"I'm an early adopter of new technology," says Gavin Tait, a 69-year-old from Glasgow, with a hint of pride. So when he received a lump sum on retirement a decade or so ago, he invested in renewable energy: solar panels on the roof, a home battery and a heat pump. "It seemed like a no-brainer," he recalls. "I could save money and help the environment - why wouldn't I?" At first, it worked. His well-insulated home stayed warm and his energy bills fell. But over the past couple of winters, things