Grid-Connected Solar Photovoltaic System for Nile Tilapia Farms in Southern Mexico: Techno-Economic and Environmental Evaluation

Abstract

Tilapia farming is the predominant aquaculture activity, with 4623 aquaculture farms in Mexico alone. It is relevant to apply technological alternatives to mitigate production costs, mainly those associated with supporting energy savings for aeration and water pumping in aquaculture farms. There is limited information confirming the feasibility of implementing photovoltaic systems connected to the grid (On grid-PV) in aquaculture farms. The working hypothesis proposed for the development of the work was that On Grid PV systems in Tilapia aquaculture farms in Mexico are technically feasible, economically viable and environmentally acceptable. Therefore, the objective of this research is to design a grid-connected photovoltaic system for rural Tilapia aquaculture farms in Mexico and analyze it with a feasibility assessment through technical, economic and environmental variables, as part of the link between academia and the productive sector. Methodologically, the On Grid-PV design was carried out in an aquaculture farm in Veracruz, Mexico, as a case study. It was developed in two stages: the field phase (1), where a non-participant observation guide and a survey with open questions were applied to perform the energy diagnosis, and the cabinet phase (2) where the calculation of the economic and environmental variables was carried out with the clean energy management software Retscreen expert, the engineering design was based on the Mexican Official Standard for electrical installations, and Sunny Design 5.22.5 was used to calculate and analyze the electrical parameters of the On Grid PV. The results revealed an investment cost of USD 30,062.61, the cost per KWp was of 1.36 USD/Watt, and the economic indicators were the net present value (USD 41,517.44), internal rate of return (38.2%) and cost–benefit ratio (5.6). Thus, the capital investment is recovered in 4.7 years thanks to the savings obtained by generating 2429 kW/h per month. As for the environment, it is estimated that 11,221 kg of CO2 equivalent would be released into the atmosphere without the On Grid-PV. In conclusion, the hypothesis is accepted and it is confirmed that On Grid-PV installations for Tilapia farms are technically feasible, economically viable and environmentally acceptable; their implementation would imply the possibility for aquaculture farms to produce Tilapia at a lower production cost and minimized environmental impact in terms of energy. It is recommended that aquaculture farmers in Mexico and the world implement this eco-technology that supports the sustainable development of aquaculture.

1. Introduction

The energy used in aquaculture farms is the second important aspect in semi-intensive and intensive systems, caused by the cost of electricity for pumping and aeration; some authors report that the cost of energy generally represents between 10% and 15% of the total production costs [1]. However, in Mexico, aquaculturists claim that the price of electricity is very high and is a reason why many farms close their operations. In this regard, the National Commission of Fisheries and Aquaculture (CONAPESCA) reported 458,260 GW/h of energy subsidies for the sector, which represented an amount of USD 9,488,197.89 for 504 producers in 29 states of the country [2,3]. Although the Mexican government covered part of the energy costs, the coverage is still limited, since the set of national UPAs (Aquaculture Production Units) is larger. The cost of energy is a key factor in the sum of production costs in aquaculture, since electricity prices in commercial and industrial tariffs in Mexico are high, compared to other producing countries, being up to 134% without subsidy and 84% with subsidy for the agricultural sector, including aquaculture [4].

Currently, the cost per kilowatt/Hour (kW/h) in the commercial tariff where most of the UPAs in Mexico are located is the so-called PDBT (Small Demand Low Voltage) up to 25 kW of energy demand; its cost is USD 0.19 per kW/h, plus a fixed charge of USD 1.87 per month, regardless of energy consumption [5]. This subsidy is important mainly due to the fact that the aeration equipment operates 24 h a day, which has an impact on the operation of farms, especially those with a semi-intensive to intensive production system.

A survey applied to 219 aquaculture farmers revealed that the cost of electricity per month (EC) in 41.13 % of the cases is a limiting factor to compete [6]. This aspect reveals that the cost of electricity in Mexican aquaculture farms is high, and an alternative is required to minimize this cost.

Competitiveness in the aquaculture sector is threatened by the growing importation of Tilapia from the Asian continent, which has been increasing in recent years, leaving the Mexican aquaculturists at a disadvantage due to the low price of the product offered in Mexico [1], in addition to the problems associated with the recent COVID-19 pandemic, which has led to a decline in the sales of aquaculture products and a substantial increase in production costs. Faced with the inability to sell, aquaculturists have maintained cultured species by feeding them, due to declining demand and increased risks caused by confinement measures, disruption of supply chains, and uncertainty about the future, all of which are disruptions in the global market [7,8,9].

Water, feed and energy use is indispensable for the development of aquaculture; however, in these uncertain times, innovation is needed to mitigate these costs and support the recovery and competitiveness of small and medium-sized aquaculture enterprises (SMEs) in coastal, urban and rural areas [10,11].

The pertinence and relevance of the research is to contribute to the acceleration of the penetration of On Grid-PV in the aquaculture sector to generate its own energy, reduce pressure on public spending on subsidies and help keep production costs low, ensuring energy and food security [1,12,13,14]. On the other hand, in the scientific literature related to Nile Tilapia production, there is no evidence of studies that propose and demonstrate the technical, economic and environmental feasibility of using Photovoltaic Systems Connected to the Grid (On Grid-PV) to mitigate production costs, which in the case of aquaculture is the second most relevant cost [6,13].

Therefore, the objective of this research is to design a grid-connected photovoltaic system for rural tilapia aquaculture farms in Mexico and analyze it with a feasibility evaluation, through technical, economic, and environmental variables, as part of the linkage between academia with the productive sector, with emphasis on the minimization of one of the indispensable resources in aquaculture, such as electricity, giving rise to the concept of Photovoltaic Aquaculture Systems (PV-AQS).

2. Literature Review

2.1. Importance of Aquaculture and Tilapia Production in Mexico

Tilapia is a type of fish of African origin whose habitat is the tropical regions, where the necessary conditions exist for its reproduction. This fish was introduced to Mexico in 1964, and Oreochromis niloticus gained importance [14], representing 80% of the Tilapia cultivated worldwide [15]. In Mexico, several types of Tilapia are mainly cultivated: Nile Tilapia Oreochromis niloticus (Linnaeus 1758), Tilapia GIFT (Genetically Improved Farmed Tilapia), Tilapia Stirling, and Genetically Male Tilapia (YY-GMT^®), Rocky Mountain derived (O. niloticus × O. aureus), Tilapia rendalli (Boulenger 1897), Oreochromis aureus (Steindachner 1864), Oreochromis mossambicus (Peters 1852), Oreochromis urolepis (Norman 1922), O. aureus (Steindachner, 1864), Red Tilapia derived (O. aureus × O. niloticus × O. mossambicus × O. urolepis hornorum), recently a hybrid called the Pargo-UNAM derived from Rocky Mountain (25%), O. niloticus pink (25%) and red Tilapia (50%), which is in expansion, was developed in Mexico. Available data indicate that Mexico is the fifth world producer in controlled systems, this species being the one with the highest national consumption [16,17].

The main species cultivated in Mexico in aquaculture are shown (Figure 1), highlighting the production of Pacific white shrimp (Litopenaeus vannamei) followed by Tilapia spp. as the main species, with 74% and 19%, respectively. This highlights the relevance of working with them, since they represent the largest number of official aquaculture farms in the Registry of National Fisheries and Aquaculture (RNPA), with 4626 aquaculture facilities [18,19,20].

Rural aquaculture in Mexico was born as a complementary activity for social support to rural communities, with the aim of increasing the consumption of animal protein and improving the nutritional levels of the population. Tilapia were introduced to Mexico from the United States of America and were first kept in the Temascal fish farm in Oaxaca, Mexico [18]. The different types of aquaculture constitute an important component in the development of farming systems, which contribute to reducing food insecurity, malnutrition and poverty by providing food of high nutritional value, generating income and employment [1,10,11]. For this reason, it is important to enhance the management of aquatic resources and increase the sustainability of farms [21,22,23].

In Mexico, according to the General Law on Sustainable Fisheries and Aquaculture, rural aquaculture is considered to be those small-scale aquatic organism production systems carried out by families or small rural groups, in extensive or semi-intensive crops, for self-consumption or partial sale of harvest surpluses [24]. Other classifications in aquaculture are Aquaculture of Limited Resources (ARELs) and Micro and Small Enterprise (AMyPEs), representing about 59,088 ARELs and 12,737 AMyPEs in Latin America and the Caribbean, where a technological change in the sustainable use of water and energy is important [25]. The above data suggest that a current census, not yet available for all aquaculture countries in the region, would yield a much higher figure [26,27]. These data suggest the importance of aquaculture and the need to initiate the development of innovative solutions for sustainable aquaculture supported by photovoltaic energy.

2.2. Global Trends in Renewable Energy Production

Coal-fired electricity generation (35% of global energy supply in 2020) and nuclear power generation decreased by 4.5% and 3.5%, respectively, and this was partially offset by increases in wind (+12%), solar (+20%) and hydroelectric (+2%) power generation. Renewable power generation increased by more than 6% thanks to continued growth in wind and solar power generation, while the share of hydropower has remained stable at around 16% of the global energy supply [28]. However, the global energy matrix is still not balanced, as the dependence on fossil fuels for electricity production is very high; globally, 28% of energy comes from renewable sources and 72% from non-renewable sources; the share of wind and solar energy is growing at a fast and steady pace (+1.2pt. in 2020), reaching 9.5%. The COVID-19 pandemic and the ensuing economic recession failed to slow down renewable installations, which reached historic records in 2020 with the addition of more than 126 GW of solar capacity and nearly 112 GW of wind capacity globally [29].

2.3. Solar Energy Potential, Regulations, Solar Resource and Costs in Mexico

Since the publication of the first interconnection contract for small-scale solar energy sources, as well as the entry into operation of the first large-scale photovoltaic plant in 2011, the installed capacity of solar energy increased, and this increase has been reinforced by the significant growth of the linked interconnection contracts (small and medium scale), in which since 2011 (Figure 2) a significant growth up to 2020 of 1388 MW can be observed [30].

In Figure 3, estimates are shown made by SENER (Ministry of Energy) and CRE (Energy Regulatory Commission), where it is projected to install between 9179 and 13,869 MW by 2035, distributed generation solar photovoltaic systems [30,31].

The legislation for the On Grid-PV Systems in Mexico was published in 2007 in the Official Journal of the Federation [33]. This regulation allowed residential and commercial users to connect to the Federal Electricity Commission (CFE) grid with the use of On Grid-PV (RES/176/2007) for electricity generation. The connection to the CFE grid is to supply the energy generated by the installed panels and thus exchange energy with the CFE through bi-directional energy meters. The low voltage limit was set at 10 kW for residential use and up to 30 kW for commercial use, and this allows users to contribute with their electricity generation from a small proportion of their total energy consumption in their electrical installation [34].

Currently, the regulations to be complied with for this type of system are described in the following laws: the Electric Industry Law [35], the Electric Power Public Service Law [36], the General Law on Climate Change [37], the Electric Transition Law [38], the Mexican Official Standard NOM-001-SEDE-2012 [39], and The CFE Specification G0100-04 for the interconnection to the low voltage electric grid of photovoltaic systems with capacity up to 30 kW [34].

The solar resource potential in Mexico stands out because the annual amount of solar radiation received is higher than that of other countries. Mexico is located in the so-called global maximum irradiation belt, between 30 north and 30 south latitudes, which makes the amount of solar radiation high throughout the national territory, with an average of 5.5 kW/m²/day [40,41]. In the structure of primary energy production, the Ministry of Energy (SENER) reported that only 2.8% of the national energy produced is obtained from sources such as geothermal, solar and wind. In this sense, the renewable sources that increased their participation in the gross domestic energy supply in 2018 were solar (58.20%) and wind (23.2%). Thus, the net generation of electricity with self-sufficient solar energy in 2018 was 327.77 GW/hour [40].

Despite the low diffusion of photovoltaic technology, it is very important to note that, over the last 10 years, it has increased favorably, incorporating even more users, and in the aforementioned data collection period production increased from 872.40 kW to 53,170.53 kW in 2019. This is a reflection of the increase in electricity tariffs, which are expected to rise by up to 50% in 2022, before softening in 2023 and 2024 [41].

On the other hand, the decrease in photovoltaic technology brings solar panel prices down from 5 USD/Watt to 1 USD/Watt and makes these investments attractive; the interconnection scheme with CFE for cogeneration has boosted the photovoltaic solar industry in our country, and as of 31 December 2015, small and medium scale interconnection contracts across Mexico reached up to 117.56 MW of installed capacity. It is estimated that, by 2022, 2.18 GW of small and medium-scale cogeneration will be reached [39,40].

2.4. Constitution of Photovoltaic Systems

Photovoltaic systems are formed by several elements to be defined [34], firstly the Photovoltaic Cell, which is the smallest semiconductor element capable of converting sunlight into electrical energy via direct current; secondly a Photovoltaic Array (PVA) consisting of a circuit formed by several branches of photovoltaic modules connected in parallel. With these elements of energy source the construction of a Photovoltaic Generator (PVG) is possible, defined as a generating unit capable of converting incident solar radiation directly into electrical energy in the form of direct current. It consists of the electrical and mechanical integration of the following components, as shown in (Figure 4).

Indeed, the photovoltaic principle is obtained from solar cells, through a set of cells that form a module; the union of several modules forms a photovoltaic panel and the connection of several panels forms a photovoltaic array, which in turn is transformed into a PVG. It should be clarified that, up to this point, the energy produced is in direct current (DC), so the element called the inverter is the power electronic device whose main function is to convert the DC signal of a PVG in AC signal (Alternating Current), synchronized with the CFE network. It is the central element of the interface between the PVG and the power grid, and the AC output can be single-phase or three-phase. In addition, it performs other protection and control functions for the efficient and safe operation of the On Grid-PV [33,34].

Additionally, there is the possibility of building autonomous or interconnected systems to the grid; an autonomous system is a generator system that converts sunlight directly into electrical energy, with the appropriate characteristics to be used by the intended electrical load [42], i.e., the user accesses this energy by connecting directly from the system to the selected load, which is used in remote locations where there is no access to electrical service for interconnection to the grid.

On Grid-PV systems are photovoltaic electricity provider systems in which direct current power from the PVG is converted into alternating current power, with the voltage and frequency specified by the grid and synchronized with it. By connecting in parallel with the grid, On Grid-PV contributes to the supply of the demanded power to the grid. If there is a local load on the property, it must be supplied by one or both sources simultaneously, depending on the instantaneous values of the load and the output power of the On Grid-PV. Surplus power from the On Grid-PV is injected into the grid and deficits are demanded from the grid.

Figure 5 shows the block diagram of an On Grid-PV system; the arrows indicate the power flow [34,43]. The PV system consists of (1) PV modules to convert solar radiation into DC electricity, (2) a power inverter to convert the electricity from the panels into AC electricity and (3) a bi-directional meter that measures both the amount of electricity consumed from the CFE and also a “discount” of the electricity that is generated in the system and delivered to the CFE; this is also known as a Distributed Clean Generation (DCG) scheme.

This type of interconnection scheme in Mexico is known as an interconnection contract with net metering of energy (Net Metering), where the energy produced is discounted from consumption, in the same supply contract with its energy company [33,44].

2.5. Photovoltaic Systems in the Agricultural Sector in Mexico

The use of photovoltaic systems in the agricultural sector shows the importance of considering that the energy consumption in this sector was 189.27 PJ, increasing by 4.04% in 2018 compared to the previous year. Diesel is the most important fuel used in this sector, which accounted for 74%, followed by electricity with 23.54% of the total energy consumed [45].

The main applications in the agricultural sector focus on pumping water in small irrigation areas for home gardens and greenhouses. On the other hand, in regions where connection to the CFE is possible, On Grid-PV systems have been used in agribusinesses seeking to mitigate production costs, including slaughterhouses, processing plants, packing plants, dairies, poultry farms, and agrotourism developments. Thus, through the Shared Irrigation Trust (FIRCO) program, from 2008 to 2016, more than 600 systems with loads less than 15 kilo Watt panel (kWp) were installed in the country [45].

An analysis of the data concludes that the application to aquaculture farms has not been developed; this gap motivates the performance of the present work, with the expectation of a specific but not limited solution proposal, which allows replication in other similar aquaculture facilities. The 4623 Tilapia farms in the country are small-scale, with conditions equivalent to those of the study site, where the main problem lies in feed and energy costs.

2.6. Photovoltaic Systems in the Aquaculture

Empirical evidence indicates that the application of On Grid-PV systems in aquaculture is scarce [46,47,48,49]; reviewing the systems developed in the world, most of them are Off Grid-PV and the most frequent uses to supply energy in aquaculture are solar aerators to oxygenate the water, solar feed dispensers, solar pumps, and solar water, heat systems, floatovoltaic, thin-film FV, submerged FV and surface mounted FV. This may be due to the fact that many aquaculture farms are not served by electricity and these types of systems are a solution to this problem.

Table 1. Photovoltaic systems in the aquaculture in the empirical evidence.

Type of System	Country	Species	Indicators			Developed Application	Reference
			Economic USD	Financial	Capacity
Off Grid-PV	Pakistan	NA	15,158.09 *****	19,190.39 *	24.7 kW	Aeration system and lights	[50]
Off Grid-PV	Turkey	NA	NA	NA	1.1 kWp	Automation system to stabilize the temperature of fish cage with water pump	[51]
Hybrid system	Vietnam	Shrimp	152,386	NA	998.65 kWp 999.09 kWr	Produce pure oxygen for oxygenation and all the energy of the farm	[52]
Off Grid-PV	Thailand	Blue Swimming Crab	NA	NA	374.2 Wp	Water pump and air compressor micro modular RAS t	[53]
Off Grid-PV	E.E.U.U.	NA	NA	NA	ND	Modeled energy requirements using a daily energy for In-pond Raceway system (IPRs)	[54]
Off Grid-PV	Thailand	NA	NA	0.61 ** USD/kWh	50 Wp	Water quality monitoring system	[55]
Off Grid-PV	Thailand	Shrimp	2350–2410 per kWp	50 ****	200 kWp	Energy system models for floating and floating-tracking PV systems	[56]
Off Grid-PV	Egypt	NA	260	0.219 *** kWh	105 kWp	Solar photovoltaic (PV) pumping for aeration of aquaculture ponds	[57]
Off Grid-PV	Thailand	Shrimp	2225	0.16 ** USD/kWh	985 Wp	Floating solar photovoltaic system to power aeration and monitoring system	[58]
Off Grid-PV	Mexico	Nile Tilapia and Beta vulgaris	25,000	46.993 * 0.438 ** USD/kWh	12.5 kWp	Energy requirements for aquaponics system	[59]
Off Grid-PV	India	NA	NA	NA	NA	Air pump and a water pump for water quality	[60]

NA: Not available; NPV Net present value *; LCOE: Levelized Cost of Energy **; Profit (USD/kWp); Cost of PV Electricity *** (USD/kWp) **** Cost ***** Note Off Grid-PV requires battery energy storage.

shows the photovoltaic research applied to aquaculture found in the literature, where Off Grid-PV applications stand out, mainly in Asian countries where aquaculture is a production power.

The limited information on both systems (On Grid-PV and Off Grid-PV) of economic, financial and environmental evaluations, some of which are non-existent, stands out. It is important to consider this type of research in order to carry out integral evaluations oriented towards the aquaculturist for correct decision making and to determine which system to implement.

2.7. Research Limitations

According to the literature review, there are not enough studies on the technical dimensioning and economic analysis of an On Grid-PV system for Nile Tilapia farming in Mexico. Therefore, this study focused on determining the design of an On Grid-PV system from a techno-economic and environmental perspective, based on the aquaculture farm under study with its specific characteristics in terms of energy consumption. The reality in Mexico is that, to date, we do not have a standard that provides us with precise instructions for drawing up single-line diagrams of photovoltaic systems, which is why international standards were used to improve on the minimum required in Mexican regulations.

2.8. Contributions

We propose an On Grid-PV system for the production of Nile Tilapia in Mexico based on the guidelines for agricultural sector projects with photovoltaic technology and current Mexican regulations; however, it can be replicated for the aquaculture of other species where grid connection is available. The system consists of a photovoltaic array capable of supporting the aeration, pumping and lighting loads and a monitoring system integrated in the inverter to observe the operation of the system with different electrical variables of interest online.

Its sizing was carried out considering the objectives of energy consumption and cost reduction of the farm, analyzed with technical, economic and environmental criteria: the main indicators are power of the photovoltaic system and its electrical installation, construction costs, net present value, internal rate of return, benefit–cost ratio, payback period, cost per kWp/USD and finally the effect of reducing CO₂ emissions.

3. Materials and Methods

3.1. Location of the Study and Unit of Analysis

The analysis and design of the On Grid-PV was carried out for an aquaculture farm of the Tierra Adentro Fish Farm company located in Tierra Blanca, Veracruz, Mexico (Figure 6). Its activities are production, as well as livestock and agricultural activities such as the production of Swiss American cattle, sugar cane and Persian lime crops.

The Fish Farm grows Spring Tilapia^® from the Akvaforsk Genetics Center; Module I has 4 polyethylene tanks of 3.10 m diameter by 1.20 m height to receive fingerlings, 12 polyethylene tanks of 6.10 m diameter by 1.20 m height for pre-fattening, and 3 polyethylene tanks of 4 m diameter by 1.20 m height for pre-fattening. Module II, for Tilapia fattening, has a surface area of 720 m³ and consists of 6 geo-membrane tanks 12 m in diameter by 1.20 m in height.

The equipment has 4 regenerative blowers of 3.72 kW for oxygen supply, and water is supplied through a deep well of 100 m deep with a water flow of 25 L per second and a 29.8 kW pump. Power is supplied through a medium voltage electrical grid (13.2 kV/440 V/220 V) with a 30 kVA three-phase transformer and a backup power system with a 40.5 kW three-phase generator; wastewater is collected in a reservoir, which is used for agricultural irrigation.

Tierra adentro is located on the climatic zone type Aw” 2 (w) (e) g, warm sub-humid, with an average temperature of 27.4 °C [61]. Precipitation in the area reaches an average annual mean volume of 1573.2 mm, with the highest rainfall in the second half of the year; it is located within the Southern Gulf Coastal Plain province [62,63,64].

The type of research was approached as a case study, whose emphasis is on the practical resolution of a previously demonstrated problem [65,66]. Thus, a case is considered as a systemic unit or entity identified in its limits and characteristics and located in relation to its context [67,68] and which is the main object or subject of study [69,70]. The unit of analysis of the present work is the Tierra Adentro Fish Farm company.

3.2. Design and Regulatory Criteria

For the design of the Photovoltaic Systems Connected to the Grid (On Grid-PV), the applicable standards were used, such as:

• Connection of photovoltaic systems to the low voltage electrical grid, with capacity up to 30 kw according to CFE specification G0100-04 [34].
• The Mexican Official Standard NOM-001-SEDE-2012, related to electrical installations (use), especially article 690 related to photovoltaic solar systems of the same standard [39].
• Technical Specification for grid-connected Photovoltaic Systems associated with productive agricultural and livestock projects [71], which establishes the minimum technical specifications to be met by photovoltaic systems interconnected to the grid, for use in productive agricultural or agribusiness projects promoted by the SADER (Secretary of Agriculture and Rural Development).
• Manual for the technical–economic evaluation of “Photovoltaic Systems Interconnected to the Electric Grid supported through the Shared Risk Trust Program” [72,73], in which the technical and financial criteria are established to ensure the feasibility and quality of photovoltaic projects in the agricultural sector and ensure the efficient allocation of economic resources for projects in the country.

The technical data collection was carried out following the recommendations previously suggested for the On Grid-PV design [74] that were adapted for the study site; Figure 7 shows the phases applied during the research and their considerations, both in the field phase (1) and in the office phase (2). A non-participant observation guide and a survey with open-ended questions were used as field tools to develop the energy diagnosis.

3.3. Software Used and Data Analysis

The Retscreen^® Clean energy management expert version 8 for Windows (Government of Canada, ON, CA, USA) and Sunny Design 5.22.5 (Niestetal, DEU: SMA Solar Technology AG Corp, Rocklin, CA, USA) were used to calculate and analyze the electrical parameters and the economic and environmental indicators.

The equations used in the RETScreen Financial Analysis Model are based on standard financial terminology that can be found in [75]. The model makes the following assumptions: the initial investment year is year 0; the costs and credits are given in year 0 terms, thus the inflation rate (or the escalation rate) is applied from year 1 onwards, and the timing of cash flows occurs at the end of the year.

The economic evaluation criteria established by [71,72,76] were also considered.

For descriptive statistics, solar radiation and air temperature, JAMOVI software 2.3 (Jamovi.org) was used. Autocad software version 2022 for Windows (SR, CA: Autodesk, Inc, San Rafael, CA, USA) was used for the design of the single-line diagram.

3.4. Solar Power Calculation and Equipment and Sources of Information

The calculation and sizing of the On Grid-PV was carried out with the instruments shown in

Table 2. The calculation and sizing of the On Grid-PV solar photovoltaic energy was carried out with the following instruments.

Equipment and Sources of Information	Description	Specifications
A non-participant observation guide and a survey.	Open-ended questions were used as field tools to develop the energy diagnosis.	Applicable to installed equipment, aeration, pumps and lighting.
Technical data of panels.	With polycrystalline technology.	International Electrotechnical Commission (IEC) and UL 1703 certifications.
Inverter technical data.	With grid-connected technology.	IEC 61727 and UL-1741 certifications.
Fluke Multimeter.	For voltage and current measurements.	CAT III, 600V, VCA ± (1.0% + 3), VDC ± (0.5 % + 2).
Solar radiation meter.	Amprobe Solar-100.	Range: 1999 W/m2; accuracy ± 5–10 W/m2; resolution 0.1W/m2
Fluke 434-II Power Quality Analyzer (ACE-Fluke 434-II).	For measurement of electrical power (W), voltage (V) and current (A)	Accuracy: Voltage: 0.5% of nominal voltage, Current: 0.5%, Power: 1%, Frequency: 0.01 Hz).
Software.	Photovoltaic system calculation and economic, financial and environmental indicators.	Retscreen® Clean energy management expert software version 8 for Windows (ON, CA: Government of Canada).
Software.	Single-line system diagram design.	Autocad SR, CA: (Autodesk, Inc, San Rafael, CA, USA).
Software.	Descriptive statistics.	JAMOVI software version 2.3 (Jamovi.org).
Electrical installation calculations.	[34,39,42,71,74] and Sunny Design Version 5.22.5 (Niestetal, DEU: SMA Solar Technology AG Corp, Rocklin, CA, USA).

, in addition to the energy billing of the aquaculture farm reported for 12 months by the supplying company (Comisión Federal de Electricidad).

The input variables of the photovoltaic system used are: air temperature, relative humidity, precipitation, daily-horizontal radiation, atmospheric pressure, wind speed and soil temperature, which were obtained with the software Retscreen^® Clean energy management expert version 8 for Windows, with the geographical coordinates of the study site.

The variables for the design of the On Grid-PV were the power consumed during 12 months of the aquaculture farm in kW/hour/month, as well as the maximum demand in kW, obtained from the energy billing of the aquaculture farm, the census of loads carried out in situ to elaborate the energy diagnosis, and the distribution and type of loads installed.

With all the elements described above, the power required for On Grid-PV was determined and the required energy was defined, determining to design the system with a target of 50% reduction of energy costs, according to the farm manager’s requirement with Sunny Design Version 5.22.5 (Niestetal, DEU: SMA Solar Technology AG Corp, Rocklin, CA, USA).

The number of solar panels was determined manually by dividing the required kW output of the system by the kW output of the PV module. On the other hand, for the determination of the inverter, several available brands were analyzed considering the required power of the system and the maximum generated power of the inverter, with the criterion of dividing the required power between two inverters to generate the required load to minimize costs and with the option of having at least 2 MPPT.

For the calculations of the electrical installation of the system, the requirements of NOM SEDE 001 2012 were followed [34]; see Supplementary Material S1.

4. Results and Discussion

4.1. Meteorological Data and Solar Hours

To determine the solar radiation potential, an average value of 4.60 kW/hour/m²/day was found at the study site, with a peak during May, June and July and a noticeable decrease in November, December and January. However, 4.60 is a very acceptable value for the system calculation.

Table 3. Meteorological data and solar radiation at the study site, obtained with Retscreen^®.

Month	Air Temperature	Relative Humidity	Precipitation	Daily-Horizontal Solar Radiation	Atmosphere Pressure	Wind Speed	Soil Temperature
Units
	°C	%	mm	kWh/m2/d	kPa	m/s	°C
January	21.6	80.2	38.44	3.65	100.7	5.5	21.8
February	22.3	79.8	26.60	4.23	100.6	5.4	22.9
March	24.3	78.4	23.87	4.86	100.4	5.2	25.1
April	26.2	77.4	36.0	5.35	100.2	5.1	27.6
May	28	77.8	74.40	5.46	100.1	4.4	29.1
June	28.3	80.2	231.20	5.07	100.1	4.2	28.4
July	27.7	81.9	285.20	5.27	100.3	3.7	27.2
August	27.6	82.4	282.72	5.05	100.3	3.5	27.2
September	27.4	81.9	307.50	4.46	100.2	4.0	26.9
October	26.2	80.2	161.20	4.29	100.3	4.6	25.6
November	24.2	80.0	84.30	3.95	100.6	5.1	23.8
December	22.3	79.8	38.13	3.55	100.7	5.1	22.2
Annual mean	25.5	80.0	1586.66	4.60	100.4	4.6	25.6

shows the data found for the study site obtained with Retscreen expert V.8.

The basis for the design of an On Grid-PV system is the availability of the solar resource in a solar site and the grid connection; the former is crucial to define the peak power of the system. The data obtained are used for the system design, concluding that the solar radiation potential is feasible, with a historical minimum of 3.55 and a maximum of 5.46 kWh/m²/d, very appropriate values for the development of photovoltaic systems. The statistics of the photovoltaic power potential [77] indicate that the average radiation of the country is 5.77 kWh/m², which represents a huge potential for electricity generation by solar energy. Internationally, Mexico is considered one of the countries with the highest sunlight capture [40,41].

4.2. Energy Consumption of the Fish Farm

Based on the energy diagnosis, a monthly consumption of 3275 kW/hour was estimated, structured in energy for water pumping (24%), energy for the aeration system (57%), energy for lighting (12%), and energy for electrical outlets (7%). Thus, the consumption of the aeration system is clearly observed as a key factor in the use of electrical energy; in aquaculture farms, about 60% of the energy used is for the aeration systems and up to 40% for water pumping [78], and these data coincide with those found by this study and highlight the importance of working more efficiently in the energy consumption of aquaculture production units. The relationship between energy consumption and Tilapia production per month is very important, since a minimum production of 143 kg per month is needed to reach energy payments. If production increases then energy consumption increases, being a directly proportional relationship. In general, with the current low voltage tariff there is an annual consumption of 39,300 kw/hour at a total cost of MXN 120,161.56, (USD 6056.14). According to this, a sale of 1716 kg of Tilapia is required to obtain economic resources to pay for electricity, with a sale price per kilogram of live Tilapia of MXN 70.02 (USD 3.52) in the local market.

4.3. The Grid-Connected Photovoltaic Systems (On Grid-PV) Design

4.3.1. Selection of Solar Panels

The energy requirements are determined as a target of 22,000 watts, so 56 panels are required to obtain the 22 kWp; therefore, it is determined to use the monocrystalline panel JAM72S09-390/PR. The technical specifications of the panels are shown in

Table 4. Specifications of the JA Solar JAM72S09-390/PR 390 Wp panels [79].

Electrical Parameters AT STC (At Standard Test Condition)		Unit
Rated Maximum Power (Pmax)	390	W
Open Circuit Voltage (Voc)	49.35	V
Maximum Power Voltage (Vmp)	40.21	V
Short Circuit Current (Isc)	10.22	A
Maximum Power Current (Imp)	9.70	A
Module Efficiency	19.5	%
Power Tolerance	0~+5	0~+5 W
Temperature Coefficient of Isc (α_Isc)	+0.060%/℃	%/℃
Temperature Coefficient of Voc (β_Voc)	−0.300%/℃	%/℃
Temperature Coefficient of Pmax (γ_Pmp)	−0.370%/℃	%/℃
STC Irradiance 1000 W/m², cell temperature 25 ℃, AM1.5G

. The following data are required for sizing the inverter.

4.3.2. Maximum Current (I max), Where (Isc) Is the Short-Circuit Current of the Panel

The maximum circuit current is calculated by multiplying the nominal Isc of the PV module by the number of source circuits, and then multiplying this value by 125% to account for extended periods of sunlight above the tested solar intensity. The maximum current obtained was 12.77 amperes.

4.3.3. Conductor Results

According to [34] on branch circuits, it establishes that, before the application of any adjustment or correction factor, it must have an admissible ampacity not less than the non-continuous load and greater than 156% of the continuous load; it specifies for the Isc (short circuit current) data that no more than three current-carrying conductors should be placed in a pipe, and the 12 AWG conductor is selected based on an ambient temperature of 30 °C.

4.3.4. For Voltage Drop (VD) in Direct Current

The conductor resistance is obtained from conductor properties of [34], which corresponds to 3.98 Ω and the distance d of the circuit is 25 m. The VD obtained was 1.27 volts, which corresponds to a voltage drop of 0.57 %.

4.3.5. Operating Voltage of The String System

(a)

RMPPV (Rated Maximum Power Point Voltage)

The operating voltage is obtained by multiplying the RMPPV of the module by the number of modules in a series source circuit, obtaining 562 volts.

(b)

The Maximum System Voltage is calculated by multiplying the value of Voc, and then multiplying that value by the number of modules in a series string.

Module Voc = 49.35 Volts Nominal temperature = 25°C Number of Modules = 14. For the above, 690.9 volts per strings <1000 Volts was obtained (compliant for a 1000 Vmax inverter). Due to the fact that the maximum open circuit voltage per string was much lower than the 1000 Volts supported by the system, the temperature correction was not calculated.

4.3.6. Inverter Sizing and MPPT (Maximum Power Point Tracking)

The MPPT is the maximum power point tracker, a circuit employed in most modern PV inverters, and its function is to maximize the power available from the connected solar module arrays at any time of operation [78]. An inverter without an MPPT circuit would result in suboptimal operating conditions between any PV module (or string of modules) and the inverter.

The MPPT circuit constantly monitors the array voltage and current and attempts to bring the operating point of the inverter to the maximum power point of the array, resulting in the highest energy harvest; in most applications with two strings or more, two MPPTs are better than one [80].

For sizing the inverter, the following data are necessary: maximum layout power (Kwp): 22 kwp divided into two inverters yields 12 kwp per inverter, maximum current (Isc): 12.77 amps, open circuit voltage (Voc): 690.9 volts, operating voltage (Vmp): 562 volts.

It is recommended to use a Solis-3P12K-4G inverter, 3-phase 220–380 Volts, 2 MMPT with two MPPT trackers, whose characteristics are shown in

Table 5. Solis-3P12K-4G three-phase 220/380 VAC with two MPPT [81].

Datasheet Solis-3P12K-4G inverter
	Value	Unit
Input DC
Recommended max. PV power	18	kW
Max. input voltage	1000	V
Rated voltage	600	V
Start-up voltage	180	V
MPPT voltage range	160–850	V
Max. input current	22/22	A
Max. short circuit current	34.4/34.4	A
MPPT number/Max. input strings number	2/4	A2:B2 Inputs
Output AC
Rated output power	12	kW
Max. apparent output power	13.2	kVA
Max. output power	13.2	Kw
Rated grid voltage	3/N/PE, 20/380, 230/400	V
Rated grid frequency	50/60	Hz
Rated grid output current	18.2/17.3	A
Max. output current	19.1	A
Power Factor	>0.99 (0.8 leading - 0.8 lagging	%
THDi	<1.5	%
Max. efficiency	98.7	%

.

4.3.7. Grounding

The minimum size of the grounding conductors for pipes and equipment following the provisions of [34] is a bare grounding conductor caliber 12 AWG; for the characteristics of the photovoltaic arrangement, the grounding system is identified with a green color in the single line diagram.

4.3.8. Overcurrent Protection

All conductors in the photovoltaic circuits and output sources must have overcurrent protection. For a continuous current of 12.77 amperes, four fuses of 15 amperes shall be used, and each series shall be protected with two fuses for the positive and negative conductors. Additionally, a 4-position cabinet shall be installed and the arrangement of fuses and fuse holders shall be placed for each inverter installed.

4.3.9. Piping

Dimensions of conductors and insulated cables for appliances, and a six-wire surface with 12 XLPE gauge will be used: two for positive, two for negative and one bare cable. For inverters, ½ inch (16 mm) thick heavy metal conduit pipe shall be used [34].

4.3.10. AC Current Results

This is in accordance with [34], which indicates in article 210 “Derived circuits”, that before the application of any adjustment or correction factor in derived circuits up to 600 volts, a permissible ampability must have no less than the non-continuous charge and greater than 125% of the continuous load.

4.3.11. Protection against Overcurrents

All the conductors of the photovoltaic circuits and of the output source must have protection against overcurrent. Thus, with data of 19.70 amperes, a thermomagnetic switch of 3 × 40 amperes is selected to protect to the system.

4.3.12. Tubing for AC Conductor

Dimensions of conductors and insulated cables for appliances of [34], and 10 AWG conductors are selected, three phase, one neutral and one ground connected (bare) will be used. Heavy 1/2-inch-thick metal conduit will be used for inverters.

4.3.13. Photovoltaic Array Structures and Inclination

An anodized aluminum structure designed specifically for the proposed photovoltaic system, fixed type, is considered for installation on a green area. It will be assembled on concrete silos with their respective mounting and fastening accessories, and these will be built for the mounting of the panels that will be carried out by means of expansive anchors with stainless steel screws capable of withstanding winds of up to 140 km/h. The location of the panels was determined by avoiding obstruction by shadows from buildings and trees at the study site. Figure 8 details that the ideal orientation for directing the solar panels is south (azimuthal angle of 180°) and the inclination was determined to be 17°. By orienting the modules in this direction, the PV module installation will receive the maximum possible solar irradiation during the day and, therefore, the system performance will be optimal.

4.3.14. Estimated Energy Generation with the System

Table 6. Estimated generation of the On Grid-PV system.

Photovoltaic Generator: 56 Panels × Shanghai JA Solar Technology Co. Ltd. JAM72S03-390/PR (09/2018), Azimuth: 180°, Inclination: 17°, Mounting Type: Land
System Size Generation: 22 kWp		Photovoltaic System Efficiency: 78%		PV Inverter Solis-3P12K-4G, 3-phase 220–380 Volts
Average Consumption: 3275 kWh		Generation Average: 2429 kWh		Module power: 390 W
Period	Year	Generation kW/h	kW/h base with On Grid-PV	Power Factor (%)	Payment with On Grid PV
July	2021	2761	439	28.09	241.75
June	2021	2590	610	37.67	211.21
May	2021	2713	487	30.88	230.36
April	2021	2657	543	34.04	220.19
March	2021	2655	545	34.15	219.88
February	2021	2088	1112	59.55	225.48
January	2021	2240	960	53.91	228.04
December	2020	2065	1135	60.34	225.38
November	2020	2400	800	47.06	235.67
October	2020	2343	857	49.61	232.20
September	2020	2378	822	48.06	234.21
August	2020	2258	942	53.18	228.60

shows the estimated energy generation with the system, with its main characteristics, carried out during a period of 12 months, where the average generation was calculated at 2429 kWh with a standard deviation of 242 kWh, using 56 panels of 390 W power per module.

On the other hand,

Table 7. Comparison of actual consumption and the photovoltaic system in USD.

Period	Years	Without On Grid-PV	Payment with On Grid PV	Savings with On Grid PV
Totals	1	5471.82	2733.03	2738.79

shows the differences between the energy billing payment without the photovoltaic system and the savings in the payment considering the installation of the system during the analysis period, in accordance with the objectives set by the company at the beginning of the research.

4.4. Costs of Grid-Connected Photovoltaic Systems (On Grid-PV)

The installation cost of the power generation system is shown in

Table 8. Construction costs of the Grid-Connected Photovoltaic Systems (On Grid-PV) in USD.

Team Description	Amount	Cost	USD
Photovoltaic Module JA Solar 390 W, 10-year direct product warranty.	56	232.24	13,005.44
Solis-3P12K-4G 3 phase Inverter, Standard 5-Year Warranty with WiFi Monitoring.	2	2503.27	5006.54
Mounting system: anodized aluminum structure, stainless steel hardware with expanding anchor.	Batch	1912.56	1912.56
Mounting service: technical support, cable installation for AC and DC piping, photovoltaic modules, inverters and grounding	Batch	3739.17	3739.17
CFE contracts (interconnection contract), delivery and start-up of the system, inspection of the installation by SENER and closing folder.	1	3187.61	3187.61
Load center and electrical installation in distribution panel.	1	865.20	865.20
Three-phase bi-directional meter at 220 Volts.	1	1421.31	1421.31
Indirect field costs.	Batch	924.78	924.78
		Total	$30,062.61

, considering the prices of panels, inverters and support structures. The corresponding quotation is requested from three equipment companies for photovoltaic installations, located in Veracruz, Mexico. With this budget, MXN 660,379 (USD 30,062.61) is required for the production of 22 kWp of photovoltaic energy. Thus, the construction cost per kilowatt installed yields a total of MXN 30.01 per watt (USD 1.36), i.e., MXN 30,017.24 (USD 1620.93) per kilowatt. In this sense it is considered a price consistent with the market. Sánchez Estone [40] states that the cost per watt has dropped to USD 1 USD/Watt; in the case of this study, the result at the exchange rate MXN 21.96 per USD 1 was 1.36 USD/Watt, and this estimate indicates that it is possible to estimate the costs of Photovoltaic Aquaculture Systems (PV-AQS) with this reference.

4.5. Objectives of the Aquaculture Farm with Grid-Connected Photovoltaic Systems

For the design (On Grid-PV), a 44% reduction in energy consumption was targeted. The current consumption was about 39,300 kW/h, and a system generating 22 kWp was calculated, mainly due to economic reasons and a user-defined criterion (See Figure 9).

With this reduction target, energy costs will be reduced by 50%, as shown in Figure 10, and the annual savings were estimated at MXN 60,144.00 (USD 2738.79), which impacts the overall cost of production, and it is possible to use it for the reinvestments required in the daily operation of the aquaculture farm.

4.6. Characteristics of the Grid-Connected Photovoltaic System (On Grid-PV)

The On Grid-PV will have a generating capacity of 22 kWp, with a system efficiency of 78%. The number of monocrystalline panels required is 56, with a power per module of 390 Wp. The one-line diagram of the system is shown in Supplementary Material S2, which will have an average consumption of the production unit of 3275 kWh per month, and the average generation was established at 2429 kWh per month, which represents a 44% reduction in energy consumption, seeking to reduce production costs per kilogram of Tilapia by 34%, representing seven Mexican pesos per kilogram (0.31 USD/kg).

The arrangement of the modules is in parallel, with a maximum I of 15.94 amperes and an Imp of 15.3 amperes of direct current. On the other hand, Vmp will be 592.2 volts and e% of 3.17 Volts, and these characteristics are supported by the two microinverters. The DC output of the array will be protected with a 20 amp fuse, which will be connected to the two microinverters, each inverter will be protected with a surge suppressor with a 3 × 40 amp thermomagnetic switch at the output, which will be connected to the AC voltage load center, also protected with a 3 × 40 amp thermomagnetic switch, and then connected to the bidirectional meter.

Finally, the entire system will be properly grounded with a bare conductor. The construction time is estimated as 30 days, and the interconnection contract procedures in 60 days, since CFE and SENER intervene for the corresponding supervisions. The schematic of On Grid-PV connected system for an aquaculture farm can be seen in Figure 11.

As for the inverter monitoring system, this can be carried out via Wi-Fi or GPRS as shown in Figure 12. This option allows the user to monitor the following variables in real time [82]. On the other hand, Brooks [83] suggest when service maintenance is required to some of the components, according to the regulations, there are disconnectors for the primary direct current circuit and for the secondary alternating current circuit by means of devices described in the diagram (Supplementary Material S2).

The variables that the user can visualize in real time are: (1) the value of the DC input voltage; (2) the value of the DC input current; (3) the grid voltage value; (4) the grid current value; (5) status: (a) the instantaneous status of the inverter (generating), (b) the instantaneous output power value (power in Watts); (6) the grid frequency value in Hz; (7) total generated energy value in kWh; (8) total energy generated this month in kWh; (9) total energy generated last month in kWh; (10) energy generated today in kWh and (11) energy generated yesterday in kWh.

4.7. Environmental Aspects: CO₂ Emissions to the Environment

An aspect not directly related but important to consider is the saving in CO₂ emissions to the atmosphere thanks to the use of photovoltaic installations; in this sense it is estimated that the designed system stops emitting 11.23 tons of CO₂ equivalent to the atmosphere, so the project offers this environmental advantage. It is equivalent to planting 288 trees, so it can be said that this facility supports the environment by mitigating 24% of the emissions to the environment thanks to the construction of photovoltaic installation. The summarized aspects are shown in Figure 13.

Poore and Nemecek [84] analyzed 14 agricultural and aquaculture products from 38,700 farms worldwide, finding that Tilapia aquaculture produces 5 kg of CO₂ per kilogram of product. This confirms the importance of relying on the application of photovoltaic technology to minimize negative effects in the agricultural sector. The authors state that producers have limits in terms of reducing impacts, so the use of technology that contributes to sustainability favors the reduction of these environmental impacts.

4.8. Financial Analysis Grid-Connected Photovoltaic Systems (On Grid-PV)

It is important to note that the economic variables are generally accepted for the evaluation of investment projects; an evaluation period of 15 years was considered, where the results confirm the economic viability of the design, and these results are shown in

Table 9. Financial results of On Grid-PV systems for Nile Tilapia farm aquaculture.

Financial Parameters	Unit	Amount
Inflation Rate	%	3.24
Project duration	Years	15
Debt Ratio	%	70
Debt interest rate	%	8
Debt duration	Years	5
Initial investment	USD	30,062.61
Annual costs and debt payments
Annual costs	USD	−3664.96
Debt payments/5 years	USD	5269.17
Total annual costs	USD	1689.54
Annual savings and income
Annual savings	USD	2738.79
Income from greenhouse gas reduction	USD	NA
Financial viability			Investment acceptance criteria
Internal Rate of Return IRR before taxes (capital)	%	33.8	Higher yield obtained with CETES (6.68%)
Internal Rate of Return IRR before taxes (assets)	%	13.5	Higher yield obtained with CETES (6.68%)
Return of capital	Year	4.7	Short investment payback period
Capital repayment	Year	5.1	Short investment payback period
Benefit–Cost Ratio (BCR)	USD	5.6	BCR > 1
Net Present Value (NPV)	USD	41,517.44	NPV > 0 and positive

. The financial results indicate that an investment of USD 30,062.61 is sufficient to obtain an average cost of 1.36 USD/Watt of the installed, proving that On Grid-PV systems for aquaculture farms offer attractive economic indicators.

The criteria for accepting or rejecting investment projects are as follows: NPV must be positive, IRR must be better than that offered by treasury certificates (CETES), for the Mexican case this is 6.52% [85], and BCR must always be higher than unity. When these three indicators are met, it is possible to consider the projects as viable [71,72,76].

Net Present Value (NPV) is the present value of future cash flows discounted at a given rate or discount rate. NPV measures the economic value of the investment as the sum of all discounted future net cash flows, all future cash inflows and outflows, and the investment cash flows are discounted in the base year using an appropriate discount rate and summed. When NPV > 0 (positive), the project will give a return in excess of the required discount rate and therefore the project is attractive to the investor; the higher the NPV, the more attractive the project [76]. The Net Present Value (NPV) obtained was MXN 911,723 (USD 41,517.44).

The Internal Rate of Return (IRR) is the discount rate at which the NPV of the project equals zero; it is the sum of the discounted net cash inflows, equivalent to the sum of the net cash outflows over the life of the project [76]. In our case, the result was 33.8%. In the case of Mexico, there is a tax incentive of zero-income tax rate (ISR) for the promotion of investments in photovoltaic energy projects. The IRR is a convenient way to compare the profitability of projects with other types of investments, such as bonds and other financial investments, being a popular measure among managers and decision makers.

The Benefit–Cost Ratio (BCR) is the ratio between the sum of the discounted net operating cash flow and the investment flow, and when the BCR > 1 it indicates that the project is feasible, since the net present value of benefits is greater than the costs. The higher the BCR value above 1, the more attractive the project [76]; the BCR of the distributed generation for aquaculture systems (DG-AQS) obtained was USD 5.6.

The capital investment is recovered in 4.7 years. Figure 14 shows the time needed to recover the investment expressed in years. It is probably the most applied financial measure in investments due to its ease of understanding; a project is “amortized” at the moment when the accumulated net cash flows are equal to the net cash flows of the investment [71]. This is why the time from the beginning of the project to reach this point is called payback period.

4.9. Sustainability in Aquaculture

Considering the principles of sustainability of aquaculture production systems, it is essential to apply environmentally friendly technologies that help mitigate impacts and minimize production costs [86]. According to FAO data [87], aquaculture currently provides more than half of the world’s seafood for human consumption. Additionally, it is increasing its share of supply as capture fisheries stagnate and the human population continues to grow. In this context, the importance of advancing the debate on the impacts and benefits of aquaculture with eco-technologies for its sustainable development is evident. Based on the information presented in Figure 15, it is clear that aquaculture requires resources to fulfill its role in the global food industry by providing quality protein for human consumption [88,89].

Most of the current aquaculture production systems aim to be intensive [90], due to the need to increase world food production from 25% to 70% by 2050 [91]. Therefore, it is necessary for these systems to be sustainable and have a technological change; for this, it is necessary to apply the eco-technologies described in Figure 16, where water and energy are vital resources. Since the oceans will not provide the protein required by the population in the future, aquaculture production will focus on production in ponds and controlled environments at sea and on land [92,93,94].

Thus, the present research aligns with the goals of sustainable development, mainly focused on zero hunger (SDG 2), affordable and clean energy (SDG 7), responsible production and consumption (SDG 12), and underwater life (SDG 14).

It is possible to develop a sustainable aquaculture with the use of eco-technologies, each with its specific characteristics, which can be used individually or in an integrated manner, depending on the approach determined by each aquaculture farm. Whether for water saving in places of low availability or for energy efficiency, or energy saving in the cases of farms where this aspect is relevant, each of them entails implementation costs with their respective economic and financial feasibility analyses that are important to analyze in future lines of research.

4.10. Policies Aimed Particularly at Development

In Mexico, the Distributed Generation (DG) support program 2013 to 2020, executed by the Trust for Electric Energy Saving (FIDE), financed 3219 photovoltaic projects interconnected to the grid with a total of MXN 1191.68 million (USD 54,234,972.70) contributing 38.82 MW of installed capacity. These projects, in addition to bringing economic benefits to the users of the electric energy service, help to increase their competitiveness and contribute to the reduction of polluting emissions into the environment. This program grants financing for the execution of projects at a preferential interest rate lower than that offered by other financial institutions; the systems to be financed are photovoltaic projects interconnected to the grid [95].

4.11. Application Conditions

Some countries in different regions of the world are already implementing programs that contribute to energy sustainability through renewable energies. There are still many areas of opportunity, particularly in Mexico due to its high solar radiation indexes throughout its territory. According to data from the Geographic Information System for Renewable Energies in Mexico and the Solar Radiation Observatory of the Geophysics Institute of the UNAM (National Autonomous University of Mexico), irradiance values in most states are higher than 5 kW/m², reaching maximum values of 6.89 kW/m², [41,77], which indicates the large amount of solar resource available during most of the year. This competitive advantage of Mexico motivates the generation of electric energy through the implementation of small, medium and large-scale distributed generation systems.

On the other hand, Figure 17 identified the following strengths, weaknesses, opportunities, and threats (SWOT analysis) for the implementation of On Grid-PV in the Mexican electricity market [72].

4.12. Financing for Aquaculture Farms for Photovoltaic Systems

Currently, there are several alternatives for the financing of photovoltaic systems interconnected to the grid, mainly from commercial and development banks, in the case of the Mexican Government:

• Distributed Generation Support Program, operated by the Electric Energy Saving Trust (FIDE) [95].
• Business Eco-credit, provided by the (FIDE) Trust for Electric Energy Saving [96].
• Solar financing offered by (NAFIN) National Financing entity [97].
• Support Program for Sustainable Projects executed by the (FIRA) Agricultural Trust Funds [98].
• Fixed asset loans operated by (FND) National Financing for Agricultural, Rural, Forestry, and Fisheries Development [99].

As for the private sector, coverage is limited, with some financial institutions observing the viability of photovoltaic projects offer financial products; among them are:

• CI Solar panel operated by CI Banco [100].
• AgroActive credit, operated by BANORTE Bank [101].
• Solar Panel credit operated by Caja Popular San Rafael [102].

This is in contrast to information obtained from SEMARNAT, [103] which published the guide of programs to promote energy generation with renewable resources 2012–2018, where unfortunately public funding for infrastructure for aquaculture farms was eliminated with the current government of Mexico (2018–2024). Among the programs that supported this type of projects were:

Bioenergy and Sustainability operated by the Ministry of Agriculture, Livestock, Rural Development, Fisheries and Food (SAGARPA) and the Risk Sharing Trust Fund (FIRCO).

Agrifood Productivity operated by the Ministry of Agriculture, Livestock, Rural Development, Fisheries and Food (SAGARPA) and the Risk Sharing Trust Fund (FIRCO).

Bioeconomy 2010, Generation and Saving of Electrical Energy through Renewable Energy Sources and Energy Eco-science Measures operated by the Ministry of Agriculture, Livestock, Rural Development, Fisheries and Food (SAGARPA) and the Risk Sharing Trust Fund (FIRCO) and the Ministry of Energy (SENER).

Fund for Energy Transition and Sustainable Use of Energy operated by the National Bank of Public Works and Services (BANOBRAS).

4.13. Limitations for Its Implementation

For its application in Mexico, subsidies of 50% of the cost of electricity are granted to aquaculture farms registered in the National Registry of Fisheries and Aquaculture, an aspect that depends on the policy of the government in power and there is a risk that in the future it could disappear. Without On Grid-PV technology, it is possible that the profitability of production will be affected. Another factor is the lack of knowledge regarding renewable energies applied in the aquaculture sector as a central axis to reduce electricity costs, leading to the limited photovoltaic applications in farms and studies reported in the literature. This can be overcome with linkage actions between academia and producers in order to demonstrate the feasibility of its application. The above demonstrates that this work is relevant because its implementation is technically, economically and environmentally feasible, aligned with the technical and financial requirements necessary to obtain financing to support its construction in Mexico.

Finally, the Program for the Promotion of Fishing and Aquaculture Productivity operated by the National Commission of Fishing and Aquaculture (CONAPESCA), an important program for the development of productive infrastructure that ceased to operate during the current administration, is an important factor for its implementation in other aquaculture farms.

5. Conclusions

The study found that with Photovoltaic Aquaculture Systems (PV-AQS) it is possible to reduce energy costs by 50%, without the need for large investments. The multi-criteria analysis (technical, economic and environmental) jointly indicated that they are a viable and sustainable solution for implementation.

The current data allow the establishing of the fact that the cost per kilowatt of a PV-AQS represents an opportunity, so it is recommended to know the benefits of On Grid-PV to plan its construction with the support of analyzed financial institutions that facilitate credits for its realization. This is based on the fact that there is a real possibility, and they are susceptible to access capital, which has an investment recovery period of less than five years.

The data on costs in Mexico per Kwp of USD are useful for all types of farms and future designs for the estimation of construction costs for small ARELs, SMEs and industrial farms. The characteristics of the farms are very varied, and the only common factor is that most of them require energy, since shrimp, carp, Tilapia, catfish or other species farms all use electrical energy, mainly for pumps and oxygenation. Therefore, with the information contained in the document, it was demonstrated that photovoltaic technology is underutilized in the sector and that it is replicable in any farm in the production of any species. For the design of an On Grid-PV for any production system, it is only required to perform an energy diagnosis and its geographical location.

Future Lines of Research

In this blue revolution it is necessary that energy is stable, reliable and efficient to promote investment, and it is suggested to focus on studying applications in aquaculture farms with different production systems, extensive, semi-intensive and intensive crops of different species. On the other hand, systems for aquaculturists with limited resources, small and medium aquaculture companies and large scale, with On Grid-PV systems and Off Grid-PV systems with energy storage to mitigate the intermittency of this type of systems can be designed and evaluated.

Depending on each case, it is important to generate studies on the efficient use of electrical energy in aquaculture facilities, because it is an important factor in the productivity of the crops, mainly due to the energy required for the operation of the facilities.

Integrated aquaculture production systems are the future of sustainable aquaculture. Photovoltaic technology coupled to Recirculating Aquaculture Systems (RAS), Biofloc Technology (BFT), Aquaponics Systems (AS), In Pond Raceway System (IPRS) and Aquamimicry Technology (AT), plus Bio- RAS systems, will be a future trend.

These production systems are expensive in their electrical power requirements but, supported by integrated hybrid photovoltaic systems with energy storage and interconnected, they will increase the growing trend towards distributed electricity generation in aquaculture farms. Therefore, converting an interconnected photovoltaic system to a hybrid system is a real option now and, in the future, obviously some technical and installation requirements must be considered for a viable and efficient project.