Hydro-Island: Undergraduate Research Modeling an Ocean Thermal Energy Conversion (OTEC) System

We are in the midst of a strong shift in climate change awareness in the U.S. The public discourse is swinging from climate denial toward climate alarm. A recent poll by the Yale Program on Climate Change Communication (YPCCC) found that Americans are around four times more likely to be alarmed by climate change than they are to dismiss the science. This is a drastic, and long overdue, shift in sentiment from 2015 poll results where the same two survey categories were almost dead even. As we transition our mindset to combat global warming, we also have to visualize the future of our existing energy systems and infrastructure. Renewable energy is an obvious choice to reduce greenhouse gas emissions, but we need to be thoughtful in our long-term vision of its deployment, including the global availability of renewably-derived fuels. Of these fuels, hydrogen may be the most promising in its broad deployment. It has a high energy density (almost 3 times that of gasoline), is readily available, can replace natural gas in existing gas pipelines and can be shipped via hydrogen tankers. Although still in the demonstration phase, hydrogen tankers would provide the capability to transport hydrogen fuel all over the world. As hydrogen shipping technologies grow more mature, the door for offshore hydrogen production opens. Hydrogen could be produced offshore using renewable energy and electrolysis, then transported to ports around the world, essentially creating Hydrogen Islands. These islands would be capable of supplying hydrogen to onshore facilities via hydrogen tankers, but could also fuel the transport ships themselves. Ships such as container ships, where a recent study found that 99% of transpacific voyages made in 2015 could have been powered by hydrogen. In an effort to further develop the idea of a hydrogen producing island, a small team of undergraduate students were formed to evaluate the feasibility of renewable offshore hydrogen electrolyzation utilizing an Ocean Thermal Energy Conversion (OTEC) system. This research is focused on the energy modeling of the Hydro-Island powerhouse; the OTEC system. The energy model was built in Engineering Equations Solver and incorporates thermodynamic, heat transfer and fluid mechanics principles. An OTEC system has a low thermodynamic efficiency (around 4-6%) due to the low temperature difference between the hot and cold thermal reservoirs. In an effort to attain higher efficiencies, we incorporate a solar pond into the OTEC system model. A solar pond is designed to absorb solar energy, thereby increasing the temperature of the hot side of the Rankine cycle. The model compares different OTEC scenarios to find the effect of solar ponds on energy production and system performance. The environmental variables utilized in the model are from Gulf of Mexico water and climactic conditions; where there is an abundance of abandoned offshore oil rigs which could potentially be repurposed to provide the platform for the OTEC system. The modeling results provide important insights into the system energy production, sizing, efficiency and pumping needs.