UCAP, ELCC and Firm Capacity: What Each ISO Actually Pays For in 2026

Noreva, an energy market data and analytics provider (formerly Karbone Research), tracks capacity forecasts across every major US power market because what actually gets paid is accreditation, not nameplate capacity. UCAP (unforced capacity) and ELCC (effective load carrying capability) are two different accreditation concepts that developers, asset owners and investors routinely conflate, and in 2026 the gap between them is widening as PJM, MISO, NYISO, ISO-NE, SPP and CAISO each rework how they value solar, wind, storage and gas.

Every ISO runs some version of the same equation: capacity revenue equals accredited MW times clearing price, and the accredited MW is set by capacity accreditation rules that differ market by market – within PJM, by PJM’s ELCC class ratings, reset every auction cycle. A project that clears at a record price can still see revenue fall if its accredited MW is cut faster than the price rises. This piece covers what nameplate, UCAP and accredited capacity mean, how each ISO calculates accreditation in 2026, what a derate does to revenue, and why the accredited-MW curve belongs in a project’s financial model.

What Do Nameplate, UCAP and Accredited Capacity Actually Mean?

The confusion between these three terms is the single biggest source of mispriced capacity revenue in developer models: each is a different number, and only one of them clears an auction.

• Nameplate capacity: The manufacturer-rated maximum output of a generating unit under standard test conditions, measured in MW. It is a physical specification, not a market value, and no ISO pays for it directly.
• Unforced capacity (UCAP): The portion of a resource’s capacity a market treats as reliably available after removing an estimate of forced outages, typically via a derating factor or equivalent forced outage rate applied to tested or installed capacity. UCAP is the currency of NYISO’s capacity market and underpins PJM’s legacy accreditation logic; it is what a Load Serving Entity must procure to meet its resource adequacy obligation.
• Accredited capacity via ELCC: Effective Load Carrying Capability measures how much additional load a resource lets the system serve reliably, given its output pattern relative to the hours when the system is actually at risk, expressed as a percentage of nameplate. ELCC is probabilistic rather than a simple derate, and it falls as more of the same resource type is added to the system – the mechanic behind the ELCC crunch Noreva documented earlier in 2026.

How Does Each ISO Accredit Capacity in 2026?

The methodology differences below are structural, not cosmetic. Two resources with identical nameplate ratings can clear very different accredited MW depending only on which ISO they sit in.

PJM: Marginal ELCC Class Ratings by Resource Type

PJM assigns marginal ELCC class ratings by resource type ahead of each Base Residual Auction (BRA), and the ratings for the 2027/2028 Delivery Year show how steep the solar curve has become: fixed-tilt solar is rated at 7% and tracking solar at 8%, onshore wind at 41%, offshore wind at 67%, and 4-hour storage at 58%, rising to 78% for 10-hour storage (PJM, ELCC Class Ratings for the 2027/2028 Base Residual Auction). Thermal resources sit far higher: nuclear clears at 95%, coal at 83%, and gas combined cycle at 74%. PJM determined that its Gas Combined Cycle Dual Fuel class had too few members and too much variation in historical performance across hours of risk to be captured by a single class rating for the 2027/2028 Delivery Year, so those units instead receive a resource-specific ELCC value. For PJM-specific coverage, see Noreva’s PJM capacity page.

MISO: Seasonal Accreditation and the Shift to Direct Loss of Load

MISO already runs a four-season resource adequacy construct across ten Local Resource Zones (see Noreva’s MISO capacity coverage), and it is now moving its accreditation methodology itself. MISO’s Direct Loss of Load (DLOL) approach would replace class-average accreditation with a calculation tied directly to a resource’s output during the hours that actually drive loss-of-load risk (MISO, Direct Loss of Load Resource Accreditation Requirements, FERC Docket No. ER24-1638-000). MISO plans to publish indicative DLOL results ahead of each Planning Resource Auction through the transition, with full implementation targeted for Planning Year 2028-2029; until then, Schedule 53 of MISO’s tariff governs Seasonal Accredited Capacity calculations.

NYISO: UCAP via Derating Factors and Duration-Based Storage Accreditation

NYISO’s core currency remains UCAP, calculated through resource-specific derating factors reviewed annually. Storage and other limited-duration resources are accredited by duration rather than by a single class number, a design also discussed in Noreva’s coverage of battery standards and capacity dynamics: NYISO’s Capacity Accreditation Resource Class (CARC) list already separates Energy Duration Limited storage into 2, 4, 6 and 8-hour classes, each with its own accreditation factor, alongside separate classes for solar, wind and landfill gas. For the 2026-2027 Capability Year, NYISO is adding a further split between firm and non-firm fuel: a new Non-Firm CARC applies to generators in Load Zones F through K that have not elected firm fuel, modeled as unavailable at NYCA loads above 22,000 MW during December, January and February, while resources that elect and demonstrate firm fuel supply receive the existing Generator CARC, modeled as available at all times with a 0% forced outage rate (NYISO, Firm/Non-Firm Capacity Accreditation Factors Methodology, ICAPWG, June 3, 2025). For more, see Noreva’s NYISO capacity coverage.

ISO-NE: Toward a Prompt, Seasonal Capacity Market

ISO-NE currently allocates qualified capacity (the MW ISO New England allows a resource to offer) through its Forward Capacity Market, using a three-year-ahead auction. FERC accepted the first phase of ISO-NE’s Capacity Auction Reforms (CAR) on March 30, 2026, in Docket No. ER26-925 (ISO New England, ISO Newswire, March 31, 2026), moving the capacity auction to roughly a month before delivery – a “prompt” design meant to reduce the risk of accrediting resources that never get built – and shortening the deactivation notice period from four years to one. The first auction under the new framework is planned for 2028, with the reforms in place for the Capacity Commitment Period beginning June 1, 2028 (ISO New England, Capacity Auction Reforms key project page, accessed September 27, 2026). A second phase, covering separate summer and winter seasonal capacity periods and an accreditation overhaul, remains in development, with the FERC filing expected in the fourth quarter of 2026 (ISO New England, Capacity Auction Reforms key project page, accessed September 27, 2026). See Noreva’s ISO-NE capacity coverage for detail as the second phase firms up.

SPP: Performance-Based Accreditation Plus ELCC for Variable Resources

SPP does not run a centralized capacity market, but FERC’s July 18, 2025 order (Docket Nos. ER24-1317 and ER24-2953) approved the accreditation framework that now governs its Resource Adequacy Requirement: an ELCC methodology for wind, solar and electric storage resources, and a Performance-Based Accreditation (PBA) methodology, built on Equivalent Forced Outage Rate (EFORd), for conventional resources, effective October 1, 2025, with PBA in force for the 2026 Summer Season. Under SPP’s prior, pre-ELCC approach, solar was accredited at a flat 60.7% once penetration passed 1,000 MW, a class-average figure the new ELCC methodology is designed to replace with a probabilistic, penetration-sensitive rating, similar in spirit to PJM’s marginal ELCC framework. SPP’s legacy methodology credited a 4-hour, 100 MW storage resource at 100 MW and a 1-hour, 100 MW resource at only 25 MW; SPP’s approved ELCC studies now use four, six and eight-hour storage curves. For SPP-specific coverage, see Noreva’s SPP capacity page.

CAISO: Resource Adequacy With Slice-of-Day and Net Qualifying Capacity

CAISO’s Resource Adequacy framework has moved to a 24-hour Slice-of-Day construct: each Load Serving Entity must show it holds enough capacity to cover its gross load profile, including its planning reserve margin, across all 24 hours of the “worst day” in each month, defined as the day with that month’s highest coincident peak load forecast (CPUC, 2026 Resource Adequacy and Slice of Day Guide). Individual resources are still accredited through Net Qualifying Capacity (NQC) values, published annually and specific to each resource’s qualifying capacity and deliverability status (CAISO, 2026 Net Qualifying Capacity Values for Resource Adequacy Resources). See Noreva’s CAISO capacity coverage for more.

What Counts as Firm Capacity, ISO by ISO?

Firm capacity is not a single line item; each ISO tests it differently. SPP’s Tier 1 wind, solar and storage resources qualify as firm capacity when they hold Firm Point-to-Point Transmission Service, and SPP layers a winter Fuel Assurance adjustment onto conventional resources that reduces PBA accreditation for any resource that underperforms during the prior winter’s highest-risk hours, a direct response to Winter Storm Uri. NYISO’s Firm CARC applies MW by MW: a single resource can carry a Generator accreditation, with a 0% forced-outage assumption, on the MW it elects as firm, and the new Non-Firm CARC on the rest (NYISO, Firm/Non-Firm Capacity Accreditation Factors Methodology, ICAPWG, June 3, 2025).

How Do the Six ISOs Compare on Accreditation Method and Status?

Capacity Accreditation by ISO, 2026 Status and Technology Treatment

What Does a Derate Actually Do to Capacity Revenue?

The formula behind every one of these methodologies is the same: capacity revenue equals accredited MW times clearing price. The accredited MW is set by whichever accreditation method the resource’s ISO uses; the clearing price is set by the auction or bilateral market. Both move independently, and a rising price does not automatically offset a falling accreditation.

Take PJM’s own 2027/2028 ELCC class ratings as a concrete example: a 100 MW fixed-tilt solar project is accredited at 7% (PJM, ELCC Class Ratings for the 2027/2028 Base Residual Auction), clearing roughly 7 MW rather than the full 100 MW nameplate figure – a further cut to that rating has an outsized effect on revenue precisely because accredited MW is already such a small fraction of nameplate. Illustrative math (not an actual auction outcome): a 100 MW resource accredited at 20% clears 20 MW; if the rating is cut to 10% the following year, it clears only 10 MW, and the clearing price would need to roughly double just to hold revenue flat. If price instead rises 30%, revenue still falls by roughly 35%, because MW halved and price rose by less than a third – the arithmetic a nameplate-based model misses, and exactly the risk Noreva’s ELCC Crunch analysis flagged.

Why Should Developers Model the Accredited-MW Curve Instead of Nameplate?

Noreva builds its capacity forecasts per ISO and per accreditation regime rather than off a single generic curve: a nameplate curve shows what a plant can physically produce, while an accredited-MW curve shows what the market will pay for. PJM’s marginal ELCC class ratings reset with every BRA, SPP’s ELCC and PBA/EFORd calculations move independently by season, NYISO now splits accreditation by firm-fuel election as well as duration, and MISO and ISO-NE are both mid-transition to new accreditation logic. A model that applies one blended capacity factor across all six ISOs will misstate project economics.

Noreva’s capacity forecasts and asset valuation work are built resource class by resource class and ISO by ISO, so the curve a developer or project finance team underwrites against is the accredited-MW curve each ISO will actually pay, not the nameplate number on the interconnection application. See the Capacity hub for Noreva’s full coverage across all six markets.

Frequently Asked Questions: UCAP, ELCC and Firm Capacity

What is the difference between UCAP and ELCC?

UCAP (unforced capacity) is a resource’s capacity after subtracting an estimate of forced outages, calculated as a derate of nameplate or tested capacity. ELCC (effective load carrying capability) is a probabilistic measure of how a resource’s output pattern reduces loss-of-load risk, and it falls as more of the same technology is added. PJM, SPP and MISO use ELCC-style methods for variable and storage resources; NYISO’s core metric remains UCAP.

What is firm capacity?

Firm capacity is capacity backed by a resource, fuel supply or transmission arrangement an ISO has determined will reliably be available when called on. SPP’s Tier 1 wind, solar and storage resources qualify when they hold Firm Point-to-Point Transmission Service; NYISO’s Firm CARC applies to resources that elect and demonstrate firm fuel supply. In both cases, the firm designation carries a higher accredited value, though the size of the gap depends on each ISO’s methodology.

Why do ELCC ratings decline as more solar and storage are added?

ELCC measures a resource class’s marginal contribution to reliability, and that contribution falls as more of the same resource type is added, because the hours of system risk shift to align with when that class is not producing. PJM’s 2027/2028 class ratings show this directly: fixed-tilt solar sits at 7% and tracking solar at 8% (PJM, ELCC Class Ratings for the 2027/2028 Base Residual Auction).

What is a marginal ELCC class rating?

A marginal ELCC class rating is the accreditation percentage PJM assigns to a class of similar resources, such as tracking solar or 4-hour storage, for a specific delivery year, based on that class’s modeled marginal contribution to reliability. It is recalculated ahead of each Base Residual Auction, so accredited MW can change year to year even when the physical asset does not.

How does Noreva’s forecast help compliance and developer teams?

Capacity accreditation sets the MW figure multiplied by the clearing price to produce capacity revenue, so a model that uses nameplate MW or a stale accreditation percentage will misstate that revenue stream. Noreva’s asset valuation work builds forward accreditation scenarios into merchant curve and project-level financial models. Book a demo to see how.

Model the Accredited-MW Curve With Noreva

Noreva’s capacity forecasts and asset valuation platform tracks UCAP, ELCC and firm capacity rules ISO by ISO and resource class by resource class, updated continuously as PJM, MISO, NYISO, ISO-NE, SPP and CAISO revise their accreditation methodologies. Whether you are underwriting a new solar or storage project, budgeting capacity revenue, or stress-testing a merchant curve against an accreditation reform in progress, Noreva provides the accredited-MW visibility your model needs.

Book a demo to access Noreva’s capacity accreditation data and forward forecasts across all six ISOs.