**1. Introduction**

Islands emit fewer greenhouse gases (GHG) globally than the emissions generated on the continents; however, they have high per capita emissions. For example, the Caribbean Islands generated 0.4% of the world's total GHG emissions in 2011, but per capita emissions exceeded 120 tons while the world average was 5 tons per person [1]. These emissions are derived mainly from the generation of energy through fossil fuels.

Due to its location far from the rest of the country, the San Andrés Island is part of the non-interconnected areas of Colombia. Currently, electricity at San Andrés Island is generated by diesel power plants, with an approximate cost of USD 0.3 per kWh, which is relatively high compared to an interconnected city whose electricity price fluctuates around USD 0.08 per kWh. This difference is due to the costs of the thermoelectric operation plant and because diesel fuel must be brought by boat from Cartagena. It should also be noted that thermoelectric plants produce greenhouse gases that reach the atmosphere and contribute to global warming. Furthermore, most developing countries have insufficient financial and legislative resources to meet the challenges of climate change [2]. In addition, sustainable energy supplies are needed to reduce greenhouse gas emissions, thus mitigating the devastating effects of climate change [2]. Furthermore, the seventh Sustainable

**Citation:** Herrera, J.; Sierra, S.; Hernandez-Hamón, H.; Ardila, N.; Franco-Herrera, A.; Ibeas, A. Economic Viability Analysis for an OTEC Power Plant at San Andrés Island. *J. Mar. Sci. Eng.* **2022**, *10*, 713. https://doi.org/10.3390/ jmse10060713

Academic Editor: Eugen Rusu

Received: 30 April 2022 Accepted: 18 May 2022 Published: 24 May 2022

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Development Goals of the United Nations Organization emphasise energy affordability and clean energy use. In this way, Colombia and, in particular, the Colombian Caribbean is consequently in need of reliant sources of energy capable of guaranteeing a continuous supply of energy sustainably.

Furthermore, the well-being of communities can be improved by increasing the supply of electricity. However, there are historical reasons why this has not happened in some regions of the Colombian Caribbean. The lack of enough energy is added to other problems concerned with access to potable water, adequate housing, quality food, and high infant mortality rate, among others [3,4]. The reports [5,6] reveal that it will be necessary to increase political commitment and investment in energy at San Andrés Island, or else energy poverty will increase.

If a small part of the energy stored in the oceans could be recovered, the world's energy demand could be satisfied. However, the technology to recover energy from the oceans is at a very incipient level of development, with the production of marine power being only residual compared to other sources of renewable energy [7,8]. Among the different technologies to harvest energy from the sea, OTEC is one of the most incipient and promising ones. According to [9], the installed capacity of ocean energy in 2050 could reach 337 GW [7]. Along the same lines, a recent analysis by [10] estimates that the industrialscale potential of an OTEC system is around 13 terawatts worldwide [7]. Moreover, the development of OTEC technologies is an opportunity to generate an industry around this type of energy generation, generating new jobs, both for the construction and maintenance of OTEC plants.

Countries located in tropical areas have the ideal conditions to develop OTEC technology; due to their proximity to the equator, the necessary temperature gradients are generated for the OTEC system operation [11,12]. Additionally, OTEC systems can be built to generate power on a small scale [13]. On the other hand, OTEC systems have greater economic viability in tropical islands not connected to the mainland electricity grid, with potable water deficiencies and air conditioning needs, since these needs could be mitigated simultaneously by an OTEC system [7]. Some developing countries that are investigating the feasibility of OTEC technology are Colombia [14], Indonesia [15–17], Panama [18] and Pakistan [7], among others.

OTEC systems use only the temperature gradient (Δ*T*) generated between the sea surface and deep water as an energy source, converting it into renewable energy. The Δ*T* is directly related to the performance of the OTEC power cycles; Δ*T* ≈ 20 ◦C is generally needed for an OTEC system to be viable [8]. Therefore, OTEC systems have a low thermal efficiency compared to other renewable energy sources. For example, an OTEC system based on the Rankine cycle generally has an efficiency of no more than 5% [19,20]. However, an OTEC system has the following two advantages. First of all, the power generation system can constantly work 24 h a day, something that is not possible with photovoltaic or wind systems; the temperature of the sea in tropical areas does not change considerably throughout the year, presenting small variations in the order of degrees due to the seasons and climate changes. Additionally, the variation of Δ*T* between day and night is around 1 ◦C [15,21]. Second, the OTEC system can generate freshwater as an indirect product [22–25].

Research on the OTEC system has focused on evaporators, turbines, generators, condensers, pumps, pipes to transport water, and moorings. For example, some investigations focus on the design of turbines to obtain the highest efficiency and net power [15]. Other investigations work on cycles; the most used are the Rankine, and double-stage Rankine [26] cycles; OTEC systems have also been implemented using various cycles such as Kalina [27], Uehara [28], which is an improvement of the Kalina cycle [19,20,27]. At the pipeline level, research is being carried out on the material and coating of the pipeline and the control that can be implemented to keep it stable. The pipe that transports deep seawater is a fundamental component of the OTEC system; this pipe, generally greater than 1000 m, must be designed to withstand the vibrations generated by deep water. Research on flexible

structures can be found in [25]. Finally, studies on the economic viability of OTEC systems can be found in [15]. Various studies [16,29] have shown that the economic viability of an OTEC system requires plants with a maximum power of 100 MW, since the cost and complexity increase considerably from systems with the higher power.

Although the technical aspects are essential for developing this technology, it is also true that it is necessary to know the economic viability due to its low efficiency and high implementation costs. In this line, different works with multiple approaches have been developed. For example, in [30], a thermo-economic analysis of a 20 kW OTEC system is conducted by calculating the unit cost of electricity generated. They concluded that OTEC systems are economically viable in regions where the surface seawater temperature is greater than 25 ◦C. On the other hand, Ref. [31] presents the design of an OTEC Ecopark consisting of a 60 MW OTEC system coupled to a marine aquaculture farm located near the Island of Cozumel. The proposed system meets part of the needs of coastal communities for energy production, desalinated water and food production. The work was based on the technical-economic evaluation of the OTEC Ecopark, and the financial evaluation showed that the OTEC Ecopark is economically viable, having a CAPEX of USD 655.38 M, an OPEX of USD 69.66 M and an annual income of USD 348 M. Studies that carry out economic viabilities can be found in [32–34], and an interesting review on economic feasibility studies is presented in [35].

This paper conducts an economic feasibility study of installing an OTEC plant at San Andrés Island. In this sense, it is assumed that the economic viability is closely related to the installation location and the plant's technical design. The economic viability is based on two analyses, (i) a cash flow analysis of the project, and (ii) a levelized cost of energy (LCOE) are carried out [36]. The latter way of measuring is usually used to assess the cost of employing different methods for generating renewable energy [35]. It should be noted that the LCOE in this work is calculated individually for the proposed OTEC system. Ideally, if it wants to have a total generation from renewable energy, the LCOE should be calculated for the entire system [37].

This study is a starting point to develop this technology on the Island, developing an OTEC system that improves electricity and potable water supply needs. Furthermore, the environmental conditions at San Andrés Island sea (optimal surface temperature, Δ*T* around 20 ◦C all year, low frequency of hurricanes, ideal depth at a short distance from the coast) favour the implementation of an OTEC plant, which could generate electricity for several homes on the island without producing polluting waste and operating costs lower than those of the diesel plants.

The paper is organised as follows. Section 2 explains the current energy and water situation at San Andrés Island and briefly describes an OTEC system. Section 3 summarises the methodology for performing the economic analysis. Section 4 exposes an OTEC system location, the technical conditions of the OTEC system, and the economic viability of two possible scenarios presented, without potable water and with potable water. Finally, Section 5 summarises the main conclusions.
