Following news that an online tool by APS funneled thousands of customers to costlier plans, a new study reveals that time-of-use tariffs can unduly harm certain vulnerable groups.

Time-of-use rates charge more for energy during high-demand hours, incentivizing customers to change their usage patterns.

Now, a study in the journal Nature Energy suggests such rates unduly drive up costs for households with elderly and disabled occupants.

The survey of 7,000-plus domiciles in the southwestern U.S. also ties such rates to worse health outcomes for disabled and ethnic minority occupants.

Previous research has shown elderly people require specific, narrow temperature ranges to remain healthy.

Low-income households frequently try to save money by reducing heating or cooling, often with negative health consequences, and are more likely to live in inefficient buildings that cost more to heat and cool.