Water is 830 times denser than air meaning that, for a given electricity output, tidal turbines can be much smaller than equivalent wind turbines.

http://www.openhydro.com/envBenefits.html

environment: benefits of tidal

At OpenHydro we believe the ultimate renewable solution will depend on a blend of renewable technologies such as tidal, wind, wave and solar working together. Tidal will play a significant part in this mix given the predictable nature of the energy and the size of the resource.

Particular benefits of tidal include:

* Energy is produced from a resource that is entirely predictable.
* Tidal turbines are located beneath the ocean surface and cannot be seen or heard.
* Water is 830 times denser than air meaning that, for a given electricity output, tidal turbines can be much smaller than equivalent wind turbines.