With all the talk of peak oil, it is hard to believe that something as important as peak water may have already come and gone with no equivalent hue and cry. The major constriction for producing food for a burgeoning population is water - not land. According to the International Food Policy Research Institute, nearly 5 billion people, about half of global grain production, and 45% of the GPD ($63 trillion dollars) will be at risk due to lack of water with current consumption practices. Eighteen countries; including the big-three grain producers China, India, and the U.S.; are now over-pumping their aquifers. For 20 years Saudi Arabia was self-sufficient in growing wheat. They have nearly exhausted their aquifer and will quit growing wheat in 2016. Recent droughts in California and Texas seem bad but there is evidence that a major portion of the Southwest U.S. underwent a 10-year drought with hardly a drop of rain several hundred years ago. Inexpensive desalination is needed.
One of the largest storehouses of energy lies quietly at the bottom of the ocean. It is not oil, and it is not methane hydrate. It is cold water. Specifically, it is deep ocean water, also known as DOW, from the upper levels of the Midnight Zone at 3,300 to 13,200 feet deep. Approximately 90% of the ocean by volume is deep ocean water. This water is at a temperature of 32˚ to 37˚F. More correctly, it might be called a storehouse of a relative lack of energy because it is only the combination with a more energetic (warmer) mass that results in an extractable form of energy. That more energetic mass would, of course, be the warm upper regions of the Twilight Zone and the Sunlight Zone of the ocean and the tropospheric layer of the atmosphere.
Although this is the coldest water, anything 2,500 feet and deeper in the ocean is about 46˚F, which is considered "cold ocean water" and is usable for the applications described here. More than 90% of the oceans are greater than 2,500 feet.
The best place to exploit this temperature differential is the Tropics where the temperatures near and above the surface of the water are mild to hot year around. Fortunately, approximately 40% of the world's surface lies in the Tropics and it includes a lot of DOW and cold ocean water. While a tropical climate is the most efficient location for extracting water and power, an appreciable percentage of the North and South temperate zones have sufficiently warm weather to make this practical. For the United States that would include the coastline and offshore of states along the Gulf of Mexico, the eastern coast of Florida and the southern coast of California.
Cold ocean water in combination with warm, humid tropical and subtropical air will provide an opportunity to meet water and power needs for the future.
For just the cost of equipment and maintenance the system described here will provide both water and electricity. It is basically a tower mounted on a spar-type, offshore platform. Deep, cold ocean water is pumped into a gas-to-liquid heat exchanger in the top of the tower. Wind is concentrated and re-directed into the heat exchanger. The air becomes cooler and the humidity condenses out onto the surface of the heat exchanger and is collected. Because cool air is denser it accelerates toward the bottom of the tower; essentially a reverse stack effect. A wind turbine at the bottom of the tower harvests the wind energy before it leaves through openings around the base of the tower. The collected water and generated electricity is sent to shore.
Another version is built on the shoreline and uses an onshore reservoir to store the water. This stored water produces electricity that makes up for slumps in production from the wind turbine.
Another version is free-floating with its own propulsion. With the ability to produce electricity and water, it will become a base for mining, aquafarming, recycling ocean plastic, or scientific studies. These could be very independent, almost like tiny nations with their own GPD and tax laws. They could move wherever needed to provide power and fresh water as well as food.
This free ranging version could work in conjunction with special sea-going barges. These would store fresh water and hydrogen from the electrolysis of sea water. When the barge is full, it is towed the nearest port in need of water and fuel.
Barge to lighter water and hydrogen to shore. Top tank is for hydrogen, bottom two for water.
The central spar provides stability for the tower even in high winds and heavy seas. Although it resembles an offshore drilling or production rig, it is much more simple and less expensive. It is even simpler than a cruise ship to construct. Cruise ships are currently running between $2 and $3 dollars per pound to construct.
A unit 120 feet in diameter, 300 feet tall (the spar below the surface counterbalances and structurally stabilizes the tower even in high wind) could produce 20MW on average and between two and five million gallons of water per day. At 7 million pounds it would cost about 18 million dollars. The electricity and water produced would retail for about 25 million dollars per year so the unit could conceivably pay for itself in a year. A hundred of these in the Gulf of Mexico could provide the same amount of water as the Brazos River watershed and as much electricity as a large nuclear plant. That would also provide the ability to cool the surface water temperature of a large area and reduce the strength of storms and hurricanes before they reach land.
- Bird deaths eliminated.
- Even if it's located onshore, the sound of the turbine is mitigated by the tower wall.
- Flickering shadows on the surrounding landscape are eliminated.
- Maintains a cool environment for heat-generating rotating parts of the turbine no matter what the external environment.
- The horizontal plane of the turbine allows more efficient, longer lasting bearings to be used.
- The horizontal plane of the turbine also eliminates gravity and wind load fluctuations making the blade construction cheaper.
- The seawater in contact with the inner, hard-to-clean surfaces of the device is too cold and salty to form algae, minimizing maintenance.
- No chemicals to leak into the environment.
- Produces power even when the wind is still due to the reverse stack effect.
- No azimuth yaw mechanisms needed to keep wind turbine aligned.
- Being at sea eliminates land purchase or rental.
- Nutrient-rich deep ocean water can be used for aquatic farming near the surface.
- There's plenty of "fuel" since 90% of the ocean's volume is between 32ºF and 37ºF and 40% of the world is tropical or subtropical.
Ever since I wrote a blog The Future of Wind Energy I've been thinking about this and it has finally crystalized into something useful.This is patent pending technology looking for a sugar daddy. A prototype needs to be built and tested. That takes money I've not raised. If you're reading this and have an "in" with the likes of Bill Gates or Richard Branson or somebody at Google, send them a link. This tech is available for licensing. It is a multi-billion dollar market that is going to keep growing. Interested in looking at the patent? Contact me through "comments."
Also, it is entered in the annual NASA Create the future contest. If you feel like it is a good idea, fill out their form and vote on it. FYI - this is a popular vote and does not affect the outcome of the contest. You can look at the entries there without signing up and there are some good ones.
At the very least, this solution can bridge the gap for humanity's needs for clean power and fresh water until nuclear fusion or some other technological breakthrough can carry the load.