Tidal power, produced from the force of our planet's oceans sloshing to and fro, has always seemed like a neat idea. But the challenges of making it work — imagine giant underwater propellers having to withstand strong currents and the unending assault of the sea — made it seem less than realistic.

But now manufacturing giant Siemens is throwing its weight behind tidal power startup Marine Current Turbines, which has had a 1.2 megawatt demonstration turbine operating beneath the waves of Northern Ireland's Strangford Lough since 2008.

Siemens' interest is simple: Tidal power is super predictable. (Predictable as the tides, even.) As Peter Fairley reports at Technology Review:

Solar and wind farm operators struggle to predict tomorrow's output, and bad forecasts can wreak havoc with power transmission planning and market prices. In contrast, the gravitational pull of the moon and sun that controls tidal cycles provides a sure means of anticipating the output from tidal generating stations. "Power output of the systems could be calculated for centuries in advance," says Axmann.

With Siemens' loot and manufacturing prowess on board, Marine Current Turbines hopes to install a string of underwater turbines, each 2 megawatts in size, throughout the U.K. The goal is to make them the same price as offshore wind by 2020.