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Summary of significant accounting policies (Tables)
 12 Months Ended
Dec. 31, 2024
Accounting Policies [Abstract]  
Schedule of sales to members
Sales to members were as follows:
(dollars in thousands)
202420232022
Capacity revenues$1,501,903 $1,082,368 $984,036 
Energy revenues643,619 599,198 990,647 
Total$2,145,522 $1,681,566 $1,974,683 
Sales to non-members were as follows:
(dollars in thousands)
202420232022
Energy revenues$34,753 $44,995 $155,372 
Capacity revenues1,572 13,624 82 
Total$36,325 $58,619 $155,454 
Schedule of members whose revenues accounted for 10% or more of total operating revenues
The following table reflects members whose revenues accounted for 10% or more of our total operating revenues in 2024, 2023 or 2022:
202420232022
Jackson EMC18.0 %15.1 %16.0 %
Cobb EMC9.0 %11.4 %9.5 %
GreyStone Power Corporation, an EMC9.3 %8.5 %10.0 %
Schedule of sales to non-members
Sales to members were as follows:
(dollars in thousands)
202420232022
Capacity revenues$1,501,903 $1,082,368 $984,036 
Energy revenues643,619 599,198 990,647 
Total$2,145,522 $1,681,566 $1,974,683 
Sales to non-members were as follows:
(dollars in thousands)
202420232022
Energy revenues$34,753 $44,995 $155,372 
Capacity revenues1,572 13,624 82 
Total$36,325 $58,619 $155,454 
Schedule reflecting details of asset retirement obligations included in the consolidated balance sheets
The following table reflects the details of the asset retirement obligations included in the consolidated balance sheets for the years 2024 and 2023.
(dollars in thousands)
NuclearCoal Ash PondOtherTotal
Balance at December 31, 2023$929,804 $463,967 $65,166 $1,458,937 
Liabilities incurred65,149 — — 65,149 
Liabilities settled— (21,593)(1,700)(23,293)
Accretion49,307 17,109 2,807 69,223 
Deferred accretion— (142)— (142)
Change in cash flow estimates(232,021)(56,171)(2,561)(290,753)
Balance at December 31, 2024
$812,239 $403,170 $63,712 $1,279,121 
(dollars in thousands)
NuclearCoal Ash PondOtherTotal
Balance at December 31, 2022$820,106 $461,528 $62,109 $1,343,743 
Liabilities incurred62,841 — — 62,841 
Liabilities settled— (14,445)(76)(14,521)
Accretion46,857 16,558 2,492 65,907 
Deferred accretion— 5 — 5 
Change in cash flow estimates— 321 641 962 
Balance at December 31, 2023$929,804 $463,967 $65,166 $1,458,937 
Schedule of estimated costs of decommissioning of co-owned nuclear facilities Our
portion of the estimated costs of decommissioning co-owned nuclear facilities for which we have recorded asset retirement obligations as of December 31, 2024 are as follows:
(dollars in thousands)
2024 site studyHatch
Unit No. 1		Hatch
Unit No. 2		Vogtle
Unit No. 1		Vogtle
Unit No. 2
Estimated costs based on site study in 2024 dollars:
Radiated structures$234,000 $242,000 $216,000 $226,000 
Spent fuel management95,000 89,000 86,000 82,000 
Non-radiated structures19,000 27,000 31,000 39,000 
Total estimated site study costs$348,000 $358,000 $333,000 $347,000 
(dollars in thousands)
2024 site studyVogtle
Unit No. 3		Vogtle Unit No. 4
Estimated costs based on site study in 2024 dollars:
Radiated structures$195,000 $199,000 
Spent fuel management27,000 29,000 
Non-radiated structures25,000 33,000 
Total estimated site study costs$247,000 $261,000 
Schedule of external and internal trust funds by type of investment
The following table outlines the fair value of our nuclear decommissioning funds as of December 31, 2024 and December 31, 2023. The funds were invested in a diversified mix of approximately 51% equity, 34% fixed income securities and 15% temporarily in cash pending reallocation between equity funds in 2024 and 71% equity and 29% fixed income securities in 2023.
2024
External Trust Funds:(dollars in thousands)
Cost
12/31/2023		Purchases
Net Proceeds(1)
Unrealized Gain(Loss)Fair Value 12/31/2024
Equity$249,063 $169,927 $(75,461)$186,129 $529,658 
Debt195,756 788,109 (781,509)(8,713)193,643 
Other(729)191,247 (192,195)— (1,677)
$444,090 $1,149,283 $(1,049,165)$177,416 $721,624 
__________________
(1)Also included in net proceeds are net realized gains or losses, interest income, dividends, contributions and fees of $100,118,000.
2024
Internal Funds:(dollars in thousands)
Cost
12/31/2023		Purchases
Net
Proceeds(1)
Unrealized
Gain(Loss)		Fair Value 12/31/2024
Equity$86,378 $— $3,257 $40,466 $130,101 
Debt49,320 139,657 (116,098)(2,180)70,699 
$135,698 $139,657 $(112,841)$38,286 $200,800 
__________________
(1)Also included in net proceeds are net realized gains or losses, interest income, dividends, contributions and fees of $26,817,000.
2023
External Trust Funds:(dollars in thousands)
Cost
12/31/2022		Purchases
Net
Proceeds(1)
Unrealized
Gain(Loss)		Fair Value
12/31/2023
Equity$228,936 $29,307 $(9,180)$201,900 $450,963 
Debt192,986 485,705 (482,935)(4,751)191,005 
Other91 20,015 (20,835)— (729)
$422,013 $535,027 $(512,950)$197,149 $641,239 
__________________
(1)Also included in net proceeds are net realized gains or losses, interest income, dividends and fees of $22,078,000.
2023
Internal Funds:(dollars in thousands)
Cost
12/31/2022		Purchases
Net
Proceeds(1)
Unrealized
Gain(Loss)		Fair Value
12/31/2023
Equity$79,122 $— $7,256 $39,134 $125,512 
Debt43,032 59,630 (53,342)(942)48,378 
$122,154 $59,630 $(46,086)$38,192 $173,890 
__________________
(1)Also included in net proceeds are net realized gains or losses, interest income, dividends, contributions and fees of $13,542,000.
Schedule of annual depreciation rates Annual weighted average depreciation rates in effect in 2024, 2023, and 2022 were as follows:
Remaining Useful Life Range in
years*		202420232022
Steam production
18-20
3.04 %3.05 %13.77 %
Nuclear production
10-59
1.88 %1.87 %2.17 %
Hydro production
42
2.00 %2.00 %2.00 %
Other production
15-29
2.71 %2.73 %2.68 %
Transmission
10-59
2.75 %2.75 %2.75 %
General
1-41
2.00-33.33%
2.00-33.33%
2.00-33.33%
__________________
*Based on estimated retirement dates as of 2024. Actual retirement dates may be different.
Reconciliation of cash, cash equivalents and restricted cash The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the
consolidated balance sheets that sum to the total of the same such amounts reported in the consolidated statements of cash flows.
Classification
Twelve months ended
December 31, 2024December 31, 2023
(dollars in thousands)
Cash and cash equivalents$337,813 $490,592 
Restricted cash included in restricted cash and short-term investments500 — 
Total cash, cash equivalents and restricted cash reported in the consolidated statements of cash flows
$338,313 $490,592 
Schedule of regulatory assets and liabilities Regulatory
liabilities represent certain items of income that we are retaining and that will be applied in the future to reduce revenues required to be recovered from members.
(dollars in thousands)
20242023
Regulatory Assets:
Premium and loss on reacquired debt(a)
$21,587 $25,476 
Amortization on financing leases(b)
24,699 28,780 
Outage costs(c)
45,749 30,040 
Asset retirement obligations –  Ashpond and other(l)
268,074 343,523 
Depreciation expense - Plant Vogtle(d)
32,702 34,125 
Depreciation expense - Plant Wansley(e)
337,181 335,884 
Deferred charges related to Vogtle Units No. 3 and No. 4 training costs(f)
54,545 55,159 
Interest rate options cost(g)
130,456 137,463 
Deferral of effects on net margin – TA Smith Energy Facility(h)
124,840 130,786 
Deferral of effects on net margin – BC Smith Energy Facility(p)
27,841 — 
Inventory adjustments - TA Smith Energy Facility(q)
14,723 — 
Other regulatory assets(o)
21,236 10,253 
Total Regulatory Assets
$1,103,633 $1,131,489 
Regulatory Liabilities:
Accumulated retirement costs for other obligations(i)
$29,975 $25,992 
Deferral of effects on net margin – Hawk Road Energy Facility(h)
15,404 16,020 
Deferral of effects on net margin – BC Smith Energy Facility(p)
— 546 
Major maintenance reserve(j)
99,987 120,547 
Amortization on financing leases(b)
— 2,658 
Deferred debt service adder(k)
186,757 170,466 
Asset retirement obligations – Nuclear(l)
102,858 47,217 
Revenue deferral plan(m)
197,373 308,507 
Natural gas hedges(n)
28,624 13,445 
Other regulatory liabilities(o)
614 922 
Total Regulatory Liabilities$661,592 $706,320 
Net regulatory assets$442,041 $425,169 
__________________
(a)Represents premiums paid, together with unamortized transaction costs related to reacquired debt that are being amortized over the lives of the refunding debt, which range up to 19 years.
(b)Represents the difference between expense recognized for rate-making purposes versus financial statement purposes related to finance lease payments and the aggregate of the amortization of the asset and interest on the obligation.
(c)Consists of both coal-fired maintenance and nuclear refueling outage costs. Coal-fired outage costs are amortized on a straight-line basis to expense over periods up to 60 months, depending on the operating cycle of each unit. Nuclear refueling outage costs are amortized on a straight-line basis to expense over the 18 or 24-month operating cycles of each unit.
(d)Prior to Nuclear Regulatory Commission (NRC) approval of a 20-year license extension for Plant Vogtle, we deferred the difference between Plant Vogtle depreciation expense based on the then 40-year operating license and depreciation expense assuming an expected 20-year license extension. Amortization commenced upon NRC approval of the license extension in 2009 and is being amortized over the remaining life of the plant.
(e)Represents the deferral of accelerated depreciation associated with the early retirement of Plant Wansley, which occurred on August 31, 2022. Amortization commenced upon the retirement of Plant Wansley and will end no later than December 31, 2040.
(f)Deferred charges consist of training related costs, including interest and carrying costs of such training. Amortization will commence effective with the commercial operation date of each unit and amortized to expense over the life of the units.
(g)Deferral of premiums paid to purchase interest rate options used to hedge interest rates on certain borrowings, related carrying costs and other incidentals associated with construction of Vogtle Units No. 3 and No. 4. Amortization commenced in August 2023 after Vogtle Unit No. 3 was placed in service on July 31, 2023.
(h)Effects on net margin for TA Smith and Hawk Road Energy Facilities were deferred through the end of 2015 and are being amortized over the remaining life of each respective plant.
(i)Represents the accrual of retirement costs associated with long-lived assets for which there are no legal obligations to retire the assets.
(j)Represents collections for future major maintenance costs; revenues are recognized as major maintenance costs are incurred.
(k)Represents collections to fund certain debt payments to be made through the end of 2025 which will be in excess of amounts collected through depreciation expense; the deferred credits will be amortized over the remaining useful life of the plants.
(l)Represents the difference in the timing of recognition of decommissioning costs for financial statement purposes versus ratemaking purposes, as well as the deferral of unrealized gains and losses of funds set aside for decommissioning.
(m)Deferred revenues under a rate management program that allowed for additional collections over a five-year period beginning in 2018. These amounts are being amortized to income and applied to member billings, per each member's election, over the subsequent five-year period.
(n)Represents the deferral of unrealized gains on natural gas contracts.
(o)The amortization periods for other regulatory assets range up to 29 years and the amortization periods of other regulatory liabilities range up to 2 years.
(p)Effects on net margin for the BC Smith Energy Facility that are being deferred until on or before January 2026 and will be amortized over the remaining life of the plant.
(q)Represents the write-down of inventory associated with the TA Smith acquisition. Amortization commenced on June 1, 2024 and will end no later than May 31, 2039.