Ameren Missouri hopes to be generating electricity by the end of the year from a new solar farm near O'Fallon in St. Charles County.
The five-member Public Service Commission unanimously approved the proposal Tuesday morning.
When finished, the 5.7-megawatt "farm" should provide enough electricity for more than 60,000 homes, commissioners said.
"It covers 19 football fields," Warren Wood, Ameren Missouri's vice president for legislative and regulatory affairs, said after the commission's vote. "It's about 19,000 panels.
"It probably will generate from 18 to 20 percent of the time," which means it won't be a steady source of electricity.
And it won't help at peak consumption times, because those tend to be in the morning and evening when the sun's power isn't as strong.
"It operates when the sun shines," Wood explained. "When it's generating, it's good for offsetting other resources like gas-fired power or purchased power."
It will help Ameren meet the state's voter-approved renewable energy requirement, that 15 percent of a utility's power come from renewable sources.
Ameren also gets electricity from a wind farm in Iowa, and from water-powered turbines at Bagnall Dam at the Lake of the Ozarks and from a dam across the Mississippi River at Keokuk, Iowa.
And during peak-load times, Ameren generates electricity by draining water from the Taum Sauk Reservoir in Southeast Missouri and running it through turbines at the base of the mountain.
Wood said building the solar farm also is a response to consumers who tell the company: "We'd like to see you diversify your energy portfolio and go to cleaner energy resources" while not driving up the costs.
The commission's vote approving the solar farm came shortly after Ameren Missouri leaders reported on major improvements to the utility's service reliability.
Last year was the company's best-ever, with the number of "extended outages per customer" dropping to 0.7.
That puts Ameren's service among the nation's top 10 percent of utilities.
But David Wakeman, Ameren's new senior vice president for Operations and Technical Services, told commissioners: "That .7 is still 800,000 outages."
And Michael Moehn, Ameren's new chairman, president and CEO, said the company wants to reduce that number even more.
"Customers certainly are becoming less tolerant of any sort of disruption of reliability," Moehn said.
Moehn said the company checks its lines and poles on a regular basis, making sure trees and other vegetation are cleared back so they don't cause additional damage or outages, and replacing poles and wires as needed.
Wakeman noted that, even though performance has improved substantially in the last six years, "When we look at the whole system, it doesn't mean there aren't continuing, repeating problems."
Wood said delivering the reliability report is part of the company's communication with the officials who regulate it.
"A lot of the dollars in our budgets go into those efforts, and we want to make sure the commission sees that those rules they worked on are achieving great success," he said.
Company officials noted that major storms - like the Joplin tornado, the Southeast Missouri ice storm or the East Coast's Hurricane Sandy - are not included in calculating a utility's service reliability, but smaller storms are a part of the statistics, including last week's tornado that caused some property damage and shut off power in University City.
Wood explained: "If you had a huge storm, with a big tornado of say, 70-, 80- or 90-mph winds, you might lose a third of the customers on your system - and a lot of your customers might have multiple failures."