I wonder where they get these numbers. From the article: While tides are a free source of energy, generating power from them is three times more expensive tha

I wonder where they get these numbers. From the article: While tides are a free source of energy, generating power from them is three times more expensive than using natural gas or coal over the life of a project, according to the Carbon Trust, a U.K. government-funded research unit. Including capital expenses, fuel and maintenance, U.K. tidal current power costs 15 pence per kilowatt hour, compared with 5 pence for coal and gas and 7 pence for wind, the trust says. It seems to me that with tidal energy, the initial cost of building a "harnessing source" would be fairly high, but the "maintenance costs," (for lack of a better phrase) would be significantly lower enough to validate investment. Coal and natural gas, which this study apparently deems "cheaper" than tidal or wind, has ongoing maintenance which includes: cost of mining, cost of shipping, not to mention external negative externalities on the environment from carbon emissions. . ..