June 17 (Reuters) - Texas and California urged consumers to conserve energy this week to reduce stress on the grid and avoid outages as homes and businesses crank up air conditioners to escape a scorching heatwave blanketing the U.S. Southwest. High temperatures were expected to top 110 degrees Fahrenheit (43 Celsius) through the weekend in parts of several states including California, Arizona and Nevada. “The public’s help is essential when extreme weather or other factors beyond our control put undue stress on the electric grid,” said Elliot Mainzer, CEO of the California ISO, which operates the grid in most of California. The ISO said its Flex Alert, or call for conservation, “is critical because when temperatures hit triple digits across a wide geographic area, no state has enough energy to meet all the heightened demand.” The ISO said “evening is the most difficult time of day for grid operations ... because demand remains high as solar energy diminishes.” So far this year, solar has provided 22% of the grid’s power. The ISO warned that “If demand still outstrips supply after Flex Alerts ... the ISO could again order utilities to begin rotating power outages.” Over the past year, both Texas and California imposed rotating or controlled outages to prevent more widespread collapses of their power systems - California during a heatwave in August 2020 and Texas during a brutal freeze in February 2021. In Texas, the Electric Reliability Council of Texas (ERCOT), expects demand on Thursday to break the June record set on Monday. But real-time prices in ERCOT have remained comfortably below $100 per megawatt hour (MWh) since Tuesday evening as more power plants returned to service from forced outages that caused prices to soar over $1,900 for two 15-minute periods on Monday. That compares with a five-year (2016-2020) average of $33/MWh. Reporting by Scott DiSavino, Editing by Nick Zieminski Our Standards: The Thomson Reuters Trust Principles.