Opponents of a proposal by Georgia Power to add more biomass to the utility’s electrical generating portfolio argued Thursday the plan is both unreliable and too expensive. Georgia Power is seeking approval from the state Public Service Commission (PSC) to buy about 80 megawatts of electricity from three plants in South Georgia that burn wood chips from waste generated by logging operations.

If there’s one thing Georgia has a ton of — actually a billion tons — it’s trees. The state leads the country in acres of private timberland and volume...