Solar energy even after the sun goes down: the two technologies vying for the attention of the government and companies to see who will keep Brazil illuminated at night

Solar energy is growing unchecked in Brazil, but excess production during the day becomes waste and threatens the electrical system at night. Megabatteries and reversible hydroelectric plants are vying to see who will save the country from energy collapse.

Solar energy has gone from being a promise to a reality in Brazil. In just a few years, the country has become… produce electricity at such a fast pace that, ironically, it began to throw some of it away. Yes, to waste it.

Today, solar panels already account for about 23% of the country’s electricity generation capacity, an impressive leap compared to just 2% recorded in 2019. 

Furthermore, at midday, when the sun is strongest, 44% of all electricity in Brazil comes from solar energy. It’s a number that is both startling and worrying.

The reason is simple: the electrical system wasn’t designed to handle so much electricity at once. Therefore, the National System Operator (ONS) is obligated to cut part of the production, a practice known as… curtailment. 

The result? About 20% of all solar and wind energy ready to go into the grid ends up being wasted every day.

Meanwhile, at night, when the sun disappears, the scenario is reversed. There is a lack of electricity. And the question that drives billions of reais now is straightforward: where to store the surplus solar energy from the day to use when we need it most?

The government’s plan: to turn excess solar energy into money.

To try to resolve this silent chaos, the federal government is preparing the first power reserve auction, scheduled for April. In practice, this means encouraging companies to create large energy storage systems.

The goal is simple and powerful: buy cheap solar energy during the day, when there is a surplus, and sell it at night, when it is scarce and more expensive.

This logic opens up space for a new type of business in the electricity sector. And two technologies are competing for this billion-dollar market: lithium megabatteries and reversible hydroelectric plants.

Megabatteries: the fast track to saving solar energy

Mega batteries, known in the industry as BESSs, function like enormous electricity vaults. They use lithium batteries, the same ones used in electric cars, but on a gigantic scale.

During the day, they buy excess solar energy that would otherwise be wasted. At night, they return this energy to the grid and sell it for a higher price. It’s a simple and extremely profitable operation.

The growth of this technology is explosive. In 2023, the world had 91 GW of battery capacity. By 2025, that number had already reached 270 GW, a leap equivalent to seven Itaipu hydroelectric plants in just one year.

This progress was only possible because the price of batteries plummeted. By 2025, they cost 55% less than in 2023, making lithium storage cheaper than many hydroelectric plants.

Furthermore, a battery system can be installed in a few months. A hydroelectric dam, on the other hand, takes years.

Therefore, the government auction targets precisely this model: the goal is to store 2 GW of energy, half of what Brazil currently wastes due to cuts in solar and wind power.

The hydroelectric plant that “rewinds” the sun.

But mega-batteries are not alone in this competition. There is an older technology, little known in Brazil, but used in 42 countries: reversible hydroelectric power.

It functions like a power plant that runs backward.

During the day, when there is surplus solar energy, the plant uses this electricity to pump water from a lower reservoir to a higher one. At night, this water flows down, passes through the turbines, and generates electricity again.

It’s as if the hydroelectric plant stores the sun in the form of water.

Today, 15% of all the world’s hydroelectric power comes from this type of plant, especially in countries like China, the United States, and several European nations.

In Brazil, none yet operate in this format. But that could change. Copel, from Paraná, plans to build the first one, with 70 MW, enough to supply a city of 200 inhabitants.

According to the company, it is also possible to adapt older plants to this model. “We can make a complementary investment in the hydroelectric plants we already have, installing new machinery. All this with the advantage that hydroelectric plants last 50 years, 100 years,” said Diogo Mac Cord, VP of Copel.

Another point in its favor is geography. “What do you need for reversible hydroelectric power? You need water – not a lot – and you need a drop in elevation. And there are very good drops in the entire coastal region: Rio de Janeiro, São Paulo, the Northeast…”, stated Amílcar Guerreiro, former director of EPE.

Batteries or hydroelectric power: who will win the solar energy war?

Megabatteries are fast, cheap, and easy to install. But they last 15 to 20 years and provide power for only 2 to 4 hours.

Reversible hydroelectric plants, on the other hand, can operate for decades and release electricity for more than 10 hours at a time.

In practice, this means that the two technologies can coexist. In some regions, batteries will be the best solution. In others, hydroelectric power will be unbeatable.

What is clear is that solar energy has ceased to be just an environmental solution. Now, it has become the center of a billion-dollar dispute that could define the future of electricity in Brazil.

And you, do you think Brazil should invest more in mega-batteries or hydroelectric plants to avoid wasting solar energy and the risk of blackouts at night?