The Tidal Irrigation and Electrical System

In December of 2014, I presented a poster at the American Geophysical Union’s conference in San Francisco titled ‘Carbon Sequestration through Sustainably Sourced Algal Fertilizer: Deep Ocean Water’. It compared the TIESystem (the central purpose of this website) with other potential users of deep ocean water (DOW). The paper then went on to examine the advantages of growing marine plants for energy uses like biofuels in a TIESystem on the continental shelf over growing algae in open ponds on the land.

While there, I met many interesting engineers and scientists who were kind enough to consider my proposal, offer advice and point out errors I had made. A few of these AGU meetings have led to collaborations that I intend to write about in a later blog. Critically, these conversations reinforced my conviction in the project and gave me new impetus.
Since returning to London, I have rewritten the poster in line with the new data. The most important change has been to the amount of marine plant growth that is to be expected in a cubic meter of DOW if it is exposed to sunlight. I had based my estimate of 5 grams on natural upwellings. However, this paper ‘Effects of Deep Seawater on the Growth of Several Species of Marine Micro-Algae’ experimentally verified a growth rate of around 147 grams per cubic meter of pure DOW.
This increase of approximately 29 times in the expected energy density of algal growth to DOW brought to the surface has profound implications for the TIESystem. Previously, I had focused on building TIESystems on tropical or subtropical continental shelves in order to gain concomitant electricity generation from the thermal potential in the seawater above 20c. Ocean thermal energy conversion (OTEC) systems, under ideal conditions, can produce ten to twenty times as much energy as the tidal flow of water through a traditional turbine. However, this new data means that marine plant growth yields nearly ten times as much energy as OTEC possibly could. What is more, this amount of growth means that it is economically viable to build TIESystems on temperate continental shelves like the North American Eastern Seaboard or the Bay of Biscayne in Europe. Temperate seas are characterized by larger tidal fluxes than most of the tropics and a TIESystem’s biological productivity goes up in direct proportion to the tidal flux.

In 2014, world energy use totalled about 150,000 tWh. My estimates suggest utilizing less than five percent of world ice-free continental shelf into a network of about 200 TIESystems would generate enough biomass to equal that amount of energy (one kg wet marine plants equals 25 mJ which is about 6.97 kWh rounded which with collection and energy lost in generation I will put it at 5 kWh.) This could replace all fossil fuels with a CO2 neutral alternative that fits into our current energy framework. In other words, we would still have diesel-, methane- and gasoline-burning cars.  However, this energy would only release the CO2 that was absorbed in the original plant’s growth. Each one of these TIESystems in the network could pay for itself in seven years and then go on producing indefinitely. To view the poster ‘Carbon Sequestration through Sustainably Sourced Algal Fertilizer’: http://seavac.org/wp-content/uploads/2015/03/TIESystemAGU2014A0.pdf