Environmental Policy News

New Global Standards Could Boost OTEC

A new collaboration that teams Ocean Energy Systems (OES) with the IEC TC-114 for the development of ocean thermal energy conversion (OTEC) standards could go a long way toward defining the future of this innovative technology.

The Ocean Energy Systems Technology Collaboration Programme (OES) is an intergovernmental collaboration between countries, which operates under framework established by the International Energy Agency in Paris. IEC TC-114 is a Technical Committee (TC) of the International Electrotechnical Commission that develops and manages standards for marine energy conversion systems, with a focus on conversion of wave, tidal and other water current energy into electrical energy. The collaboration between OES and IEC aims to develop a unified international standard to provide the guidelines for suitable site selection, design bases and productivity estimations for OTEC plants based on objective standards.

OTEC techniques utilize the temperature differential between deep seawater and surface seawater to generate electrical power. Commercial applications are beginning to emerge and there is a need for global standards. Recent efforts have shown a widespread interest in reviving OTEC, but remain subject to formidable funding hurdles. Accordingly, a number of partnerships were established in recent years that seek to leverage the necessary technical and financial means to build OTEC pilot plants. For example, Xenesys Inc. of Japan and Pacific Petroleum Company formed a joint venture for the industrialization and commercialization of OTEC in French Polynesia.

Meanwhile, a consortium of French industrial and public partners launched the initiative IPANEMA aimed at facilitating the emergence of marine renewable energy technologies. Lockheed-Martin (LM) and the Taiwan Industrial Technology Research Institute (ITRI) pledged to collaborate on a 10 MW plant project in Hawaii after LM completed their 100kW prototype there in 2015. And in October 2016, BARDOT Group signed a contract for the first commercial OTEC system to be installed in an eco-resort in Maldives. That project is expected to be completed early 2018.

OTEC in the Maldives

OTEC uses ocean water to produce electricity, air-conditioning and drinking water. Electricity is generated by a turbine in a closed cycle, activated through heat exchangers by the difference of temperature between warm surface seawater and cold deep seawater. The technology brings associated technologies such as SWAC (Sea Water Air Conditioning) and SWRO (Sea Water Reverse Osmosis) which are used for air cooling and water purification. Because OTEC requires a difference of seawater temperature, it works in coastal and insular areas in tropical regions.

Once built, OTEC can be a cost-effective solution for remote locations like the eco-resort Bardot is servicing in a South Maldivian archipelago. BARDOT Ocean’s OTEC technology uses pumps to bring in large volumes of cold and warm water to feed the exchangers of the system. The warm surface water (20-25°C) is flowed through heat exchangers that transfer the heat to a closed circuit and boil a working fluid into vapor under pressure at 19°C. The vapor then expands through unique turbines which then drive generators and create electricity. The cold water (4-7°C) is pumped up from depths of 700 to 1000m and flowed through exchangers to condense the vapor back to its liquid state. The cold liquid working fluid returns to the evaporators where it is heated and boiled all over again. Used waters, both hot & cold, are then sent partially back to the ocean. To avoid any environmental impact, waters are rejected at depths corresponding to their temperature. A small volume of the cold water can be used to create cold through a Sea Water Air Conditioning (SWAC) system or fresh water through a Sea Water Reverse Osmosis (SWRO) system.

Designed to accommodate 300 people, the resort will be fully powered in electricity, air-conditioning, hot and cold water, and fresh water by a revolutionary OTEC system that produces carbon-free energy. The OTEC plant will be located on an individual island from where it will pump the warm surface water and cold deep water. Electricity and fresh water will be transferred to the resort island through a water pipeline and a power cable. Altogether, 7km of HDPE pipe will be installed off the island’s shore.

These kind of projects mean that OTEC may transform the way we think of green energy, especially for remote islands.

Closed Cycle, Open Cycle, and Hybrid Systems

The differences between these three forms of ocean thermal energy conversion simply lies in the water, temperature, and location. For closed cycle OTEC, the system utilizes fluids with a low boiling point such as ammonia to rotate the turbine and, in turn, create the energy. By pumping warm water through a heat exchanger, the ammonia or other low boiling point fluid is vaporized where it then pressurizes and rotates the turbine. From there, cold deep seawater is pumped through a second heat exchanger where it condenses the steam back into its liquid state and repeats the process over and over again.

Although open cycle OTEC is somewhat similar in its conversion process, an open cycle system works best in areas with tropical warm water where it can take said water, pump it through a low-pressure container, and ultimately transform the water to steam in this fashion. After it is turned into steam, the vapor rotates a low-pressure turbine attached to an electrical generator and finally is combined with cold deep seawater in order to turn it back into its liquid state and repeat the process in the same fashion as the closed cycle system does.

The hybrid OTEC system is simply the mixture of both of these forms of conversion. It takes warm seawater, pumps it through a vacuum chamber, and turns it to steam as the open-cycle process would, but then vaporizes a low boiling point fluid that drives a turbine to produce power as the closed-cycle process does.

To make OTEC a viable form of energy conversion, determining which system works best in what environment will allow the pioneers of this form of energy efficiency to showcase its strengths as well as improve upon its weaknesses in a complimentary setting.

How to Avoid Potential Negative Impacts

The original mind behind OTEC, French physicist Georges Claude, found that a major setback in his progress was the sheer amount of tropical storms in the locations necessary to test and create open-cycle systems. In fact, these setbacks were the main reason for him retiring the idea. Similarly, many scientists fear that this process may disrupt marine life and, if a nation were dependent solely on oceanic energy, it could mean that a serious weather event (such as a hurricane or tsunami) could spell utter disaster for everyone using this form of energy. However, with interest increasing in the project, the potential of substantial upfront capital investment may allow the engineers at the forefront of this form of renewable energy to find ways to create stormproof locations and, in turn, make the conversion process far more reliable and likely to be considered by major corporations.

The other issue for OTEC is its relative inefficiency. As currently designed, OTEC spend a significant amount of the energy they generate pumping the huge amounts of water needed for their operation. Therefore, to produce power, they must be built at a very large scale, often in the prime (and vulnerable) real estate of shorelines, which makes them expensive investments. Standardization can help with the impact of OTEC on coastal wildlife, such as mangroves and corals, but tackling the efficiency problem of these large scale devices is a daunting task that may relegate them to limited usage, like at naval bases, ocean resorts, and remote islands.

By: Samantha Donaldson, ECO Contributor

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