"Turning AC into the direct current required to power transistors (the heart of all electronic equipment) is a nuisance. The usual way is through a mains adaptor. These ubiquitous little black boxes are now cheap and light. But they are often inefficient, turning power into heat. And they are dumb: they run night and day, regardless of whether the price of electricity is high or low. It would be better to have a DC network, of the kind Mr Daniel has rigged up, for all electronic devices in a home or office. ¶ This is where USB cables come in. They carry direct current and also data. That means they can help set priorities between devices that are providing power and those that are consuming it: for example, a laptop that is charging a mobile phone. “The computer can say ‘I need to start the hard disk now, so no charging for the next ten seconds’,” says Mr Bhatt. The new standard, with variable voltage and greater power, enlarges the possibilities. So does another new feature: that power can flow in any direction." - × × ×

“This chimes with another advantage. A low-voltage DC network works well with solar panels. These produce DC power at variable times and in variable amounts. They are increasingly cheap, and can fit in windows or on roofs. Though solar power is tricky to feed into the AC mains grid, it is ideally suited to a low-voltage local DC network. When the sun is shining, it can help charge all your laptops, phones and other battery-powered devices.” - × × ×