Written By: Dr. Stephen Oney
The scarcity of potable water is a growing problem worldwide, particularly in arid regions and among developing countries. Compounding this problem is the increasing contamination of freshwater sources, which comprise only about 2.5% of all water on Earth. Of this small portion, only 0.5% of the total fresh water available is found in easily accessible sources such as lakes, rivers and aquifers. The rest is frozen in glaciers. The remaining 97.5% is seawater.
In the United States alone, each person consumes an average of 400 liters of fresh water per day. That is more than 87 gallons daily per U.S. citizen. By contrast, in other western countries, the consumption level reaches only 150 liters per day. Some countries in Africa have daily consumption rates as low as 20 liters, which is at the World Health Organization’s recommended lower limit for individual survival. When considering infrastructure and communal needs such as those of schools and hospitals, the necessary level is more than doubled to 50 liters per person per day. With the rising global population, industrialization of developing nations and overall increase in quality of life throughout most parts of the world, fresh water consumption levels are rising rapidly. Approximately 67% of the world’s population will be water stressed by 2025, as reported by the UN.
According to the United Nations Atlas of the Oceans, more than 44% of the world’s inhabitants live within 150 kilometers of the coast. In the United States, this is true for 53% of the population. In another 30 years, it is estimated that over 70% of the global population will be coastal. The crowding of the population in limited areas inevitably leads to overexploitation of regional resources including fresh water. Given the number of people within access of the coast and the sea, it is naturally advantageous to turn to the ocean for adequate fresh water supplies.
Over 75% of the world’s desalinated water capacity is used by the Middle East and North Africa according to the USGS. The United States is one of the most important industrialized countries in terms of desalinated water consumption at about 6.5%. California and Florida are the major consumers of desalinated water in the US.
Additionally, populated areas struck by natural disasters are faced with a great need to quickly supply potable water to the victims for drinking, cooking and sanitation purposes. In industrialized nations, the existing freshwater infrastructure is often damaged during a disaster or contaminated to the point that it is unusable in the immediate recovery period. In developing nations, freshwater infrastructure might be entirely absent, making the acquisition and distribution of potable water all the more difficult.
Importance of water production in association with OTEC
Seawater desalination requires a significant amount of energy regardless of the technique used. There are several renewable energy (RE) technologies currently in use to power desalination processes. Some of these relationships are in commercial operation today; others have yet to be demonstrated. Solar and wind are proven, and tidal and wave energy have very recently begun to show much promise, but are still in the early phases of commercialization.
Ocean thermal energy conversion (OTEC) is unique in that it naturally combines opportunities for power production with seawater desalination. Using the temperature differential between warm ocean surface water and cold deep water to generate clean baseload (24/7) renewable energy, in a closed cycle OTEC system, the heat from the surface water is used to boil a working fluid with a low boiling point (such as ammonia), creating steam which turns a turbine generator to produce electricity. The chill from the cold deep water is then used to condense the steam back into liquid form, allowing the system to continuously repeat this process, perpetually fuelled by the sun’s reliable daily heating of the surface water. Because massive amounts of seawater are pumped through an OTEC system in order to generate this baseload (24/7) power, the proximity of the voluminous energy and water supplies allow OTEC to function efficiently and economically with typical thermal desalination processes, as well as those driven solely by electricity.
The environmental impact of desalinating seawater is quite high when using fossil fuels. Replacing the energy supply with a renewable energy source, such as OTEC, eliminates the pollution caused by fossil fuels and other problems associated with the use of fossil fuels to produce potable water. Greater self-sufficiency is also achieved through the use of a readily available source of energy like OTEC, making it unnecessary to rely on increasingly expensive fossil fuels imported from often unstable or unfriendly countries.
In the last two decades, rising fossil fuel prices and technical advances in the offshore oil industry, many of which are applicable to deep cold water pipe technology for OTEC, mean that small (5-20MW) land-based OTEC plants can now be built with off-the-shelf components, with minimal technology/engineering risks for plant construction and operation. In fact, the authoritative US Government agency NOAA issued a 2009 report concluding that, using a single cold water pipe (CWP), a 10MW OTEC plant is now “technically feasible using current design, manufacturing, deployment techniques and materials.” These two historic changes have now made OTEC electricity pricing increasingly competitive, particularly in tropical island countries where electricity prices, based almost entirely on imported fossil fuels, are currently in the exorbitant range of 30-60 cents/kwh. Adding potable water production to the equation only further improves the economic attractiveness of this technology’s unique symbiosis between clean reliable energy and fresh water.
With the growing global need for potable water, the lack of available fresh water sources, increasing concentration of populations in coastal regions, and rising energy prices, pairing potable water production with baseload (24/7) renewable energy from the sea is a natural fit.
And with data from the National Renewable Energy Laboratory of the United States Department of Energy indicating that at least 68 countries and 29 territories around the globe are potential candidates for OTEC plants, the technology’s world-wide capacity for fresh water production and CO2 emissions diminution is truly staggering.
Although it has not yet reached its commercial potential, OTEC is now a technically and economically viable option that is rapidly emerging not only as a top contender in meeting the energy demand for coastal communities in years to come, but also a major global player in the sustainable potable water generation market as well. While there is certainly truth in the old adage that oil and water do not mix, OTEC is concrete proof that the same cannot be said of energy and water.
Dr. Oney is Chief Science Advisor for Ocean Thermal Energy Corporation and has over 25 years of extensive experience in ocean engineering. He is well published on the subjects of Ocean Thermal Energy Conversion (OTEC) and Sea Water District Cooling (SDC), and has been called upon frequently to deliver lectures on these technologies. Dr. Oney has hands-on experience with both OTEC and SDC design and was integral in the research leading to the design and development of the first Net Power Producing Experimental (NPPE) land-based OTEC plant in Hawaii.