Something amazing happened last weekend. For the first time in many years, people were talking about energy – and they were excited. They weren’t bemoaning their bills, or their service, or wondering what the new government would do to fix the market. People from outside the industry, people at parties and in cafes, were talking about Tesla’s new 4ft domestic battery, which according to founder Elon Musk, heralds a “fundamental transformation in how the world works”.