(Adds hydropower and generation details)
May 9 (Reuters) - California’s electric grid operator has forecast power supplies will be tight this summer due to below average hydropower production and reduced generation, according to an assessment released on Wednesday.
The California Independent System Operator (ISO), the grid operator, said the system’s capacity to serve consumers will be tight in high-load periods in the summer months, especially during the evenings of hot days when solar power dissipates.
But it forecast only “an extremely low probability it will be forced to initiate rotating power outages” this summer.
The ISO, which forecast peak demand during the summer would be about the same as last year, said hydropower production is expected to be down 1,300 megawatts (MW) by late summer compared with 2017’s above-normal hydropower output.
One megawatt can power about 1,000 homes.
In addition, the ISO said natural gas-powered generation will see a drop of about 800 MW due to plant retirements.
The ISO assessment came a few days after a group of state regulators and regional power firms, including the ISO, released a technical report warning of a “moderate threat” to gas and electric reliability this summer and a “more serious threat” next winter because the Southern California Gas (SoCalGas) system is operating at less than full capacity.
SoCalGas cautioned that pipeline outages and restrictions on its giant Aliso Canyon gas storage facility in Los Angeles, which suffered a devastating leak between October 2015 and February 2016, could reduce its ability to deliver gas to fuel power generation facilities in Southern California this summer and winter.
SoCalGas is a unit of California energy company Sempra Energy.
The ISO projected there will be 51,947 MW of generation available to serve demand this summer with peak usage expected to reach 46,625 MW under normal conditions.
If temperatures are warmer than normal, as they were last year, the ISO said supply margins will tighten significantly as consumers crank up their air conditioners.
Last year, peak demand hit 50,116 MW in September.
The California Department of Water Resources said water content of snowpack in the mountains was just 51 percent of average as of April 2.
In addition, the ISO said 860 MW of generation retired since last summer, including 837 MW of gas-fired resources. Energy firms added 692 MW of new power sources since last year but 60 percent of that was solar, which will not supply much when supplies are tight in the evenings.
Reporting by Scott DiSavino Editing by Paul Simao and Leslie Adler