An assessment of global Ocean Thermal Energy Conversion resources under broad geographical constraints

Abstract

Rates of Ocean Thermal Energy Conversion (OTEC) are assessed with a highresolution (1 Â 1 ) ocean general circulation model when broad geographical restrictions are imposed on the OTEC implementation area. This may correspond to practical or legal limitations, such as the cost of long submarine power cables or the extent of Exclusive Economic Zones. Because some environmental effects predicted under large-scale OTEC scenarios exhibit a strong asymmetry among major oceanic basins, numerical experiments where the OTEC domain is restricted to such specific areas are also conducted. Results suggest that in all cases, a rate of about 0.2 TW per Sverdrup of OTEC deep cold seawater is sustained when overall OTEC net power peaks. At that juncture, temperature profiles in the OTEC implementation areas are affected in similar ways, while the strength of the Thermohaline Circulation roughly doubles. Overall geographical constraints simply defined by distance to shore, given the model's 1 horizontal resolution, produce global OTEC net power maxima of 12-14 TW. In such cases, OTEC net power density approximately increases in inverse proportion to the OTEC implementation area. Limiting OTEC development to the Indo-Pacific yields results similar to the global case with a maximum proportional to the implementation area (12 TW), but simulations restricted to the Atlantic behave quite differently. In the latter case, OTEC net power peaks a little over 5 TW. It is estimated that producing half the predicted power maxima would substantially limit large-scale environmental temperature changes in each case. V C 2013 AIP Publishing LLC.

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

“…The predicted maximum for global OTEC power production dropped to 14 TW, while environmental effects were essentially confirmed. A later study examined OTEC scenarios where geographic constraints were imposed on the OTEC implementation region [18]. Taken as a whole, this body of work represents a considerable improvement over previous analyses, when considering large-scale OTEC deployment.…”

“…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.…”

“…Even results from the much less drastic scenarios described in supplementary material available via a web link, may not adequately represent OTEC implementation on a large scale. 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.…”

“…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.…”