Assessing Hydrokinetic Energy in the Mexican Caribbean: A Case Study in the Cozumel Channel

: This paper presents a techno-economic assessment of hydrokinetic energy of Cozumel Island, where ocean currents have been detected, but tourist activities are paramount. The main objective of this research is to identify devices that have been used to harvest hydrokinetic power elsewhere and perform an economic analysis as to their implementation in the Mexican Caribbean. First, the energy potential of the area was evaluated using simulated data available through the HYCOM consortium. Then, for four pre-commercial and commercial turbines, technical and economic analyses of their deployments were performed. Socio-environmental constraints were reviewed and discussed. Three optimal sites were identiﬁed, with an average annual hydrokinetic energy density of 3–6 MWh/m 2 -year. These sites meet the socio-environmental requirements for marine kinetic energy harvesting. Of the turbines considered in the analysis, the best energy price/cost ratio is that of SeaGen device, with a maximum theoretical energy extraction of 1319 MWh/year with a Capacity Factor of 12.5% and a Levelised Cost of Energy (LCOE) of 1148 USD/MWh. Using this device, but assuming a site-speciﬁc design that achieves at least 25% of Capacity Factor, 20-year useful life, and a discount rate of 0.125, the LCOE would be 685.6 USD/MWh. The approach presented here can be applied for techno-economic analyses of marine turbines in other regions.


Introduction
The wide range of renewable energies are increasingly seen as feasible alternatives to generate electricity. Some of these technologies are well documented and in an advanced stage, while others are still in their infancy [1,2]. Among the latter, ocean energy has recently gained attention due to the diverse harvesting possibilities it offers [3][4][5]. In a project involving any of these ocean energy sources, three steps are required: (1) a theoretical assessment of resources; (2) a technical assessment, considering the devices available; and (3) a practical assessment, including in-site evaluations [6,7].
In some parts of the world, ocean currents exist that can be harnessed to provide energy. There are eight main regions with an average kinetic energy flux of over 0.5 kW/m 2 , (HYCOM [8] data, 2009-2012, at a depth of 20 m); the South African coast (Agulhas Current), the southeast U.S. and Mexican coasts (Gulf Stream-Cape Hatteras, Florida current-Florida Straits and Yucatan current in Cozumel), Japan (Kuroshio current), Indonesia, Somalia, Brazil (Brazil Coastal Current), Madagascar (Madagascar Currents), and Australia (South West Rocks). At four of these sites, the direction of the current is persistent and there are no reverse flows: north of Madagascar, off part of the Brazilian coast, and Florida current and Yucatan current [9]. conversion in the most prospective regions, such as in Cozumel. In this region, availability and persistence of hydrokinetic energy has been identified; however, this is a region with active tourist activities where social and environmental constrains should also be taken into account. Furthermore, more technical analysis, including feasibility studies of existing devices in pre and commercial stages are still needed.
To help fill this knowledge gap, a techno-economic assessment of energy from ocean currents off Cozumel, Mexico, is presented in this paper as a continuation of former theoretical resource assessments (e.g., [6]). The main objective of the work was to identify which device has the best cost-benefit relationship. In addition, technical factors related to the design of devices commonly used for tidal energy were evaluated, and environmental, touristic, and social considerations, relevant in the study zone, are also discussed.
It is hoped that the work presented here will be useful in bringing to fruition projects in marine current energy generation in Mexico. The manuscript is organized as follows: Section 2 presents the methodology, including the description of the four hydrokinetic devices, descriptions of the databases employed, as well as the analytical methods used in the techno-economic analysis. The results of the technical and economic analysis are presented in Sections 3 and 4, respectively. Section 4 includes the estimated Capacity Factors of the devices considered as well as the Levelised Cost of Energy (LCOE). In Section 5, the main technical, social, and environmental challenges are described. Finally, the main conclusions and future perspectives are summarized in Section 6.

Methodology
To assess the objectives of the present work, a brief review of the state of the art of the technology used for hydrokinetic energy conversion of ocean currents was performed, including previous studies of energy potential in the study area. Considering the available energy power of ocean currents in this region and technical information from different devices, four devices were selected for the economic analysis, which estimates the most convenient project costs for the planning and installation of the devices in the study area. The feasibility of each turbine was discussed, including technical challenges related to installation, mooring, soil, climate, and distance to infrastructure. Finally, challenges related to environmental restrictions, sites of touristic interest, military activities, marine transportation routes, and possible social resilience in the region of interest, were described.

The Present Energy Scenario in the Mexican Caribbean
The Mexican government has promised that by 2024,~35% of the nation's electricity demand will be met from renewable energy sources. Various energy sources are considered, including that from tides and ocean currents. The Mexican Secretary for Energy established the aim to reduce the use of fossil fuels to 65%, 60%, and 50% by the years 2024, 2035, and 2050, respectively.
In a report on electricity consumption by the Mexican System of Energy Information [41] in the state of Quintana Roo, where Cozumel is found, it was shown to have consumed 3224 GWh in 2007, and 4504 GWh In 2017; an average increase of 128 GWh.

The Study Area
The area examined in this paper is the Cozumel channel (shown as a red polygon in Figure 1a,b), off the east coast of the Yucatan peninsula, 90 km SW of Cancun, between the island of Cozumel and Playa del Carmen. The main town on the island is also called Cozumel, located on the west coast ( Figure 1c). Tourism is the main economic activity of the island and there is an international airport, a dock for cruise ships, and an hourly ferry connection to Playa del Carmen (Figure 1c).
The morphology of Cozumel Island is described fully in [43]; it lies 18 km in front of Playa del Carmen, Quintana Roo; has a maximum length of 53 km, SW-NE; and a width, NW-SE of 16 km in the centre ( Figure 2). The island has an area of ~470 km 2 and a coastline of 124 km, mostly rocky. The west coast of the island has a narrower platform (500 to 1000 m to the −50 m isobath where the barrier reef begins). In this part of the island, there are three reef terraces at −5 m, −10 m, and −20 m. On the east coast, the insular platform is 1500 to 2500 m to −50 m, where the shelf edge begins, and there are five reef terraces at −3

The Study Area
The area examined in this paper is the Cozumel channel (shown as a red polygon in Figure 1a,b), off the east coast of the Yucatan peninsula, 90 km SW of Cancun, between the island of Cozumel and Playa del Carmen. The main town on the island is also called Cozumel, located on the west coast ( Figure 1c). Tourism is the main economic activity of the island and there is an international airport, a dock for cruise ships, and an hourly ferry connection to Playa del Carmen (Figure 1c).
The morphology of Cozumel Island is described fully in [43]; it lies 18 km in front of Playa del Carmen, Quintana Roo; has a maximum length of 53 km, SW-NE; and a width, NW-SE of 16 km in the centre ( Figure 2). The island has an area of~470 km 2 and a coastline of 124 km, mostly rocky. The west coast of the island has a narrower platform (500 to 1000 m to the −50 m isobath where the barrier reef begins). In this part of the island, there are three reef terraces at −5 m, −10 m, and −20 m. On the east coast, the insular platform is 1500 to 2500 m to −50 m, where the shelf edge begins, and there are five reef terraces at −3 m, −10 m, −20 m, −30 m, and −50 m, which are remnants of abrasion platforms from the Holocene era. The area of the northern platform is almost flat, at −20 to −30 m and  Figure 2 shows the bathymetry of the study area [44]. According to [45],~5.05 Sv. (Sverdrups, equivalent to 10 6 m 3 /s) passes through the channel.  Figure 1). Figure 2 shows the bathym etry of the study area [44]. According to [45], ~5.05 Sv. (Sverdrups, equivalent to 10⁶ m 3 / passes through the channel.  . On the Playa d Carmen side, the continental platform stretches less than a kilometre and the slope is ve pronounced, ~68° (the green line in Figure 3b). On the other side of the channel (Figu 3c), the continental platform is 750 m in width, and the slope is ~29°. This is importa when considering whether to install turbines on the sea bottom, in foundations or wi anchors.

The Turbines
Although often ocean current turbines are often installed as arrays of devices, in this work, four individual commercial turbines were compared. (Figure 4). Two criteria were considered for the selection of the turbines. The first was that the stage of development of the devices is advanced, that is, at least at pre-commercial level. The second criteria was that there is information in the literature on the power curves, or sufficient data to estimate    Carmen side, the continental platform stretches less than a kilometre and the slope is very pronounced,~68 • (the green line in Figure 3b). On the other side of the channel (Figure 3c), the continental platform is 750 m in width, and the slope is~29 • . This is important when considering whether to install turbines on the sea bottom, in foundations or with anchors.

The Turbines
Although often ocean current turbines are often installed as arrays of devices, in this work, four individual commercial turbines were compared. (Figure 4). Two criteria were considered for the selection of the turbines. The first was that the stage of development of the devices is advanced, that is, at least at pre-commercial level. The second criteria was that there is information in the literature on the power curves, or sufficient data to estimate this, which is important as it allows comparisons between devices at sites previously identified as having hydrokinetic potential.
Of these turbines, there is the most information about the SeaGen and the NOVA, and the least information about the Kairyu. A brief description of the turbines is given, and summarized in Table 1. Three are axial turbines, with a horizontal axis of two blades, a cut in speed of 0.6-1 m/s, and nominal speeds of 1.5-2.2 m/s.

•
The NOVA M100-D turbine (100 kW), Figure 4a, was developed by NOVA INNOVA-TION Ltd., UK [47]. It has a direct drive technology, using a simple rugged low-speed generator to directly convert the rotation of the blade into electricity. The rotor is 8.5 m in diameter and its nominal power is 100 kW at 2 m/s. The rotor is bi-directional. The system is fixed by gravity onto the seabed, so it does not require anchors or drilling.

•
The Sea Gen turbine (1.2 MW), Figure 4b [48], was developed by Marine Current Turbines Ltd., now called Atlantis, UK. A prototype using this turbine was installed in 2008, but it is currently out of service. It had two 600 kW turbines working at 2.5 m/s current speed, with two 16-meter diameter rotors. It lies on the seabed, needing foundations that require drilling.

•
The Kairyu (100 kW), Figure 4c [49], is a floating turbine system. It generates~100 kW at~1.5 m/s. It is still at pre-commercial stage and is being developed by IHI Co., New Energy and Industrial Technology Development Organization (NEDO), Japan.

•
The TidGen (150 kW), Figure 4d [50], was developed by Ocean Renewable Power Company ORPC, USA, and has four helical-type cross flow turbines, coupled to a single generator. Because of its elongated shape, it works well at shallow sites. At present, it is being considered for a tidal power project in Cobscook Bay, Maine, USA. It lies on the seabed and does not require anchors or drilling.

Simulated Data for the Estimation of Available Power
The estimated current velocities at the nodes in the channel were obtained from simulations using the HYCOM model (HYbrid Coordinate Ocean Model) [8]. Simulations using this model give predictions for the velocity components with a periodicity of 3 h and are distributed through a web repository accessed with the OPeNDAP protocol [57].
The database used was the Global Ocean Forecasting System 3.1 [58], which has records from July 2014. In this study ( Figure 5), data was taken from the web repository from July 2014 to December 2019, for the geographic coordinates of the study area and the desired time range.
The data were obtained in Network Common Data Form (netCDF) format and were restructured to build a probability distribution of the current velocity at all available nodes in the study area. The data extraction, transformation, and loading process were carried out using the R programming language and the ncdf4 library [59].

Simulated Data for the Estimation of Available Power
The estimated current velocities at the nodes in the channel were obtained from simulations using the HYCOM model (HYbrid Coordinate Ocean Model) [8]. Simulations using this model give predictions for the velocity components with a periodicity of 3 h and are distributed through a web repository accessed with the OPeNDAP protocol [57].   [53]. ii [51]. iii [54]. iv [55]. v [48], vi From [51], vii [49]/Data year 2019, viii [56]/data year 2010. m/s. Figure 5 shows the bathymetry of the study area and the nodes analysed. As can be seen, most of these nodes are at depths of <100 m. In Figure 5, the measurement sites used by [40] were included (see Sites (a), (b) and (c)).
In that study, Acoustic Doppler Current Profilers (ADCPs), attached to a buoy at 130 m depth, were used providing useful data from 22 to 121 m water depths. These measurements were taken from August 2002-August 2003 along the Mexican Caribbean coast.

Potential Hydrokinetic Estimates and Theoretical Use
To compare the theoretical energy harvested by the device with the potential hydrokinetic energy available, the mean annual power density in MWh/m 2 -yr [37] was used.  [44]. The red line shows the study area, in which 16 HYCOM nodes (n1 to n16) are plotted. Sites (a), (b) and (c) are those evaluated by [40]. Figure 5 shows the bathymetry of the study area and the nodes analysed. As can be seen, most of these nodes are at depths of <100 m. In Figure 5, the measurement sites used by [40] were included (see Sites (a), (b) and (c)).
In that study, Acoustic Doppler Current Profilers (ADCPs), attached to a buoy at 130 m depth, were used providing useful data from 22 to 121 m water depths. These measurements were taken from August 2002-August 2003 along the Mexican Caribbean coast.

Potential Hydrokinetic Estimates and Theoretical Use
To compare the theoretical energy harvested by the device with the potential hydrokinetic energy available, the mean annual power density in MWh/m 2 -year [37] was used. Equation (1) was applied to the velocity data for each node, (See Appendix A), to obtain the hydrokinetic energy (in MWh/m 2 -year) as the current passes the shallowest 50 m of the total water depth. With these values, an average theoretical energy potential was obtained for depths of 0-50 m [0, 2,4,6,8,10,12,15,20,25,30,35,40,45,50].
Equation (3), presented by [60], was reformulated and then applied to obtain the energy generated by the turbines in specified operational site conditions. This type of calculation, applied to marine turbines, is described by [9], who considers it necessary to have the following data:

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The energy potential available at a given site (latitude, length and depth, period of time (Appendix A, Table A1).

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The electrical output power curve (Appendix A, Table A2) considers the cut-in and cut-out velocities. This is the power curve, which is a function of the design characteristics of the turbine, such as the power coefficient (C p ), turbine subsystems (e.g., the gearbox), generator conversion efficiency, and other energy losses. In this work, the resulting marine hydrokinetic energy for the site of interest in a certain time is considered as the theoretical power estimation approach.

•
It was also assumed that in the case of seabed-based technologies such as SeaGen, Nova, and TidGen, the evaluation of their performance is based on a floating type of installation.
Considering the approach of [37], the energy density in terms of a period of 1 hour (E in Wh/m 2 ) in a defined period of time (T) is given by Equation (1).
where P is the power density (W/m 2 ) of the marine current (Equation (2)), U is the speed of current (m/s), and ρ is the sea-water density (kg/m 3 ). To compare the energy generated by each device, the MWh/m 2 -year was used, i.e., the energy extracted by the device, theoretically, from the hydrokinetic potential available at each node (Equation (3)). Subsequently, this value was multiplied by the area of the selected turbine, shown in Figure 4, giving the total energy generated in a year, in MWh/year; in other words, the technical power availability for each turbine.
where P e (z,n) represents the estimated production of electrical energy for every HYCOM node, n, and for every depth value, z ∈{0,2,4,

Delimitation of the Most Suitable Area
Three criteria were used to identify which areas have the most potential for this type of energy generation.

1.
First, whether the device would be floating or placed on the seabed. As seen in Table 1, it is suggested that for floating devices, their anchors are no deeper than 100 m [54], while for water depths <50 m, it is recommended that the devices rest on the seabed.

2.
The second criterion is the average hydrokinetic potential generated per year obtained with Equation (1).

3.
Thirdly, social and environmental constraints that would restrict installation or manoeuvring at the energy use site must be taken into account.
The results of the first two criteria suggest that the best sites for floating technology would be between the −30 m and −100 m isobaths, while for technology resting on the seabed, optimal sites would be between the −30 and −50 m isobaths. For these conditions, the height of the turbines, seen in Table 1, and the bathymetric charts of the Mexican Navy [63] were taken into account (YE. 922.1, S. M. 922.4) as well as the Bathymetric Chart of the IBCCA (sheet 1-06) [44].
To meet the needs of the third criteria, areas which have restrictions regarding maritime traffic; protected natural areas [64]; strategic infrastructure, such as cables for electricity or telecommunications; and sites close to airports, military zones, and research centres, must be excluded from the study. All these restrictive elements should be documented on maps and web pages of the relevant agencies, such as the Secretariat of the Mexican Navy [65] Figure 6 shows the average hydrokinetic potential per year for each node shown in Figure 5, from the sea surface to a depth of −50 m (MWh/m 2 -yr). The values range from 0.0075 MWh/m 2 -yr to 6 MWh/m 2 -yr for nodes 4 and node 5, respectively. It can be seen that the area with greatest potential is 6-7 km off the Cozumel coast, where the channel depth is over 400 m (Figure 2), in front of Punta Francesca and Punta Langosta.

Estimating Power Availability
The areas with depths of −30 to −50 m, which could be used for devices based on the seabed, have low hydrokinetic energy potential, around 1 MWh/m 2 -yr. Even for floating devices anchored at −100 m or less, the potential is only 2 MWh/m 2 -yr ( Figure 6).

Estimating Energy Costs
In order to compare the cost of the energy produced by each of the devices, the methodology of [68] was used to obtain LCOE estimates for the various ocean technologies. The LCOE is the sum of the initial investment cost, plus operational costs, divided by the production of energy during the useful life of the system. This methodology defines the parameters of capital expenditures (CAPEX), operating and maintenance expenses (OPEX), and input resource data. As it is expected that the LCOE for the deployment of the first array will prove uncompetitive, the LCOE was applied for a project with a minimum installed capacity of 0.3 MW, CAPEX of $ 5100/kW, and OPEX of $ 160/kW-year, and a maximum installed capacity of 10 MW with CAPEX of $ 14,600/kW and OPEX of $ 1160/kW-year.
CAPEX is the capital expenditure, and OPEX is the operational expenditure (for year t), AEP is the annual electricity production (at year t), r is the discount rate, n is the lifetime of the system, and t is the year from the start of project. CAPEX includes both fixed and variable investment costs such as planning, manufacturing, and construction. The OES [68] recommends a discount rate r of 8.5 to 12.5% and t of 20 years.
The C.F., expressed by Equation (5), is the Capacity Factor, which is the ratio of energy actually produced by an energy generating unit or system, in a given period T (8760 h per year), compared to the hypothetical maximum. This can be expressed as a percentage (over a given reference period) or as full load hours per year. AEP is the total energy produced by the system during a year in MWh/year or kWh/year. P is the nominal power of the turbine in kW or MW [69].
The CAPEX value was estimated for each device as [60].
In Equation (6), the costs in C i (in USD) are the generator, rotor, coupling, installation (cable; network connection, and foundations), and their participation percentages λ i . The percentage of each category was calculated depending on the characteristics of each device with the mathematical models of [60].

Methods for Evaluating Environmental and Social Restrictions
Any project that would affect coastal, marine, or jungle ecosystems in the study area must be discussed in a process of public consultation [70]. Therefore, regulations for the protected natural areas (PNA) [64] and the ecological management programs in the study area were reviewed [71]. With this information, descriptive maps of the study area were made, showing the area that can potentially be impacted.
Parallel to these environmental criteria, the parts of the study area described as strategic were also mapped: (a) power transmission lines and power plants; (b) the airports, cabotage ports, shipping routes, and military zones; (c) areas with important economic activities, mainly tourism; and (d) any areas with major infrastructure, such as roads or towns. The mapping was done using the geo portal of the National Commission for the Knowledge and Use of Biodiversity [72], and the bathymetric charts of the Secretariat of the Navy [63], information from the Federal Electricity Commission (CFE), and the National Commission of Natural Protected Areas (CONANP), To organize this information, free software QGIS 3.10, 64 Bit, WGS 84, Windows 10, under General Public License [62] was used. And Google Earth Pro 7.3.3.7786 (64-bit), Microsoft Windows Operating System (6.2.9200.0) from © 2020 Google LLC, was used to produce georeferenced KML information [73]. To adapt the figures, © 1993-2012 Golden Software Inc, Surfer version 11.0.642 (64-bit) Surface Mapping System [74] was also used. Figure 6 shows the average hydrokinetic potential per year for each node shown in Figure 5, from the sea surface to a depth of −50 m (MWh/m 2 -year). The values range from 0.0075 MWh/m 2 -year to 6 MWh/m 2 -year for nodes 4 and node 5, respectively. It can be seen that the area with greatest potential is 6-7 km off the Cozumel coast, where the channel depth is over 400 m (Figure 2), in front of Punta Francesca and Punta Langosta.

Estimating Power Availability
The areas with depths of −30 to −50 m, which could be used for devices based on the seabed, have low hydrokinetic energy potential, around 1 MWh/m 2 -year. Even for floating devices anchored at −100 m or less, the potential is only 2 MWh/m 2 -year ( Figure 6). Table 2 shows the hydrokinetic potential for the reference sites of [40], as well as the average direction of the current and its standard deviation. Based on these data, the site with greatest potential is site (a), in the Cozumel Canal, followed by sites (b) and (c), which are shown in Figure 5. In the case of site (a), the measurements reported by [40] are close to those for Node 15 using HYCOM. The HYCOM hydrokinetic potential ( Figure 6) is around 2 MWh/m 2 -year; about five times less than the 9.85 MWh/m 2 -year obtained using the data reported by [40]. Table 3 shows the theoretical energy extracted in 1 year for the four turbines considered in this analysis. The MWh/year values at each of the 16 nodes are reported. The HYCOM nodes used to evaluate the energy potential were 5, 9, 11, and 13. These results indicate that SeaGen uses 40% of the energy potential, Kairyu 39%, Nova 36.4%, and TidGen 5.5%.  Table 4 shows the average capacity factors (in percentages) calculated for each node and the four turbines. The capacity factors (Table 4) for each device were located for the best site, which was node 5 ( Figure 5). The device with the highest plant factor was the Karyu with almost 31%.  Table 5 shows the Public CAPEX (cost from official web pages of the turbine manufacturers) and the calculated CAPEX (obtained using the methodology of [68]) compared with the Ranc CAPEX (first array/first project) of [68]. The most expensive devices are Nova and Kairyu. SeaGen and TidGen have more competitive Public and Calculated CAPEX.  Table 6 shows the levelised cost of energy (LCOE) for the devices evaluated, for node 5, which is the best location in terms of the energy potential available, using HYCOM data. In the table it can be seen that there are no public LCOEs available. However, an LCOE calculated with the methodology of [68] is shown. Comparing the referenced LCOE of [68], it is seen that these are well above the international references of 210-470 USD/MWh for a second for tidal technology project, as no LCOE references for ocean current technology exist as of yet. The reason for these high values is the low Capacity Factors of the four devices, as three were designed for marine conditions not found in the Cozumel channel. To offer a more competitive LCOE, possible scenarios of LCOE estimated with the public CAPEX of each device are included in Figure 7, which describes scenarios for the four turbines, considering two lifetimes (15 and 20 years), and varying discount rates (r) from 0 to 0.25, and Capacity Factors of 0 to 1. It is seen that the high costs of the NOVA and Kairyu devices give high LCOE costs that are not within the LCOE reference for tidal technology, 5100 USD/kW to 14,600 USD/kW (Tables 5 and 6). The SeaGen device does attain the LCOE reference values of [68], only when the energy potential is 2500 W/m 2 (21.9 MWh/m 2 -year), but the closest value in the area is the one obtained with data from ADCP [40] of 9.85 MWh/m 2 -year. The best scenario was found for a lifetime of 20 years, with a low discount rate of around 0.1, Capacity Factor of at least 0.4, and CAPEX of less than 15,000 USD/kW. , and varying discount rates (r) from 0 to 0.25, and the Capacity Factor from 0 to 1. The public CAPEX and OPEX values were used. The maximum and minimum international LCOE value is shown in the blue and red lines, respectively [68]. The symbols rhombus , circle , cross , and triangle

Levelised Cost of Energy
show the LCOE at a Capacity Factor of 0.4, at a discount rate of 0.1 and with public CAPEX, respectively.

Technical Challenges for the Optimal Turbine
From the results of obtained in the previous section and the literature reviewed, it is seen that there are challenges that had not been previously identified, related to the installation of turbines in the Cozumel channel. The tree diagram presented in Figure 8 shows the technical challenges to be faced, if we are to better take advantage of the energy potential of this area.
One of the greatest technical constraints is that the highest energy potentials are found at depths of around 400 m. Another important challenge is the design of the turbine blades, which must be capable of taking advantage of the hydrokinetic potential at low  (15 and 20 years), and varying discount rates (r) from 0 to 0.25, and the Capacity Factor from 0 to 1. The public CAPEX and OPEX values were used. The maximum and minimum international LCOE value is shown in the blue and red lines, respectively [68]. The symbols rhombus N, circle G, cross , and triangle show the LCOE at a Capacity Factor of 0.4, at a discount rate of 0.1 and with public CAPEX, respectively.

Technical Challenges for the Optimal Turbine
From the results of obtained in the previous section and the literature reviewed, it is seen that there are challenges that had not been previously identified, related to the installation of turbines in the Cozumel channel. The tree diagram presented in Figure 8  Design of the turbine blades. It was found that the designs analysed in this work make poor use of the energy potential in the Cozumel channel. Energy generation cannot be defined only by the cut-in speed, but also by the energy conversion efficiency curve of each device. The turbine that takes most advantage of the current is the Kairyu with a Capacity Factor of 30.7%, which means that a turbine design more suited to the Yucatan Current would significantly increase the Capacity Factor. On the other hand, the design of these turbines must allow the turbine to survive storms, hurricanes, and biological fouling. In all the above assessments, low investment and operation costs are prioritized, (Figure 7), yielding an investment cost of <12,500 USD/kW (Table 5) even with a Capacity Factor (CF) of 0.5 resulting in an LCOE < 470 USD/MWh.
The anchoring system. As reported by [51], the depth range for the anchoring system for floating or bed-based devices is 20 to 30 m, because these systems are placed in shallow channels where the current is intensified by the effects of the tides. Only one system was designed for ocean currents: the Kuroshio current, in Japan. This floating device operates at 30-50 m depth, although it may be anchored at up to 100 m depth. In the Cozumel channel, the best sites are in areas with depths of around 400 m, with potentials in the first 50 m depth of up to 6 MWh/m 2 -yr. Areas with depths of less than 100 m have almost 1 MWh/m 2 -yr. For these water depths, the anchoring system presents a serious challenge. Regarding the possible use of depths between 30 and 50 m deep, Muckelbauer [43] mentions that on the terraces of the channel, which are up to 50 m deep, there are various coral, sponge, algae, and sea grass species, therefore, special measures are needed to avoid affecting these ecosystems.
Connection to the electric grid. Electric transmission lines must be installed from the seabed, either above or below ground. This could impact on the areas of reef or seagrass. Also the associated electromagnetic fields could pose a risk for the orientation of some species [75][76][77].
Installation logistics. As the highest energy potentials are found at depths of around 400 m, it is important to consider the complications involved in installing devices at this depth, since both the availability of vessels, and qualified personnel for them, is of the utmost importance. One of the greatest technical constraints is that the highest energy potentials are found at depths of around 400 m. Another important challenge is the design of the turbine blades, which must be capable of taking advantage of the hydrokinetic potential at low speeds. In addition, the difficulties involved in installing a device in an area with a unidirectional current, and waves with a different direction, are very challenging.
Design of the turbine blades. It was found that the designs analysed in this work make poor use of the energy potential in the Cozumel channel. Energy generation cannot be defined only by the cut-in speed, but also by the energy conversion efficiency curve of each device. The turbine that takes most advantage of the current is the Kairyu with a Capacity Factor of 30.7%, which means that a turbine design more suited to the Yucatan Current would significantly increase the Capacity Factor. On the other hand, the design of these turbines must allow the turbine to survive storms, hurricanes, and biological fouling. In all the above assessments, low investment and operation costs are prioritized, (Figure 7), yielding an investment cost of <12,500 USD/kW (Table 5) even with a Capacity Factor (CF) of 0.5 resulting in an LCOE < 470 USD/MWh.
The anchoring system. As reported by [51], the depth range for the anchoring system for floating or bed-based devices is 20 to 30 m, because these systems are placed in shallow channels where the current is intensified by the effects of the tides. Only one system was designed for ocean currents: the Kuroshio current, in Japan. This floating device operates at 30-50 m depth, although it may be anchored at up to 100 m depth. In the Cozumel channel, the best sites are in areas with depths of around 400 m, with potentials in the first 50 m depth of up to 6 MWh/m 2 -year. Areas with depths of less than 100 m have almost 1 MWh/m 2 -year. For these water depths, the anchoring system presents a serious challenge. Regarding the possible use of depths between 30 and 50 m deep, Muckelbauer [43] mentions that on the terraces of the channel, which are up to 50 m deep, there are various coral, sponge, algae, and sea grass species, therefore, special measures are needed to avoid affecting these ecosystems.
Connection to the electric grid. Electric transmission lines must be installed from the seabed, either above or below ground. This could impact on the areas of reef or seagrass. Also the associated electromagnetic fields could pose a risk for the orientation of some species [75][76][77].
Installation logistics. As the highest energy potentials are found at depths of around 400 m, it is important to consider the complications involved in installing devices at this depth, since both the availability of vessels, and qualified personnel for them, is of the utmost importance. Figure 9 shows social and environmental impacts that hydrokinetic energy harvesting in Cozumel may occasion, considering the various processes involved. Public consultation is one of the most critical factors regarding environmental impact statements. Existing environmental restrictions are also decisive in decision making.  Figure 9 shows social and environmental impacts that hydrokinetic energy harvesting in Cozumel may occasion, considering the various processes involved. Public consultation is one of the most critical factors regarding environmental impact statements. Existing environmental restrictions are also decisive in decision making. Protected areas. In the study area, there are four Protected Natural Areas (PNAs), the largest of which covers the entire Mexican Caribbean, and is shown in green in Figure  10a. The other PNAs around Cozumel island are shown in Figure 10a: the northern portion and the eastern, terrestrial, and marine coastal strip of the island of Cozumel (number 1); Cozumel reefs (number 2); and close to the study area are the Puerto Morelos reefs (number 3) [64]. In addition, the mangrove areas are priority sites (Number 5) [72]. Ecological management programs. The study area has two ecological ordering programs, one regional that includes the Gulf of Mexico and another local that depends on the State of Quintana Roo:

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The Marine and Regional Ecological Planning Program for the Gulf of Mexico and the Caribbean Sea [71] provides guidance on the use of natural resources and the development of productive activities. It identifies, guides, and links the policies, programs, projects, and actions of the public administration that contribute to achieving the regional goals set, and to optimizing the use of public resources (Figure 10b).  [82] operate in the area. For passengers, ferries run from Playa del Carmen to Cozumel, and for cargo from Punta Venado Calica to Cozumel, running regularly throughout the day, 7 days a week. Cruisers also use the Cozumel Channel, arriving at the Maritime Cruise Terminal, at Punta Langosta on Cozumel, from the north, and leaving from the same direction ( Figure 11). Ecological management programs. The study area has two ecological ordering programs, one regional that includes the Gulf of Mexico and another local that depends on the State of Quintana Roo:

•
The Marine and Regional Ecological Planning Program for the Gulf of Mexico and the Caribbean Sea [71] provides guidance on the use of natural resources and the development of productive activities. It identifies, guides, and links the policies, programs, projects, and actions of the public administration that contribute to achieving the regional goals set, and to optimizing the use of public resources (Figure 10b). Protected species in the area. Some species in the area are protected by NOM-059-SEMARNAT-2010 [79]. This covers the protection of native Mexican species of flora and fauna, including those at risk.
Maritime transit. Two trans-Caribbean companies [80]: Ultramar passengers [81] and Ultramar Carga, [82] operate in the area. For passengers, ferries run from Playa del Carmen to Cozumel, and for cargo from Punta Venado Calica to Cozumel, running regularly throughout the day, 7 days a week. Cruisers also use the Cozumel Channel, arriving at the Maritime Cruise Terminal, at Punta Langosta on Cozumel, from the north, and leaving from the same direction ( Figure 11).  Infrastructure. Restrictions as to the feasibility of operating a marine turbine facility include the underwater cables that would take electricity to Cozumel from the substations in Playa del Carmen. There is also the international airport on the island of Cozumel (CZM) and two airways, one on Cozumel, and another in Playa del Carmen, used for local air transport ( Figure 11). The cruise ship dock and the local ferry and cargo ports could also impede the development of a marine turbine facility project ( Figure 11).
Tourist areas. The tourist zone of this area is called the Riviera Maya, which includes the towns of Puerto Morelos, Playa del Carmen, Puerto Aventuras, Akumal, Tulum, Cobá, and the Sian Ka'an Reserve. The study area only includes the first two ( Figure 10). The island of Cozumel is also important for tourism, including the towns of Cozumel and El Cedral, and the coastal areas of the island, used mainly for tourism activities ( Figure 11).
Research facilities. There are several research centres in the area, such as the Institute of Marine Sciences and Limnology (ICMyL) and the Academic Unit of Reef Systems (UASA) of the National Autonomous University of Mexico (UNAM), which has a monitoring system for meteorological and oceanographic parameters, called the Academic Meteorological and Oceanographic Monitoring Service (SAMMO). This centre is in Puerto Morelos (Figure 6), as is the Regional Centre for Fisheries Research (CRIP), which works on the lobster Panulirus argus, shrimp, queen conch larvae Lobatos gigas, sharks, and rays, and also has a coral nursery and carries out coral restoration [83].
Military installations. There is a Military Air Base on the same site as the Cozumel International Airport (CZM), as well as the Cozumel Naval Sector, next to the cruise ship dock in Punta Langosta Isla ( Figure 11).
Considering these social and environmental restrictions, three areas seem to offer the most possibilities for the installation of a marine turbine park ( Figure 11). Table 7 shows areas vertices of the promising areas delineated in Figure 11. These three areas could be enlarged or reduced, depending on the results of more specific studies. Infrastructure. Restrictions as to the feasibility of operating a marine turbine facility include the underwater cables that would take electricity to Cozumel from the substations in Playa del Carmen. There is also the international airport on the island of Cozumel (CZM) and two airways, one on Cozumel, and another in Playa del Carmen, used for local air transport ( Figure 11). The cruise ship dock and the local ferry and cargo ports could also impede the development of a marine turbine facility project ( Figure 11).
Tourist areas. The tourist zone of this area is called the Riviera Maya, which includes the towns of Puerto Morelos, Playa del Carmen, Puerto Aventuras, Akumal, Tulum, Cobá, and the Sian Ka'an Reserve. The study area only includes the first two ( Figure 10). The island of Cozumel is also important for tourism, including the towns of Cozumel and El Cedral, and the coastal areas of the island, used mainly for tourism activities ( Figure 11).
Research facilities. There are several research centres in the area, such as the Institute of Marine Sciences and Limnology (ICMyL) and the Academic Unit of Reef Systems (UASA) of the National Autonomous University of Mexico (UNAM), which has a monitoring system for meteorological and oceanographic parameters, called the Academic Meteorological and Oceanographic Monitoring Service (SAMMO). This centre is in Puerto Morelos (Figure 6), as is the Regional Centre for Fisheries Research (CRIP), which works on the lobster Panulirus argus, shrimp, queen conch larvae Lobatos gigas, sharks, and rays, and also has a coral nursery and carries out coral restoration [83].
Military installations. There is a Military Air Base on the same site as the Cozumel International Airport (CZM), as well as the Cozumel Naval Sector, next to the cruise ship dock in Punta Langosta Isla ( Figure 11).
Considering these social and environmental restrictions, three areas seem to offer the most possibilities for the installation of a marine turbine park ( Figure 11). Table 7 shows areas vertices of the promising areas delineated in Figure 11. These three areas could be enlarged or reduced, depending on the results of more specific studies. In Area A (Figure 11), a simple arrangement of axial turbines, spaced at a lateral distance equal to the diameter of the turbine, would accommodate around 150 SeaGen turbines, for maximum theoretical electricity production: 150 turbines × 1319 MWh/year = 197 GWh/year. In the case of the Nova device, this value would be 323 Nova turbines = 48 GWh/year; while for Kairyu device, 90 Kairyu turbines = 24 GWh/year.
In Areas B and C, with similar theoretical energy extracted in 1 year ( Figure 11) and for the same number of turbines for each device, the maximum theoretical electricity production is~100 GWh/year for SeaGen. For Nova, this value would be~21 GWh/year, and for Kairyu~11 GWh/year.

Conclusions
Of the 16 potential sites analysed, that with highest energy potential was Node 5 (Latitude 20.48; Longitude -87.04) with <6 MWh/m 2 -year, equivalent to an average of <685 W/m 2 . This energy potential is for the uppermost 50 m of the water column. At this depth, there are no energy-generating devices operating at present, so it will be a challenge to harness these energy potentials at depths of over 100 m.
Of the four types of devices evaluated, none is wholly perfect for the site conditions, mainly because of the depth of the Cozumel channel, around 400 m. The device most suitable for the area is that designed to take advantage of the Kuroshio current, off Japan, the Kairyu turbine. This floating device can operate at a maximum depth of 50 m, but has an anchoring system for a depth of up to 100 m. However, this device was seen to have one of the highest investment costs in the economic analysis performed.
Since the devices evaluated were designed for other speed ranges, we limited the Capacity Factor to reduce the LCOE. This is something that could be explored in future research. If a specific turbine design could be developed to use more of the hydrokinetic energy available, for the speeds in the study area, the Plant Factor and technical feasibility could be increased.
In a theoretical scenario, the SeaGen has the most competitive LCOE, at 564.3 USD/MWh, with a Capacity Factor of 50% for 15 years and r = 0.2. The LCOE was 342.8 USD/MWh, for a Capacity Factor of 50%, for 20 years and r = 0.125. In general, the best scenario for every device was for a lifetime of 20 years, with a low discount rate of around 0.1, Capacity Factor of at least 0.4, and a CAPEX value of less than 15,000 USD/kW. Sites previously identified by other authors as having good potential are nodes 9, 11, and 13, with an energy density in the order of 3-4 MWh/m 2 -year. For example, research in the Cozumel channel area mentions power densities in the order of 1.54 MWh/m 2 -year to 4.48 MWh/m 2 -year, [6]. Alcérreca-Huerta et al. [17] reported values of 2.63-8.76 MWh/m 2 -year, although using the data from [40], values up to 9.85 MWh/m 2 -year were obtained. Similarly, at Cape Hatteras, values of 8.76-6.92 MWh/m 2 -year were found [9]. All these power densities refer to ocean currents, and not tides.
This paper describes an initial technical evaluation showing a theoretical annual electricity production of 197 GWh/year using a 150 SeaGen turbine, which is 4.37% of the 2017 total electricity consumption of Quintana Roo. However, 197 GWh/year is more than all the energy generated from Turbogas technology in the state that year. The energy balance for Quintana Roo is positive, at 86 GWh/year. It is estimated that for every Turbogas plant in Quintana Roo, the equivalent of 50,000 tons of CO 2 would be saved