Rafael Viñoly predicted building might reflect sun but joins developers in blaming 'current elevation of the sun in the sky'

The architect of the Walkie Talkie building in London has admitted that he predicted it might reflect hot sun rays to the street below but "didn't realise it was going to be so hot".

Visiting London this week, Rafael Viñoly said the original design of the building had featured horizontal sun louvres on its south-facing facade , but these are believed to have been removed during cost-cutting as the project developed.

"We made a lot of mistakes with this building," admitted Viñoly, "and we will take care of it."

The 37-storey building at 20 Fenchurch Street in London's financial district has a distinctive shape – widening as it reaches the top – which led to its being nicknamed the Walkie Talkie.

But it was this week renamed the Walkie Scorchie when it was found that the concave shape of the building was channelling the sun's rays into a concentrated beam onto Eastcheap, capable of singeing carpets, blistering paintwork and even melting parts of a car's bodywork. One cafe in the focus of the building's glare even managed to toast a baguette and fry an egg outside their shop.

"I knew this was going to happen," said Viñoly, speaking to the Guardian on Friday. "But there was a lack of tools or software that could be used to analyse the problem accurately."

"When it was spotted on a second design iteration, we judged the temperature was going to be about 36 degrees," he said. "But it's turned out to be more like 72 degrees. They are calling it the 'death ray', because if you go there you might die. It is phenomenal, this thing."

A two-storey scaffolding structure covered in netting has now been erected in the street to absorb the concentrated rays, while three parking spaces have been suspended. The developers, Land Securities and Canary Wharf group, say they are "continuing to evaluate longer-term solutions."

The architect has a track record of creating buildings that burn. His Vdara hotel in Las Vegas, with a similarly concave form, focused sunlight onto the pool terrace in 2010, hot enough to melt loungers and singe guests' hair. The glass has since been covered in non-reflective film.

"That was a completely different problem," said Viñoly, insisting he was following a masterplan that specified arc-shaped towers. "We pointed out that would be an issue too, but who cares if you fry somebody in Las Vegas, right?"

Environmentalists have commented that such "death ray" buildings could actually be harnessed as a useful power source, saying the magnifying effect demonstrates the principles of solar power tower technology. Used in Spain and parts of the US, these power plants employ a radial field of parabolic mirrors to channel sun rays towards a central focal point at the top of a tower, where the heat is stored and converted to power. Viñoly says he designed a similar building for a site in China with a bowl-like facade, specifically shaped to focus sunlight on to an obelisk energy receptor – but it remains unbuilt.

In London, he said the issue was the result of the nature of the development process in the UK, in which the architect is often sidelined.

"One problem that happens in this town, is the super-abundance of consultancies and sub-consultancies that dilute the responsibility of the designer," he said, "to the point that you just don't know where you are any more."

The developers have blamed the problem on "the current elevation of the sun in the sky," a position Viñoly seems inclined to share.

"When I first came to London years ago, it wasn't like this," he said. "Now you have all these sunny days. So you should blame this thing on global warming too, right?"