Two of the world’s biggest wind energy companies have warned of difficult conditions as slower-than-usual winds and supply chain difficulties delay manufacturing. Ørsted, a Danish company, said lower-than-normal wind speeds throughout the third quarter had affected its earnings. Across the first nine months of 2021 slow winds cost the company 2.5bn Danish kroner (£290m) compared with the previous year. Ørsted makes about two-thirds of its revenues from offshore wind including off the UK’s coasts. Vestas, the world’s largest wind turbine manufacturer, on Wednesday cut its profit guidance for the second time this year, citing supply chain instability and cost inflation that was hitting the wind power industry. It came as political and business leaders gathered in Glasgow for the Cop 26 UN climate summit, with green energy high up the agenda. Increasing the supply of renewable energy is a key part of ambitions to limit global heating. However, the slower winds have contributed to the global increase in the prices of gas and other fossil fuel sources of energy before winter in Europe. In the UK, wind energy has provided 60% of energy needs at peak times but becalmed conditions have forced the country to resort to burning gas and coal to keep the lights on. Higher gas prices have fed through to retail energy providers, and 18 have gone bust since the start of September after failing to protect themselves against price moves. At the same time, manufacturers have endured months of delays to parts as the rapid recovery from the coronavirus pandemic has knocked timetables out of joint. Shares in Vestas slumped by 15% on Wednesday in early trading after it revealed that profits had halved during the third quarter of 2021 to €206m (£175m). It also cut its forecasts of future earnings. Vestas’s chief executive, Henrik Andersen, said the company had faced an increasingly challenging global business environment for renewables. He cited “supply chain instability and rising energy prices as well as accelerated cost inflation from raw materials, transport, and turbine components, which severely impacted profitability and limits visibility”. Marika Fredriksson, Vestas’s chief financial officer, said: “The prices are something I don’t think anyone has experienced previously and it’s a very, very tough environment. “I think it’s likely it’s going to continue into next year and I don’t see the trend changing,” she said, adding that the company had not cancelled any projects but there had been several delays. Mads Nipper, Ørsted’s chief executive, said the company had achieved “good financial results in the third quarter despite low wind speeds and unusual market conditions”.