How ERCOT grid rules Texas set wholesale power prices

What to take away

How ERCOT market design sets the price of power in Texas

ERCOT runs the electric grid for most of Texas and operates a market where generators sell power. The price you see is not a bill from a utility. It is a clearing price set in a series of auctions, and it changes every five minutes.

The market has a day ahead auction and a real time market. In the day ahead market, buyers and sellers commit to amounts of power for each hour of the next day. In real time, ERCOT balances actual supply and demand, and prices settle every five minutes.

Generators submit offers to sell power at certain prices. ERCOT stacks those offers from cheapest to most expensive and picks the ones needed to meet demand. The highest offer used sets the price for everyone in that interval. That is how a market design turns individual bids into a single public price.

This is a wholesale market. Retail prices are set separately by retail providers, some of which pass wholesale costs through to customers. That split matters when wholesale prices spike, because the retail effect depends on the contract.

The price is meant to do two jobs. In the short run it moves power to where it is needed. In the long run it signals when to build new generation. Whether it does those jobs depends on the rules around it.

The Public Utility Commission of Texas and who writes the rules

The Public Utility Commission of Texas, often called the PUC, writes the rules that govern ERCOT, and those rules are collected in Title 16 of the Texas Administrative Code, Chapter 25. The Texas Legislature sets the broad statutes, and the PUC fills in the details through rulemakings.

The PUC has three commissioners appointed by the governor and confirmed by the Texas Senate. They set the offer cap, define operating reserves, and approve market changes. ERCOT proposes changes through its stakeholder process, and the PUC can accept, modify, or reject them.

The rulemaking record is public. Proposed rules are published for comment in the Texas Register, and the commission's orders and filings are available through the PUC's own records.

The Texas Public Information Act plays a similar role at the state level.

When the PUC adopts a rule, it publishes the text and the reason for it. That record is where you check whether the price you saw matches the rule that was supposed to produce it. The same discipline applies to policy tools compared across legislation and regulation.

Scarcity pricing, operating reserves, and the offer cap

Scarcity pricing is the practice of letting prices rise when supply is tight. In ERCOT, the trigger is operating reserves, the cushion of available generation above expected demand, and the mechanism is the Operating Reserve Demand Curve, which adds a scarcity price to the energy price as that cushion shrinks.

When operating reserves fall below a set level, ERCOT can enter an emergency condition and allow prices to approach the offer cap. The offer cap is the highest price a generator may offer and the highest price the market may clear.

The cap exists to limit financial risk and market power. It also limits the incentive to build. If the cap is too low, generators may not recover the cost of a plant that runs only a few hours a year. If it is too high, customers pay a lot in a short period.

ERCOT uses a value of lost load calculation to set the cap. The idea is that the cap should reflect what customers would pay to avoid an outage. That number is an estimate, and the PUC revisits it from time to time.

The high system-wide offer cap in force is $5,000 per megawatt hour. The commission lowered it from $9,000 per megawatt hour in a rulemaking adopted in 2021, and the lower cap has applied since January 2022. The value of lost load figure behind the cap is $5,000 per megawatt hour, set in the same rulemaking.

During Winter Storm Uri in February 2021 the cap in force was $9,000 per megawatt hour.

Operating reserves are measured in megawatts and as a percentage of forecast demand. ERCOT publishes reserve levels and the conditions that follow from them. The rules tie specific actions to specific reserve thresholds, so the price is supposed to follow the reserve level.

What happened during Winter Storm Uri, hour by hour

Winter Storm Uri hit Texas in February 2021 with record cold and frozen equipment. Generators lost gas supply, wind turbines froze, and demand for heat and power rose at the same time.

The sequence matters because the rules are written as a ladder. As operating reserves fell, ERCOT moved from normal operations to conservation alerts, then through its Energy Emergency Alert levels — EEA1, EEA2 and EEA3 — and finally to controlled outages.

On the night of February 14 and into February 15, reserves dropped fast. ERCOT called for conservation and then declared an energy emergency. Prices in the real time market rose toward the offer cap.

The PUC issued an order that kept wholesale prices at the cap for a period during the event. The order was later reviewed and its cost was a subject of dispute. The key point for readers is that the price was not simply left to the market; a regulator acted.

Controlled outages began on February 15 and lasted for days in some areas. Millions of customers lost power, and some lost it for extended periods. The grid came close to a broader collapse, which is why the outages were ordered.

When the storm passed, the market returned to normal operations, but the financial effects lasted. Several generators and retail providers failed, and the legislature passed reforms in the following session, led by Senate Bill 3, which requires generators and gas facilities to weatherize for winter.

The event is a case study in how a rule written for scarcity behaves when scarcity is extreme. It is also a case study in how a failure produces a flood of documents and competing accounts, the kind of record trail that follows any grid failure.

Whether the price signal matched the rules as written

After Uri, regulators and outside reviewers asked a simple question: did the price follow the rules? The reviews that followed — the FERC and NERC staff report on the February 2021 cold weather outages, and reports from ERCOT's Independent Market Monitor, Potomac Economics — found no rule break in the prices themselves, because the rules allowed prices to reach the cap when reserves were low.

That finding does not settle the policy question. A price can follow the rules and still be a poor signal if the rules set the wrong cap or the wrong reserve threshold. The distinction between compliance and wisdom is where most of the debate sits.

One criticism was that the cap stayed too high for too long after the emergency ended. Another was that the reserve threshold did not reflect the speed at which the system can actually run short. Both are arguments about rule design, not rule breaking.

What is in force now: the commission rewrote how ERCOT measures operating reserves, moving from available capacity alone to a firmer count of capacity that can respond within minutes. ERCOT added the Emergency Contingency Reserve Service, live since June 2023, which can be called before rotating outages.

The commission also revised how prices are set once an energy emergency is declared. Those changes are the current rules, and they are what the next event will test.

For a reporter, the check is straightforward. Find the rule that was in effect at the time, find the reserve level, and compare it to the price. If they match, the story is about design. If they do not, the story is about execution.

The records behind the numbers are public. Requests for PUC files go through the Texas Public Information Act; ERCOT is not a state agency, and it posts market data, board materials and stakeholder filings on its own site.

How to read an ERCOT price report

ERCOT publishes market reports that show prices, quantities, and system conditions. The price is a clearing price for a five minute interval or an hour. The cost is what a load serving entity pays over a period, after settlements and contracts.

Use the reports in this order:

A report shows a real time price of $9,000 per megawatt hour for one interval. If the cap at the time was $9,000, the price followed the rule. If the average price for the day was $200, the daily cost is far lower than the peak suggests. Both numbers are true, and they answer different questions.

Reporters often mix these up, and the same error shows up in market coverage when a single data point is treated as a trend. The fix is to name the interval and the rule.

The same care applies when a rule has a compliance date that differs from the date it took effect. And when you compare price series across markets, remember that a different market design runs on different rules.

The rulebook is public too. The PUC publishes the rules and the orders that change them, and ERCOT publishes the system conditions it saw. Put the two side by side and a price claim checks itself.

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