A drama is presently unfolding in the coastal city of Cape Town, South Africa, and maritime technology could offer a solution here and in other cities around the world.
Cape Town depends on winter rainfall to replenish the city’s water storage dams that located in the nearby coastal mountains. Last winter, Cape Town received minimal rainfall, and the city’s largest dam is below 20 percent capacity. Tanker ships carrying water offers modern coastal cities new options for enduring temporary droughts, and an analogous solution could also provide support to cities during power outages.
El Nino and La Nina weather occurrences deliver excess precipitation to some regions of the world and drought to others. During earlier times, such weather occurrences forced populations to relocate and abandon many cities and towns. In the U.S., the state of California recently received rainfall after a drought that lasted eight-years. Water diverted from other regions through channels provided some relief to California. Centuries earlier, this was not an option, and drought decimated much of the thriving Mayan Empire of Central and South Africa.
Even in modern times, the situation can be challenging. Some 10-years ago, a change in wind direction reduced rainfall over a watershed region of Quebec, Canada that was home to multiple hydroelectric power dams that supplies much electric power into the northeastern U.S. While the drought was short lived, it reduced water storage in Quebec’s hydroelectric power dams to the point where it became a matter of much concern. Several years ago, a prolonged drought emptied a main storage dam in Southern Australia and threatened the quality of life in the communities that depended on the dam. Drought has threated the water supply and power generation in other nations.
Maritime Water Tankers
During such times, converted tanker ships could carry potable water from a region of generous rainfall to a drought-stricken region. Ocean going tanker ships have periodically been converted to carrying potable water. In the Mediterranean Sea, such a ship has carried potable water from the south of France to Israel.
The viable operation of such ships would require that some regions become regular seasonal customers for potable water carried onboard tanker ships. Generous seasonal monsoon rainfall occurs in areas of Malaysia and Indonesia, for example, while regions of Southern India or Western Australia could endure the occasional drought. A location along the route of the water tanker ships that experiences an unexpected seasonal drought could prompt the shipowners to revise sailing schedules to deliver emergency potable water.
At some locations, the combination of oversea and submerged water pipelines could represent a competitive alternative to ship transport. However, excess seawater depth in some regions would discourage the installation of such pipelines and relegate water transport to the maritime sector. In Canada, discussions about transporting water from northwestern Canada to places such as California have also resulted in some public opposition to such transport.
Many navies operate nuclear powered ships and nuclear powered submarines while the commercial maritime sector operates ships powered by diesel and by natural gas with engines capable of 30MW to 100MW output. Siemens build a gas turbine engine of 300MW capability, and such an engine could easily be installed within the hull of a ship. The market for electric power fluctuates seasonally in some regions of the world and an energy ship that visits seasonally could be a future option. There are also coastal cities that experience emergencies such as prolonged reduction of hydroelectric power due to weather occurrences.
An available energy ship could provide relief to a coastal city that faces a seasonal or unexpected shortage of electric power. Such a ship could either berth at an available dock or moor offshore in protected waters, with an undersea power cable providing a connection to the shore and to a local power distribution system. A floating LNG tanker barge could provide several days or several weeks of energy storage capacity. Advances in small scale thorium-based nuclear energy conversion could result in future energy ships using such technology to provide short term electric power.
Wind Powered Ships
During the early 20th century, German inventor Anton Flettner installed several vertical-axis turbines on the deck of a ship that sailed across the North Atlantic. Wind energy interacted with the Flettner rotors and provided sufficient power to drive the propeller and propel the ship across the ocean. Shipping companies are again considering wind-assisted propulsion for ships, and the choice of technologies includes deck mounted wind turbines. While such a ship is moored in a windswept bay, the deck mounted turbines could drive electric generators to produce power for shore-based applications.
Airborne kite sails are one of the technologies being used to assist in providing ship propulsion along routes where trade winds blow parallel to sailing direction. The winds blow at higher speed at higher elevation.
On land, certain designs of kites have been used to alternately pull and release tension on cables connected to ground level electrical generators. There may be scope to modify airborne sails to provide propulsion when the vessel is sailing at sea and drive electric generators when the ship is stationary and moored to provide electric power for local land-based consumption.
The development of energy ships allows for the development of desalination ships that may moor alongside the energy ship. A long pipe that leads far offshore would carry brine from the desalination ship. Such ships would become the option where extended sailing distances of water tanker ships would be impractical.
A desalination ship could include both reverse-osmosis-membrane technology as well as thermal desalination technology to provide potable water. Either a short-distance water pipeline would connect the desalination ship to the shore, or a water tanker ship would shuttle potable water from offshore desalination ship to shore-based water tanks.
Desalination ships could source energy from multiple sources. Offshore wave energy technology could drive wave pumps and push seawater under pressure through a pipe to ships with reverse-osmosis technology. Wind energy ships could use rotary turbines or airborne sails to directly drive water pumps that could produce sufficient pressure to sustain operation of reverse-osmosis desalination technology.
Large ships could also carry arrays of solar PV panels to generate electric power for reverse-osmosis desalination or carry solar thermal concentration technology to sustain operation of thermal desalination technology. Small-scale, ship-based nuclear power could also provide energy for seawater desalination.
Drought has occurred throughout the earth’s history and even at the present day, regions of the world experience prolonged drought. During earlier times, drought forced populations to relocate and abandon established cities and towns. Modern day drought reduces hydroelectric power generation.
During modern drought periods, maritime based technology can achieve much in terms of providing temporary relief to drought-stricken coastal regions. Maritime based technology can provide electric power and potable water on a seasonal basis to many locations around the world, thereby making such technology viable.
The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.