Lights returned to households as well as to Puerto Rico's hospitals, water plants and sewage facilities after the massive outage that exposed the persistent electricity problems plaguing the island.

Triple-digit temperatures are expected as energy officials warn the electrical load on Tuesday could reach the state's highest demand ever. Four deaths were reported as multiple wildfires burned.

Power outages are increasingly common, putting everything from clean drinking water to medical equipment at risk. Some communities are installing solar power and large batteries to protect themselves.

From potential long-term rate hikes to repairs of broken pipes, Texans could be paying for years after the state's devastating blackouts.

"When you've not had power for 3 1/2 days ... you begin to question whether [blackouts] are rolling at all," says Mansfield Mayor Michael Evans.

Texas Gov. Greg Abbott deployed the Texas National Guard to move people without heat and power into shelters.

Extreme heat waves are on the rise, but California regulators didn't plan for what that would do the state's electricity grid.