In March I went to see Henrik Poulsen, the boss of Dong Energy, in Copenhagen. Dong stands for Danish oil and natural gas. It was, like Shell and BP, involved in fossil fuel exploration and production. But in less than a decade it has become an 85% offshore wind company, and is divesting its coal, oil and gas interests. By 2023, Dong Energy will be very close to zero carbon. That is a pretty staggering transformation in a very short space of time. Talking to Poulsen made me realise that we were on the cusp of a quiet revolution. From being the most expensive form of renewable energy, offshore wind was fast becoming the cheapest form of large-scale, low-carbon generation bar none. As Poulsen said: "When you go 10 years into the future and you look back, I think we will look at these years, 2016, 2017, 2018, as the inflection point. I think we'll look back and say wow ... Something happened for wind and solar energy during those years that completely changed the dynamic." But he also said that "without the UK government and what they have done for the past five or six years, we wouldn't have been where we are today. I'm glad to see that it's paying off." There's a pleasing symmetry in fighting climate change, a truly enormous problem that remains invisible to most people in the UK, with offshore wind, an equivalently huge and equally invisible solution.