Electric Reliability Council of Texas Inc. logged the smallest percentage gain in spot power prices in December 2021 as its generator margins declined.

Across the U.S., average day-ahead market on-peak power prices climbed 57.9% year over year to $48.14/MWh, with the highest increases recorded in the West, ISO New England, South and Midcontinent ISO regions.

Meanwhile, natural gas prices at hubs serving generators rose at a slower pace than power prices on a nationwide basis, with average spot natural gas prices climbing 48.4% year over year to $4.292/MMBtu.

Spark spreads were mixed, with gas-fired implied heat rates — the rate at which the market cost of power equals the cost of burning natural gas to generate electricity — rising 6.4% to 11,217 Btu/kWh, as increases in some regions largely offset the others' declines.

The market to see the biggest decline in implied heat rates year over year was ERCOT, retreating 5.6% to 9,415 Btu/kWh. Coal-fired implied heat rates were also mixed in December.

With the exception of Alberta and California ISO, the average hourly load in December 2021 was down across most of the regions by as much as 5.2% year over year. CAISO recorded a 4.8% year-over-year increase in average hourly load, while Alberta recorded a 4.2% increase.

Market prices and included industry data are current as of the time of publication and are subject to change. For more detailed market data, including power and natural gas index prices, as well as forwards and futures, visit our Commodities pages.