An Assessment of Global Ocean Thermal Energy Conversion Resources With a High-Resolution Ocean General Circulation Model

Abstract

Global rates of ocean thermal energy conversion (OTEC) are assessed with a highresolution (1 deg  1 deg) ocean general circulation model (OGCM). In numerically intensive simulations, the OTEC process is represented by a pair of sinks and a source of specified strengths placed at selected water depths across the oceanic region favorable for OTEC. Results broadly confirm earlier estimates obtained with a coarse (4 deg  4 deg) OGCM, but with the greater resolution and more elaborate description of key physical oceanic mechanisms in the present case, the massive deployment of OTEC systems appears to affect the global environment to a relatively greater extent. The maximum global OTEC power production drops to 14 TW, or about half of previously estimated levels, but it would be achieved with only one-third as many OTEC systems. Environmental effects at maximum OTEC power production are generally similar in both sets of simulations. The oceanic surface layer would cool down in tropical OTEC regions with a compensating warming trend elsewhere. Some heat would penetrate the ocean interior until the environment reaches a new steady state. A significant boost of the oceanic thermohaline circulation (THC) would occur. Although all simulations with given OTEC flow singularities were run for 1000 years to ensure stabilization of the system, convergence to a new equilibrium was generally achieved much faster, i.e., roughly within a century. With more limited OTEC scenarios, a global OTEC power production of the order of 7 TW could still be achieved without much effect on ocean temperatures.

An Evaluation of the Large-Scale Implementation of Ocean Thermal Energy Conversion (OTEC) Using an Ocean General Circulation Model with Low-Complexity Atmospheric Feedback Effects

“…For example, the shapes of the disrupted average thermoclines from OTEC operations at maximal power production in Rajagopalan and Nihous [18] (their Figure 4), and from the mildest scenarios in Kwiatkowski et al [19] (their Figure S18), are significantly different. This and other results concerning potential impacts on ocean circulation suggest that the flow singularities representing the OTEC process in an uncoupled ocean model are important in shaping environmental responses [16][17][18], even if the benefits of numerical experiments run on a fully coupled model like CESM are undeniable. mechanisms underlying the large-scale environmental effects predicted when OTEC power production peaks would be valuable.…”

“…Following previous investigations of the large-scale implementation of OTEC [16][17][18], the open-source ocean general circulation model MITgcm was selected for this study [15,21]. Discretized transport equations for momentum, potential temperature, and salinity are solved using a finite-volume technique.…”

“…It predicted a global OTEC power maximum of about 30 TW, but also showed persistent environmental effects, such as surface cooling in the tropics balanced by surface warming elsewhere, with a net transient heat input into the oceanic water column, as well as a boost in the deep oceanic circulation. Given the opportunity to access greater computing resources, Rajagopalan and Nihous were able to use a version of MITgcm with a much greater horizontal resolution (1 • × 1 • ), and more vertical layers [17]. The predicted maximum for global OTEC power production dropped to 14 TW, while environmental effects were essentially confirmed.…”

“…Taken as a whole, this body of work represents a considerable improvement over previous analyses, when considering large-scale OTEC deployment. While details about the model can be found elsewhere and are summarized in Section 2, a potentially important drawback in the MITgcm implementation used by Rajagopalan and Nihous is that the atmosphere is not explicitly modeled [16][17][18]. Instead, fluxes between the ocean and the atmosphere are permitted, for example as a result of oceanic perturbations, but atmospheric fields are assumed to be fixed.…”

“…The next section presents a summary of the existing model of large-scale OTEC using MITgcm, In view of the above discussion, the purpose of the present work is twofold. The first objective is to modify the ocean-atmosphere thermal boundary condition in the MITgcm protocol used previously to investigate the implementation of large-scale OTEC scenarios [16][17][18]. In these studies, the atmosphere was not explicitly modeled, and any adjustment to temperature changes in the ocean surface layer consisted of restoring heat fluxes defined in reference to a fixed atmospheric temperature field.…”