RTC+B (real-time co-optimization plus batteries)
ERCOT's market redesign that prices energy and reserves together every five minutes and gives batteries a first-class state-of-charge model.
Filed under Storage — How a grid battery earns its money, what limits it hour to hour, and the ERCOT market redesign that finally models it as one resource.
RTC+B is the largest redesign of ERCOT's wholesale market since it went nodal, and it took effect in December 2025. Before it, ERCOT bought ancillary services — the standby reserves that protect the grid — once, in the day-ahead market, and those assignments stayed mostly frozen through the operating day. Real-time co-optimization changed that: every five minutes, the market now decides how each resource's capability is best split between producing energy and holding reserves, and prices both accordingly.
The 'plus batteries' part gives storage a proper seat at the table. Instead of modeling a battery awkwardly as a generator bolted to a load, the market treats it as a single resource with a state of charge, letting the optimization know how much energy it actually has and dispatching it within those limits.
Why it matters: under the old design, a tightening system could strand reserve obligations on resources that would have been more valuable producing energy. Co-optimization lets the market continuously reshuffle who provides what, which is meant to price scarcity more accurately and send reserves to whoever can provide them most cheaply at that moment. For battery operators, it rewrote the playbook — the market itself now makes many of the energy-versus-reserves trade-offs that operators previously had to guess at, shifting the edge toward better price and SOC forecasting.
For the technical reader
Under RTC+B, SCED becomes a joint clearing of energy and all ancillary products at five-minute granularity, with ancillary demand curves defining scarcity pricing product by product; reserve prices become consistent by construction with real-time energy prices, since both emerge from one optimization sharing the same marginal units. Ancillary obligations, previously fixed by day-ahead awards, are now continuously re-optimizable positions settled against real-time AS prices.
The battery-specific changes: a combined Energy Storage Resource model replaces the split generation/load representation, with ERCOT-monitored state of charge as a dispatch constraint, and offers structured so the optimizer can move a battery between charging, discharging, and reserve provision within one interval's clearing. For quantitative operators, the binding question shifts from 'which market do I commit to day-ahead' to bid-curve design under joint energy-AS price uncertainty.
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Related terms
- Ancillary servicesThe standby products — reserves and fast response — that grid operators buy to keep the system stable when something goes wrong.
- Battery arbitrageCharging a battery when electricity is cheap and discharging when it is expensive, earning the spread.
- State of charge (SOC)How full a battery is right now, usually expressed as a percentage of its usable energy capacity.
- Day-ahead vs. real-time marketsThe two-stage structure of wholesale power: a forward market that schedules tomorrow, and a spot market that trues up what actually happens.