Integration Assessment of Renewable Energy Sources (RESs) and Hydrogen Technologies in Fish Farms: A Techno-Economical Model Dispatch for an Estonian Fish Farm

Abstract

A fundamental aspect of fish farms is their energy consumption, which is essential for various activities like water supply, pool aeration, thermal conditioning, lighting, filtration, and recirculation systems. Due to volatile prices and rising energy use, costs have surged, requiring energy-optimization solutions for economic viability and pollution reduction. In this context, this study aims to evaluate renewable energy integration in these installations based on real data, assessing current operations, proposing renewable energy optimization, and exploring hydrogen systems for energy needs, using HOMER PRO^® to analyze different scenarios. For this purpose, it targets a rainbow trout farm in Estonia, and by simulating the various hybrid configurations proposed, it aims to optimize its energy production and storage, ensuring feasibility and technical integration. The results of the simulations primarily demonstrate the potential for using the byproduct of electrolysis to cover the oxygen demand in these types of processes, reducing the demand for raw materials. Additionally, it is observed that storage enhances performance in isolated systems; however, the economically viable integration of hydrogen technology requires three assumptions: a regulatory framework allowing surplus energy sales to the grid, an existing infrastructure for hydrogen trading, and high energy purchase prices.

1. Introduction

In a context where energy efficiency and sustainability are increasingly important, projects seeking innovative solutions to facilitate the energy transition toward a cleaner and more sustainable landscape emerge. Many of these projects are encompassed within the European Union’s Horizon 2020 Programme [1], through which funding is secured to carry out initiatives such as the project “New Energy Solutions Optimised for Islands” (NESOI), which aims to facilitate the transition to clean energy on European Union (EU) islands [2,3].

The development of the present study is framed within the NESOI project, through which the various islands involved in the program are provided with access to training, technical assistance, collaboration opportunities, and solid financing options. Its objective is to effectively transform the Insular Sustainable Energy Action Plans into concrete projects that promote the use of Renewable Energy Sources (RESs), the modernization of buildings and energy infrastructure, the reduction in energy costs, and the generation of local employment, among other initiatives.

Specifically, this paper is based on a rainbow trout fish farm located on an island in Estonia, where the main goal is to provide a comprehensive technical solution for its energy system, simulating generation and consumption and evaluating the integration of renewable and hydrogen technologies.

Fish farms are part of a highly competitive market, and the existing electrical infrastructure in this case study is saturated at the mainland’s most remote point. Therefore, an additional off-grid energy system is required to ensure a secure power supply. It is important to note that, within the context of decentralized island systems, a significant advancement is the incorporation of electrolysis byproducts into agro-industrial processes that require oxygen for production. In this context, this study presents a detailed techno-economic analysis of the integration of renewable energy sources (RESs) and hydrogen technologies/facilities into fish farms. This will provide insights into the technical and economic feasibility of these solutions, as well as their impact on environmental sustainability and the daily farm operations. Lastly, it also aims to identify the benefits and challenges associated with these solutions and propose recommendations for their effective implementation.

In Section 2 of this document, an extensive literature review on the current status of fish farms and the integration of innovative technologies into their processes can be found, as well as the latest advancements in the energy field. Section 3 focuses on describing the methodology employed to conduct this study, while Section 4 presents the obtained results. Finally, the analysis of these results is discussed in Section 5, followed by a compilation of conclusions in Section 6.

2. Literature Review

Table 1. Summary of literature review topics.

Main Focus Areas/Key Topics	[4]	[5]	[6]	[7]	[8]	[9]	[10]
Year	2022	2020	2018	2023	2021	2022	2023
Use of O2 as a byproduct in electrolysers
Analysis of the energy system in fish farms
Study in real environments
Hydrogen in fish farms
Disconnection from the grid
Demand forecasting and simulation

summarizes the different research topics detected in the analysis of the state of the art. In recent years, the integration of renewable energy resources has become a priority for reducing energy consumption and pollutant emissions across various sectors. Achieving an effective transition to a more sustainable energy supply requires the development of new technologies that balance the production of and demand for green energy. In this context, hydrogen emerges as a key solution; however, despite its potential, green hydrogen production still faces significant economic challenges, mainly associated with its storage in tanks [4]. Therefore, conducting economic feasibility analyses on the integration of these technologies is essential to ensure that their benefits outweigh the current financial costs. This approach also provides a well-founded basis for decision-making, helping to identify potential financial barriers and develop strategies to mitigate risks and maximize returns.

Multiple studies highlight the utilization of oxygen generated by water electrolysis as an opportunity to significantly reduce the total costs of integrating hydrogen technologies. Some research indicates the possibility of using this oxygen in wastewater treatment plants, where improvements in the Net Present Value (NPV) of up to 13% are achieved in scenarios using only grid electricity and up to 58% when supplemented with photovoltaic systems [8]. However, a sector where significant potential for utilizing this byproduct has been found is in the aeration processes of fish farms [6,8], where oxygen supply is crucial for biomass growth, and its energy consumption represents a high percentage of the total consumption of such facilities [7]. Producing oxygen in situ for water oxygenation while generating hydrogen with surplus renewable energy offers technical, economic, and environmental advantages over conventional aeration systems [6], potentially resulting in up to 30% savings in energy demand and costs [9].

Most of this research focuses on the development of hybrid systems adapted to the aquaculture sector to make it more sustainable [4,5,6,9]. These facilities face a continuous increase in the demand for fishery products and, as a result, the need to optimize their processes and reduce their environmental footprint. Energy efficiency is highlighted as a crucial factor for improving the profitability and sustainability of these operations. In the open literature, there are evident reviews on energy consumption in fish farms addressing various key aspects. This includes, among other things, the optimal design of sustainable hybrid energy systems [4,5], where their technical, economic, and environmental performance is evaluated both in off-grid mode and connected to the grid [4]. Other research focuses on analyzing the sector’s energy needs, exploring the feasibility and impact of the transition to renewable sources, the utilization of byproducts such as residual heat [5], and the importance of regulatory support and technological innovation [8].

It is also essential to emphasize the importance of basing studies on real data to strengthen their validity and relevance. Some publications analyze the advantages of different proposed energy systems, demonstrating their effectiveness in existing facilities such as an actual shrimp farm [4]; others use real process data, taking into account the context and costs related to the country in which the facilities are located [8,9]; and others use their energy demand data to carry out simulations of different scenarios [10].

For such developments of sustainable technologies, the literature highlights the importance of approaching sustainable development from a historical and interdisciplinary perspective, as suggested by classical political economy. This multidisciplinary approach is crucial for tackling the complex challenges of sustainable development, just as the integration of innovation and an understanding of nature are essential for achieving sustainable economic growth [11,12].

Despite the numerous research efforts on energy systems in the aquaculture sector and their significant advancements, there are still underexplored areas that require more detailed analysis. Specifically, the utilization of oxygen as a byproduct of the water electrolysis process and its integration into fish farms represent fundamental aspects that have so far received limited attention in the existing literature. Additionally, the evaluation of the influence of climatic variables on the energy demand of fish farms is not integrated into studies to determine the real impact on their facilities. Finally, there is a notable lack of research on the feasibility of disconnecting fish farms from the public grid, particularly in isolated areas where the security of the electricity supply is crucial due to the infrastructure’s vulnerability and dependence on external sources. Analyzing these elements could be potentially important for improving energy efficiency and sustainability of these installations. To address this gap in the literature, this study focuses on analyzing the integration of hydrogen technologies for the utilization of byproducts and the evaluation of different scenarios of complete grid disconnection. To achieve this, a model is defined for estimating electrical demand based on climatic parameters and process data. The proposed methodology is outlined in the following sections of this study.

3. Materials and Methods

This section describes the specific technical and energy characteristics of the fish farm under study.

3.1. Fish Farms’ Operational Value Chain: Main Description

Fish farms can have a variety of infrastructure, including breeding tanks or ponds, water filtration and recirculation systems, oxygenation systems, automated feeding systems, and environmental monitoring and control systems. In this case, the analyzed facilities use Recirculating Aquaculture Systems (RASs) combined with a flow-through system.

The fish farm has various production lines, but this study focuses on Production Line 3 (P.L 3) due to the high biomass density that accumulates, requiring a heterogeneous mix of demand coverage. P.L 3 consists of two identical RAS systems, each with a capacity of 135 m³. These systems are divided into two sections, where the biomass density increases from the beginning (E) to the end of the stages (F) (see Figure 1).

The biomass moves longitudinally through the pools in the opposite direction to the fluid flow.

Table 2. Production lines’ metrics.

Production Line	Raceway	Section	Biomass Density	Mass	Oxygen Flow
Unit			kg/m3	kg	Nm3/h
P.L 3	1	1	41	5535	0
P.L 3	1	2	58	7830	0
P.L 3	2	1	47	6345	0
P.L 3	2	2	72	9720	1.5

shows data on the biomass density in the different sections of the two existing RAS systems for P.L 3.

An adequate level of oxygen ensures efficient respiration, optimal growth, and the reduction in stress and diseases. The oxygen level can fluctuate due to factors such as temperature, salinity, biological density, and metabolic activity, making rigorous control essential to maintain a healthy aquatic environment and prevent water quality issues. Below is a list of existing equipment used to effectively regulate dissolved oxygen in the fish farm:

• Airlifts: An aeration system in which air is pumped through small ducts located several meters below the water level is shown in Figure 2. The oxygen in the air dissolves in the water as the air bubbles push the water upwards, creating a forward movement for circulation in the raceway channel. This system supports a fish density demand of up to 65 kg/m³. An air compressor is used, consuming electricity to continuously inject pressurized air into the pools.

• Airstones: A small weighted bubbler produces fine bubbles in the water. It helps to diffuse air in the tank and minimizes the amount of bubbling noise. Airstones allow the passage of 12 L/min of pure oxygen, which is generated by the generator OXYSWING OS-24, with the capacity to provide oxygen at 90% vol at a nominal rate of 8 Nm³/h or at 95% vol at a rate of 7.6 Nm³/h. The use of these devices is limited to providing extra oxygen in cases of biomass densities exceeding 65 kg/m³, which are covered with the airlifts.

The diagram in Figure 3 shows how the oxygenation system of the fish farm pools works as a function of the biomass density. The first air input is through the airlifts, which inject compressed air into the pools, with a constant electricity consumption from the air compressor (A). In this way, a suitable growth environment is maintained up to a biomass density of 65 kg/m³. When the biomass density exceeds this limit, the high-concentration O₂ generator “OXYSWING OS-24” (B) is activated to improve the oxygenation of the pools, allowing biomass densities up to 75 kg/m³ to be cultivated. Therefore, there is no O₂ storage at the facilities, and the activation of the systems is determined by the oxygen demand levels of the existing biomass.

On the other hand, oxygen demand fluctuates not only due to population density but also because of water temperature and the availability of sunlight for photosynthesis. Thus, during daytime hours, the pools will require an increased injection of air/water. Therefore, this study analyzes the influence of external conditions on the energy demands to meet the oxygenation requirements for the proper cultivation of biomass.

3.2. Demand Characterization

The energy consumption at the facilities aims to meet the oxygen demand described in the previous section, and it is also necessary for other auxiliary demands such as water pumping systems, lighting, office climate control, and finally, adjusting the pool temperatures to optimal breeding conditions. To meet the previously described demands, both thermal and electrical, the facilities are equipped with end-use devices powered by electricity, such as

• Water circulation and recirculation pump: electricity-consuming devices that regulate flows and volumes within the facility;
• Compressor for pool aeration: air compressors that consume electricity to generate pressurized air and inject it into the pools to increase the general O₂ concentration;
• High-concentration O₂ generation: electricity-consuming devices that generate pure O₂ and inject it into the pools;
• Auxiliary lighting systems: electricity-consuming devices used to illuminate the offices and the process, ensuring proper operation at both office and technical levels;
• Auxiliary systems for office climate control: electricity-consuming devices, primarily high-efficiency heat pumps, that meet the thermal demand of the offices;
• Heat generation for adjusting the operational temperature of the pools: electricity-consuming devices that use the Joule effect to heat the network water if an extra input is needed to achieve the minimum operational temperature of 12 °C.

The facilities are connected to the national grid to meet the electricity demand of P.L 3, serving as the primary source for covering the electrical demand. Additionally, a 30 kW_p photovoltaic system is available to provide support, and, in case of emergency, diesel generators are available as a backup.

This section characterizes the existing thermal and electrical energy demands in the facilities and predicts the consumption for different expected biomass densities. Thermal demands are met with electricity-consuming equipment, such as heat pumps or electric boilers utilizing the Joule effect. In other words, no energy sources based on thermal fuels and/or biomedicals are available. Therefore, the total electrical demand for P.L 3 is calculated as follows:

$$D_{P.L3}^{Total}=D_{Elec.Airlift}^{Total}+D_{Oxyswing}^{Total}+D_{Airconditioning}^{Total}+D_{Thermal.Poolwater}^{Total}+D_{AuxiliarySystems}^{Total}$$

(1)

In summary, for the characterization of hourly demand, data about the process shown in

Table 3. Hourly demand characterization process data.

Demand	Comments
$D_{Elec.Airlift}^{Total}$$+D_{AuxiliarySystems}^{Total}$	Known demand. 30 kW constant load
$D_{Oxyswing}^{Total}$	Unknown demand. Calculated
$D_{Airconditioning}^{Total}$	Unknown demand. Calculated
$D_{Thermal.Poolwater}^{Total}$	Unknown demand. Calculated

are used. This information is obtained directly from actual measurements at the plant, and it is observed that the power demand is constant with a value close to 30 kW. This energy is used directly to power the plant’s airlifts and auxiliary systems.

• $D_{Elec.Airlift}^{Total}$: The electrical demand of the compressor and the airlift circulation system itself is required to inject pressurized air into the pools. These systems allow for a maximum biomass density of 65 kg/m³ within the pools.
• $D_{AuxiliarySystems}^{Total}$: The electrical demand of the auxiliary equipment is necessary for the proper operation of the facilities.

T calculated data are as follows.

• $D_{Oxyswing}^{Total}$: Electrical demand to generate high-concentration O₂ and support maximum biomass production densities up to a target value of 75 kg/m³. To determine the consumption of these devices, the technical data of the OXYSWING OS-24 equipment shown in

  Table 4. Additional oxygen supply data.

  Additional Oxygen Flow at P.L 3 at Normal Temperature Pressure (NTP)
  Maximum rate	5.76	Nm3O2/h
  Maximum consumption	26.07	kW
  Additional O2 needed	1.50	Nm3O2/h
  Real power demand	6.79	kW

  have been used, in addition to the extra need for 1.5 Nm³_O2/h to achieve the target value in the pools.

• $D_{Airconditioning}^{Total}:$ Electrical demand required to maintain comfort temperature in offices, with a set point of 19 °C. To climatize the facilities, individually operated heat pumps are used, running during office hours from 08:00 h to 20:00 h. The total installed power is 20 kW. The hourly consumption curve has been generated based on the hourly outdoor temperatures at the fish farm, specifically from the weather station located in Mõntu, Estonia. Figure 4 shows the demand curve for the heat pumps during the period, with the average recorded power being 4.59 kW.
• $D_{Thermal.Poolwater}^{Total}:$ Electrical demand required to maintain the operating temperature of the RAS, with a suitable fish breeding set point of 12 °C. Hourly temperatures of the well water, which is used to compensate for the eliminated water, are available and constitute approximately 0.57% of the total water. This means that the hourly heat demand has been calculated to compensate for the well water temperature to reach the operating temperature of the pools before injecting this water. An electric boiler is used to heat this volume of water. In

  Table 5. Water heating data for 1 January 2021 01:00.

  Variable	Unit	Data
  Water temperature	°C	2.9
  Set point	°C	12
  ΔT	°C	9.1
  Total volume	m3	135
  Recirculation water	m3	0.77
  Pool recirculation ratio	%	0.57
  Cp	kWh/m3 °C	1.16
  Energy Demand	kWh	8.1

  , an example calculation is shown for hour 1 on 1 January 2021.

The well water temperature is 2.9 °C, and it is necessary to heat this replenishment water, which represents 0.57% of the 135 m³ pool, i.e., 0.770 m³, to 12 °C before injecting it into the pool. Given a specific heat capacity of water of 1.16 kWh/m³·°C, the energy consumption required during that hour will be 8.075 kWh. Considering a Joule effect boiler efficiency of 100%, the electrical power demanded by the equipment is 8.075 kW.

Using all the information mentioned, an hourly demand curve is generated and is shown in Figure 4.

3.3. Current Energy Mix for Demand Coverage

Table 6. Technical specifications of systems for electrical demand.

Component	Grid Connection	Photovoltaic (PV) Panels	Diesel Generator	Wind Farm	Electrolyser	Battery
Status	Existing	Existing	Existing	Planned	To be optimized	To be optimized
Power [kW]		50	200	330	1	1
Investment [EUR/kW]		-	-	833.33	380.00	300.00
Replacement [EUR/kW]		600.00	173.84	833.33	300.00	300.00
O&M [EUR/kW year] *		30	75	24	1500	10
Power/fuel price	0.086 EUR/kWh	-	1.994 EUR/L	-	-	-

* Operation and maintenance (O&M).

presents the technical characteristics of the existing and planned systems at the facilities to meet the electrical demand.

3.3.1. Grid Characterization

The facilities are connected to the national grid in low voltage mode, with a voltage of 220 V and a network frequency of 50 Hz. For the facilities, the maximum available current is 160 A and the purchase price of energy is 0.086 EUR/kWh; however, due to the current regulation in Estonia, it is not possible to receive financial compensation for surplus energy fed into the grid.

3.3.2. Solar Energy Power

There is a solar installation on the roof of the facilities with a total capacity of 50 kWp. For this type of photovoltaic system, a useful life of 25 years is considered, with a replacement cost of 600 EUR/kW installed. The Operation and Maintenance (O&M) cost considered for the simulations is 30 EUR/kW per year.

3.3.3. Generator

A diesel generator is available, which is recommended solely to cover the electricity demand in emergencies due to outages or failures in the national grid supply. The installed power is 200 kW with an O&M cost of 75 EUR/hour of operation and a diesel cost of 1.994 EUR/L. The replacement cost amounts to 173.83 EUR/kW.

3.4. Planned RES Infraestructure

The property plans to upgrade the generation system to minimize grid dependence and maximize self-sufficiency. This means that the data on investment and technical characteristics of the installation are real; however, the construction has not yet been executed.

Wind Farm

The installation of a 330 kW wind turbine for self-consumption and grid connection has been planned. For this type of wind energy system, an expected lifespan of 25 years is considered, with installation and replacement costs estimated at 833.33 EUR per kW of installed capacity. The O&M cost considered for the simulations is 24 EUR/kW per year.

3.5. Proposed H₂ Technologies and Storage Systems for Managing Surpluses and Utilizing Existing Generation Systems

This section describes the technical and economic characteristics of hydrogen technologies and conventional storage systems available on the market. The study aims to evaluate and quantify the incorporation of these systems and economically assess the options. The selection of the best options will be based on economic criteria and the utilization of the byproduct of electrolysis. The technical data of the components are referenced to a unit of power or capacity so that the system evaluation yields an optimal and scalable output from the existing one.

3.5.1. Electrolyser

An electrolyser is proposed as an alternative for installation at the plant to manage the surpluses from the new planned generation mix. The installation cost is 380 EUR/kW, with an O&M cost of 1500 EUR/kW per year. On the other hand, the lifetime of the electrolysers is 15 years, and due to technological maturity, the replacement cost is expected to be 300 EUR/kW.

3.5.2. Conventional Storage Systems

The option to size conventional storage systems to combine with the current setup has been included, considering the following equipment characteristics. The cost for both installation and replacement is 300 EUR/kW, with maintenance costs of 10 EUR/kW per year.

4. Results

After describing the context, materials, and methods used for the development of this study, this section presents the various proposed configurations of the energy system and the results obtained from the respective simulations.

Starting from the current situation, analyzed in 4.1. Scenario 1 as a starting point, the first variation evaluated is the increase in production due to the planned opening of two new production lines in the existing facilities. This allowed us to analyze in Scenario 2 to what extent the current energy system can meet future demand using renewable energies and assess its dependence on the public grid. On the other hand, in Scenario 3, the feasibility of disconnecting from the grid and becoming self-sufficient with current production and demand is analyzed. Finally, in Scenario 4 and Scenario 5, conventional and hydrogen-based storage systems. respectively, are incorporated to maximize the use of renewable energies and evaluate their viability. These variations are shown schematically in Figure 5.

The main parameter analyzed for the different scenarios is the total Net Present Cost (NPC), which provides a perspective on the economic viability of the proposed system configuration. HOMER^® calculates the life-cycle cost of a system using NPC. This metric consolidates all costs and revenues throughout the project’s duration into a single sum in present-day dollars, discounting future cash flows to their present value using a specific discount rate. Costs include initial capital investment, replacement expenses, operating and maintenance costs, fuel costs, the cost of purchasing electricity from the grid, and other miscellaneous costs such as penalties for pollutant emissions. On the other hand, revenues are derived from selling electricity back to the grid and any residual value at the project’s end. Additionally, for Scenario 5 (see Section 4.5), the economic quantification of the utilization of O₂ in the pools and the use of H₂ for other purposes has been included.

$$NPC={\displaystyle \frac{C_{tot,annual}}{CRF(i,L_{project})}}$$

(2)

where

• $C_{tot,annual}$ is the absolute annual cost in EUR/year.
• $CRF$ is the capital recovery factor.
• $i$ is the interest rate.
• $L_{project}$ is the designed project lifetime.

4.1. Scenario 1

Scenario 1 represents the current situation of the fish farm, also considering the planned wind turbine. This baseline scenario starts from a situation of connection to the public grid, in addition to using the photovoltaic system, the wind turbine, and the diesel generator as a backup, as shown in Figure 6. On the other hand, Electric Load 1 represents the total electrical consumption of the fish farm when only P.L 3 is active.

All simulation results are summarized in

Table 7. Summary of results for each scenario.

Scenario	1	2	3	4	5
NPC [EUR]	463,361	795,623	6,828,371	1,246,060	7,202,209 *
Operating costs [EUR]	17,645	48,771	613,912	65,225	689,286
Load met by RES [%] **	74.89	56.30	32.23	92.12	32.23
Max. renewable penetration [%]	100	100	931	931	532
Production [kWh/year]	1,052,543	1,414,472	1,224,230	983,216	1,224,230
Public grid purchase [%]	9.60	32.73	-	-	-
PV panels production [%]	5.29	3.93	4.55	5.66	4.55
Diesel generator production [%]	0	0	22.28	3.23	22.28
Wind farm production [%]	85.11	63.34	73.18	91.10	73.18
Demand [kWh/year]	402,400	1,059,400	402,400	402,400	402,400
Excess electricity [kWh/year] **	650,143	355,072	821,830	580,816	821,830
Grid surplus [kWh/year]	650,143	355,072	-	-	-
Non-grid surplus [kWh/year]	-	-	821,830	556,070	591,246
Battery [kWh/year]				24,746
Electrolyser [kWh/year]					230,584
Conventional storage capacity	-	-	-	229 kWh

* Electricity purchase savings are accounted for using hydrogen (EUR 355,756) and oxygen (EUR 94,013) from surplus. Homer NPC without considering any saving is EUR 7,651,978. ** Calculated value based on HOMER results.

. In this case, an NPC of EUR 463,361 is obtained, with a total operating cost over the 25-year life of the system amounting to EUR 17,645. From a technical perspective, the optimization results show that the solution can cover 74.90% of the demand with renewable energy and only requires 101 MWh of grid consumption. The annual electricity production comes mainly from the wind turbine, representing 85.11% of the total, while the photovoltaic system and the public grid cover the remaining 9.60% and 5.29%, respectively. In this scenario, it is unnecessary to use the backup diesel generator.

Figure 7 presents the monthly electricity production during the year according to the energy source for the proposed system configuration in Scenario 1. It is observed that, during the summer, the use of photovoltaic energy increases while wind energy decreases. On the other hand, May and August show the highest consumption of public grid energy.

4.2. Scenario 2

In Scenario 2, the base electrical load is replaced by Electric Load 2, which represents the total consumption of the facilities after a planned increase in production. This increase is expected to take part in the opening of the other two production lines that are currently idle. Thus, the configuration would be as shown in Figure 8.

With this new configuration, an NPC of EUR 795,623 is obtained, with a total operating cost over the 25-year life of the system amounting to 48,771 EUR. On the other hand, the optimization results in Table 7 show that the solution can cover 56.30% of the demand with renewable energy and requires 463 MWh of grid consumption. The annual electricity production comes mainly from the wind turbine, representing 63.34% of the total, followed by the public grid, which covers 32.73%, and finally, the photovoltaic system, which produces only the remaining 3.93%. In this scenario, energy production from the diesel generator is not necessary.

Figure 9 presents the monthly electricity production during the year according to the energy source for the proposed system configuration in Scenario 2. The demand during the autumn and winter months is mainly covered by the energy generated by the wind turbine, while in the spring and summer months, there is a greater use of photovoltaic energy and primarily the public grid.

4.3. Scenario 3

This scenario is like the initial situation but with no connection to the public grid. It generates energy only from the two renewable systems and uses the backup diesel generator if necessary. As shown in Figure 10, Electric Load 1 is reconsidered.

With the disconnection from the grid, the NPC rises to EUR 6,828,371, and the operating costs over the system’s lifetime to EUR 613,912. In this way, 32.20% of the total demand is covered by renewable energies, requiring 272,722 kWh/year from the diesel generator and generating energy surpluses of 821,830 kWh/year. The distribution of annual energy production by component with the configuration of this scenario is shown in Table 7, where it is observed that 73.18% would come from the wind turbine, 22.28% from the diesel generator, and the remaining 4.55% from the photovoltaic system.

Finally, the annual production is distributed throughout the months as in Figure 11. In this scenario, wind energy production is primarily concentrated in the autumn and winter months, while photovoltaic output peaks during the spring and summer when solar radiation is at its highest. The backup diesel generator is used more frequently in May and August, when wind generation is reduced.

4.4. Scenario 4

In this scenario, a configuration is presented as shown in Figure 12, where a battery is added as a conventional storage system to the base scenario.

This new configuration results in a total NPC of EUR 1,246,060, with operating costs of EUR 65,225 and a percentage of demand covered by renewables of 92.10%. The total energy generated comes mainly from the wind system, representing 91.10%, followed by the photovoltaic system and the diesel generator, representing 5.66% and 3.23%, respectively. Additionally, there is a total of 556,070 kWh/year of surplus energy, representing 56.60% of the total energy generated.

The monthly distribution of this generation is shown in Figure 13, where it is observed that the energy consumption from the diesel generator is minimal, except in August, when wind production is at its lowest. Photovoltaic production peaks in the summer, while wind energy generation is most prevalent during autumn and winter.

4.5. Scenario 5

In the fifth scenario, an energy system configuration is proposed, as shown in Figure 14. This is the base scenario with a hydrogen-based system, including an electrolyser and a hydrogen tank. It is important to note that for the simulation of this scenario, the tank represents a component that measures the generated hydrogen but is not part of the proposed energy system, as the use of this product is not evaluated.

The proposed energy system in this scenario results in a total NPC of EUR 7,202,209, operating costs of EUR 689,286, and 32.20% of the demand covered by renewable energy. In this case, 73.18% of the energy generated comes from the wind turbine, 22.28% from the diesel generator, and the remaining 4.55% from the photovoltaic system. Of the total produced energy, 48.30% is lost as surplus.

The monthly production by energy source is shown in Figure 15. It is observed that the diesel generator is used more frequently during the hotter months, especially in May and August, when wind energy output is lower. PV systems are most utilized during the summer, while the wind system gains increased use in the colder months.

An overview of the use of the electrolyser and hydrogen production throughout the year is shown in Figure 16. It shows how the input power to the electrolyser is distributed throughout the days of the year using a color map, where warmer colors represent higher power and cooler colors represent lower power. It is observed that during the central hours of the day, both the highest and lowest power levels are concentrated, as evidenced by orange and dark blue colors, respectively. This suggests that during these hours, there are greater energy surpluses due to photovoltaic generation. The power variation during the central hours is due to increased activity at the facilities. During the early morning and late evening hours, more intermediate colors, as well as warmer colors, appear. The absence of minimal power levels in these time frames indicates more consistent surpluses since photovoltaic production is not added, and demand is minimal. The presence of high-power levels during the central hours of the day throughout the year suggests that both solar and wind energy play important roles in different seasons. However, it is observed that these power levels are more consistent during the summer and winter months, where photovoltaic and wind generation are higher, respectively.

5. Discussion

Table 7 summarizes the optimal results for energy management and the installation of new equipment, obtained through the HOMER^® software v 5.1 to provide the most cost-effective solution for the system.

5.1. Analysis of Results for Scenario 1

In Section 4.1 Scenario 1 represents the operation and performance of the current energy system configuration with the addition of the planned wind generation. The simulation results show a positive scenario in terms of sustainability and energy efficiency, as 74.89% of the energy used to meet the demand comes from renewable sources. Thus, only 101 MWh per year is required from the public grid, reducing the pressure on the existing infrastructure. Additionally, there are periods where the total energy used to meet the demand is entirely from renewable sources, validating the system’s robustness and reliability in ensuring a continuous and stable energy supply.

The projected wind installation is viable for covering a high percentage of the energy demand, justifying its initial investment. However, this generation capacity also creates the need to manage energy surpluses, as the total production exceeds the total energy demand for the year by more than double. In this scenario, excess energy is fed into the grid without compensation, limiting the potential for positive economic outcomes in the case of high renewable penetration and low self-consumption. In other words, a high purchase price for energy and proper system sizing to minimize surpluses is the perfect solution for achieving economically viable scenarios. The current NPC for the baseline scenario is EUR 463,361, which is the lowest among all alternatives.

5.2. Analysis of Results for Scenario 2

In Section 4.2 Scenario 2, the demand is increased to serve additional production lines compared to the initial case. The results show a significant reduction in the fraction of renewable energy used to cover the new situation. Specifically, the percentage of renewable energy in the demand coverage mix is reduced, increasing the dependence on the public grid. A reduction in surplus electricity is also detected, improving the self-consumption ratio with renewables. This scenario highlights the importance of the proper sizing of energy installations to avoid inefficiencies that could lead to economic deficits and excess grid injection. Additionally, proper sizing helps prevent local grid congestion, ensuring the infrastructure is available for other end users.

Compared to the initial situation, energy demand increases by 263%; however, the NPC only increases by 172%. This discrepancy demonstrates an improvement in the compatibility of the existing and planned energy systems with the expected energy situation in this second scenario.

5.3. Analysis of Results for Scenario 3

The impact of complete disconnection from the electrical grid compared to the baseline case is evaluated in Scenario 3. The results show that a total of 272 MWh of energy from diesel generators, representing 67.59% of the total energy demand, is required to operate continuously without access to the grid. Although wind turbines serve as the primary source of electricity for the facilities, the demand curve does not align with the wind production schedule, leading to a significant amount of unutilized generation. The PV systems face a similar situation but with a smaller surplus of unutilized energy. In summary, to meet a demand of 402 MWh, a total of 1224 MWh is generated, leading to the wastage of 821 MWh of surplus energy, while achieving a renewable penetration ratio of 32.23%.

A storage system could positively impact the energy aspect of the facilities. However, due to the current high cost of such equipment, a substantial improvement in the NPC is not anticipated. This configuration has an NPC of EUR 6,828,371, making it almost fifteen times higher than the baseline NPC. In other words, the national grid significantly reduces the energy supply costs for the facilities. The use of diesel generators negatively affects both the economic and environmental aspects of the solution.

5.4. Analysis of Results for Scenario 4

A storage system can positively impact off-grid systems with high renewable penetration. This scenario simulates the configuration to quantify and evaluate the real impact on the performance of the facilities on energy, environmental, and economic aspects. The results show that 92.12% of the energy demand is met with renewable sources, and only 32 MWh from the diesel generator is used to complement the demand. Despite the high coverage of the energy demand with renewables, there is 556 MWh of surplus electricity per year.

According to the optimization results, to maximize the use of renewable energies and reduce the loss of generated energy, it is necessary to include a conventional battery with a capacity of 229 kWh. This simulation shows a considerable improvement in technical–economic results compared to Scenario 3. Additionally, the maximum renewable energy generation reached at any given hour of the year is 931% of the demand. This situation indicates that at certain times, nine times more energy is generated than needed at that moment. This highlights the need for a storage system to manage these production peaks and better utilize the produced energy. Regarding the NPC, this configuration has one of EUR 1,246,060, representing only 18% of the previous case and 269% higher than the baseline case due to the investment in the battery.

5.5. Analysis of Results for Scenario 5

The hybridization of hydrogen technologies with renewable energies, evaluated in Scenario 5, presents optimal results for applications in fish farms. The ideal configuration includes a 50 kW electrolyser designed to absorb energy surpluses. However, this solution only manages to cover 32.23% of the energy demand with renewable sources, requiring 272 MWh from the generator to meet the total demand. There are 591 MWh of unused electricity annually.

In addition to producing H₂ for multiple uses and energy storage, the O₂ generated as a byproduct of electrolysis is utilized in the rainbow trout farming process. This approach not only reduces energy consumption by avoiding artificial O₂ production but also enables the conversion of renewable energy surpluses into H₂, which can be stored and later converted back into electricity. Here, an estimated annual production of 4969 kg of H₂ and 79,504 kg of O₂ represents 165,468 kWh and 43,727 kWh, respectively. This utilization represents 28% of the currently wasted generated energy, thereby improving demand coverage with renewable energies and reducing dependence on fossil fuels.

From an economic perspective, over the system’s lifecycle, the use of generated hydrogen is estimated to save EUR 355,755, while the use of oxygen is expected to contribute an additional EUR 94,013 in savings. These savings constitute approximately 4.94% and 1.23% of the total NPC of the Scenario 5 configuration, respectively. However, the comparative NPC analysis indicates that these solutions present significant costs. This marginal improvement underscores the ongoing need for research and optimization to increase economic efficiency in the implementation of these advanced technologies.

6. Conclusions

In general, the extensive use of renewable energies significantly reduces the dependence on conventional sources and national grids, especially in island regions or areas with deficient or overly saturated electrical infrastructure. For effective integration, optimal management that balances demand and production is essential, along with the implementation of storage systems to mitigate the mismatch between generation and consumption.

Currently, Estonia does not offer financial compensation for injecting surpluses into the grid, and the fish farms lack storage systems to utilize them. The high percentage of self-consumption helps to alleviate grid congestion in an island environment, but the generation is oversized, resulting in many surpluses. The proper planning and sizing of renewable installations are essential to avoid these problems, especially in an adverse regulatory context and without available storage.

For existing facilities, increasing demand improves energy self-consumption and reduces surpluses injected into the grid, thus benefiting the efficiency of the current energy system. However, it also decreases the fraction of renewable energy used to meet the demand. In terms of economic efficiency, the specific cost of energy is reduced, which is a favorable indicator of the system’s capacity to adapt and optimize resources in the face of variations in demand and renewable energy availability. Even for potential production expansions, the results highlight the need to improve planning and the integration of renewable energies to maintain a high percentage of clean energy and ensure the long-term sustainability and efficiency of the energy system.

When evaluating disconnection from the electrical grid, it is concluded that it negatively affects the economic and environmental viability of the facilities. The main effect of this disconnection is the intensive use of diesel generators, which increases fossil fuel consumption and emissions. Economically, the cost of a kWh purchased from the grid is much lower than the cost of a kWh generated directly on-site. Additionally, it is concluded that it is necessary to introduce electrical storage systems, as there is a 67% surplus of the total generated energy. This is mainly due to the mismatch between the generation and demand curves, with production peaks significantly exceeding existing loads.

The integration of storage systems improves energy management by eliminating surpluses and reducing the operational time of diesel generators. This substantially increases the proportion of demand covered by renewable energies, tripling their effectiveness. From an economic perspective, the inclusion of batteries notably reduces the NPC, demonstrating economic viability even with high initial investments.

In summary, the integration of hydrogen technologies with renewable energies in fish farms proves to be a viable and beneficial option. The production of H₂ for various uses and the utilization of O₂ as a byproduct in rainbow trout farming represent significant energy savings and a reduction in fossil fuel dependence. Despite these benefits, economic viability remains a crucial challenge. The high NPC of the proposed solutions indicates that they are less economically viable than conventional methods. Although the utilization of O₂ generates financial savings, this benefit is marginal, highlighting the need to optimize and reduce costs to improve the economic efficiency of these technologies.