The setting is decidedly modest: a utility room in a red-brick house at the end of a cul-de-sac in Wales. But if the hype turns out to be right, this may be the starting point for an energy revolution in the UK. Householder Mark Kerr has become the first British owner of a Tesla Powerwall, a cutting-edge bit of kit that the makers say will provide a “missing link” in solar energy. Like many owners of solar panels, Kerr and his family have a basic problem. They tend to be out at work and school when the sun is shining and the 16 solar panels on the roof of their home in Cardiff are producing power. The excess they miss out on is fed into the grid and they make a return on it but it does not seem right that they do not get to use the power from their panels.