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The Lowest Cost Renewable Energy Comes With a 2000 Percent Environmental Dividend

ocean heat and energy

NASA and NOAA have proclaimed 2014 the warmest year ever recorded. It was the year also in which scientists identified heat movement into the ocean depths as the reason an atmospheric warming hiatus has existed for the previous 15 years.

Just as climate change is anthropogenic, the conditions that brought about the hiatus can be replicated with human effort using heat pipes that utilize the phase changes of working fluids to move surface heat to deep water.

The 2nd law of thermodynamics states that when heat is moved from a warmer to cooler region, through a heat engine, work is produced.

Researchers from the University of Hawaii have estimated that the oceans have the potential to produce 14 terawatts of energy this way – more than is derived from all of the world’s fossil fuels – with ocean thermal energy conversion or OTEC.

The efficiency of this process is determined by the difference in absolute temperatures between the warm and cooler heat sink in accordance with the formula

 

where:              n is thermodynamic efficiency

                        W is work derived from the system

                        QH is heat input

                        TC is temperature of the cold sink, and

                        TH is temperature of the hot source.

OTEC systems typically operate where surface temperatures are at least 20oC above the 4oC found almost universally in the oceans at a depth of 1000 meters.

Solving for these values the theoretical efficiency of the system would therefore be 1-277/297 or about 7 percent.

Realistically this value would not be achieved, but assuming 5 percent was a possibility, 20 times more heat would have to be moved to the depths than energy produced.

At first blush this seems like a problem but factoring in the recent finding that heat movement into the depths means a slower increase in atmospheric warming, it is the reverse, In fact for every kilowatt of energy you produce with such a system you are rewarded with a 20 kilowatt (2000 percent)  environmental heat dividend.

Scaling this to 14 terawatts of energy production with 280 kilowatts of heat movement to the ocean depths takes care of 89 percent of the 330 terawatts of heat/year NOAA determined in 2010 the oceans are taking up on account of global warming. 

So why wouldn’t you immediately start taking advantage of this environmentally rehabilitating form of energy?

The only rational reason for not doing so would be cost, but guess what?

OTEC is demonstrably the most inexpensive form of renewable energy that can be produced!

The following table from the recent MIT masters thesis by Shylesh Muralidharan shows the capacity and levelized capital costs of various energy technologies.

 

Although not shown in the table, Muralidharan points to a study that shows the deep water condenser architecture for OTEC, which is the design that moves heat most deeply into the depths and thus prolongs the time it would stay down there, brings down the installed capital cost of a 100 MW plant ship from 4000 $/kw to 2650 $/kw.

He also explains how the doubling of OTEC plant size leads to a cost/kW reduction of approximately 22%.

Using CO2 as the working fluid allows for OTEC plants of gigawatt capacity or more, so extrapolating from the study’s data a 1 GW plant of the deep water condenser design would cost $86*2650/4000*78/100*(1-(.22*(200/800))) or 42 $/MWh for the lowest levelized capital cost of all energy sources but for combined cycle natural gas.  

By a considerable margin it would be the cheapest of the renewable energies and  therefore what our rapidly warming planet is crying out for.

In view of the futile response to two years of advocacy for the lowest cost, most environmentally effective form of energy, one is left to ponder the question Casey Stengel posed of his 62 Mets Baseball Team, Can’t anybody play this here game?”

Put another way, paraphrasing the late Frank Sherwood Rowland, 1995 Noble Prize Laureate in Chemisty, What’s the use of developing a solution if, in the end, all we’re willing to do is stand around and wait for the resolved problem to destroy us?

Photo Credit: Ocean Energy Sources and Decarbonization/shutterstock

Content Discussion

Bas Gresnigt's picture
Bas Gresnigt on January 29, 2015

Jim,
Sorry, but reading this I do not understand how you get energy from bringing the warmer, so lighter, water down to the heavier 4°C water 1000m deep?

I may not be very smart, but still I think that if I don’t understand most people don’t.
And people do not sign up for something they don’t understand.

Btw.
The link to the recent MIT masters thesis by Shylesh Muralidharan doesn’t work.

donough shanahan's picture
donough shanahan on January 29, 2015

Professing to know the cost of something that has hardly started it pilot phase is stupid.

Engineer- Poet's picture
Engineer- Poet on January 29, 2015

Adding to this, how far are the suitable OTEC sites from load centers and how much capital and operating cost is added to transmit the power?

Bas Gresnigt's picture
Bas Gresnigt on January 29, 2015

Thank you!

Engineer- Poet's picture
Engineer- Poet on January 29, 2015

It may have escaped your notice, but we don’t ship electricity from as far away as the Middle East, and no grid on earth converts electricity to forms shippable by tanker then converts it back.

The one positive thing I can see about OTEC is that as a base-load source of generation it would allow electrolyzers and such to run at their full rated capacity all the time, maximizing the use of the capital investment.

Robert Bernal's picture
Robert Bernal on January 29, 2015

I like the explanation you gave to Bas – I also forgot how it works. I need to look up the priciples of refrigeration!

How much materials are required to withstand what kind of (and natural) forces for 1,000 meter tubes?

Engineer- Poet's picture
Engineer- Poet on January 29, 2015

There are lots of things we could do with HVDC grids.  I don’t expect that to make it any easier to get them built out, especially over land.

Nathan Wilson's picture
Nathan Wilson on January 29, 2015

So rather than being content to sell OTEC to coastal/tropical communities, you want to convince the world to switch from one imported fuel to another, and you want people to use that imported fuel for not just transportation but also electricity?  Wow, tough sell.

I suppose the good news is that interest in OTEC could increase interest in carbon-free energy carriers (hydrogen and ammonia).  These can be made from any sustainable energy source (e.g. solar, wind, nuclear) using just water and air as feedstock.

This TEC article looked at power-to-fuel technology.  It basically concluded that the economics will be challenging, but most promising when the produced fuel replaces expensive imported oil; trying to economically replace cheap coal in electricity production would obviously be much, much harder.

donough shanahan's picture
donough shanahan on January 30, 2015

They are no further from their markets than Middle East oil is from theirs. The power would be converted to an energy carrier for transport as described in the paper.”

Expect the infastructure to build the mid east oil is built, relatively easy to expand under known principles and more importantly, proven on a mega scale. OTEC can currently power a couple of lightbulbs. 

Robert Bernal's picture
Robert Bernal on January 30, 2015

Nice work!

Mark Heslep's picture
Mark Heslep on January 30, 2015

Those electrolyzers working at full capacity produce hydrogen”

You would transport compressed or liquified hydrogen by ship?

Hops Gegangen's picture
Hops Gegangen on February 1, 2015

 

I suppose large scale OTEC would actually heat the planet more because instead of warm surface waters creating storms that push heat into the upper atmosphere to radiate into space, it pushes the heat into the deep ocean. There it will cause additional thermal expansion of the oceans, contributing to sea level rise.

 

Hops Gegangen's picture
Hops Gegangen on February 1, 2015

 

Western Pennsylvania is full of old coal mines that have filled with water. I read about one commercial establishment tapping an old mine for geothermal heating and cooling.

Could such a mine be used in OTEC-like fashion? In the summer, you could put a sort of solar hot water heater on the surface and exchange heat into the water below. By the end of summer, it might be too warm to use, but then in winter could it be turned around?

Hops Gegangen's picture
Hops Gegangen on February 1, 2015

 

Good points.

One other interesting thing, though, about the storms and poles, is that the atmosphere at the poles is thinner than around the equator because the planet is spinning. 

So, if a tropical storm goes into the Arctic, it will not just warm the Arctic mass but also radiate a lot of heat.

Robert Bernal's picture
Robert Bernal on February 1, 2015

Perhaps conversion into ammonia or DME would be less toxic, as I just read that MCH is “very toxic”. However, since electrolysis is needed, wouldn’t energy saved from the electrolysis process better benefit the case for underwater power lines?

Robert Bernal's picture
Robert Bernal on February 1, 2015

Thanks, I don’t know how much such long lines would cost, just being laid on the ocean floor at 1,000 meters.

I remember someone, I think NNadir, was promoting DME, I think he said it was a better car fuel than ammonia because it was less toxic (and probably more liquid). Ammonia would probably be easier to make, though, because no carbon needed from the air. If ever NG gets expensive, then one of these for sure!

Alistair Newbould's picture
Alistair Newbould on February 6, 2015

I haven’t researched  this much but have wondered about the efficiency and benefit of doing as Hops said using solar water heating technology to heat water in a large themrally insulated tank buried in the dessert, then heat exchange power generation at night. Could easily get 60 degrees temperature differential between dessert night time temperature and the heated water. The benefit would be shifting the production time from day to night, thus evening out the solar peaks and a degree of load following (storage). I wonder if anyone could do a back of envelope calculation on efficiency of such a system compared to PV or solar thermal electrical generation. I can see quite a few losses in my proposal – solar to thermal , heat leakage from the hot water tank, then thermal to electrical via heat exchangers. The released heat would radiate back into space due to the clear dessert atmosphere just as it would have if not used through the system.

Mark Heslep's picture
Mark Heslep on February 6, 2015

STES with underground water has been tried here and there, and technically it can work, that is, run ~95% off only solar in frigid climattes.  But so far it has been found more expensive than local incumbents. 

http://www.dlsc.ca/

 

 

Alistair Newbould's picture
Alistair Newbould on February 6, 2015

I had noticed your “focus” Jim! I also thought an onshore “upside down” version of OTEC (which is essentially what I am describing once the heat has been collected) might provide a testing / proving ground for the some of the elements of OTEC. But then again likely that work has already been done and proven. The deep well option (coal mine full of water) may also provide answers to some of the technical questions surrounding very long pipes imersed in water and circulating CO2 in its various phases. Is there a current state of play type website where progress on this technology can be followed?

Alistair Newbould's picture
Alistair Newbould on February 6, 2015

Thanks Mark. One of my clients has such a system installed in her house – some technical issues to sort. What I was proposing was a much shorter timeframe – 12 hours or so. Very hot dessert in the day with full sun heating water, then at night temoerature plummets to near zero allowing the heat sink needed for the refridgerant circulation mechanism to work. I just don’t now the relative efficiencies of PV, solar water heating in evacuated tubes, and conversion of the het to electricity by the refridgerant system.

Spec Lawyer's picture
Spec Lawyer on February 6, 2015

If OTEC is so great, they need to go build a system and get it up and running.  

Robert Bernal's picture
Robert Bernal on April 11, 2015

60 years of global warming condensed into an “instant” surely would cause a massive increase. To me, that is also another proof which might be able to convince skeptics that warming actually has already occured.

We need to find the least costly, most quick way to remove excess CO2  – and implement surface heat removing OTEC. It’s definitely “sustainable” for a period of time which is longer than without it (due to the fact that there is so much water in the deep)!

Thanks for working on solutions!

Clayton Handleman's picture
Clayton Handleman on May 16, 2015

Jim,

Sorry to have missed this thread when it being discussed.  You have done a thorough job with it and brought a number of excellent points to light.  However, I think there are a few fundamental weaknesses to the overall concept in comparison to others. 

1) Once you have decided to build a hydrogen energy economy, intermittency and CF are no longer at issue and $ / MWhr becomes the primary evaluative figure of merit.  With a hydrogen based energy economy, solar and wind no longer have any issues with intermittency since the energy is stored. 

2) Your cost figures appear to be based upon projections for OTEC at scale where solar and wind are based upon (almost) up to date numbers.  Lazards puts utility scale solar at $72 / MWhr with projections only 3 years out at $60.  Your proposal assumes both hydrogen and HVDC.  Under the assumption of that infrastructure wind power can be land based and land based wind is currently at $37 / MWhr at favorable sites. PPAs are already beating this even when adjusted for PTC.  The experience curve for wind is about $14% per cumulative doubling of deployment. 

The economics of wind and solar are quite good and if the grid and hydrogen infrastructure you suggest is built then the intermittency concerns are no longer at issue.

Finally the cost of OTEC is hypothetical.  These things can get more expensive as projects go on.  So, while the wind and solar costs are pretty firm, OTEC costs are not.

 

Robert Bernal's picture
Robert Bernal on May 16, 2015

I have to question the fundamental energy requirements for a solar/hydrogen setup. I believe less than 50% of the energy put into hydrogen is available for end use. Whereas, in batteries, up to 80 or 90% depending on how many cycles and discharge rates. This would require far less solar coverage for the same amount of stored energy.

As for OTEC, it might be a necessary cost justification since it is the only means to reduce surface temps.

Another (perhaps) necessary action is excess CO2 removal. Olivene crushed and distributed would sequester about 20x the CO2 emitted by the conventional diesel feuled process. A tariff placed on all goods made with dirty energy could easily pay for this new industry.

Clayton Handleman's picture
Clayton Handleman on May 16, 2015

Where would you put your sequestered CO2

Robert Bernal's picture
Robert Bernal on May 16, 2015

Cool. I believe we should all support OTEC, especially in light of the economic consideration! We might still have to remove excess CO2 from the air, though.

Robert Bernal's picture
Robert Bernal on May 16, 2015

This is the report I was refering too

http://www.innovationconcepts.eu/res/literatuurSchuiling/olivineagainstclimatechange23.pdf

 

I believe a thin layer of crushed olivine sread out over farmland and beaches converts to carbonates within 5 years in this accelerated weathering process. From there, it ends up in the oceans, presumably also neutralizing acidification. They say that it might not be logistically posible to remove ALL the excess within financial constraints, however, it would be possible if scaled up to less than that of the coal industry. This is why I believe tariffs on all goods made overseas would help.

However, OTEC can sequester the excess in the water (as I just learned, here), thus the two technologies could work together, along with greening deserts with water shipped from the mouths of major rivers worldwide.

Jenny Sommer's picture
Jenny Sommer on May 16, 2015

I would suggest Oxymethylenether or use the sunfire plants on site to produce “blue crude”.

OTOH it should be cheaper save the transport and produce it on land with wind/pv/hydro.
There is a lot of underutilized pumped hydro that can run the synfuel plants 24/7.
When all the pumped overcapacity is used one could just built more pumped hydro.
It’s not done because it is unprofitable at current low utilisation.

Jenny Sommer's picture
Jenny Sommer on May 16, 2015

I don’t doubt the effectiveness of the process but there are cheaper messurements. Just reverse deforestation. We are losing around 13Million ha of forrests every year. That’s a lost 130000Mt (or 230 OTEC plants) to 260000Mt CO2 sink/storage.

I don’t see how OTEC combined with some fuel production could be as cost effective as wind/PV even including p2g or p2l.
You could still run your synfuel plants 24/7 by using pumped hydro for puffer storage.
At least here in Europe we could save us the shipping and use existing gas infrastructure (over 200TWh existing storage in Germany alone and existing pipes with a transport capacity up to 70GWt).
Existing pumped hydro is underutilized and electricity is so cheap that it is not economially to develope new PuH now (There is a huge potential though with existing reservoirs)
Synfuel plants could swallow that storage cost (the missing arbitrage) and still come out ahead of OTEC.

OTEC would also have to have a greater potential cost advantage over future technologies to attract investment. I don’t like these investment realities too as I would really love to see KiteGen technology (Which proponents claim to have a potential of 6€/MWh) developed but I guess that is the way the world rolls.