A surge of wind power in Texas has made predicting electricity supply more difficult, boosting opportunities for natural gas generators that have been battered by the rise of renewables.

Fluctuating renewable supplies can leave grid operators short of power and create price spikes, a phenomenon that’s set to worsen as additional wind and solar hit Texas’ grid, William Nelson, an analyst at Bloomberg New Energy Finance, said in a report. That could force grid operators to search for last minute more often, and that’s where gas plants that can start up quickly step in.

It’s a twist for Texas wind...