Peak power prices in the western United States fell as heat exited and demand started to flag following the Labor Day weekend.

California Independent System Operator demand peaked at 46,475 MW Sept. 6, which should be the week's high. Demand fell as the week progressed. Between Sept. 6 and Sept. 7, demand dropped 10.5 percent, but between Sept. 6 and Sept. 10, when energy usage reached 30,936 MW, demand fell by roughly 33 percent.

Daytime peak power prices lost between 55 cents and as much as $96.50 between Sept. 4 and Sept. 10. California-Oregon Border lost the most value, plummeting $96.50 in trading to $38.50/MWh.

By Sept. 10, daytime power prices ranged from $33.75/MWh at Mid-Columbia to $38.50/MWh at North of Path 15 and COB.

Markets were closed Sept. 7 in observance of Labor Day.

Nighttime power values varied, with North and South of Path 15 each adding roughly $1.50 in trading while other hubs lost value. Mid-C fell the most, down $10.05 to $23.50/MWh. Off-peak power prices ended trading at between $23.50/MWh and $31.40/MWh at NP15.

Renewable resources supplied CAISO with 13,222 MW, or almost 33 percent of demand, Sept. 4. That same day, solar generation reached 10,987 MW. Solar supplies were disrupted by ash fallout from wildfires, particularly on Sept. 9 (see related story). The week prior, solar peaked at 11,240 MW. On Sept. 6, thermal generation reached 25,142 MW, which fulfilled roughly 54 percent of demand, and imports peaked at 10,905 MW, or roughly 23.5 percent of demand.

Meanwhile, Western natural gas prices dropped by as much as $2.77 in trading. SoCal CityGate posted the greatest loss, plunging from $5.01/MMBtu to $2.24/MMBtu. SoCal Border natural gas values fell $1.63 in trading to $1.86/MMBtu. PG&E CityGate gas had the highest price among Western hubs at $3.47/MMBtu.

Henry Hub natural gas values lost 19 cents to $2.13/MMBtu.

Southern California Gas Co. in a Sept. 3 ENVOY post noted that an error was made in how it allocates storage under the California Public Utilities Commission's 2020 Triennial Cost Allocation Proceeding Decision [D20-02-045].

SoCal Gas modified its allocation for the storage capacity reserved for balancing starting May 1, but said that since that time, it "has been inadvertently prorating summer withdrawal and injection capacities above the maximum authorized capacity in D.20-02-045." It indicated this would be addressed by mid-September, after information technology modifications are made.

In a different ENVOY notice, SoCal Gas said it will continue testing-related withdrawals from Aliso Canyon on Sept. 17 and 18.