Millions of Californians will soon pay more for electricity during periods of high demand, thanks to a new policy that will begin in March.

The California Public Utilities Commission, which regulates the state's utilities, will require all major utilities to boost electricity prices during weeknights between 4 p.m. and 9 p.m., according to Stateline . Utility companies, including Southern California Edison, Pacific Gas & Electric and San Diego Gas & Electric, will lower costs during non-peak hours, meaning that customers can save money if they avoid using electricity in the evenings. Costs will also vary by season , with higher rates in the summer and lower rates over the winter.

Officials hope the new regulation, known as time-of-use pricing, will curb the high demand for electricity in the evenings when people are returning home from work. When millions of residents increase their electricity use at the same time, utility companies are often forced to activate additional generators that rely on fossil fuels and release greenhouse gases. Electricity is also more costly to produce during this time.

Stateline reported that the new policy --which applies to investor-owned utilities and will impact around 6 million Californians-- will first be enforced in San Diego and Sacramento, and will take effect in Los Angeles and San Francisco in 2020.

Individual utility companies in other states, including Arizona and Tennessee, use time-of-use pricing, but California is the first state to adopt this method for all major utilities.

Barbara Alexander, a consumer affairs consultant on utility issues, told the publication that the time-of-use-pricing model can benefit customers who can set timers on their air conditioning units.

"But there are other customers who are maybe renting, who are low-income, who are working class, who have old appliances, and may not be financially, economically or even intellectually capable of monitoring their energy use on an hourly basis," she said.

Notably, customers will be able to opt-out of time-of-use pricing, so they don't have to follow the new model if they see their bill go up. And those who rely on programs for financial assistance or medical devices are exempt from the new policy.

But a study published in December by Ohio State University revealed another potential issue with time-of-use pricing: many customers don't understand exactly how to minimize their electricity use, and they aren't good at estimating how much money they will save by changing certain behaviors.

The researchers looked at data from nearly 9,000 customers of a large power utility who participated in a pilot where they tested different time-of-use models. Results showed that participants thought they were saving far more money than they were.