LOS ANGELES — Pacific Gas and Electric promises that its customers’ lights will stay on if it follows through on plans to file for bankruptcy this month. But companies that supply the California utility’s electricity may have more to worry about.

PG&E said Monday that it would use bankruptcy to resolve huge liabilities arising from two years of deadly wildfires. Such a move would allow the company to try to revoke or renegotiate contracts it signed with suppliers when power prices were higher than they are now. That, analysts said, could hurt companies that borrowed based on the higher prices — especially those whose power comes from renewable resources.

That prospect was underscored this week when credit-rating agencies downgraded the debt of Topaz Solar Farms, which is owned by a unit of Warren E. Buffett’s Berkshire Hathaway and whose sole customer is PG&E, and Genesis Solar Farm, a large project in the Mojave Desert developed by NextEra Energy. Both companies said they were operating normally, but were monitoring PG&E’s problems closely.

“People often think utilities are safe investments, but this is such a crazy situation,” said Daniel Lowenthal, a partner at the law firm Patterson Belknap Webb & Tyler who specializes in bankruptcy and corporate restructuring, referring to PG&E’s suppliers, shareholders and lenders.