Accredited Capacity: When 100 MW Isn’t 100 MW

Accredited capacity is not simply nameplate megawatts

A bring-your-own-capacity (BYOC) portfolio must bring enough accredited capacity to satisfy the utility’s Resource Adequacy obligation, including the planning reserve margin. Accreditation converts nameplate megawatts into the capacity that counts toward that obligation. FirmaOS forecasts how that credit changes by technology, asset, season, market, and year, applying each market’s methodology—including ELCC, DLOL, and performance-based accreditation—to estimate contribution during periods of system risk. We also integrate forecasts from other providers in order to assess accredited capacity risk across scenarios.

The following plot shows an example of what these capacity-accreditation forecasts can look like for a specific technology class and RTO.

Resource Adequacy rules become portfolio constraints

The FirmaOS Portfolio Designer requires the selected resources to meet the load’s capacity obligation in every year and season of the load ramp, including the planning reserve margin. Resource Adequacy also requires deliverability, as discussed in our ATSS scenario analysis, so we additionally take into account the study pathways, tiering, and modeled transmission upgrades and timing influencing the deliverability component of Resource Adequacy.

See how the rules differ across ISOs →

The seasonal trajectories also differ by technology. Solar, wind, and storage have the potential to counterbalance one another, as in MISO, where it is often forecasted that both wind and storage will receive lower summer accreditation relative to winter because summer scarcity hours tend to coincide with lower wind production and occur in longer events that a four-hour battery cannot fully cover. Optimal portfolio construction enables Firma to leverage these trends so the portfolio is effectively more than the sum of its parts—minimizing seasonal excess capacity in order to drive down overall portfolio costs. Further, it is possible to leverage stochastic optimizations to directly minimize tail risk across a range of accreditation trajectories for each of the technologies. The upshot is a portfolio that is cost-optimal and de-risked relative to potential grid buildout scenarios.

*MISO’s DLOL methodology and underlying weather and resource profiles continue to evolve, so future seasonal accreditation relationships may differ.

Firma manages the capacity position over time

Firma Power manages the accredited-capacity position over the term of the project—forecasting changes, filling capacity gaps when the portfolio runs short, and selling surplus when it runs long. The load receives one Portfolio Capacity Agreement that Firma stands behind.