The increase in renewable energy production plays a crucial role in reducing carbon emissions and expanding the variety of energy sources globally. In this scenario, the use of hybrid power plants emerges as an effective approach to maximize renewable resources, while energy storage systems play a crucial role in mitigating fluctuations in the availability of these energy sources.

Brazil enjoys a privileged position globally when it comes to hydropower generation. According to data from the National Energy Plan (PNE) 2030, the country holds the third-largest hydropower potential in the world, accounting for 10% of this resource, behind only China (with 13%) and Russia (with 12%).

Currently, the country has a total installed capacity of 187.7 GW, according to information from the 

, and there is still a considerable hydropower potential of 137 GW to be explored. It is important to note that a substantial part of this hydropower potential has already been exploited and converted into power plants.

1. Scarcity of Rainfall and Reduction in Hydropower Generation

In recent years, Brazil has faced a series of droughts that have highlighted the country's need for complementary renewable resources to mitigate energy risks resulting from a scarcity of rainfall. In 2021, only 66.3 GWh were generated, marking the lowest energy production in 26 years (Itaipu Binacional, 2021).

2. Changes in the Energy Generation Complex

Additionally, significant changes in the energy generation complex are altering the structure of the national electrical grid. The Decennial Plan for National Energy Expansion indicates that wind and solar energy will experience growth of over 30% by 2030.

According to research by the Brazilian Photovoltaic Solar Energy Association (Absolar), the operational installed capacity of solar energy reached 23.9 GW in 2022, surpassing wind energy, with 23.8 GW, thus becoming the second most representative source in the national electricity matrix.

1. Difficulties in Meeting Energy Demands

Given this scenario, the Brazilian electrical system will face new challenges in the coming years. An example is the increasing difficulty in meeting hourly energy demands due to the reduction in the capacity to regulate hydropower reservoirs, along with the unpredictability of these uncontrollable alternative energy sources, such as wind and solar.

Marginal Operating Cost (MOC) Load Level by Subsystem | Source: ONS (2022b)

2. Synergy between Photovoltaic Energy and Hydropower Plants in Brazil

If a hydropower plant is located near a photovoltaic energy plant, there is an opportunity for these two sources to work together, thus expanding the quality of energy generation and providing competitive advantages over other intermittent sources. This solution for hydropower plants allows for greater predictability and energy generation time.

The real growth of solar energy, which totaled in January 2022 and represented 11% of the total load in the National Interconnected System (SIN), significantly exceeded the Ref. projections, which predicted less than 0.2% of SIN. Another segment that demonstrates robust growth in solar energy is related to hybrid power plants, which can be associated with hydropower plants, quite common in Brazil.

Additionally, Deng et al. explored the growing competition of solar energy due to cost reduction and its combination with hydropower, being a more reliable energy source. Their results indicated that the ideal installed capacity ratio varies depending on the characteristics of the hydropower plant, providing valuable information to optimize economic performance, based on case studies in Africa.

Development of Methodologies for Hydro-Photovoltaic Projects

Furthermore, Zhang et al. developed a methodology resulting in an optimized grid-connected hydro-photovoltaic (PV) project, emphasizing joint short-term operations for hydro-PV. In a case study in China, the results demonstrated the feasibility of the proposal; more specifically, the research highlighted a significant expansion in energy transmission capacity, achieving maximum utilization.

The combination of hydropower and PV in an energy generation system is projected to become more flexible with the expected cost reduction over the next few decades.

These approaches can reduce plant costs in areas with low hydropower potential, where interconnection costs may be project obstacles.

It has been observed that reducing energy supply failures is associated with greater complementarity of elements for renewable energy production. Preliminary results demonstrate that complementarity can be used to design more efficient hybrid generation systems.

Considering errors in projections, solar energy tends to be higher than expected, indicating a lower future energy capacity, reinforcing the need for investment in energy storage technologies, such as pumped hydro storage (UHR).

From an energy production perspective, UHR is essentially traditional hydropower generation, associated with a pumping station, and is therefore considered an integrated technology, both renewable and low operational cost. On the other hand, some aspects are clearly different from conventional hydropower applications, such as arrangement concepts, operational criteria, and functions performed by the electrical system.

Pumped storage energy plants consist of two reservoirs located at different levels and connected by an intake system and a set of reversible machines. These machines operate as pumps and turbines in the following cycle: during peak hours, water flows from the upper reservoir to the lower one, driving the electrical generator through the hydraulic turbine. During periods of low consumption, water is pumped back to the upper reservoir for reuse during periods of high energy consumption.

Benefits of Pumped Storage for the Brazilian Electrical Grid

Pumped Storage (UHR) can produce complementary energy, meet peak energy demand, and facilitate the use of transmission systems. These factors favor a better balance between demand and generation in the National Interconnected System (SIN).

In this sense, the adoption of UHR can mitigate the intermittency of renewable energy sources, such as wind and solar, thus increasing energy security through decentralization of energy storage, which is currently predominantly concentrated in the southeast region of Brazil.

Hydraulic pumping systems can increase water availability for multiple water uses and contribute to the decentralization of energy storage, thus offering greater energy security.

Like other energy storage systems, UHRs still do not have their own regulatory licenses in Brazil. Although the country has great hydropower potential, new Small Hydropower Plants (SHPs) projects are planned without considering the formation of reservoirs to preserve the environment. Additionally, they do not have storage capacity and operate according to the natural flow of rivers and, due to these characteristics, are called "run-of-the-river" plants.

Thus, the operation of the Brazilian energy system has become increasingly dependent on favorable rainfall. Thus, with climate change and the increasing participation of intermittent sources, such as solar and wind, the country's generation system is becoming more susceptible to insecurities and failures every day.

Brazil has great hydropower potential and many power plants. Therefore, it becomes increasingly important to ensure the reliability of the system, especially considering that the risk of energy shortages is likely in times of lower water availability. Given that the country already has numerous reservoirs, there is greater potential for the installation of UHR technology to replenish reservoir levels throughout the country.

Hybrid power plants have become an effective solution for maximizing renewable resources and mitigating distribution fluctuations.

Solar Energy as a Complement to Brazilian Hydropower

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