Economic and Sustainability Assessment of Floating Photovoltaic Systems in Irrigation Ponds: A Case Study from Alicante (Spain)

Abstract

Environmental problems, along with the increasing energy demand and high electricity costs in the agricultural sector, justify the need to explore renewable energy sources in order to improve irrigation efficiency and sustainability. Therefore, the objective of this study is to analyse the feasibility of installing floating photovoltaic panels in the irrigation ponds of irrigation communities (ICs) in the province of Alicante. To this end, a practical case study based on the operating data of a photovoltaic installation on an irrigation pond, which shows 31% self-consumption and a 27% reduction in energy costs, is presented. Based on these results, this type of installation has been considered for the rest of the ponds in the province of Alicante, with an estimated total investment of EUR 130 million and annual savings of EUR 23 million in energy costs. Additionally, barriers such as the initial investment and the need for public financing for large-scale implementation are identified. Finally, it is concluded that the adoption of floating photovoltaic energy represents a key opportunity to reduce dependence on fossil fuels, mitigate environmental impact, and promote the circular economy in the agricultural sector.

1. Introduction

Environmental problems, such as global warming, which is a direct consequence of an increase in the concentration of greenhouse gases (GHGs), and air pollution, are considered to be among the most important global challenges. Furthermore, increasing energy demand and the depletion of primary sources are additional global concerns [1].

In recent years, scientific evidence has shown that high carbon dioxide emissions are responsible for global warming, which requires a radical change in the energy sector model [2]. To counteract this serious environmental impact, the trend of reducing fossil fuels by increasing the efficient use of renewable energy can be considered as one of the solutions, primarily through the replacement of these fuels by more sustainable and environmentally friendly energy sources [3,4].

In the last two decades, solar energy has become one of the most important renewable energy sources [5]. Recent initiatives at the European level call for climate neutrality by 2050, whereby the European Commission holds Member States accountable for approving national plans that integrate energy and climate. Spain recently fulfilled this commitment with the approval of the National Integrated Energy and Climate Plan 2021–2030 (PNIEC). This plan aims to achieve a 23% reduction in GHG emissions by 2030 compared to 1990, in addition to obtaining 42% of end-use energy from renewable sources, increasing energy efficiency by 39.5%, and achieving 74% renewable energy for electricity generation [6]. Additionally, over the last few years, intense regulatory activity in the energy sector has been noted, such as in 2020, when Royal Decree-Law 23/2020 was approved, within which new administrative milestones for access permit holders were included; Royal Decree 1183/2020 was also approved that year, which introduced the new framework for access and connection, as well as Royal Decree 960/2020, which introduced auctions. These decrees established the regulatory framework for the development of renewables in our country in the coming years [7].

As an example, in 2021, in the European Union, photovoltaic installations reached an increase in installed capacity of 25.9 GW, 34% more than the 19.3 GW installed in 2020. In this way, a new historical record was broken in the solar market, making it the year with the largest photovoltaic installation in the history of the continent. That year, Spain continued to maintain its second position in terms of growth in the sector at the European level, only surpassed by Germany, which installed 5.3 GW. The forecasts for 2025, according to SolarPower Europe, indicate that there will be an accumulated capacity of 328 GW, doubling every five years until it reaches 672 GW in 2030 [7].

Photovoltaics (PV) has the potential to be a major source of energy in the future [8] due to its scalability and simplicity [9]. In fact, in the coming decades, it may account for up to 69% of total energy generation. However, due to its intermittent nature, PV requires a large amount of storage to stabilise energy supply [10]. Even today, its development faces the problem of the time mismatch between peak PV generation and electricity consumption [11,12].

Another major challenge is the integration of PV systems into the grid, as the amount of energy produced is highly dependent on weather conditions and therefore subject to large fluctuations [13]. This unpredictable energy production can lead to grid instability or, in the worst case, even blackouts [14]. Solutions such as combining PV systems with energy storage systems could mitigate this problem [15].

Furthermore, the climatic conditions of our planet are increasingly adverse as a consequence of the pollution we have generated throughout history, which has a clear effect on the socio-economic development of society, and it is at this time that the circular economy takes on special importance, as it is one of the main ways of dealing with this situation [16]. The circular economy is an economic concept that is linked to sustainability and whose main objective is that the value of products, materials, and resources (such as water, glass, paper, metals, energy, etc.) remain in the economy for as long as possible, thus reducing the generation of waste to a minimum. Therefore, it involves replacing the linear economy with a circular one, where the premise is to extend the useful life of services, products, water, materials, and energy through their reuse [17].

For these reasons, in this specific case study, the linear economy approach of using fossil fuels should be eliminated, and renewable energies should be promoted to remove from the equation the waste that affects the environment, generating renewable energy with a lower pollution impact [16]. In addition, PV generation using solar panels provides an important economic boost by generating new business opportunities and associated jobs. As an example, in 2021 in Spain, according to the estimates, the direct contribution of photovoltaics to the Spanish Gross Domestic Product (GDP) was EUR 4916 million, and the total economic footprint of the sector, estimated as the aggregation of direct, indirect, and induced GDP generation, was EUR 13,228 million. In terms of employment, the total footprint amounted to 89,644 national workers linked to the PV sector (21,596 direct, 39,479 indirect, and 28,569 induced) [7].

However, it is important not to lose sight of the fact that the advantages listed above could be overshadowed by significant drawbacks, such as the considerable installation and maintenance costs associated with them, as well as the low efficiency achieved with the installed solar panels [18]. Nevertheless, these problems have been addressed over the years, giving rise to clear improvements in efficiency and considerable cost reductions, which have led to a significant increase in the number of installations commissioned [19]. Therefore, these improvements have resulted in a major boost in the sector, linked to the enormous potential of solar energy in Spain, which has led to a reduction in GHGs, without forgetting the high turnover obtained and the employment generated [20].

The water sector is one of the most dependent on and closely linked to the electricity supply [16], which makes it highly sensitive to fluctuations. Cost recovery for water services is one of the fundamental pillars of the Water Framework Directive (WFD), with the energy component accounting for a very large part of these costs. This is evidenced by the high costs of services such as water transfer, reuse, and desalination [16]. The development of photovoltaic energy applied to proximity infrastructures, purified and regenerated water treatment plants, desalination plants, pumping, and impulsion systems in the water sector as a whole will reduce the energy and environmental bill [21].

Spanish hydrological planning has attempted to reduce these costs linked to those water services with higher consumption by implementing measures that include the installation of self-consumption photovoltaic plants to minimise energy pressure and contribute to the circular economy. As an example, the Segura Basin Hydrological Plan 2022/27 (SBHP 22/27) proposes actions, to be developed in the coming years, for the construction of a solar photovoltaic plant to supply electricity to different desalination plants for photovoltaic self-consumption and storage, which will make it possible to reduce the rate of water use and the carbon footprint, with an investment of more than EUR 350 million [22].

However, one of the main problems with this type of installation, in addition to the investment costs, is land use. The execution of these macro installations requires large areas to house the photovoltaic plants, giving rise to additional costs and limited availability, especially in locations very close to the sea, where this type of seawater treatment facility is located. Therefore, as the total surface area of the regulation reservoirs in Spain exceeds 56,000 km², there is a large surface area available for the construction of floating photovoltaic panels [21]. Moreover, this type of renewable energy system does not generate further impacts on the environment [7].

Historically, it should be noted that the world’s first floating photovoltaic (FPV) array project was installed in Aichi, Japan [23], with a capacity of 20 kW. The project was researched and developed by the National Institute of Advanced Industrial Science and Technology (AIST) in 2007, comparing the energy efficiency of power generation under water- and air-cooling systems. The success of this project led to FPV systems being installed all over the world, including the United States, South Korea, France, Spain, Italy, China, India, and others, with Japan becoming the country with the largest installation of this technology. The first commercial grid-connected FPV project was developed in 2008 by SPG Solar in the US [24], with a generating capacity of 400 kW. In 2012, the French company Ciel and Terre, installed the world’s first one-megawatt FPV system in Okegawa, Japan [25].

Subsequently, more and more FPV systems have been installed in various inland waters, such as lakes, canals, ponds, irrigation reservoirs, coal mine subsidence areas, etc. The installed capacity of FPV power plants has experienced significant growth worldwide, from 100 MW in 2016 to more than 3 GW in 2021 [26]. According to the Wood Mackenzie report, the global installed capacity of FPV will exceed 6 GW by 2031 [27].

This type of installation consists of a solar module attached to a photometer anchored to the water surface by way of a mooring device [28,29]. The solar panels, inverter, mounting structure, transmission cables, transformer, and mooring line and anchoring constitute the different parts of a typical solar photon system [30].

The main advantages of FPV that make it an attractive solution for harnessing solar energy are the availability of land, where it is limited; the conservation of water and soil; and being able to offer a higher power output compared to conventional terrestrial PV systems [30]. In terms of thermal performance, recent studies [31] have compared terrestrial and aquatic PV systems deployed in Singapore and the Netherlands, with substantial improvements in aquatic systems, in the order of 3° for the Netherlands and 14.5° for Singapore. Further research shows that passive water cooling under FPV reduces the operating temperature of the panels by 2.7 °C (on average), with a maximum of 3.7 °C for 700 < G < 800 W/m². This water-cooling process has led to an improvement in panel efficiency by 1.75% (absolute), being around 17.22% (relative) [32].

No less important are the results obtained in terms of evaporation improvements, as reductions of around 50% have been obtained in FPV designs with photoresistors covering 30% of the total area [33]. Other studies have found that the shading effect can reduce evaporated water by 30%, covering approximately 17% of the water sheet [32].

On a smaller scale, it should be highlighted that energy costs have a significant weight in irrigation farming, especially in extensive irrigation. In the distribution networks of ICs, water is often pumped to elevated reservoirs from where it is then distributed by gravity. To this, the energy required for pressurised irrigation systems [33] and groundwater abstractions should be added. This situation represents an opportunity to minimise this small-scale energy consumption, which could generate great economic relief for one of the sectors that has been the hardest hit historically. The SBHP 22/27 also contemplates an action of this type, specifically measure number 2221, which presents the project for the implementation of renewable energies through photovoltaic panels in the Las Colleras ICs (Albacete), with an investment of EUR 1.5 million [22].

Additionally, it is worth mentioning similar projects that have recently been developed in Spain, including the installation of FPV systems for self-consumption. The first example involves the installation of 680 photovoltaic panels on a regulating reservoir (70,000 m³) in the municipality of Elche (province of Alicante), at an approximate cost of EUR 730,000, where an annual production of around 557,000 kWh/year is expected [34]. Another example refers to the installation, in Campo de Cartagena IC (Region of Murcia), of a photovoltaic installation for self-consumption without surpluses on a reservoir belonging to the irrigation community itself, which will cover an area of 290,684 m². The project contemplates the installation of 2340 photovoltaic solar panels, mounted on floating modules and reaching a power of 1,752,618.37 kWh/year, with an estimated cost of EUR 1.1 million [35].

Therefore, due to the energy costs associated with the agricultural sector that mainly affect the ICs, the aim of this report is to determine the advantages of installing self-consumption photovoltaic plants on floating structures on their own irrigation ponds. Preliminarily, significant energy savings could be envisaged, and existing surface area could be made available to free up installation costs. This could involve such a high investment that it would be economically unviable for this type of company, which could be considered, with the aim of achieving the objectives set by the European Commission for the integration of energy and climate, through the promotion of renewable energies.

2. Characterisation of the Area of Study

The province of Alicante, located in southeast Spain (Figure 1), covers an area of 5817 km² and the management of resources, demands, and hydrological planning corresponds to 80.8% of the Júcar River Basin (JRB), with an area of 4701 km², and 19.2% to the Segura River Basin (SRB) with an area of 1117 km² [36]. A large part of the province has a semi-arid Mediterranean climate with high variability in rainfall (230 and 900 mm/year) and an average temperature of 18 °C [37,38]. On the other hand, it represents the fifth most populated province in Spain, distributed in 141 municipalities, currently reaching a total of 1,901,594 inhabitants [39], mainly located in the areas closest to the coast, with large seasonal increases mostly due to tourism in summer [40], when the number of tourists exceeds four million [39].

On the one hand, the province has serious issues in terms of water deficit and resource scarcity, largely due the development of agriculture, industry, and urban areas, combined with its unique climate. In this sense, one of the main consequences is the overexploitation of groundwater bodies, directly affecting the availability of natural resources [41]. On the other hand, political differences between states and individual and local interests over water control have led to a kind of “water war” that has challenged the transfer of resources reallocated by the Tajo–Segura Transfer (TST) through different mechanisms, causing a lack of guarantee of fundamental water resources for the development of the agri-food sector and for urban supply [42].

Figure 1. Location map of the province of Alicante. Source: [43,44], own elaboration.

Figure 1. Location map of the province of Alicante. Source: [43,44], own elaboration.

From an institutional perspective, the province of Alicante has a water management structure involving all levels of administration [45]. In addition to managing water uses, the State also intervenes through other organisations, such as the Mancomunidad de los Canales del Taibilla (MCT) and Waters of the Mediterranean Basins (ACUAMED in Spanish), with a major role in the building of desalination plants [46].

Likewise, the Regional Government of Valencia has important competences in agricultural and environmental matters, through different agencies. Of particular relevance is the Entidad Pública de Saneamiento de Aguas Residuales (Public Wastewater Treatment Entity) (EPSAR), which manages the building and operation of wastewater treatment plants [47]. It should be noted that on 13 November 2018, by means of a resolution of the Regional Department of Housing, Public Works and Territorial Planning, the Territorial Action Plan (TAP) of the Vega Baja del Segura (27 municipalities) was approved as a comprehensive territorial planning instrument on a supra-municipal scale [48]. The Vega Baja del Segura district, where the analysed FPV is located, has a surface area of 957 km² (Figure 2), and is located in the part of the province of Alicante within the SRB, which represents only 5% of the total of the SRB and 4% of the total of the Regional Government of Valencia. It has a large area of traditional irrigated land with flows from the Segura River, diverted by means of dams to the network of irrigation ditches, the returns of which are channelled through irrigation channels, allowing them to be reused in market gardens downstream [49]. On the other hand, it has a population of 355,924 inhabitants, representing 7.18% of the total population of the Regional Government of Valencia, with a very high population density of over 400 inhabitants per km² [48].

The local authorities in the province of Alicante are responsible for the management of the secondary phase of the water supply for urban uses. This service is declared by the local regime legislation as minimum and compulsory for all municipalities, which can choose the specific management modality: direct (concentrated, deconcentrated or decentralised), indirect, or through the constitution of mixed companies, with the mixed modality being the option chosen by the majority [50]. The Provincial Council of Alicante focuses on legal, economic, and technical support and assistance to municipalities for the provision of municipal water services. The internal decentralisation of the functions related to the integral water cycle in a specific department of the provincial body, such as the Water Cycle, has yielded very good results [51].

Together with the territorial administrations and public bodies of institutional nature, other organisations constitute a fundamental pillar in water management in this province, namely the communities of users, to which the Water Law grants the status of corporate administrators [45]. There are many basic (or first-degree) communities in the province due to the enormous importance of the agricultural sector and, in particular, irrigated agriculture. Furthermore, the complexity of the distribution of the scarce water resources available has led to the creation of derived or second-degree communities, which articulate the common interests of the ICs and individual users [50].

The study presented contemplates the Albatera IC, which was officially constituted by the Segura Hydrographic Confederation (SHC) in 1992 and has 1505 members. The SHC processes a surface area of 2938 ha, with a water concession of 7,815,324 m³ from the TST, which means an allocation of 2660.44 m³/ha/year. Currently, the cultivated area is 2653 ha, leaving 285 ha uncultivated, with 54% planted with citrus fruits, 16% with pomegranate trees, 10% with fig trees, and 20% with other crops [52].

The water needs of the cultivated area are estimated at 13.38 hm³/year. The average endowment in the hydrological period 2015–2019 was 7.05 hm³/year, representing 52.70% of the volume of water needed to ensure optimal irrigation. The Albatera IC has three reservoirs, number 1 with a capacity of 18,000 m³, number 2 of 115,000 m³, and number 3 of 88,000 m³, with a total volume of 221,000 m³. Additionally, there are 194 private reservoirs, with a total capacity of 1,739,260 m³ [52].

In recent years, Albatera IC has carried out works to modernise irrigation with an investment of EUR 23 million, with the construction of three reservoirs, filtering stations, an irrigation automation control house, irrigation pipes, and impulsion pipes, with a total of 163.5 km of piping [52].

In 2020, Albatera IC presented a PV self-consumption project, developed by the company Domus Energy Engineering, with the aim of harnessing the solar energy received by pond number 3 (surface area of 14,350 m²), as can be seen in Figure 3. To this end, the installation of a PV generator was proposed, located on floats, to reduce the energy cost of irrigation activity, connecting the generator to the internal network and enabling the self-consumption of this energy. The project contemplated the installation of 690 PV panels on a floating structure (surface area of 2185 m²), with a power generating capacity of 314 kW and an efficiency of 20.5%. The total cost amounted to EUR 370,000, of which EUR 106,029 corresponded to the costs associated with the solar modules, EUR 20,800 to the inverters, EUR 94,920 to the floats, and EUR 24,325 to the wiring and protections [52].

The executed project contemplates the electrical installation responsible for the distribution of energy from the PV generator to the main switchboard of the indoor installation located inside the filtering and pumping building. The photovoltaic generator is located on photovoltaic panels on the pond itself and the inverters on the edge of the pond. JASolar JAM72S20 panels were selected, with a unit power of 455 Wp, 20.5% efficiency, a unit weight of 90 kg, and a surface area of 2185 m². The useful life of these panels is 25 years, with an annual maintenance that exceeds 2000 EUR per month, guaranteeing 80% of the nominal power, which would mean an investment at the end of its useful life of approximately EUR 130,000, with EUR 110,000 corresponding to the cost of new panels and EUR 20,000 to the costs of eliminating the current ones (recycling cost of EUR 300 per ton) [52].

The photoresistors used are of a hollow modular type with a concave design, a 5° inclination, and a southerly orientation, with a 16° deviation towards the east, manufactured by ISIGENERE, specifically the ISIFLOATING 4.0 model. The resulting supporting structure is the safest and most reliable. It is easy to transport, simple to install, resistant to weather conditions (wind, sun, snow, etc.), efficient in terms of maintenance, and competitive in terms of market cost [52]. Figure 4 shows the details of the installation after it had been completed and commissioned.

3. Methodology

The methodological development for studying the viability of the floating photovoltaic (FPV) installations for self-consumption in irrigation ponds has required, first, an analysis of the information for the FPV recently implemented in the Albatera IC, as well as the self-consumption data obtained in the first years of production. This information was provided directly by the IC and consisted of the following data:

• Project report;
• Modifications made to the original project;
• Description of the Albatera IC;
• Total construction costs of the FPV of Albatera IC;
• Production-consumption-supply documents.

For this analysis, the total consumption data of the IC during its period of operation (2021–2024) have been extracted, both the fraction of imported energy and that corresponding to self-consumption. The results have made it possible to obtain the annual costs of each component; that is, both the cost of imported consumption and the savings provided by the FVP. To estimate the cost of energy, the average annual billing term obtained from Red Eléctrica Española [53] has been used, corresponding to 0.26718 EUR/kWh in 2021, 0.19005 EUR/kWh in 2022, and 0.17976 EUR/kWh in 2023 (since there is only information for three months in 2024, the 2023 data has been used for this year). This information will be essential to determine the payback period of the installation and the savings that will be made on the cost of the resource, corresponding to the processes through which the water passes until its final use.

Second, having analysed the operating data of the Albatera IC FPV, it has been considered that these results could be extrapolated to all those irrigation ponds that meet the conditions for contemplating the FPV. The determination of viability will be based exclusively on an assessment of the surface area of the water, and for this purpose it must have a similar extension to that studied in the case of the Albatera IC, since, as they are located in very close proximity and with almost identical climatic conditions, any possible variations are not considered to be relevant.

Therefore, in order to obtain this inventory of irrigation ponds, it was necessary to download, in shape format, the hydrographic information available at the National Geographic Institute (IGN in Spanish), both for the SRB and the JRB. Within the available geographic information, “artificial water bodies” have been selected, including irrigation ponds, defined as “hydraulic works consisting of artificial structures for the storage of water located outside a watercourse and delimited, totally or partially, by retention dams, for agricultural, livestock or extractive use” [54].

The total number of “artificial water bodies” in the province of Alicante amounts to 103,123 units. However, this category also includes swimming pools and ponds, so it has been necessary to filter this information according to their plan view area (seen from above), considering those water bodies larger than 500 m² as irrigation ponds. This screening has resulted in a total of 5604 irrigation ponds larger than 500 m² in surface area. These are the bodies that will be analysed.

In the analysis in the province of Alicante, a final screening was required, focusing on the ponds located in the Vega Baja del Segura, where the conditions are exactly the same as the Albatera IC, as this is also located in the Vega Baja del Segura.

Finally, we have considered analysing an area very close to the Albatera IC and the Vega Baja del Segura, with very similar geographical and climatic characteristics. This area includes the slopes of the Mar Menor in the Region of Murcia and is characterised by the importance of the agricultural sector, which is an example of technification and economic performance, colloquially known as the “market garden of Europe”.

4. Results

4.1. Results in the Albatera IC

The plant installed in the Albatera IC has been in operation since September 2021 (29 months) with a total self-consumption production of 637 MWh, which represents 31% of the total energy consumption of the IC. In economic terms, this solar energy production has meant a saving of EUR 155,000 [53], which represents 27% of the total expenses derived from energy consumption, as shown in

Table 1. Overall results obtained from the operation of the FPV of the Albatera IC for the period 2021–2024. Source: [52], own elaboration.

2021–2024	kWh	EUR
Total consumption	2,053,911.45	565,785.57
Imported	1,416,998.71	410,763.70
Self-consumption	636,912.74 (31%)	155,021.87 (27%)

.

The graph below (Figure 5) shows the data for energy consumed, imported, and from FPV (self-consumption) from the start-up in September 2021 to April 2024. As can be seen, the seasonality of FVP production is aligned with the seasonality of the electricity consumption of irrigation communities, which is extremely valuable, since during times of greatest energy needs, FVP production reaches its maximum value, coinciding with the summer–autumn months, when irrigation needs are greatest.

With these results from the start of operation, it could be determined that the annual self-consumption production is 264 MWh/year, with a saving of 64,147 euros/year, as summarised in

Table 2. Annual averages obtained from the operation of the FPV of the Albatera IC for the period 2021–2024. Source: [52,53], own elaboration.

Annually	kWh/Year	EUR/Year
Total consumption	849,894.39	234,118.17
Imported	586,344.29	169,971.19
Self-consumption	263,550.10 (31%)	64,146.98 (27%)

:

After analysing the results obtained, it is possible to estimate the payback period of the installation, from which the savings generated will have a direct impact on energy consumption. Therefore, with an investment of EUR 370,000 and an annual saving of EUR 64,000, the period necessary to amortise the investment would be 5 years and 10 months.

Additionally, in order to calculate direct savings in water costs, it would be necessary to determine the origin of the energy costs of each irrigation community and which of these could be directly linked to water. In the case of the Albatera IC, before the FPV, the cost of water, mainly caused by pumping and filtering, was EUR 7.3/h on average, while after the FPV, the average water costs decreased to EUR 3.8/h, representing a considerable decrease [52,53].

4.2. Extrapolation to the Province of Alicante

After conducting an analysis of the data on the operation of the FPV of the Albatera IC, they could be extrapolated to all those irrigation ponds that meet the conditions for considering the FPV. As indicated above, in the province of Alicante, a total of 5604 irrigation ponds (artificial water bodies with a surface area greater than 500 m²) have been inventoried. However, due to their small surface area, many of them did not allow the installation of self-consumption by means of photovoltaics. For all these reasons, a screening of these ponds was carried out according to their plan view area, obtaining the following results (

Table 3. Classification of irrigation reservoirs in the province of Alicante according to their surface area. Source: [54], own elaboration.

Scope	Total Number of Ponds (over 500 m2)	Number of Ponds over 2500 m2	Number of Ponds over 5000 m2	Number of Ponds over 10,000 m2
Province of Alicante	5604	1814	837	359

).

Those irrigation ponds with a plan view area of more than 10,000 m² could reach a volume of approximately 50,000 m³, assuming an average height of 5 m. These would allow a considerable amount of water to be stored, with sufficient surface area to maintain an acceptable level of water for the installation of the infrastructure necessary for the PV self-consumption elements. Therefore, in the study area, the initial possibility of installing self-consumption PV production in 359 irrigation ponds would be possible. Figure 6 shows all the ponds larger than 500 m².

Consequently, with the extrapolation of the data obtained from the FPV of the Albatera IC (the same unit values are considered, since, as stated in the methodology, the geographical and climatic characteristics are very similar), the cost of the FPV in these 359 irrigation ponds would constitute an investment of EUR 133 million which would allow self-consumption values of 95,000 MWh/year to be obtained, generating an annual saving of EUR 23 million/year, as shown in

Table 4. Extrapolation of the results of the VFI of the Albatera IC to ponds larger than 10,000 m² in the province of Alicante. Source: [52,54], own elaboration.

Scope	Number of Larger Ponds 10,000 m2	FPV Cost (EUR)	Self-Consumption	Savings (EUR/Year)
Albatera IC pond	1	370,000	264 MWh/year	64,000
Province Alicante	359	132.8 million	95,000 MWh/year	23.0 million

.

The district where the Albatera IC is located, Vega Baja del Segura, stands out as the area of the province of Alicante where the largest irrigated surface area is concentrated. This area belongs to the management area of the SRB, and as stated in the Hydrological Plan, the gross irrigation surface area amounts to 58,000 ha and the net surface area 42,000 ha, with a gross demand of 255 hm³/year [55]. Most of the irrigation reservoirs inventoried throughout the whole of the province of Alicante are located in this area, as reported in

Table 5. Classification of irrigation reservoirs in the Vega Baja del Segura according to their surface area. Source: [54], own elaboration.

Scope	Total Number of Ponds (over 500 m2)	Number of Ponds over 2500 m2	Number of Ponds over 5000 m2	Number of Ponds over 10,000 m2
Vega Baja del Segura	3358	1162	505	201
Province of Alicante	5604	1814	837	359

and Figure 7.

Therefore, considering the data obtained from the FPV of the Albatera IC, the cost of the FPV in these 201 irrigation ponds in the Vega Baja del Segura (56% of the ponds in the province of Alicante) would constitute an investment of EUR 74 million, which would allow self-consumption values of 53,000 MWh/year to be achieved, generating annual savings of EUR 13 million/year, as shown in

Table 6. Extrapolation of the results of the FPV of the Albatera IC to the ponds larger than 10,000 m² in the Vega Baja del Segura. Source: [52,54], own elaboration.

Scope	Number of Larger Ponds 10,000 m2	FPV Cost (EUR)	Self-Consumption	Savings (EUR/Year)
Albatera IC pond	1	370,000	264 MWh/year	64,000
Vega Baja del Segura	201	74.4 million	53,000 MWh/year	12.9 million
Province Alicante	359	132.8 million	95,000 MWh/year	23.0 million

.

4.3. Extrapolation to the Campo of Cartagena

Located to the south of the Vega Baja del Segura is the area of Campo de Cartagena, belonging to the Region of Murcia, and whose watershed (called Zone XI Mar Menor in the SBHP 22/27) of more than 1600 km², extends towards the Mar Menor (the most representative wetland of the SRB). This area is characterised by being a clear example of efficiency and optimisation of resources for irrigation, which annually exceeds 50,000 ha. It is possibly the most technologically advanced irrigation area in Europe, where important yields are achieved, together with a fundamental economic sustenance for the Region of Murcia. Under these conditions, the number of irrigation ponds with potential for FPV is considerable, as reported in

Table 7. Classification of irrigation ponds in Zone XI of the Mar Menor according to their surface area Source: [54], own elaboration.

Scope	Total Number of Ponds (over 500 m2)	Number of Ponds over 2500 m2	Number of Ponds over 5000 m2	Number of Ponds over 10,000 m2
Zone XI Mar Menor	4219	1655	716	230

.

Figure 8 shows all the ponds in Zone XI Mar Menor, and the data obtained evidence of the importance of irrigation in the area, as they account for 75% (4219 compared to 5604 in Alicante) of the ponds in the whole province of Alicante and 64% of the ponds larger than 10,000 m² (230 compared to 359).

Therefore, extrapolating the data obtained from the FPV of the Albatera IC, the cost of the FPV, in these 230 ponds located in the Campo de Cartagena area, would require an investment of EUR 74 million, which would allow self-consumption values of 53,000 MWh/year to be achieved, generating annual savings of EUR 13 million/year, as shown in

Table 8. Extrapolation of the results of the FPV of the Albatera IC to the ponds larger than 10,000 m² in Zone XI Mar Menor. Source: [52,54], own elaboration.

Scope	Number of Larger Ponds 10,000 m2	FPV Cost (EUR)	Self-Consumption	Savings (EUR/Year)
Albatera IC pond	1	370,000	264 MWh/year	64,000
Zona XI Mar Menor	230	85.1 million	60,000 MWh/year	14.7 million

.

Within this Zone XI of the Mar Menor, the Campo de Cartagena IC, which concentrates most of the crops in the area, should be highlighted. It has a gross surface area of more than 45,000 ha and annually exceeds 25,000 ha of irrigated land. Figure 9 shows the perimeter of this IC as well as the main irrigation reservoirs of the IC itself.

This information on the ponds is available on its website and only includes the most important ones, since, as can be seen in

Table 9. Classification of irrigation reservoirs in the Campo de Cartagena IC according to their surface area. Source: [54], own elaboration.

Scope	Total Number of Ponds (over 500 m2)	Number of Ponds over 2500 m2	Number of Ponds over 5000 m2	Number of Ponds over 10,000 m2
Campo Cartagena IC	27	27	25	17
Zone XI Mar Menor	4219	1655	716	230

, among the 27 inventoried ponds, 25 are larger than 5000 m² and 17 are larger than 10,000 m²:

Transferring the data obtained from the FPV of the Albatera IC to the main reservoirs considered by the Campo de Cartagena IC, an investment of EUR 6 M would be reached, which would allow self-consumption values of 4500 MWh/year to be achieved, generating annual savings of EUR 1 M/year. However, as shown in

Table 10. Extrapolation of the results of the FPV of the Albatera IC to the ponds larger than 10,000 m² of the Campo de Cartagena IC. Source: [52,54], own elaboration.

Scope	Number of Larger Ponds 10,000 m2	FPV Cost (EUR)	Self-Consumption	Savings (EUR/Year)
Albatera IC pond	1	370,000	264 MWh/year	64,000
Campo Cartagena IC	17	6.3 M	4500 MWh/year	1.1 M
Zone XI Mar Menor	230	85.1 M	60,000 MWh/year	14.7 M

, the possibility of FPV is much wider than those represented by the 17 reservoirs of the Campo de Cartagena IC.

5. Discussion

The main variable to be taken into account is the viability of this type of photovoltaic installation for self-consumption. First, this type of installation must have sufficient economic viability to allow the necessary investment for its installation. As previously mentioned, institutions are promoting large solar parks to reduce consumption in terms of desalination and reuse, without considering end-users in the water sector. While these individual initiatives do not have a significant impact, the combined impact could be greater. The burden of these costs on these user communities could become an insurmountable barrier to their final implementation; therefore, the need for public investment or financing could determine the feasibility of their implementation.

Another variable that cannot be ignored is the price of energy and the competition that may affect it. Recent fluctuations in the price of electricity have clearly increased the costs associated with the water sector, adding to the usual charges. In a sector already suffering from other climatic and market pressures, this variability and instability of energy prices could lead to the disappearance of many companies in the sector. Therefore, the implementation of these kinds of facilities would ensure that part of the costs derived from the energy necessary for their processes would not fluctuate and would provide them with a certain stability.

There is another relevant variable that can have a considerable influence on the consideration of this type of facility. Currently, the main projects are based on large on-site installations, generating important unknowns such as the availability of land, especially on coastal or productive (agricultural) land, and the investment cost required to purchase this land, which would add a significant cost to the installation. The large solar parks serving desalination plants have both of these conditions, located in areas close to the sea where the availability of land is limited, with high purchase prices, and with the need for large areas to obtain sufficient energy to provide service for this type of water treatment plants.

First and foremost, water availability is one of the main problems in the agricultural sector. Obtaining quality resources at competitive prices has become a utopia that is far from being achieved. One solution resides in increasing savings, reducing losses, optimising irrigation systems, and the water needs of the crops themselves. These losses occur from the final irrigation systems on the plots to the main storage elements (reservoirs). The installation of photovoltaic panels on floating structures could reduce the solar incidence on the sheets of water and therefore reduce their evaporation, with application from the small irrigation ponds to the large regulation and storage reservoirs of the hydrographic demarcations. The results obtained in recent international studies have highlighted this circumstance, obtaining reductions in evaporation of up to 50% with floats covering 30% of the total surface area. In addition, it has been demonstrated that with the installation of FPV, the operating temperature of the panels is reduced, improving their efficiency and performance.

For all these reasons, it is one of the most developed technologies for energy generation worldwide. Between 2007, when the first FVP was installed in Japan, and 2016, there has been a significant growth, with an installed power of 100 MW being reached, being exponential with 3 GW in 2021. This power is expected to double by 2031.

Finally, but no less importantly, is the consideration of the environmental variable in the installation of photovoltaics. The reduction in the use of fossil fuels, which minimises the carbon footprint and greenhouse gas emissions, represents a strong positive impact that tips the balance towards the use of this type of renewable energy. However, energy storage requirements may involve the use of batteries and other systems, which have a strong environmental impact both in their manufacture and in their replacement at the end of their useful life. Another aspect to be taken into account is the need for further research to analyse the possible consequences of FPV systems on ecological status, in particular with regard to aquatic habitats, as this type of installation can produce variations in temperature, pH, and dissolved oxygen that can affect natural habitats. Therefore, it is important to study these variables when developing this type of project, as they can play an important role in determining its environmental viability.

6. Conclusions

The construction of PV systems on floating structures is one of the fastest growing renewable energy solutions worldwide in recent years. This type of installation reduces the use of fossil fuels, minimises evaporation losses, increases efficiency and yields with respect to terrestrial installations, generates substantial economic savings, and reduces land occupation.

As previous studies show, on a small scale, these installations can enable irrigation communities to cope with economic variables and uncertainties. Specifically, in the Albatera IC (Alicante), it has been shown that with a minimum surface area of 2185 m² and an investment of EUR 370,000, it had been possible to achieve a self-consumption of 263,550 kWh/year (30% of the total energy consumed) and an annual saving of EUR 64,000, which would allow a rapid amortisation of the installed infrastructure.

Nevertheless, one of the first considerations to bear in mind is being able to secure this investment capital or funding to enable it to be implemented. For these types of entities in the agricultural sector, the investment to be made is practically unfeasible and it is necessary to study other investment channels, such as institutional investment. Nowadays, administrative efforts focus on providing these self-consumption infrastructures to large water treatment facilities, where it is also necessary to reduce the energy cost for the viability of their treatments, but entities of minor importance in absolute terms have been left out, which, taken together, could represent a considerable amount.

The province of Alicante is one of the most important agricultural regions in Spain, generating the possibility of installing photovoltaics in many irrigation ponds. In this study, more than 5600 irrigation ponds have been inventoried in the province of Alicante, of which 259 ponds would have a surface area of more than 10,000 m², offering the characteristics required for their installation. This would mean that more than 2.5 km² of water surface would be available for the installation of floating photovoltaic plants, which would represent an added value in terms of land availability, a very scarce resource in this area of eastern Spain. Moreover, in terms of economic savings, it would not be necessary to purchase or expropriate land for their implementation. The installation of new FPVs close to the study area would make it possible to compare the results obtained in order to consolidate the premises established in this study.

There are many infrastructures in Spain that meet the conditions indicated above and which would allow the construction of photovoltaic plants on floating structures. These include large storage and regulation reservoirs, which would provide a large surface area available for their installation and the complementary use of the energy generated, for example in combination with hydroelectric power, where photovoltaic energy could be used to supply the pumping stations and allow the water to be raised again, thus achieving a renewable energy production circuit, opening up future lines of research in this sense.

As previously analysed, the installation of photovoltaic plants on floating structures on irrigation ponds in the province of Alicante (359 ponds larger than 10,000 m²), similar to the one installed at the Albatera IC, would generate 95,000 MWh/year of self-consumption, which would mean a saving, in economic terms, of EUR 23 million/year. The necessary investment would be around EUR 130 million, which is less than the figure considered in the SBHP 22/27 for the “construction of a PV solar plant for the electricity supply to the Torrevieja desalination plant, extended for photovoltaic self-consumption and storage”, which would exceed EUR 155 million. It is here where it becomes clear how the sum of small investments could exceed the profitability of large installations, although, without renouncing any of them, with the combination of both, truly optimum returns could be obtained. This comparison would allow further research to be carried out, taking into account the components installed in each of them and the savings generated compared to the investment made.

This study has also determined that, in a more limited area of the province of Alicante, but with a higher concentration of cultivation areas such as the Vega Baja del Segura, there are 200 ponds with an area larger than 10,000 m² (compared to 359 in the province as a whole). In this area, generation for self-consumption would reach 53,000 MWh/year, which would mean an annual saving of EUR 13 million with the necessary investment for the execution of these installations being very close to EUR 75 million. As analysed above, this type of installation does not have energy storage elements, and the energy produced is used directly in the different consumptions of the irrigation community. Therefore, future studies could consider extending the installations to generate energy reservoirs or extending their application to other nearby uses (industrial and/or urban).

Another area close to the province of Alicante constituting a clear example of efficiency and optimisation of resources for irrigation is the area of Campo de Cartagena, one of the main economic engines of the Region of Murcia and a leader in agri-food exports. In this area, the concentration of irrigation reservoirs is even greater than in the province of Alicante, with 230 reservoirs of more than 10,000 m² in an area of only 1600 km². There are many origins of the water resource that are combined in this irrigation area (desalination, reuse, groundwater pumping, etc.) that require a large amount of energy for water distribution. For all these reasons, it is of great importance to consider this type of photovoltaic installation, which could generate an annual self-consumption of 264 MWh and a saving of EUR 15 million, with an investment of EUR 85 million. In addition, the study could be extended to the entire of the Segura River Basin, an area that has been particularly hard hit by the cuts in the TST and replacement by desalinated resources, with clearly higher tariffs and which, with the installation of photovoltaic installations, could reduce certain costs to mitigate the economic impact.

As a result, the advantages of this type of floating photovoltaic installation on irrigation ponds have become clear, both in the province of Alicante and in the Region of Murcia, areas where agriculture is of great importance and which are continually subjected to major obstacles and economic pressures. The installation of these reservoirs should not be left just to private investment, as public administrations should consider the importance of compensating for the losses that will be caused by the recent decisions taken on water policy. In addition, and no less importantly, the high environmental value of these types of renewable energy projects cannot be overlooked, as it minimises the negative impact of fossil fuel consumption, reducing greenhouse gas emissions, complying with European climate change objectives and promoting the circular economy.

The upswing in this type of installation will have a major global impact in the coming years, consolidating its use and allowing it to compete with traditional PV systems. However, it will be necessary to open up future lines of research to clarify the doubts or gaps in knowledge that currently exist, highlighting the unknowns regarding the alteration of habitats, long-term risk factors, and the waste generated by this type of solution.