Renewable energy in the form of wind and solar power can only provide power while the wind is blowing or the sun is shining. But turbines that capture energy from the relentless tides in coastal channels can keep going and going and going. Tidal turbines may also be able to store tidal energy for later -- a feat neither wind nor solar power can match.

Few tidal power stations are currently in operation, but farms of underwater turbines could potentially generate power from the daily back-and-forth currents in a tidal channel. The amount of power generated depends on the speed of the water flowing through the turbine farm. Faster water flow equals more electricity.

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What if farm operators could manipulate the flow of water within a tidal channel, creating the fastest flow of water at the times when energy demand is highest? Researchers Ross Vennell and Thomas Adcock mathematically modeled large tidal channels such as the Cook Strait that separates New Zealand’s two main islands.

By varying the drag of the fan-like turbines on the water, the simulated farms could slow the tidal pulse through the channel, building up water pressure. Releasing that pressure resulted in fast flow of water through the turbines, generating up to three times more power in some simulations than at a normal high tide, the researchers write in Proceedings of the Royal Society A, which published their results.

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Tidal power plants’ production ebbs at low tide, and any demand for power above the turbines’ output must be met by other energy sources. But by storing tidal energy, turbine farm operators could time the farm’s peak energy production to match the hours of highest electricity demand.

The authors estimate that by storing tidal inertia, a turbine farm in the 15-mile-wide Cook Strait could meet up to 90 percent of peak energy demand.

Photo: An Evopod tidal stream turbine is installed in Strangford Lough near Portaferry, Northern Ireland. Credit: Wikimedia Commons/Ocean Flow Energy Ltd.