battery system would cost $63,000. But two weeks before installers were scheduled to show up, an email from the company raised the price to $85,000.

She wanted the system to protect her family from losing electricity when her utility, Pacific Gas & Electric, shuts off power to prevent its equipment from setting off wildfires. She also hoped to lower her electricity bills, which have jumped from about $200 a month to as much as $400 in the four years since her family moved to California from New York.

She sought out Tesla’s shingles because contractors had told her that they could not attach conventional solar panels to her composite roof.

Tesla never offered an adequate explanation for the price change, Ms. Bianchi said, so she canceled the job: “It’s just outrageous.”

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