Consumers Energy, Michigan's largest utility, said its extensive underground storage system helped save its natural gas customers about $295 million during last winter's polar vortex.

In a statement Monday, the utility, the principal subsidiary of CMS Energy, said it plans to invest more in its storage system, which serves 1.7 million homes and businesses. Although it did not disclose the amount of the additional investment, the utility said it would go toward increasing the system's "safety, deliverability and flexibility," adding that storage provides more than 50% of its gas supply in winter, increasing to 80% on the coldest days. The system includes 15 storage fields.

"Our storage system, one of the largest in the U.S., protected homeowners and businesses from higher heating bills last winter," said Tim Sparks, Consumers Energy's vice president for energy supply operations. "Gas prices are still historically low -- lower than they were five or 10 years ago. The average home spends $3 a day throughout the year for natural gas."

Consumers Energy provides gas and electricity to 6.5 million residents and serves all 68 counties in Michigan's Lower Peninsula.