Clambering across the sloped roof of King’s College Chapel with the agility of an undergraduate, Toby Lucas, 56, pointed to where his craftsmen had welded solar panels to an expanse of newly installed lead. It was the scariest part of the project, he said, because an errant spark could have ignited the 500-year-old timbers underneath, which hold up the roof of this English Gothic masterpiece.
“It’s an iconic landmark in Cambridge, and it’s part and parcel of where I live,” said Mr. Lucas, whose firm, Barnes Construction, did the restoration. “You don’t want to be the person who is responsible for burning part of it down.”
The chapel came through the project unscorched and now stands at the heart of Cambridge University, no longer just a glorious relic of the late-medieval period but also a cutting-edge symbol of the green-energy future. Its 438 photovoltaic panels, along with solar panels on the roofs of two nearby buildings, will supply a shade over five percent of the college’s electricity.
King’s College Chapel is one of several landmark houses of worship in England that have installed solar panels in recent years. The cathedrals in Salisbury and Gloucester have them, and this project may open the door to more: A neighboring Cambridge college, Trinity, is contemplating whether to put photovoltaic panels on the roof of its chapel, which dates to the 16th century.
But this being a college town, and King’s College Chapel being such a nonpareil work of architecture, the debate over installing panels was long and lively — a heady mix of aesthetics, economics and politics. Even now, with the scaffolding dismantled and the panels beginning to soak up the late-winter sunlight, critics are eager to point out why the project was a mistake.
“You have this extraordinary openwork parapet, which is a really bold feature,” said John Neale, gesturing toward the top of the chapel, where a crenelated wall runs along the north and south sides. “You can see through the parapet.”
“Now what you can see through the parapet, and indeed above it, depending on where you’re looking from, is a reflective layer of solar panels,” said Mr. Neale, the director of development advice at Historic England, a preservation group. “That will be radically at odds with the historical character of the building.”
In truth, the solar panels are scarcely visible from ground level, though they are more noticeable from a distance. But Mr. Neale noted that they change color depending on the weather, as light plays off them. While the effect is muted during the frequently overcast winter, it could become more conspicuous in the summer, with clouds scudding across a blue sky.
Mr. Neale was at pains to say that he does not, on principle, oppose retrofitting old buildings with new features. He pointed to a nearby cafe in the nave of St. Michael’s Church as a worthy example of converting an old building into new uses. Historic England, he said, has endorsed panels on other churches.
But “on the whole, you shouldn’t put panels on prominent roofs,” Mr. Neale said. Far from setting a precedent, “this actually is the outer limit, and we think has crossed a line that shouldn’t have been crossed.”
Other critics argued that the relatively small percentage of electricity generated did not justify the aesthetic cost. In a hint of a culture war, some suggested the solar panels were the kind of politically correct gesture typical of a progressive institution like King’s College, whose graduates include the economist John Maynard Keynes, the World War II code breaker Alan Turing and the novelist Zadie Smith.
“There are many ways to address fears about rising temperatures,” David Abulafia, an emeritus professor of history at Cambridge, wrote in the right-leaning Spectator magazine last year, as Cambridge City Council weighed whether to approve the project. Installing solar panels, he added, was “quite simply, another example of virtue-signaling.”
Asked how he viewed the panels now that they were in place, Professor Abulafia kept his sword sheathed. “It’s happened now!” he said.
The leaders of King’s College were aware of these critiques when they considered installing panels, along with a new lead roof. The dean of King’s College Chapel, Rev. Dr. Stephen Cherry, said he was initially skeptical of the idea, which came up during a planning meeting several years ago.
“We needed to think very carefully about the visual impact and the amount of energy generation we would achieve,” he said. “I was very concerned that we would be tempted to make an empty symbolic gesture.”
A study concluded that the photovoltaic panels would generate an estimated 123,000 kilowatt-hours of energy per year. That is enough to reduce the college’s carbon emissions by more than 23 tons each year or the equivalent of planting 1,090 trees. The college’s nearby Wilkins Building and Old Garden Hostel have panels, but no other surface offered that kind of opportunity.
As for the visual impact, Dr. Cherry said it was mitigated by the fact that the panels virtually covered the roof, which at least made it consistent. While the polished sheen of the panels was a change from the textured gray of the lead, both were utilitarian rather than decorative features, he argued.
“Nobody has said, ‘Goodness me, that’s quite an eyesore,’” Dr. Cherry said.
Among the students, he said, the project has been popular, perhaps even giving the chapel a currency it has not had at King’s College for years. With its magnificent fan vault, carved between 1512 and 1515 and the world’s largest, the chapel almost stands apart from King’s College, a tourist attraction that draws visitors who barely linger to look at the manicured frontcourt or the dining hall.
“It’s not so much signaling virtue as signaling a clarion call for change,” Gillian Tett, the provost of King’s College and a columnist for The Financial Times, told The Guardian in November. “Yes, it’s a symbol, but symbols reinforce what’s normal, and we’re trying to change what’s thought of as normal.”
For Mr. Lucas, the construction supervisor, who has restored several old buildings in Cambridge, it was an engineering challenge and a labor of love. To reduce the risk of fire, he used thermal imaging every evening to make sure his workers did not leave behind hot spots. In laying the frame, they had to compensate for a barely perceptible sag in the middle of the 289-foot-long roof.
After months on the roof, Mr. Lucas became a student of its ways. He pointed out peregrines that alight on the chapel’s four corner towers to hunt. He noted how over centuries, visitors carved their initials in the stone wall along the spiral stairs leading to the roof. “Helen 2009,” reads a recent inscription.
Given that the chapel has stood for half a millennium — the product of a 70-year construction project under four kings: Henry VI, VII and VIII, plus Richard III — the furor over the solar panels will end up being at most a transitory distraction.
“The new roof should last 100 years,” Mr. Lucas said. “The life span of these panels is 25 to 30 years. They can always take them off.”