From plant retirements and new generation projects to the rapid expansion of battery storage and growing demand to record breaking capacity prices – 2024 had it all. The years ahead will be pivotal, with even more transformation on the horizon. Below, we will break down some of the changes we saw this past year by ISO.
PJM
PJM’s grid underwent significant changes in 2024, with things like solar generation growth, plant retirements, soaring capacity prices, and increasing demand.
One of the most notable retirements was the Homer City coal plant. The final 626 MW of the plant was removed this past April. Thankfully, the PJM grid still survived the sweltering summer without this coal plant in the thermal stack.
The 2025/2026 PJM capacity auction marked another major shift for the region, and the results made one thing clear, prices did not respond well to recent retirements. PJM Capacity Auction Prices soared to unprecedented levels. The main reasons for this? Demand growth, plant retirement causing supply and demand issues, and a lagging interconnection queue.
But another major factor was also co-location. This past year, co-location became a hot topic as data centers sought ways to integrate into the grid more efficiently. While some viewed it as a strategy to navigate system constraints, it also contributed to the growing strain on capacity.
The good news is regulators are reevaluating market rules to help bring capacity prices down in the future. However, relief in the short term appears unlikely. The coming years will determine just how much these reforms accelerate the interconnection process and ease pricing pressures.
PJM also saw significant solar growth in 2024, adding at least 2.5 GW over the past year. At the start of the year, the region’s maximum solar record output was just under 5.4 GW. By year’s end, it had surged to 8 GW. This was a monumental leap that highlights how quickly solar is being added to the grid.
With these changes, PJM also experienced record-breaking summer demand. The system operator had forecasted a peak of, 151,254 MW, but actual demand exceeded expectations, reaching 152.55 GW on July 16th. This day was a true scorcher.
ERCOT
New demand peak alert! This past summer, ERCOT demand soared to new heights (the limit does not seem to exist!). On August 20th, ERCOT set a new all-time peak of approximately 85,559 MW at HE18, surpassing the previous record of 85,508 MW set last August. This surge was driven by some of the hottest temperatures of the summer and continued load growth, pushing real-time prices to the $5,000 market cap.
Beyond record demand, 2024 was a huge year for solar and battery storage in ERCOT. At the start of the year, the solar peak record stood at 14.8 GW, supplying 23% of the Texas grid’s demand at the time. By year’s end, solar peak records surpassed 21 GW, a massive leap.
Battery storage followed a similar trajectory. Early in 2024, battery peak output was 3.2 GW, climbing to 4.3 GW by December. According to the December 2024 EIA 860 Inventory report, ERCOT closed out the year with 7.4 GW of total battery storage capacity, with 3.8 GW added in 2024 alone.
With these numbers, ERCOT is edging closer to CAISO’s renewable dominance. If this trend continues, we could eventually see days where renewable generation supplies 100% of ERCOT’s demand for multiple hours at a time.
MISO
Like PJM, MISO experienced significant shifts in 2024, from rising Energy Market Auction prices to an explosive increase in solar generation.
At the start of the year, MISO’s maximum solar generation consistently hovered just below 3.3 GW. By the end of 2024, solar peaks had surged to 8.2 GW, a 5 GW increase, more than doubling the capacity on the grid in just one year!
While MISO’s capacity price increases were not as dramatic as PJM’s, trends suggest a similar trajectory in the coming years. Some zones saw stable clearing prices, while others, like Zone 5, cleared much higher, due to coal plant retirements, rising demand, and supply and demand issues. These price spikes were particularly pronounced in spring and Fall when seasonal demand is lower and generation outages peak.
Additionally, according to the EIA-860 Monthly Electric Generator Inventory, coal plant retirements dominated MISO’s grid changes in 2024.
South Oak Creek Unit 5 & 6 (299 MW each) finally retired May 2024 after going through a few delays. Units 7 & 8 (about 300 MW each) are expected to retire in 2025.
Rush Island Coal Plants units 1 & 2 (totaling 1,178 MW) officially retired in October of 2024, shortly after MISO hit its summer peak demand of 121.6 GW on August 26th. This upcoming summer will be the first without Rush Island’s 1.1 GW of capacity, which could drive higher capacity auction prices and potential supply concerns.
ISONE & NYISO
In 2024, ISONE bid farewell to the Mystic Combined Cycle Power Plant, a 1,403 MW facility that officially retired in June. As one of the oldest power plants in the country, its shutdown marked the end of an era.
While grid growth remained modest, ISONE’s interconnection queue surged, with approximately 40,000 MW of proposed capacity, an overwhelming 97% of which is renewable energy and battery storage. By the end of 2024, renewables made up 12% of ISONE’s total generation, a number expected to rise in the coming years.
The Vineyard Wind offshore project had a milestone-filled but turbulent year. Once completed, the large-scale wind farm is expected to generate enough clean energy to power 400,000 homes in the region. At the beginning of 2024, the project added five turbines to the grid, producing 68 MW of electricity. This number soon grew to ten turbines before progress was abruptly halted in July when a turbine blade fell into the ocean. The incident led to a month-long pause in both energy production and construction. While construction has since resumed, energy production remains suspended, with the working turbines not yet supplying power to the grid. As 2025 approaches, major developments are expected for this 800 MW wind farm. Additionally, 219 MW of solar generation and 239 MW of battery storage is also expected to come online in the coming year.
In 2024, NYISO repeatedly broke records for wind generation. At the start of the year, the grid reached 2,176 MW of wind generation in a single hour. By December 16th at HE23, a new record was set at 2,309 MW, supplying 14.4% of the system's energy demand at that time. While these figures may not be as large as those in other ISOs, they signal a strong trend toward future growth, with exponential expansion on the horizon.
CAISO
This past year, CAISO saw huge shifts in its grid with renewables taking center stage and the market evolving rapidly. First, solar generation soared, setting a new record of 19,650 MW on August 23, frequently pushing CAISO into net exporter mode during the day.
Wind also held steady, but the real game-changer was battery storage growing by 4.19 GW in 2024, nearly doubling the 2.68 GW added the previous year. By year-end, total battery capacity reached 11,454 MW, up from just 4,515 MW at the end of 2022 – a massive shift in how the grid manages renewables.
But it was not all smooth sailing. California’s energy needs kept growing with peak demand for the year reaching 48,323 MW on September 5 – one of the highest in recent years (though short of 2022's record of 52,061 MW). Transmission congestion led to price swings, especially with large deltas in SP15 and NP15 during the midday driven by south-north energy flows. This spring saw record breaking negative pricing which was a result of renewable curtailments hitting an all-time high. The new monthly record was set at 839,582 MWh curtailed in April as excess solar flooded the system.
Despite challenges, CAISO avoided Flex Alerts all year, showing that storage, imports, and better forecasting kept things stable even in tight conditions. By year-end, renewables continued expanding, further shifting California’s grid toward a more storage-driven and intermittent-resource-heavy system.
SERC
SERC experienced two major changes this year which marked the ending of one chapter and the beginning of another. The 626 MW Seminole Electric Cooperative Coal Plant Unit 1 saw its final days on the grid and was officially retired. Meanwhile, Vogtle Nuclear Power Plant Unit 4 began commercial operation, joining Unit 3 in the generation stack for the first time.
With each new unit adding 1,114 MW of capacity, Vogtle is now the largest nuclear power plant in the United States, with a total capacity nearing 5 GW. Notably, this expansion provides carbon-free energy, playing a key role in Georgia’s emissions reduction efforts.
SPP
This past year, SPP saw major shifts in its market, shaped by lower gas prices, evolving generation mixes, and persistent congestion. Natural gas prices averaged between $1.26/MMBtu and $2.25/MMBtu in 2024 – down sharply from $3.33/MMBtu in winter 2023 – driving wholesale power prices lower. Wind remained the dominant generation source, accounting for 30-47% of generation depending on the season, while coal declined, and gas-fired generation increased. At the end of November 2024, wind capacity reached 34,556 MW in nameplate capacity, up 1,200 MW from November 2023.
According to the Summer 2024 SPP state of the market, average hourly load for the 2024 summer was 3% above 2023, while the peak hourly load was down 3% compared to 2023. But winter was a mixed bag. While January 2024’s winter storm drove an 15% increase in monthly peak load from the previous year, the average hourly load in winter – and spring – only grew slightly. Nonetheless, system reliability held.
Congestion remained a challenge. Oklahoma (in fall 2024), North Dakota (in winter 2024), and Kansas City (in spring 2024) all experienced congestion issues primarily attributed to transmission and generation outages, wind impacts, increased local loads, and external parallel flows. Day-ahead congestion costs increased in winter but eased in spring and fall, while market-to-market payments from MISO to SPP rose – highlighting the need for shared resource adequacy across ISOs amid ongoing load growth.
SPP maintained system reliability throughout 2024. By year-end, the market saw increased renewable integration, with wind surpassing coal in the summer for the first time. Coal generation declined across all seasons, while gas generation fluctuated in response to lower fuel prices. Transmission congestion remained a challenge, with constraints occurring in multiple regions. Economic dispatch patterns reflected fuel price shifts, influencing generation trends across the market.
In 2025
It's worth pondering over these regional nuances and their effects on the market. There’s CAISO who was an early adopter of renewables, grappling with the infamous duck curve and the volatility that followed. But 2024 marked a turning point. Thanks to battery storage, grid reliability reached its highest level in years.
Meanwhile, ERCOT, who has surged ahead as a wind power leader, is now experiencing rising prices and shifts in net demand. Coupled with demand growth, balancing the grid and reliability concerns remain a major issue for them.
Now, PJM, MISO, ISO-NE, and NYISO are entering the fray. Old power plants are being retired and replaced with renewables. The question is: Can they bypass the growing pains of their predecessors by rapidly deploying batteries to maintain balance? 2025 might be the tipping point for how things go.
Sources:
Key Statistics Library – CAISO, QX 2024 Report on Market Issues and Performance
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