The problem is that, until now, schemes for tapping that power have required building dams and barrages so gigantic they would have given even the most wild-eyed Victorian engineer pause. As a more economical alternative, Kepler Energy has announced plans for a 30 MW tidal energy fence to be built in the Channel. With an estimated cost of £143 million (US$223 million), the underwater fence would be built in the water somewhere along the line between Aberthaw and Minehead and could be operational by 2021.

According to some estimates, if the tides that flow in and out of the Bristol Channel could be properly harnessed, they could supply up to five percent of Britain's energy needs. It's a challenge that has attracted engineers for over a century, but while on paper there's a tremendous amount of energy waiting to be tapped, a viable plan of how to actually go about it has proven elusive.