The Tidal Irrigation and Electrical System

renewable energy, carbon dioxide sink, biodiesel, and food from the ocean

Biodiesel best from Open Ponds

Posted by on Thursday, September 2nd, 2010

The Tidal Irrigation and Electrical System can be considered a giant open pond for the growth of marine plants which can then be turned into biodiesel. The potential growth rates of aquatic plants far outstrip terrestrial plants. The question has been what is the best method to grow the plants so they can be converted to biodiesel. The first of these methods has been to fill clear plastic tubes with water, fertilizer and some of the algae that will be grown and then pump the water around to maximize mixing and exposure to sunlight. The second of these methods is to grow the algae in an open pond.

There are advantages to both systems but now a detailed analysis by Anna Stephenson at the University of cambridge has compared them and found that open air ponds are 16.8 times more efficient than perspex tubing (Energy and Fuels, DOI: 10.1021/ef1003123). In an article published in the New Scientist, it is pointed out that pumping through plastic tubes results in a higher energy cost per unit than traditionally sourced fossil diesel. However, this is not the case for open air ponds.

As Ms. Stephenson says, the major drawback to open air ponds is evaporation. So much water can be needed that ponds in many countries would be in direct conflict with traditional demands for water, if they want to produce enough biofuel to replace their domestic consumption. This is not an issue for the Tidal Irrigation and Electrical system because it does not use fresh water, it uses the ocean. Also, the tidal flux is being harnessed in a TIE System to do the pumping and deep ocean water is used as the both the fertilizer and source water for the open air pond, making it much more efficient than the land based ponds envisioned by Ms. Stephenson.

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