Reactive Technologies sent data over the UK's national grid by modulating its 50Hz hum

Virtual power plants — software systems that tie together electricity from many renewable sources so a central body can sell it at varying cost — had only been shown in small trials: RWE combined wind and rooftop solar in Germany, and a New York project tied 300 homes' panels into a 1.8-megawatt plant. Scaling them nationally required all the parts to communicate.

A UK trial on the National Grid, carried out with systems from Reactive Technologies, showed a shortcut: the grid itself can carry the messages. Huge resistors generated messages by modulating the 50-hertz AC signal, and detectors scattered around the grid recorded them accurately — what the Guardian called the first time data had been successfully transmitted across a national-scale power grid.

The payoff is demand that follows supply: when prices fall, an industrial pump can work harder; when they rise, a thermostat can gently adjust its set point. Unlike smart-metering, the company claims, devices only ever receive messages, so there is no privacy intrusion — and no need for an internet connection.

Every device already listens to the grid's 50Hz wave, so the delivery channel exists and needs no new wiring.

Receive-only devices sidestep the privacy objections that slow smart-meter rollouts.

Sporadic renewables make price-signalled demand the cheapest way to balance supply at national scale.

The infrastructure you already own can be a network: before building a new channel, ask whether the existing one is quietly already carrying capacity you can modulate.

The first commercial customers were expected to start using the service within 18 months of the 2016 trial, with the first tests to be carried out in commercial settings before any move into people's homes.