**1. Introduction**

The sun serves as the main source of energy on the planet. The incident radiation is absorbed by the ozone in the stratosphere and much by the clouds. About 35% of it is reflected into space, and then 66% of the remaining energy is absorbed by the Earth's surface. Considering that more than two-thirds of the Earth's surface is hosted by water, the oceans represent the most prominent solar energy collectors and, thus, the largest global energy reservoir [1,2].

The most considerable ocean thermal energy is hosted near the Equator [3–5]. Geographically, Panama is located in Central America, bordering the Caribbean Sea and the Pacific Ocean, between 7◦ and 10◦ North latitude and 77◦ and 83◦ West longitude. Therefore, Panama's ocean scenario displays thermal energy resource potential [6–8]. However, since Panama has a broad oceanic scenario, knowing its location is not enough to guarantee the sustainability of implementing marine energy exploitation, such as OTEC (ocean thermal energy conversion).

OTEC technology uses the temperature difference between warm ocean surface waters and deeper cold waters. The zones that achieve adequate thermal differences to take advantage of the oceanic thermal resource are generally close to tropical areas, near the

**Citation:** Lopez, G.; Ortega Del Rosario, M.d.l.A.; James, A.; Alvarez, H. Site Selection for Ocean Thermal Energy Conversion Plants (OTEC): A Case Study in Panama. *Energies* **2022**, *15*, 3077. https://doi.org/10.3390/ en15093077

Academic Editors: Kostas Belibassakis, Eugen Rusu and George Lavidas

Received: 18 March 2022 Accepted: 13 April 2022 Published: 22 April 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Equator, as shown in Figure 1. However, because temperature jumps are around 20 ◦C, a low efficiency can be reached. Despite this, the global theoretical potential for OTEC has been estimated at 44,000 TWh/year, making OTEC an attractive alternative to cater to particular needs of society [9–11].

**Figure 1.** Global oceanic thermal resource and location of Panama (enclosed in the light blue circle) [12].

A good site selection is a key factor in implementing a sustainable and successful project that aims to exploit ocean thermal energy, regardless of the targeted objective or benefit [13]. Therefore, the proper site selection for the implementation and viable installation involves the analysis of various variables, qualitative and quantitative.

Many criteria can help assess the potential of the thermal resource for a site that can later be used by OTEC technology addressing sustainability. For instance, this technology's efficiency depends on variables such as depth, the temperature of deep cold seawater, warm sea surface temperatures, and anomalies of warm sea surface temperatures [13,14]. Thus, site selection can quickly become a multi-criteria decision-making (MCD) problem, and it generates a conflictive scenario that houses technical, social, economic, environmental, and legislative criteria [13]. Moreover, studies on this topic implementing the classic methods of MCD are limited because many of the decisions for selecting OTEC sites are subjective concerning the criteria of each decision-maker (DM). The accurate decision regarding the site selection for OTEC systems represents the fundamental basis in the planning process for the use of ocean thermal energy and sustainability of this technology [15].

The difficulty for a site selection process lies in the number of indicators or the amount of data available and comparing each set of indicators corresponding to each alternative of interest, besides granting an assessment that justifies a degree of importance among the criteria considered. Then, it is paramount first to identify the aim to use the local oceanic thermal resource. OTEC allows obtaining various benefits from the use of the oceanic thermal resource [14,16], including different classifications for OTEC plant (On-Shore or Off-Shore). OTEC technology is used for: electric power generation [17], air conditioning [11], industrial refrigeration [6], aquaculture [18], liquid hydrogen production [19] and desalinated water [19]. Then, the alternatives with the most significant potential within the oceanography can be selected considering the environmental legislative regulations, for instance, whether the planned lands belong to the group of areas or regions environmentally protected. After this, appropriate criteria set can be drawn by means that match the project's goals of interest.

This problem addresses various variables, some of which are not directly related to the nature of the oceanic scenario. For instance, some qualitative aspects generate added value to the implementation of this technology, such as environmental, political, and social impact [14]. Most studies that have been conducted are related to the analysis of one or more of the criteria influencing decision-making for the selection of OTEC sites. These criteria include temperature gradient, bathymetric characteristics, environmental, social, and economic impact [16].

Addressing sustainability according to environmental, social, and economic impacts can be a rather difficult task since the lack of absolute instruments for evaluations or available data can endanger the precision and reliability of the results. Even though some of them have been assessed previously in the literature, such as environmental impact assessment and sustainability [14,16], sustainability of society [13,14], energy sustainability [3,20], economic sustainability [14], sustainability of construction and maintenance [13,21], and sustainability of the auxiliary condition [14].

These considerations and several variables that categorize the site selection for OTEC render the site selection a complex study scenario. Furthermore, one must consider the dependence between the relevance given to each of these aspects by specialists or researchers during the decision-making process and the discrepancy that this can project due to the degree of knowledge and experience each possesses.

In Panama's scenario, the lack of legislation and regulations and the lack of information and specialists can render a complex task for implementing OTEC technology. This research only includes variables or quantitative indicators justified and validated with software that use oceanographic data in real-time, such as the World Ocean Atlas and the NOAA database, compared with the corresponding literature.

The qualitative variables depend on the evaluator's degree of knowledge, experience, and specialty. Therefore, it carries the uncertainty corresponding to the sensitivity of human perception, which generates a more complex scenario in the validation and justification of the weighting for assessing the importance of these indicators.
