The U.S. electrical grid is better managed and more flexible a decade after its largest blackout but remains vulnerable to increasingly extreme weather, cybersecurity threats, and stress caused by shifts in where and how power is produced.

Many worry the grid isn’t fully prepared for the new and emerging challenges, even though an analysis conducted for The Associated Press shows maintenance spending has steadily increased since North America’s largest blackout.

“This job of reliability is kind of impossible, in the sense that there’s just so many things that could happen that it’s hard to be sure that you’re covering all the bases,” said William Booth, a senior electricity adviser with the U.S. Energy Information Administration.

The industry has mostly addressed the failures blamed on a tree branch in Ohio that touched a power line and set off outages that cascaded across eight states and parts of Canada the afternoon of Aug. 14, 2003, darkening computer screens, halting commuter trains, and cutting lights and air conditioners for 50 million people. Grid operators who didn’t initially realize what was happening now have a nearly real-time view of the system and are better equipped to stop problems from growing. Utilities share more information and systematically trim trees near high-voltage power lines.

Electricity customers have been giving the grid a bit of breathing room. Power demand has remained flat or even fallen in recent years as lighting, devices, appliances, homes and businesses have gotten more efficient and economic growth has been sluggish. All that reduces stress on the grid.

At the same time, aging coal and nuclear plants are shutting down in the face of higher maintenance costs, pollution restrictions and competition from cheap natural gas. Renewable generation such as wind turbines and solar panels is being installed, adding power that’s difficult to plan for and manage.

Temperatures and storms are getting more extreme, according to federal data, and that increases stress on the grid by creating spikes in demand or knocking out lines or power plants. Some regulators and policymakers are increasingly worried about cyberattacks that could target systems that manage power plants or grids.

“The grid that exists today wasn’t designed for what everybody wants to do with it,” says Joe Welch, CEO of ITC Holdings Corp., the largest independent transmission company in the U.S.

The electric power industry did respond directly to the issues that sparked the blackout. An analysis of spending on maintenance and transmission equipment by more than 200 utilities nationwide conducted for the AP by Ventyx, a software and data services firm that works with electric utilities, shows that spending rose sharply in the years after the blackout.

The number of miles of transmission line remained roughly the same, suggesting new money was mostly spent on equipment to make the existing system stronger and more responsive, according to Ventyx analyst Chris Tornow.

Those higher transmission costs have trickled down to customer bills, but they’ve been largely offset by lower electricity prices, thanks to cheap natural gas. Since 2003, average residential power prices have risen an average of 0.85 percent per year, adjusted for inflation, according to the Energy Information Administration.

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