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OTEC and Energy Innovation: The Willie Sutton Approach

ocean thermal energy conversionWillie Sutton is purported to have claimed he robbed banks “because that’s where the money is.”

Whether or not those were his words; it is the right approach to energy.  

Robert Stewart of Texas A&M points out in Oceanography in the 21st Century,”18 times more heat has been stored in the ocean since the mid 1950s due to global warming than has been stored in the atmosphere.

When a liquid is heated it expands and because its molecules move apart it becomes less dense. As a consequence the oceans are becoming thermally stratified which negatively impacts phytoplankton that are the base of the ocean food chain and the lungs of the planet. They absorb more atmospheric carbon dioxide than the world’s forests.

The Nature article, “Global phytoplankton decline over the past century” by Daniel G. Boyce of Dalhousie postulates the volume of phytoplankton in the world’s oceans, which produce half of the oxygen in the atmosphere by consuming the equivalent amount of carbon dioxide, has been declining steadily for the past half century-down about 40 percent since 1950.

“What we think is happening is that the oceans are becoming more stratified as the water warms,” said Boyce. “The plants need sunlight from above and nutrients from below; and as it becomes more stratified, that limits the availability of nutrients.”

Expanding oceans have no place to go but up onto the land and warming oceans and air melt the polar icecaps which exacerbates the sea level problem.

Contrary to the IEA’s recent report that we have five years to prevent “dangerous” climate change, a Canadian Centre for Climate Modelling and Analysis study concluded that even if we stopped putting CO2 into the atmosphere today the seas may rise by at least four metres, over the next 1,000 years.

The insurance company Allianz has estimated that $28 trillion worth of infrastructure will be at risk by as early as 2050 and the outlook for Small Island States is bleak.

Increasing evaporation is another consequence of warming oceans and the conventional wisdom has been this moisture produces cloud cover and an albdedo effect that will produce ocean cooling.

A recent study however indicates that this may in fact be wrong and instead warming oceans transfer heat to the overlying atmosphere, thinning out the low-lying clouds to let in more sunlight that further warms the ocean. This feedback warms both the air and water and may lead to thermal runaway and catastrophe.

As Will Rogers was wise enough to note:


Unfortunately, many of the actions proposed in response to global warming are likely to do more harm than good.

Fusion has been referred to as the holy grail of energy because it mimics the sun which is the source of virtually all of our power but for fission. The problem is like fission; fusion boils water to produce electricity which is a process that is only about 33 percent efficient.

Richard Smalley, Nobel Laureate in Chemistry, estimated a population of 10 billion by the year 2050 will require as much as 60 terawatts to meet its needs, including massive desalination.

To produce this 60 terawatts with either fission or fusion an additional 120 terawatts of waste heat would be produced, most of which would end up in the ocean, exacerbating thermal expansion and accelerating the collapse of the West Antarctic ice sheet.

Solar panels, wind and hydro do not produce waste heat but neither do they remedy sea level rise, thermal runaway or our dying oceans.

Only one energy source, Ocean Thermal Energy Conversion (OTEC) converts accumulating ocean heat to energy, produces renewable energy 24/7, eliminates carbon emissions, and increases carbon dioxide absorption (cooler water absorbs more CO2).

A NASA study recently published in Nature determined the average amount of energy the ocean absorbed each year over the period 1993 to 2008 was enough to power nearly 500 100-watt light bulbs for each of the roughly 6.7 billion people on the planet.

This 330 terawatts is about 20 times the total amount of primary energy consumed globally every year.

It must be noted that even though the ocean is accumulating more solar energy than we can use, it is the cold denser water available due to the thermohaline circulation that makes conversion of this heat to electrical or mechanical energy possible.

Conventional OTEC would be so effective cooling the ocean, one of its major drawbacks is the potential to overturn the the thermohaline circulation which is vital to the maintenance of the deep water heat sink required to produce energy by this method.

As Dr. Paul Curto, former NASA Chief Technologist, puts it in his Op Ed American Energy Policy V — Ocean Thermal Energy Conversion, last year “The size of the heat sink represented by the “cold ocean mass” in the tropics needs to be more than roughly 300 times or larger resource than that of the OTEC power generation over a year so that OTEC may become a third order effect. If we estimate the total volume of water below 500m depth in the tropical oceans, roughly 500 million cubic kilometers, 5e17 cubic meters, or 5e20 liters, we arrive at an estimated 5e20 joules per degree Celsius differential in the heat sink, or 139e6 TWh, over 317 times that from 2.5 TWe of OTEC each year. The efficiency of OTEC conversion is proportional to the temperature difference (dT) between the surface layer and the mean temperature of the heat sink (~3C). If we assume very large OTEC utilization, say 2.5 TWe as shown, with an average dT of 20C, the average efficiency is roughly 70% of the Carnot efficiency (taking into account parasitic losses), or 4.73%. The amount of heat dumped by that much OTEC into the ocean’s heat sink at depth is therefore just over 50 TWth, and that is also equal to the heat removed from the surface plus the power output, about 53 TW. The heat sink is replenished by cold arctic and antarctic waters sinking to the bottom at the poles. The reradiation from the world’s oceans should also be enhanced by the elevated temperatures due to global warming, but the amount of water sinking to the bottom will likely remain in balance. In other words, as long as the heat sink is replenished by the arctic currents at near to or the same as is done today, the added heat from OTEC will not measurably impact the thermocline for centuries or longer, after which OTEC’s cooling effect on the ocean may enhance the replenishment of cold water at the poles. The surface layers of the ocean have relatively small volume, three orders of magnitude less, compared to that of the heat sink at depth. Therefore, OTEC’s impact on reducing the surface water temperature over time will be much larger, on the order of one degree F per decade at this power level.”

The North Atlantic thermohaline circulation is responsible for much of the total oceanic heat transport towards the north pole, peaking at about 1.2 + 0.3 Peta Watts (1015 Watts) at 24oN latitude.

To produce Smalley’s 60TW with conventional OTEC you would therefore dump 60TW*20 or 1.2 Peta Watts of heat to the depths and remove the same from the surface which would overturn the thermohaline.

GWMM OTEC uses a heat pipe to take exhausted vapors from a turbine to the depths for condensation, instead of using massive and expensive cold water pipes to bring water to the surface, and a counter-current heat transfer system to recirculate the latent heat of condensation back to the surface rather than dumping the heat to the depths. This solves OTEC’s problems of cost, limited potential, efficiency and reduces the environmental impacts on the thermohaline and aquatic life.

To produce 60 TW with this approach you would extract 120 TW from the surface and ideally dump 60TW worth of heat to the depths or about the same as you would to produce 2.5 TW with the conventional approach. (A large hurricane extracts 50 or more terrawatts of heat from the ocean’s surface and on average there are 21category 3 or greater storms around the globe each year plus many smaller storms.)

They do not impact the Thermohaline because most of the heat is returned to the surface in falling rain, which is the same principle GWMM OTEC seeks to employ.

In the process of creating all of the renewable energy mankind needs, you simultaneously draw down the fuel hurricanes thrive on as well as the cause of thermal expansion and prevent the potential for thermal runaway and mass extinctions.

When it comes to energy Mr. Sutton and Mr. Rogers had it right.

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