CAISO curtailed 3.4 million megawatt-hours of renewable energy in 2024, a 29% jump from the previous year. That's clean electricity generated, then discarded because the grid couldn't absorb it. At prevailing wholesale prices, the wasted energy represents roughly $130 million in lost value—and the problem is accelerating faster than the renewable buildout itself.
The pattern now extends across every major US grid operator. ERCOT, SPP, and MISO each set curtailment records last year. What began as a California curiosity has become a nationwide infrastructure failure, revealing systematic underinvestment in the transmission and storage capacity needed to deliver clean energy from where it's generated to where it's consumed.
The Physics of Waste
Curtailment occurs when renewable generation exceeds what the grid can physically accept. Three constraints drive the problem, and all three are worsening simultaneously.
Transmission bottlenecks prevent moving power from generation-rich zones to load centers. West Texas wind farms can produce power at $15/MWh, but without adequate lines to Houston, that electricity dies on the vine. California solar hits the same wall—abundant generation in the Central Valley cannot reach Arizona or Nevada demand centers without interregional ties that don't exist.
SPP's experience illustrates the concentration risk. The grid operator curtailed over 3 million MWh of wind in 2024, with curtailment rates reaching 7% in the Oklahoma panhandle zone where wind density far exceeds transmission capacity. ERCOT's West Texas zone accounted for 68% of total Texas curtailment—a geographic bottleneck that's been identified for years but remains unresolved.
Minimum generation constraints on thermal plants compound the problem. Nuclear units cannot reduce output below roughly 50% without stability issues. Gas plants held online for reserves and frequency response occupy dispatch space that renewables cannot claim even when the sun is shining and the wind is blowing. The grid's thermal floor creates a ceiling for renewable absorption.
California's Curtailment Crisis
California's Curtailment Crisis. Source: CAISO via Canary Media. Up 29% from 2023—enough wasted clean power to run 400,000 homes.
When wholesale prices turn negative—increasingly common during spring afternoons in California—economic curtailment kicks in. Renewable generators without production tax credits face a choice: pay to generate, or shut down. Most shut down.
The Transmission Deficit
DOE's National Transmission Needs Study identified 47,000 miles of new high-voltage transmission required by 2030 to integrate planned renewable additions. Current construction rates total approximately 1,500 miles annually. The arithmetic is unforgiving: at that pace, the US builds roughly one-third of what's needed.
CAISO's planning documents reveal the timeline problem in granular detail. The grid operator identified 3,500 miles of needed transmission in its 2022 plan. Permitting timelines extend five to seven years. Construction adds another three. Projects approved today reach completion around 2032—long after the renewable capacity they're meant to serve is already curtailing.
Meanwhile, the interconnection queue continues swelling. Lawrence Berkeley National Lab's latest analysis shows approximately 2,000 GW of generation capacity waiting for grid access nationally—roughly double the entire existing US generation fleet. Most of that queue consists of solar, wind, and storage projects that will face curtailment if transmission doesn't materialize first.
The sequencing problem is structural. Renewable projects take two to four years from development to commercial operation. Major transmission takes a decade or more. Every solar farm built in a transmission-constrained zone adds to the curtailment tally before any wires arrive to relieve it.
The Transmission Gap: What's Needed vs. What's Being Built
The Transmission Gap: What's Needed vs. What's Being Built. Source: DOE National Transmission Needs Study. At current construction rates, the US will build only one-third of needed transmission by 2030.
Storage: Necessary but Insufficient
Battery storage offers a partial solution by absorbing curtailed energy during oversupply hours and discharging during evening peaks. California's aggressive storage buildout—now exceeding 10 GW of capacity—has demonstrably bent the curtailment curve.
FERC's latest demand response assessment shows CAISO's storage fleet absorbing hundreds of thousands of MWh that would otherwise face curtailment. Without that capacity, California's 2024 curtailment would have approached 4.5 million MWh rather than 3.4 million. Storage is working, but not fast enough.
The technology faces inherent limits. Four-hour batteries—the dominant duration in today's fleet—cannot absorb entire days of surplus generation. Spring weekends in California routinely produce twelve consecutive hours of oversupply. Longer-duration storage technologies exist but remain expensive; economics limit deployment to niche applications rather than grid-scale absorption.
ERCOT's experience demonstrates that storage alone cannot solve transmission-constrained curtailment. Texas added over 4 GW of battery capacity by end of 2024, yet curtailment continued climbing. When the constraint is wires rather than timing, batteries simply shift the problem rather than solving it.
Global Comparisons Highlight the Investment Gap
Germany faced similar dynamics during its renewable buildout, with curtailment peaking at 6.5 TWh in 2019 as wind additions outpaced grid infrastructure. The German response included accelerated transmission permitting through federal override of state-level objections—a politically painful but physically necessary intervention. The North-South HVDC corridors now under construction will enable moving offshore wind to industrial centers in Bavaria and Baden-Württemberg.
China's Curtailment Success Story
China's Curtailment Success Story. Source: Article data. China built 40,000 km of ultra-high-voltage transmission and cut curtailment by 75%—a trajectory the US is nowhere close to matching.
China's approach offers a starker contrast. State Grid Corporation built 40,000 km of ultra-high-voltage transmission between 2010 and 2023, enabling renewable generation in northwestern provinces to reach eastern load centers. Curtailment fell from 12% in 2016 to 3% in 2024—a trajectory the US is nowhere close to matching.
India now confronts the same challenge as solar additions accelerate. Rajasthan curtailed over 4 TWh of solar in 2024, with interstate transmission constraints preventing surplus from reaching deficit states. The Central Transmission Utility's plan calls for 27,000 km of new lines by 2030, but permitting and right-of-way acquisition remain contested.
The common thread: countries that treat transmission as strategic infrastructure build it. Countries that treat it as an afterthought to generation watch clean energy evaporate.
Stakeholder Calculus
For renewable developers, curtailment risk increasingly shapes project economics and siting decisions. Locations with firm transmission access command premium land costs but face lower curtailment exposure—a tradeoff that's becoming more pronounced as constrained zones saturate. Lenders now factor curtailment projections into financing terms; higher expected curtailment increases cost of capital and compresses returns.
For storage developers, curtailment patterns identify value opportunities. Co-located storage captures otherwise-lost energy at zero marginal cost, improving project economics. But the business case depends on curtailment persisting—a bet that transmission investment will remain inadequate. It's a profitable position, but an awkward one for the clean energy transition.
Where Curtailment Hits Hardest
Where Curtailment Hits Hardest. Source: EIA, BNEF. Geographic bottlenecks concentrate waste—West Texas alone accounts for more than two-thirds of all Texas curtailment.
For utilities and load-serving entities, curtailment represents stranded procurement. A utility contracting for 500 MW of solar receives less than 500 MW of actual energy if 6% gets curtailed. Resource adequacy planning must now account for curtailment risk alongside capacity factors and weather variability.
The Regulatory Pipeline
FERC Order 1920 addresses regional transmission planning reform, requiring transmission providers to conduct long-term planning that incorporates anticipated generation changes rather than reacting to interconnection requests. Implementation proceedings continue across each RTO, but the order's impact remains years away.
CAISO's current transmission planning process includes $7.3 billion in proposed network upgrades specifically addressing curtailment-prone zones. The proposal faces cost allocation disputes—zones that would fund upgrades aren't necessarily the zones that would benefit from reduced curtailment. These fights add years to already-long timelines.
ERCOT's Competitive Renewable Energy Zone expansion would add 3,400 MW of export capability from West Texas to the Houston area. But Texas's unique regulatory structure—outside FERC jurisdiction, with no capacity market to provide long-term price signals—complicates cost recovery for major transmission investment.
Watch for Q2 tariff filings in PJM and MISO implementing Order 1920 requirements. The details of cost allocation methodology will determine whether transmission investment accelerates or continues its current crawl. Every year of delay is another year of mounting curtailment—clean energy generated, then thrown away.
About the Author
Dr. Sayonsom Chanda
Dr. Sayonsom Chanda is an electrical engineer and senior scientist with more than a decade of experience in developing AI, ML, and other advanced computing solutions for the electric utility industry in US and India. He is also an energy policy thinker and a published author with more than 20 papers and 1 book.
