California’s wholesale electricity prices can fall below zero when abundant solar and other renewable generation coincides with relatively low demand. The negative price applies to a particular market interval and location—not automatically to household electricity bills. CAISO’s latest detailed figures available here show negative-price frequency fell in the second quarter of 2025, so the pattern is real but not a one-way trend.
Why does California have negative electricity prices during the day?
The California Independent System Operator (CAISO) operates the grid and wholesale electricity markets for most of California. In those markets, prices are calculated for specific time intervals and locations. When renewable output is high and demand is low, renewable generators are more likely to set the marginal price, and some low-cost renewable resources offer power at or below zero. The market-clearing price can therefore turn negative for a particular interval.
A negative wholesale price is a signal about the balance of supply and demand under market and grid conditions. It does not mean electricity has no use: demand rises as solar generation declines toward evening, creating a need for replacement energy. Nor does a negative price at one location mean prices are negative everywhere in California at that time.
Negative prices vary by time and location
CAISO tracks prices in day-ahead, 15-minute, and 5-minute markets. A negative interval in one market or location is not an all-day statewide price. Local transmission congestion can leave one constrained area with very low or negative prices while prices elsewhere remain higher. The California Public Utilities Commission’s 2025 grid report characterized local congestion as accounting for around 70–80% of CAISO renewable curtailment in recent years, with systemwide oversupply accounting for around 20–30%; those are historical shares, not a 2026 estimate.
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How often have wholesale prices been negative?
CAISO Department of Market Monitoring figures published in its October 2025 Q2 report show that negative-price intervals became less frequent from the second quarter of 2024 to the second quarter of 2025:
| CAISO market | Q2 2024 | Q2 2025 |
|---|---|---|
| Day-ahead | 22% | 14% |
| 15-minute | 23% | 14% |
| 5-minute | 24% | 14% |
These are historical shares of intervals in the CAISO balancing area, not a current 2026 measurement or a count of hours when retail customers received negative rates. The report also found that overall negative-price frequency for its day-ahead and real-time participating group decreased by 40% over the compared period from April 2024 through June 2025. The CAISO report index lists a Q2 2026 report posted October 6, 2026, but the detailed negative-price figures cited here are from Q2 2025.
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Does negative electricity pricing mean my power is free?
No. Wholesale market prices and household bills are different things. A wholesale price applies to a market interval and location; a residential customer’s bill is based on the applicable utility tariff and includes costs beyond wholesale energy. Retail rates also vary by utility and customer. The California Legislative Analyst’s Office reported in January 2025 that average residential electricity rates in California were close to double those in the rest of the nation. A negative wholesale interval does not by itself make a customer’s electricity free or mean the utility pays the customer to use it.
Why does California curtail solar power?
When generation exceeds what the grid can consume or export, CAISO can instruct renewable generators to reduce output. Curtailment is an operational balancing tool, not proof that the electricity is useless; it can reflect a mismatch in timing, transmission capacity, storage, or demand. CAISO says curtailment is most common in spring and fall, when moderate temperatures can keep demand relatively low while sunny or breezy weather supports abundant renewable production.
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California’s annual renewable curtailment rose from around 400,000 MWh in 2017 to almost 2.7 million MWh in 2023, according to the CPUC’s 2025 report using CAISO data. Those figures describe past years, not a current annual total. CAISO says it stopped publishing its former production-and-curtailment report as of June 1, 2025, and directs readers to its daily renewable reports for curtailment data.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What can the grid do with surplus daytime electricity?
Export power to neighboring regions
CAISO can trade with neighboring balancing authorities to sell surplus renewable electricity. The U.S. Energy Information Administration reported that the Western Energy Imbalance Market avoided more than 274,000 MWh of curtailment in 2024—about 8% of the electricity curtailed that year. Those are EIA’s 2024 figures, not a current total.
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- INSTALLS IN CIRCUIT PANEL of most homes with clamp-on sensors. Supports Single phase, Single-split phase, and 2-wire systems. 3-wire systems; 3-phase, 4-wire Wye systems with earthed (TN or TT) neutral (no-Delta) are supported with an additional 200A sensor (sold separately).
- 24/7 ENERGY MANAGEMENT AND MONITORING: Automate, manage and control your home's real power anywhere, anytime to prevent costly repairs, conserve energy, and save costs. Monitor solar / net metering. PROTECTED BY A 1-YEAR WARRANTY.
- LOWER YOUR ELECTRIC BILL: Configure settings in the Emporia Energy App to automate energy management for time of use, peak demand, excess solar, and rewards programs. You can even see live reporting and invaluable savings opportunities instantly. Gauge real-time spending and get actionable notifications and automated energy management to help you reduce costs.
- REAL-TIME ENERGY DATA: REQUIRES 2.4 GHz WIFI WITH AN INTERNET CONNECTION to monitor energy use with iPhone / Android / Web app. Vue sensors collect energy data and are accurate from ±2%. The Vue is UL and CE Listed for your safety. 1 second data is only available in the app (when actively open) and retained 3 hours. Minute and hour data are retained in the cloud. 1 minute data is retained 7 days, 1 hour data is retained indefinitely. Export cloud data whenever you want in the app.
Store energy for later
Batteries can charge when solar is abundant and demand is relatively low, then inject stored energy when solar output falls and load remains high. Storage can reduce some curtailment by shifting energy from periods of surplus to periods of greater need; it cannot eliminate every constraint or guarantee that all excess generation can be stored. California had installed over 17,000 MW of cumulative grid battery power capacity after additions in 2025, according to the California Energy Commission in 2026. MW measures power capacity, not stored energy or a guaranteed amount of electricity available to discharge.
Expand transmission and flexible demand
Transmission planning can help move electricity from areas with surplus generation to areas that need it. Flexible demand and a diverse mix of flexible grid resources can also help balance changing supply. These are planning and system-integration measures, not instant fixes for every negative-price interval.
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- INSTALLS IN CIRCUIT PANEL of most homes with clamp-on sensors. Supports Single phase, Single-split phase, and 2-wire systems. 3-wire systems; 3-phase, 4-wire Wye systems with earthed (TN or TT) neutral (no-Delta) are supported with an additional 200A sensor (sold separately).
- 24/7 ENERGY MANAGEMENT AND MONITORING: Automate, manage and control your home's real power anywhere, anytime to prevent costly repairs, conserve energy, and save costs. Monitor solar / net metering. PROTECTED BY A 1-YEAR WARRANTY.
- LOWER YOUR ELECTRIC BILL: Configure settings in the Emporia Energy App to automate energy management for time of use, peak demand, excess solar, and rewards programs. You can even see live reporting and invaluable savings opportunities instantly. Gauge real-time spending and get actionable notifications and automated energy management to help you reduce costs.
- REAL-TIME ENERGY DATA: REQUIRES 2.4 GHz WIFI WITH AN INTERNET CONNECTION to monitor energy use with iPhone / Android / Web app. Vue sensors collect energy data and are accurate from ±2%. The Vue is UL and CE Listed for your safety. 1 second data is only available in the app (when actively open) and retained 3 hours. Minute and hour data are retained in the cloud. 1 minute data is retained 7 days, 1 hour data is retained indefinitely. Export cloud data whenever you want in the app.
Why does the issue matter to household finances?
For most households, a negative wholesale interval is not a direct discount on the bill. Its significance is indirect: it reflects how the grid is matching generation, demand, storage, exports, and transmission at a particular time and place. Whether a customer can benefit from shifting consumption depends on the customer’s utility tariff and circumstances; the wholesale price alone does not establish a household incentive or savings amount.
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