In Mississippi Power’s first integrated resource plan, solar was not selected in any scenario until 2027, and did not show up in most scenarios until 2032, according to the advocacy group Southern Renewable Energy Association (SREA).
No battery resources were added in any scenario through 2031, and wind power was excluded from the modeling, the group said.
“Looking across the scenarios, does the Mississippi Public Service Commission really believe that zero renewable energy sources will be developed in the state for the next decade?,” asked SREA Executive Director Simon Mahan in formal comments. He said that “any reasonable analysis” would find that outcome “highly improbable and undesirable for Mississippi ratepayers.”
Solar facilities are achieving 20-25% capacity factors, comparable to the fossil facility’s 21% capacity factor, SREA said.
SREA said that because Mississippi Power is in the Southern Company’s power pool, its avoided costs are summertime afternoon peaking costs “even though the utility claims to be a winter peaking utility.”
The omission of solar until 2031 showed that either the utility’s modeling did not allow solar to be selected in the near term, said SREA, or that the model did not find opportunities to reduce costs by lowering the dispatch of existing fossil units, or retiring them altogether.
“Either problem should cause major concern regarding validity of the resource plan results,” SREA said. The group called on Mississippi regulators to reject the utility’s plan.
Mississippi Power is a subsidiary of Southern Company and serves southeast Mississippi. SREA said that only one of the utility’s modeled scenarios, the “carbon intensity” scenario that would add 390 MW of solar in 2027, “would come close to achieving Southern Company’s net zero carbon commitment.” The group called for adding at least that much solar by 2027.
Room for improvement
SREA also challenged Mississippi Power’s choice to assign a 0% capacity value to solar. The group said that grid operator Midcontinent Independent System Operator (MISO) assigns a capacity value of 50% to solar and 15% to wind power. Combining these resources and adding energy storage would increase overall capacity value across all seasons, SREA said, citing MISO research.
Overall, SREA listed 16 “significant deficiencies” in Mississippi Power’s IRP, including:
- Not benchmarking generation costs—for example, for renewables and battery storage—against the National Renewable Energy Laboratory’s Annual Technology Baseline.
- Assuming battery capital costs were higher than the utility’s evaluation of reported estimates.
- Not using sub-hourly modeling, which can capture the value of storage and hybrid (solar+storage) resources.
- Offering “no plans” to issue an all-source request for proposals for renewable energy resources.
SREA also made 11 recommendations that it said would help regulators “protect ratepayers against poor resource planning in the future.”
SREA said Mississippi Power’s action plan only covers decisions already approved by state regulators or the company itself, concluding that the IRP process “appears to have had no effect” on the utility’s future plans.
The Southern Alliance for Clean Energy also filed comments on the resource plan, focused on demand side management issues. A filing from the Sierra Club focused on coal plant retirement and transparency in resource planning.
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