The installation of floating photovoltaic plants (FPVPs) can bring many benefits, such as increasing energy efficiency, does not use fossil fuels, and reduces energy losses due to shading [16]. The joint energy system contributes to the social development of communities close to the reservoirs, enabling the management of essential water resources for agriculture and river transport [17]. Found a gain of 11% in producing floating photovoltaic energy compared to a conventional system with fixed structures in the ground [3]. With the growth of electricity consumption and periods of drought, the water storage level in hydroelectric reservoirs decreases. Therefore, there is a risk of an energy deficit in the coming years as demand increases and stricter laws to protect the environment for new projects. According to World Bank study [17], the potential for generating photovoltaic energy in the reservoirs by continent, results in 5,211 TWh/y considering 1% of the use of the surface area of reservoirs, minimizing environmental impacts, as shown in Figure 1.

Figure 1.

Floating Photovoltaic Plant potential in reservoirs by continent (World Bank Group, 2019)

This study aims to prove the technical feasibility of the hybrid operation of a floating photovoltaic plant (FPVP) with hydroelectric power plant (HPP) by modeling the fluctuation of solar energy in the different proposed scenarios, considering the fast activation of the hydroelectric power plant (HPP), and verifying the compensation for the reduction in the flow of turbinate water for electrical generation in critical periods of severe drought [18]. The photovoltaic system connected directly with the transmission line of the hydroelectric substation. The system operates so that hydroelectric and photovoltaic power generation complement each other. After the addition of the floating photovoltaic plant (FPVP), the Electrical System Operator begins to release more power at the dispatch set point during the day [19]. As expected, the output of the hydropower plant reduces on an average day, especially between 11:00 a.m. and 4:00 p.m. when the generation of the photovoltaic plant is high.

The Electrical System Operator requests the saved energy and uses it at the beginning of the morning and the end of the afternoon [19]. Although electricity generated daily by hydraulic potential is relieved, water storage is maintained at the same level to meet water demand from other downstream reservoirs [20]. The grid completely absorbs all the energy generated in the hybrid system without any limitation. This system demonstrates that hydro turbines can adequately respond to demand and photovoltaic supply fluctuations during the day and seasons [21].

The technical feasibility of operating the HPP in conjunction with the FPVP to balance the production of the two energy sources must achieve a constant level throughout the day and ensure that the electricity generated is connected to the transmission system to meet the planned and contracted production. The daily energy output of the HPP and FPVP is the sum of the values obtained per hour in a day, according to the following equations:

$EH={\displaystyle \sum _{i=1}^{24}EHi}$ (1)

EH: Daily hydropower production.

EHi: Hydropower production in i-th hour.

$EPV={\displaystyle \sum }_{i=1}^{24}EPVi$ (2)

EPV: Daily photovoltaic production.

EPVi: Photovoltaic production in i-th hour.

From the point of view of the electrical system, the FPVP acts as a virtual water turbine that complements the energy production of the HPP [4]. The photovoltaic system offsets all energy generated and stored in the reservoir in the form of potential energy and maintenance of water volume. The estimation of the equivalent flow (m³/s) and the equivalent volume (m³/d) of the FPVP's energy production, the "C" coefficient defines the monthly energy ratio (MWh) and monthly flow (m³/s) of the HPP. The ratio between the monthly energy and the monthly flow of hydropower generation:

$C=\frac{\text{Monthly energy (MWh)}}{{\text{Monthly flow (m}}^3\text{/s)}}$ (3)

Determination of the maintenance of the reservoir water flow according to the operation of the FPVP in the hybrid system:

$VDi{\text{ (m}}^3\text{/s)}=\frac{PV\text{ (Monthly energy (MWh))}}{{\text{Monthly flow (m}}^3\text{/s)}}$ (4)

The equation for FPVP equivalent monthly water flow:

$VDi={\displaystyle \sum }_{i=1}^{24}VDi{\text{ (m}}^3\text{/s) }\times 3600$ (5)

VD: Equivalent flow in 1 (one) day (m³/d)

To estimate the equivalent non-turbocharged water flow when using the FPVP in a hybrid system, the estimated calculation of the use of the photovoltaic source during the 24 hours of the day, considering the maximum and minimum power generation of the HPP and in which months of the wet and dry seasons the highest equivalent flow could occur.

On Ilha Solteira, the temperature varies between 15 °C and 33 °C throughout the year; with an average daily maximum temperature above 32 °C, even in the winter the temperatures are higher than 25 °C. The duration of precipitation is 5.3 months, from October 24 to April 3, with a greater than 37% probability that a given day will have precipitation, as shown in Figure 4a. The windier part of the year lasts for 4.3 months, from June 27 to November 5, with wind speeds of more than 10 m/s, the average wind speed is about 6 m/s, as shown in Figure 4b.

Figure 4.

Average temperature and rainfall (a); Average wind speed (b)

The PVsyst software version 7.2 simulated a photovoltaic potential of 480,000 kW_p in the reservoir lake of the HPP on Ilha Solteira-SP considering; occupation of a maximum of 1% of the reservoir area, monocrystalline modules of 600 W_p, data with location, generation power, and selected photovoltaic inverter module. PVsyst process the number of modules, inverters, and the necessary configuration to obtain the required power generation. The result is shown in Table 1.

The HPP energy production before and after hybrid operation in the wet season (December, January, February, March, and April), considering the FPVP power generation from 7:00 a.m. to 5:00 p.m. on sunny, cloudy, and rainy days, it is possible to reduce the power generation of the HPP significantly. The FPVP contribution is relevant for sunny and cloudy scenarios; 1 (2,216 MWh d^-1), 2 (1,330 MWh d^-1), 4 (2,245 MWh d^-1), and 5 (1,347 MWh d^-1). Even in the rainy scenarios, 3 (466 MWh d^-1), and 6 (449 MWh d^-1), there is a substantial contribution of energy generation from FPVP in joint system, as shown in Figure 5.

Figure 5.

Contribution of Floating Photovoltaic Plant in the daily contracted dispatch of Hydroelectric Power Plant in the wet season

The reduced production of the HPP for the dry season (May, June, July, August, September, October, and November). The contribution of the FPVP is relevant for sunny and cloudy scenarios; 7 (2,172 MWh d^-1), 8 (1,303 MWh d^-1), 10 (2,266 MWh d^-1), and 11 (1,360 MWhd^- 1). Significant contribution in the rainy scenarios; 3 (466 MWh d^-1), and 6 (449 MWh d^-1) considering the joint systems, as shown in Figure 6.

Figure 6.

Contribution of Floating Photovoltaic Plant in the contracted daily dispatch of Hydroelectric Power Plant in the dry season

The database of the Electrical System Operator [19] for the year 2022 determined the maximum and minimum values of hydroelectric production and the FPVP based on the PVsyst simulation data. Considering the daily energy production of HPP and FPVP together, there is a decrease in HPP energy production under all scenarios evaluated, which is more pronounced on sunny days, as expected. However, the energy contribution always observed was of FPVP, as shown in Figure 7.

Figure 7.

Hydroelectric Power Plant production before and after integration in all evaluated scenarios

The difference between the turbinate flow of the power plant before and after a hybrid operation with the FPVP allows for a statistical survey that resulted from the estimated daily flow of water not consumed in the power plant reservoir and converted the daily production of electrical energy of the FPVP from 7:00 a.m. to 5:00 p.m. into an equivalent flow of turbinate water in 12 scenarios. These amounts of water are essential during long periods of drought.

The HPP turbinated flow before and after hybrid operation with FPVP in the wet season (December, January, February, March, and April). The reduced HPP turbinated flow is relevant for sunny and cloudy scenarios; 1 (5,924,217,654 m³dˉ¹), 2 scenarios, there is a considerably reduction in the HPP turbinated flow; 3 (6,388,855,517 m³dˉ¹), and 6 (5,928,547,947 m³dˉ¹), as shown in Figure 8.

Figure 8.

Statistical water storage scenarios for the wet period

The dry season (May, June, July, August, September, October, and November) is relevant for sunny and cloudy scenarios; 7 (8,234,177,000 m³d^-1), 8 (8,427,091,824 m³d^-1), 10 (4,817,499,348 m³d^-1), and 11(5,018,635,289 m³d^-1). Even in the rainy scenarios, there is a considerably reduced HPP turbinated flow; 9 (8,620,006,608 m³d^-1) and 12 (5,219,771,230 m³d^-1), as shown in Figure 9.

Figure 9.

Statistical water storage scenarios for the dry period

There is an improvement in the system, as the amount of turbine water is reduced for power generation after the joint operation of the HPP and FPVP systems, with the effect observed in both wet and dry periods, as shown in Figure 10.

Figure 10.

Daily water flow before and after Hydroelectric Power Plant and Floating Photovoltaic Plant integration

Emissions of greenhouse gases (GHGs) (atmospheric substances that cause global warming and climate change) are crucial to understanding and solving the climate crisis [25]. Although most GHGs are released naturally, human activities are also causing an increase in the amount of GHG concentrations in the atmosphere, which can result in adverse effects on the climate, including an increase in the frequency and intensity of extreme weather events such as floods, droughts, fires and hurricanes that affect thousands of people and cause economic damage [26]. The CO₂ Balance (or Carbon Footprint) is a measure of the total amount of carbon dioxide emissions that are direct or caused by production activities (ordering, manufacturing, transportation, distribution, and recycling) or people (consumption, leisure, travel, and disposal) [27]. The carbon footprint also expressed as pure CO₂ or CO₂ equivalent (CO₂ eq) [25].

The FPVP does not emit greenhouse gases (GHGs). However there are some emissions into the atmosphere during panel manufacturing, installation, and maintenance [8]. Determining whether this technology can help protect the environment requires establishing the carbon footprint, which is responsible for accounting for the net carbon inputs and outputs from energy activities [28]. This carbon footprint study is based on a simulation performed in the PVsyst software, considering a system operating lifetime of 30 years. The estimated photovoltaic electricity generation is 684,684.24 MWh/yr and the CO₂ emissions from the life cycle of the devices that make up the photovoltaic system at 8,670.89 t CO₂/yr. Thus, the CO₂ emissions avoided with the FPVP are 1,663,782.7 t CO₂/yr. The diagram of CO₂ emissions avoided over 30 years is shown in Figure 11.

Figure 11.

Balance of Carbon Dioxide emissions avoided with the use of Floating Photovoltaic Plant

Installation of floating photovoltaic plants (FPVP) involves higher costs compared to photovoltaic plants (PV) in the ground. The investment costs of a conventional photovoltaic plant (PV) and a floating photovoltaic plant (FPVP), whose prices are higher due to the floating structure and monitoring system. The *CAPEX and **OPEX of (FPVP) are almost 20% higher for floating structures [17] [29]. On the other hand, the necessary cost of land acquisition and transmission system for ground (PV) is not considered compared to the cost of transmission of FPVP installed in the lake of the reservoir of an HPP and connected to the existing transmission system, as shown in Table 2.

The total investment cost (CAPEX) required for the implementation of a 480 MWp floating photovoltaic plant (FPVP) in the reservoir lake of the Ilha Solteira hydroelectric power plant (HPP), is shown in Table 3.

The total investment cost (OPEX) required for the operating expenses on equipment maintenance of a 480 MW_p floating photovoltaic plant (FPVP) in the reservoir lake of the Ilha Solteira hydroelectric power plant (HPP), is shown in Table 4.

The calculation of the investment return (ROI) is crucial. The analysis carried out concerning the cost of implementing the technology regarding the benefit obtained. That is, the result obtained demonstrates how long the benefits will equal the investment. Considering the valuable life of the system of 25 years, and the average price of photovoltaic energy of US$1695/MWh, according to the Electric Energy Commercialization Chamber. The production of electricity from solar sources is 684,864 MWh/yr, calculated in the PVsyst, and the project's total investment of US$350,400,000.00, it will take the FPVP system 13 years to start producing a profit, as shown in Figure 12.

Figure 12.

Return on investment