Marine Energy Technologies

Marine technologies are devices immersed in the earth's ocean capturing the energy from waves, tides and the heat stored in the water. They offer huge potential, as the resource is largely untapped so far. This is a relatively young branch of renewables. Unlike in the wind industry, no dominant deisgn has emerged yet.

Waves are caused by wind blowing over the ocean.

The movement of the moon around the Earth is responsible for gravitational forces, causing ebb and flood.

Ocean surface temperature is 15C higher than in 1km depth.

Energy in waves is in the wave height and the wave period (or horizontal speed).

Typical wave heights 3m (storm- 15m), waver period 8s (storm - 15s)

Because of the two types of energy within waves, the conversion process is complex.

Challenges & Outlook

Good locations are far off-shore, and technologies are complex.

Tidal Barrages exploit the height difference between ebb and flood.

Require 10m vertical difference between ebb and flood.

Technology is similar to conventional dams with hydro energy.

Challenges & Outlook

Very few suitable locations. Environmental concerns have so far limited expansion.

Tidal stream turbines exploit the kinetic energy from the water flowing in and out.

Good sites have flow speeds of more than 4m/s in 40m depth. Most sites are near shores.

Technologies are similar to wind turbines.

Challenges & Outlook

Apart from tidal barrages, this is the most developed marine technology with some projects verging on the brink of going commercial. Low environmental impact favours tidal stream over barrages.

The temperature difference between surface and deep water can be used to drive a turbine:
Warm surface water vaporises an expanding gas that drives a turbine. Cold, deep ocean water cools the gas down to liquid, which is pumped back to the vaporiser.

Challenges & Outlook

Although the thermal energy stored in oceans is huge, the low temperature difference of 20C over a length of 1km, makes it very difficult to exploit. No commercial application built.

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