels, strategically positioned to follow the sun through the day. The panels provide so much power that he makes about €1,000 a year reselling some of it to the electricity company, EDF. He only has to use electricity from the grid when there’s no solar available — chiefly at night.

Diab spent €17,000 having the panels installed. The sum was unusually high partly because his house is so big: the average cost of home installation in France is about €10,000, without a storage battery. But Diab reckons his panels will become profitable within seven years. “It’s green sun,” he marvels, “much cheaper than fuel. The price of energy is much too high right now.” No wonder, he says, that around Rognac “you see more and more panels”.

Solar panels have so far been installed in only about 600,000 French homes, or less than 2 per cent of the country’s housing stock. However, the market is growing fast. The boom is helping answer two questions currently resonating well beyond France: what kind of homes are best suited to solar? And what’s the fastest way to get more of them kitted out with it?

First, a caveat: solar panels aren’t a perfect solution to climate change. Their production emits CO₂, even if, over the panels’ lifetimes, the emissions are much lower than those of fossil fuels. Most panels need to be replaced after about 25 years, though recycling options are emerging. And more than 80 per cent of the manufacturing of the world’s solar panels occurs in China, some of it using forced labour from Muslim Uyghurs. Still, solar energy is one of our best options to slash emissions.

Residential solar has received two boosts since 2020: first from lockdowns, when more people had time to sit at home thinking about their power supply, and then from the energy crisis caused by Russia’s invasion of Ukraine. The French home solar market doubled between 2021 and 2022, says Jérôme Mouterde, cofounder of DualSun, the company that supplied Diab’s panels. “It’s not a big market,” he adds wryly, “so doubling is possible.”

The sky-high cost of energy is incentivising homeowners to generate their own power. France’s centrally regulated electricity prices jumped 15 per cent in February and another 10 per cent on August 1. Higher prices shorten the period in which people earn back their outlay on installing solar panels. The average time to profitability is now seven years in sunny southern France, and 10 years in the darker north, says Mouterde. Measured over 25 years, he estimates average annual return on investment at 12 per cent.

Moreover, he says, installing panels tends to raise a property’s value, because the next owner gets a self-generating energy system. DualSun guarantees that its panels will operate for 25 to 30 years, depending on the model. They can last beyond that, after which 95 to 100 per cent of the components can be recycled.

A good place to witness large-scale solar use is Lyon, 400km south of Paris. I visited on a typical summer’s day in the new climate: 30C, with blazing sunshine. Métropole de Lyon, the local government, is aiming for a tenfold multiplication of solar use on its territory by 2030.

Lyon’s hotbed for solar is La Confluence, the neighbourhood sandwiched bet­ween the confluence of the Saône and Rhône rivers in the city centre. It used to be an ugly industrial zone but in the past two decades, homes, offices and shops have replaced decayed factories, warehouses, rail yards and a prison. Today, La Confluence bills itself as a walkable “green neighbourhood”; well-off workers stroll and cycle about and have lunch on restaurant terraces.

The push for solar here began about 15 years ago. A public company, Lyon Confluence, now hopes to get panels installed on every suitable building in the neighbourhood. One day, in the noontime sun, the company’s sustainable development director, Maxime Valentin, took me up on to the roof of the Marché Gare. The building, once a wholesale market, is now a cultural centre. But more than that: the Marché Gare has become an energy source.

Its roof is covered with slanted black solar photovoltaic panels, which produce more energy than the building consumes. There’s enough surplus to power the Confluence company’s headquarters across the street. (Photovoltaic panels convert sunlight into electricity, whereas solar thermal panels produce energy to heat water, space heaters and the like.)

What kind of homes are suited to solar? And what’s the fastest way to get more of them kitted out with it?

The roof we are standing on offers several object lessons in what makes a building suitable for solar panels. First, the roof is large. Valentin explains: “The bigger your surfaces, the more profitable it is, the more energy savings you will make.” Second, the roof is flat and almost empty, allowing panels to be easily installed. Third, the building was being renovated anyway: the price of installing the panels, about €50,000, was a mere detail in the overall cost of renovations. Last, the Marché Gare isn’t in the shadow of any neighbouring buildings, so it gets plentiful sun.

Not all rooftops in La Confluence are suited to solar, but the aim is to use each one for something. Valentin points to a lower roof in the shadow of the Marché Gare. Since it’s too dark for solar panels, grass is being grown there instead. Then he indicates an older, slanting roof opposite us, studded with chimneys and TV antennas. It too is unsuited to solar, but on sunny days its residents could, in theory, get their power from solar panels on a nearby building. At times when there’s no sun, they would rely on other energy sources in the French grid.

“The idea,” says Valentin, “is to create energy communities so that the solar benefits local people.” When a panel on a roof produces a kilowatt of electricity, that kilowatt could be consumed by a nearby household. The notion of a direct transfer of energy is, he admits, in the case of Lyon Confluence, “a fiction”. In fact, all solar power produced here goes into the national grid. It’s impossible to trace where an electron produced by the Marché Gare’s roof is ultimately consumed. But the idea of “auto-consumption” makes residents — who have to sign official agreements to use solar energy — feel they benefit from the panels. For now, many don’t seem aware of receiving power from the sun.

Standing on the Marché Gare’s roof, you glimpse the black edges of solar panels on several nearby buildings. The neighbourhood has more than 40 solar installations, says Bruno Gaiddon of Hespul, an association specialising in renewable energies, which advises Lyon Confluence. He adds, “This neighbourhood is a kind of laboratory for what will be generated in France in future.” And not just in France: Lyon is one of eight European cities participating in the EU’s ASCEND project, to help identify solutions for the energy transition.

What works in La Confluence could work in similar neighbourhoods even in colder climes. The key to solar power isn’t sun, but light. Even after nightfall, the Marché Gare produces a little solar power from the moon, street lights and light pollution. Indeed, several northern countries lead sunny France in solar production. Germany has the most solar-powered homes in Europe, about 1.8mn, but even Poland and Belgium and the Netherlands each has more in absolute numbers than France, reports the research and consulting firm LCP Delta.

To reach more of the 98 per cent of French homes that don’t have solar will by definition require putting panels on less suitable older buildings. The city of Dijon, 200km north of Lyon, is attempting just that. Dijon’s École Buffon has become France’s first “energy-positive” school, its solar panels supplying energy to 14 public buildings. Some of the city’s older social housing apartment blocks have also installed panels.

Dijon’s learning curve has been steep. Sarah Bello, director of urban renovation and housing at Dijon Métropole, the local government, says the decision was eventually made not to place the panels directly on to apartment buildings’ roofs. The tops of lift shafts and ventilation apparatuses got in the way and cast shadows. Instead, the panels were put on the railings around the rooftop. She says, “If I were to tell you it was easy, no, that wouldn’t be true. But we learnt a lot from our beginners’ mistakes.”

For each solar project, she says, you have to understand which roofing materials you’re dealing with. They will need to support the panels for decades. The building’s electricity cables must be strong enough to “inject” the solar into the grid. Project managers have to learn to navigate bureaucracy. But progress does happen. Now, says Bello, “We are hearing the first questions about solar panels from condominium owners.”

Last year, a potentially game-changing French regulation came into force: renewables must be able to cover or exceed the energy needs of each new-built home. That should encourage the take-up of solar, predicts LCP Delta. Ask French experts how to accelerate take-up further, and the suggestions pour out. Simplify the state’s administrative procedures around putting panels on homes, cut VAT on it, and facilitate interest-free loans to help bear the cost of installation, advises Gaiddon.

DualSun’s Mouterde says that, above all, France needs more qualified panel installers. “That’s more of a limiting factor than the number of roofs.” He notes that in France you can follow a training course to become a certified plumber or electrician, but not a certified solar-panel installer. DualSun plans to create its own academy to train installers.

Solar has vast potential. “In the residential market, we are only at the very start,” says Mouterde. Remove some obstacles, and a decade from now, the black panels on Diab’s house and in downtown Lyon could be routine sights across the continent.

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