Comision Federal de Electricidad (CFE), Mexico's state-owned utility, said the massive blackout on December 28, 2020 was caused by fire and renewable energy. The blackout caused 10.3 million consumers to lose power for nearly two hours.

At a news conference on Tuesday, CFE, led by director general Manuel Bartlett, said the blackout itself was caused by a fire in the northeastern state of Tamaulipas. With the help of strong winds, flames burn shrubs and grasslands, sending smoke, hot air and ashes to overhead lines.

As a result, two 400 kV lines connecting Tamaulipas and Nuevo Leon were shut down within one minute. Cenace, the Mexican power grid and electricity market operator, also revealed that more than 9000 megawatts of fossil fuel and renewable energy power plants have been shut down protectively.

According to CFE, the event occurred when the system demand was 32000 MW, which was very low in the last week of the year. Meanwhile, the share of wind and solar power generation is 28%, the highest ever.

However, when the power grid needs to be restored, intermittent energy such as renewable energy can not be restored directly, resulting in prolonged power restoration time.

Like Tamaulipas, where a large number of wind and solar farms are concentrated in one area, there are not many plans to consider the resilience of the grid. CFE spokesman Luis Bravo Navarro said that although it is normal for a small part of the transmission line to fail due to force majeure, blackouts are more common in Mexico due to "excessive intermittent power generation".

According to projects approved by the Energy Regulatory Commission (CRE), Mexico's intermittent power generation capacity (wind and solar) is expected to double in the near future, which will increase the reliability risk of the entire national system.