Ocean Thermal Energy Conversion may have finally arrived as a serious alternative energy contender

Updated Again May 22,2006: This post has been featured in Scian Melt#19. Also OTEC technology is now available in Chennai! details below. Updated May 8,2006: Toronto has been using this technology using Lake Ontario’s cool water to aircondition downtown areas since 2004. Project executed by Enwave. See below for more details. Almost a year ago, I had read an intriguing article in the Wired Magazine with a provocative title “The Mad Genius  from the Bottom of the Sea“. It talked about the usage of Ocean Thermal Energy Conversion (OTEC) with a hard-to-believe sub title:

Unlimited energy. Fast-growing fruit. Free air-conditioning. John Piña Craven says we can have it all by tapping the icy waters of the deep.

And take this, anti-aging:

As the official tour winds on, Craven drags a plastic chair to the middle of the lawn, plunks himself down, and resumes talking about his anti-aging experiments. Investigating the osmotic and thermodynamic properties of plants led him to wonder about the human body, and now he’s hooked. “I’ve patented my cold-water therapy, and I want to open a cold-water health spa right there,” he says, pointing to the rocky coast. “The doctors don’t agree with me, but that’s because innovation is the enemy of the status quo – it puts people out of business.”

All this is enough to justify the title of the article and also to turn your sceptic antennae to full strength. Anyway, almost a year later, I was browsing India Today’s May 2006 Spice Magazine supplement and I see a blurb on Page 8:

The $70MM Intercontinental Resort and Thalosso-Spa Bora Bora’s USP –  a unique eco-friendly air-conditioning system supported by a 7,874 foot pipe (the deepest ocean pipe in the world) which will pump deep sea water through a titanium heat exchanger. Voila! the freezing temperature of the depths is transferred from the sea water into the fresh water circuit that powers the resort’s total air conditioning. [Link added]

This system has been built by Makai Ocean Engineering  (Makai means “towards the sea” in Hawaiian). It doesn’t look like Makai has any connection to John Pina Craven, the mad genius.

Apparently, OTEC has been studied since 1975.  This page on Makai’s site explains the system with excellent flash-animated pictures. It also says that the electricity costs are 1/10th of a regular air-conditioning operation. However, its not clear how you can pump the water from such depths without expending a lot of energy? Cornell University may have the answer. It has been running a Lake Source Cooling Project operational since July 2000 that serves as the air-conditioning plant for the Cornell University’s Ithaca Campus. It uses the same OTEC principle but it uses Lake water instead of Ocean Water. It boasts some impressive results:

The Lake Source Cooling (LSC) project began providing 16,000 tons of cooling (1 ton of cooling = 12,000 Btu/hr, or approximately one large residential window air conditioner) to Cornell University’s Ithaca campus in July of 2000 with an 86% reduction in energy use versus conventional cooling alternatives. This project has almost completely replaced mechanical refrigeration for the Cornell district cooling system with the following benefits:

LSC has replaced over 40,000 pounds of CFC refrigerants which are known to deplete the ozone layer.

LSC saves approximately 25,000,000 kilowatt-hours of electricity each year. This reduced Cornell’s electricity demand by 10%.

LSC has reduced associated emissions of greenhouse gasses by up to 37 tons/year of SO2, 16 tons/year of NOx, and 11,000 tons/year of CO2

LSC is a model for sustainability and has become an invaluable community outreach and educational tool.

Data collected in association with LSC have been invaluable for regional and local watershed planning efforts.

The chilled campus water is pumped up to the campus to cool equipment and buildings via a closed-loop system, and because heat flows naturally from hot to cold, no extra energy is required beyond that needed to move the water through the pipes.

Its still not clear, but the last line above seems to indicate that the energy required to pump the water from the depths is not that much. It will be helpful if someone can provide the exact calculations. If indeed, the energy for the pump is the main expense, I started wondering if in places like India, where we have sunshine throughout the year, we could make the pump solar-powered giving us a completely renewable energy-based air-conditioning system. Enter, a company called Sea Solar Power International (Via Treehugger) which combines OTEC and Solar Power for creating desalination plants! Given that commercial establishments like Intercontinental Hotel have started using this technology, its usage is going to expand further making it a serious contender in the alternative energy marketplace. Update: Enwave‘s project in downtown Toronto has a capacity of 75,000 tons of refrigeration. This is enough capacity to air condition 100 office towers, or 3.2 million square metres of office space, 6,800 homes. <Via Alternate Energy blog> Update2: Aswin of Neosagredo has featured this post in Scian Melt#19 – a carnival of science blog posts. Thanks Aswin.  I also learnt recently that National Institute of Ocean Technology based in Chennai is proposing a 1MW floating power plant using OTEC off Tamilnadu’s coast. Its not clear what stage the project is in? But isn’t it cool to finally trace something back to your own town!

Notes & References:
1. The first documented reference to the use of ocean temperature differences to produce electricity is found in Jules Verne’s “Twenty Thousand Leagues Under the Sea” published in 1870. Brilliant isn’t it? <Via OTEC Paper by Dr. L.A. Vega> 2. OTEC invented in 1881 (yes, 1881) by Arsene D’Arsonval, a French Scientist. (Via Dr. L.A.Vega’s paper above) 2. Heat Exchanger at the Wikipedia.This is the key component of an OTEC. Also see the link Heat Exchangers in Nature for how whales use this principle to keep themselves warm. 3. Japan is considering installing a OTEC system in the Okinotorishimo Atoll. Technorati Tags  – Ocean Thermal Energy Conversion, Alternative Energy


  1. Anonymous said May 7, 2006, 2:23 am:

    Very interesting Sukumar.

    I think it is imperative for India as a developing nation, and one that boasts a huge population, to exploit such cheaper and more importantly eco-friendly energy alternatives.

    I believe the push for this needs to come from both bottom-up and top-down –

    1. Government – providing tax and other benefits to private sector companies that use such alternat sources of energy and

    2. At the grass-roots level – panchayats, seva organizations becoming aware of such alternatives and wresting the initiative to exploit it themselves. I know that certain villages have been successful in setting up gober-gas units for cooking and heating.


  2. Anonymous said May 8, 2006, 12:31 am:

    Good point Ganesh. This whole rainwater harvesting idea mandated by the Government in Chennai has worked very well. I think the government should mandate solar enery harvesting as well and give subsidies in support of it. Something like OTEC if done well can provide AC at a low cost in coastal areas in Chennai. It will be a boon to the people living in the sweltering heat.

  3. Anonymous said June 15, 2006, 12:15 pm:

    You seem concerned about the cost of pumping the water from depth. Why would this be a problem? The pressure at the bottom of the pipe will do most of the work.

    The pumps only need to overcome the friction in the pipe (which will be quite small for large diameter pipes) and the small imbalance in densities due to the lower temperature of the water being pumped relative to the warmer surface waters.

    If the heat exchanger is less than about 10 metres above the sea or lake’s surface there will not even be a need to pump the water to that height as the syphon effect can be used instead.

  4. Anonymous said June 16, 2006, 12:10 am:

    Thanks for the comment Ed. I need to understand more about the siphoning effect. To my understanding Siphon requires that the recipient be at a lower level than the source. That will not be the case here because the Heat exchanger is at the surface.