Georgia utility regulators approved a plan Thursday that would shut down a number of Georgia Power Co.'s coal-fired power plants, but not before postponing the death warrant for two units.

The vote came as the Georgia Public Service Commission approved Georgia Power's plan to meet electricity demand from its 2.7 million customers over the next 20 years.

The five Republican commissioners also voted to require the unit of Atlanta-based Southern Co. to increase its investment in energy efficiency and created a process that could lead to an outside contractor building large batteries to store renewable energy until it's needed on the grid.

However, commissioners on a 3-2 vote turned back an effort to expand by 75,000 the cap on the number of rooftop solar panel installations where Georgia Power pays a high rate for power generated. Instead, commissioners voted for a study of the costs and benefits of rooftop solar to be done by the time they vote on a rate increase for Georgia Power in December, leaving the number of participants frozen at the current level of 5,000 until then.

"We simply do not have the cost information necessary to set just and reasonable rates, terms and conditions for rooftop solar," said Commissioner Jason Shaw, citing Georgia Power's disputed contention that rooftop solar customers unfairly shift costs onto less affluent customers who don't have solar panels.

Georgia Power must file the integrated resource plan every three years. Last month, Georgia Power filed for a 12% rate increase, driven in part by the need to pay for the investments.

The commission is scheduled to vote on the rate plan in December. If approved, a residential customer who uses 1,000 kilowatt hours of electricity per month would see their bill increase from $128 now to $144.29 at the end of three years.

Southern Co. has set a goal of 2050 to be a net-zero emitter of gases that cause global warming, mostly carbon dioxide. Environmentalists want the company to move more quickly.

Thursday's vote will close all other coal-fired units by 2028, some within weeks. But commission staff, the company and industry groups reached a deal that would actually keep two coal-fired units at Plant Bowen near Cartersville alive longer, driven in part by concerns over high natural gas prices, how much customers will pay to retire coal plants, and concerns about maintaining reliable electricity for metro Atlanta. Even though Georgia Power said the Bowen units are money losers, the commission will reevaluate in 2025 whether they should be closed.

The commission approved plans for Georgia Power to contract with Southern Power, another subsidiary of its parent company, for 2,400 megawatts of natural gas-generated electricity from 2022 to 2028. That would help Georgia Power bridge coal plant shutdowns with a form of power that still emits carbon, but less than burning coal. Some groups opposed the move, saying it was self-dealing that would leave customers paying for unneeded capacity that is dirtier than wind or solar.

The company says it would add 2,300 megawatts of renewable power by 2025 and a total 6,000 megawatts by 2035, although advocates had pushed for a more in the short term. Commissioners nixed a plan for ratepayers to cover the cost of a pilot program to test supertall wind turbines in the state, saying customers shouldn't pay for an experiment. They added a call for Georgia Power to seek generation from biomass, which often means burning wood pellets, and added a call for contractors to be able to bid on building 500 megawatts of batteries that Georgia Power would operate, in addition to a 265-megawatt facility Georgia Power will own. The batteries could store solar and wind-generated electricity when there is surplus power on the grid and release it later.

The plan says nothing new about Georgia Power's plans to clean up coal ash ponds at various locations statewide. The company had been planning to cap some of them in place, but the U.S. Environmental Protection Agency has recently said that is a misinterpretation of federal rules, despite approval by Georgia's Environmental Protection Division, and that utilities must dig up all coal ash and store it in lined landfills where toxic heavy metals can't seep into groundwater.

The company said it would seek to renew its license to operate the Hatch nuclear plant near Baxley. Georgia Power also said it would seek permission to overhaul three hydroelectric generating plants at Lake Sinclair, Lake Burton and the North Highlands Dam on the Chattahoochee River in Columbus.