IRWINDALE >> As high clouds slipped in front of the sun, executives from MillerCoors flipped the switch Thursday on the largest solar panel array of any brewery in the country.

When the sun is out — a pretty sure bet in Southern California — the 10-acre, 10,000-unit, fixed solar panels installed in three locations on the grounds of the Irwindale plant will generate enough energy to produce 7 million cases of beer per year.

The black solar panels, which are very similar to those affixed to rooftops and parking lots, will provide between 7 percent and 40 percent of the plant’s electrical energy, said Kim Marotta, MillerCoors director of sustainability.

Marotta, who flew out for the ceremony from Milwaukee, said the Irwindale site was chosen from among eight brewery plants because of its location. It’s the only MillerCoors facility in sunny Southern California.

When asked if MillerCoors, or its parent companies, SABMiller, a South African company, or Molson Coors Brewing Co., intend to market their solar beer with distinct labeling or ads, she laughed.

“We will have great opportunities with the Gold Line coming in and the great six-pack (that overlooks the 210 Freeway). People, millennial, beer drinkers, they care about this, especially here in California.”

Going green is more than a marketing tool for the brewery. The Irwindale plant, in operation for 35 years, already reduced its water and energy use by 30 percent since 2009, said Fernando Palacios, executive vice president who spoke at the unveiling ceremony.

“Throughout California, energy costs are increasing. There is pressure on the energy grid. By installing these solar panels, we can get immediate environmental benefits and lower our greenhouse gas emissions,” he said.

Lawmakers from Sacramento to Washington praised MillerCoors on Thursday as a corporate leader in sustainability, safety and job creation. About 500 people are employed at the Irwindale plant.

Rep. Grace Napolitano, D-El Monte, used the occasion to challenge other businesses to reduce water use during what is now a four-year drought in California and shrink their carbon footprint.

“Other businesses, you can produce the same results. You don’t have to reinvent the wheel,” she said.

The beer company partnered with SolarCity, the largest solar provider to Fortune 500 companies, cities and schools, Palacios said.

SolarCity’s recent clients include Walmart and Hewlett-Packard, said Jim Cahill Jr., regional vice president of their Southern California and Hawaii operations. SolarCity has installed solar energy panels at Los Angeles Unified School District and Glendale Unified School District campuses, he said. Last year it installed 80 megawatts of solar power in the United States.

Cahill said the three separate arrays at the beer plant are pointed south to capture the most sunlight. They will generate 3.2 megawatts an hour, about 16 MW a day or 5,840 MW per year. The energy flows into an inverter that converts it from direct current (DC) to alternating current (AC) which gets sent into the plant’s electric plant. Electricity is used to heat, cool and pasteurize beer, Marotta said.

MillerCoors can guarantee up to 40 percent of its power for 25 years. He said. Because solar panel is supported by Southern California Edison, the same amount of solar power is taken off the electricity grid. It also saves the company money.

“They are huge users of electricity here so this will be helpful,” Cahill said, pointing to the array on the northeast property, near the future Gold Line light-rail station.

Philip van Rensburg, packaging manager, said the company wants to reduce costs and make beer with less of an environmental impact. It also extracts methane from waste water to run engines used in beer-making.

“Sure, MillerCoors makes great beer but that is not enough,” he said in his opening remarks.