Two years and four months after the project broke ground, the massive Ivanpah power-tower solar energy plant in the California desert is heating water.

BrightSource Energy said that this week, for the first time, it had focused the reflected sunlight from more than 1,000 heliostats – each comprising two mirrors the size of a garage door – onto a solar receiver atop one of Ivanpah’s three 459-foot-tall towers. This “first flux” brought water to just below the point of steam generation.

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Unit 1 of the Ivanpah Solar Energy Generating Station (image via BrightSource Energy)

“First flux essentially demonstrates operational readiness of the project,” Mike Bobinecz, BrightSource VP for construction management, said in a statement. “After years of planning, engineering, manufacturing and construction, we are entering the final stage of start-up of the equipment and systems.”

Unit 1 is the furthest along of the trio of mirror-ringed towers that make up the 377-megawatt Ivanpah Solar Electric Generating System, which is backed by a $1.6 billion U.S. Department of Energy loan guarantee, and is owned jointly by BrightSource, NRG Energy and Google. BrightSource said Unit 1 was 90 percent complete, with Unit 2 at around 80 percent and Unit 3 “more than 70 percent complete.”

BrightSource said that through December and January, more than 2,000 construction workers were working on the plant. The aim is to have power flowing from Unit 1 by the end of June, with Unit 2 coming online in September and Unit 3 up and running before the end of the year.

For now, with “first flux” under their belts, plant developers said the next step is to point more of the sun-tracking heliostats at the boiler.

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image via BrightSource Energy

“We are now focused on reaching the point where we can place a full load of heliostats onto the boiler and push the project towards commercial operation,” said Gil Kroyzer, BrightSource VP for modeling and solar field design. “Push” in quite the literal sense, it seems: BrightSource said that “when a certain level of pressure is reached, the system will be ready for steam blows to clear out any debris inside the pipes so that it does not damage the steam turbine once operational.”

When the plant is completed it will have a total of 173,500 computer-controlled heliostats pointed at the towers. Those heliostats are being assembled at the project site, at the rate of more than 500 a day.

A 29-MW version of BrightSource’s concentrating solar technology began operating in Coalinga, Calif., in late 2011 to provide steam for enhanced oil recovery at a Chevron oil field. There had been earlier power-tower demonstration projects in the U.S., and Spain has three plants functioning. In addition to Ivanpah, before the end of the year SolarReserve’s Crescent Dunes plant in Nevada, which comes with molten-salt energy storage, is expected to begin producing energy as well.