(Bloomberg) -- Texas came uncomfortably close to another round of rolling blackouts Tuesday night because grid operators misjudged the weather.The Electric Reliability Council of Texas, which manages most of the state’s grid, had counted on a mild cold front sweeping the state, lowering demand for power. It didn’t happen. As a result, demand on the grid was about 3,000 megawatts higher than anticipated -- or the equivalent of 600,000 homes.The forecasting error, coming as 25% of power generation was off line for seasonal repairs, was another grim reminder of the vulnerability of Texas’s grid. Two months ago, a deep winter freeze knocked out almost half the state’s generating capacity, leaving millions of people in the dark for days. But Tuesday’s weather was hardly extreme, and the close call has raised questions about whether the grid operator, known as Ercot, can prevent a repeat of the February energy crisis.“It’s a disgrace for a power grid in modern times to struggle to keep the lights on during a mild day,” said Daniel Cohan, an associate professor of environmental engineering at Rice University. “We’ll be in trouble when a summer heat wave comes in and demand is one-and-a-half times as much as it was yesterday.”Shoulder SeasonWeather typically usually doesn’t have a big impact on electricity demand in spring and fall. Those are the so-called shoulder seasons when customers are neither cranking their heaters nor blasting their air conditioners. On Tuesday, temperatures in Dallas, Brownsville and Houston were moderately higher than normal, reaching or exceeding 80 degrees Fahrenheit (27 Celsius). That, combined with a dearth of generation, prompted Ercot to ask for conservation efforts for almost four hours.“Yesterday was an odd day,” said Matt Rogers, president of the Commodity Weather Group LLC in Bethesda, Maryland. “There were thunderstorms in West Texas that kept wind generation lower than normal. They are going to have another West Texas wind dip today, but not as much as yesterday.”Texas has long taken a laissez-faire approach to its power grid, allowing market forces -- rather than regulations -- to ensure there’s enough power on hand to satisfy demand. State lawmakers have been reluctant to rethink that method as they consider addressing the problems that led to the crisis in February.Yet the market is designed to operate with thin reserve margins. Unless lawmakers intervene to change that, weather will continue to beget volatility and chaos, said Katie Bays, an analyst at FiscalNote Markets.“Texas is a goat rodeo,” Bays said in an interview. “The state doesn’t want to intervene in the market, but the way that Ercot is operating is a feature -- not a bug.”Role of RenewablesErcot officials emphasized during a press call Tuesday that the amount of generation down for maintenance wasn’t unusual for this time of year, as utilities often schedule repairs for the spring when weather is mild and demand is lower. They added that solar and wind generation came in lower than expected Tuesday, a claim that may be used as ammunition by Texas lawmakers who view renewable energy as inherently less reliable than that from fossil fuels.Clean-energy advocates pushed back on Ercot’s explanation. Thought solar output was weaker than normal on Tuesday, it actually met or exceeded the forecast for most of the day, according to the Advanced Power Alliance. Wind generation similarly met or exceeded forecasts for most of the day, said Jeff Clark, the group’s president.“We have close to half of our state’s thermal generation off line for maintenance, and that’s what killing us,” he said, referring to coal, gas and nuclear plants. “We have plenty of generation in the state, but it has to run.”Tests AheadThe coming weekend may present another test for grid operators. Temperatures are set to dip into the 40s across Dallas, Fort Worth and Austin and fall to the 50s in Houston and San Antonio. While hardly the frigid readings that sparked the winter crisis in Texas in February, that could drive heating demand that’s largely powered by electricity in the state.“That’s chilly for them for late April and could invoke a bit of overnight to morning heating demand,” Rogers said.Summer could be ever worse. Already, almost 75% of Texas is gripped by drought, and more than 91% is abnormally dry. Drought makes heat worse because the sun’s energy goes into warming the air rather than evaporating ground moisture.“This doesn’t bode well for summer when they are already issuing these kind of alerts,” said Jim Rouiller, lead meteorologist at the Energy Weather Group. “The cold killed people. The heat will kill a lot more people.”(Adds detail beginning in the seventh paragraph.)For more articles like this, please visit us at bloomberg.comSubscribe now to stay ahead with the most trusted business news source.©2021 Bloomberg L.P.