What happens when a reservoir operates at dead volume? 

The sequence of drops in the level of Brazilian reservoirs sent a warning signal throughout society for a likely energy rationing in the country, even with the Federal government vehemently denying the possibility and activating thermoelectric plants to guarantee supply to the population.

The fact is that, regardless of any situation, only in the last week two hydroelectric plants that make up the Southeast/Central-West subsystem – responsible for storing around 70% of water in the country – started operating at dead volume, a negative record that tends to worsen due to the lack of rain.

Despite this, a question that is still little understood by people is: what does it mean to say that a hydroelectric plant operates in dead volume and what really happens when these projects start operating in these adverse conditions?

To answer these questions, the Canal Solar spoke with Paulo Cunha, researcher at FGV (Fundação Getúlio Vargas) and former technical director of ABRACEEL (Brazilian Association of Energy Traders). The professional explained that the dead volume is a term used to refer to the moment when the water in the dams drops below the catchment level.

In other words, it is water that was not programmed to be used on a daily basis, but which functions as a kind of “savings” in case of emergency. “The reservoir is like a large water tank, which has different height levels,” he commented.

Cunha also explained that a large plant is capable of keeping its operation running, but that this is far from ideal. “Capturing at deeper levels does not guarantee water quality, because it will be mixed with contaminants and elements that do not allow adequate use of the resource,” he said.

“This is what dead volume means. It is the volume of water that is below the level that is not considered suitable for use,” he pointed out. “The more you operate under these adverse conditions, the more difficult it becomes to replenish the volume in the next rainy season,” he emphasized.

The professional also points out that reservoirs that operate close to their limit, in addition to running the risk of drying up, may also have their operating system damaged. “If a plant operates in a region where the level is so low that the water quality is already beginning to deteriorate, you start to introduce an operational risk to the machines themselves, which is not yet our case,” he stressed.