The 377 megawatt Ivanpah Solar Energy Generating Station (SEGS) being built by BrightSource for NRG Energy has reached a significant milestone with construction now more than 75 percent complete. Since construction on this (concentrating solar power) CSP—or solar thermal—project got underway earlier this year it’s been going at a breakneck pace. By August, construction reached its halfway point and four months later it reached its three-quarters completion point, showing that the project is well on its way to producing energy for California in 2013.

This monolithic project, consisting of three tower and heliostat field units is the first major SEGS project in the U.S. since the 1990s. Unit 1 is expected to start supplying power to PG&E in mid 2013. Units 2 and 3 are contracted to start delivering power to Southern California and PG&E by late 2013.

Once completed it will be the largest single solar plant on the earth. Until—of course—it’s outsized by other projects underway by BrightSource and other solar developers, some photovoltaic and others, CSP. Subsequent BrightSource projects, including its Hidden Hills and Rio Mesa projects—both in California, will reach 500 megawatts each, for instance. And they’ll include molten salt thermal storage, allowing both plants to operate as base load power, even when the sun isn’t shining.

But for now, Ivanpah is the big kid on the block. Currently, more than 2,100 construction workers are toiling into the winter months to make sure the three unit project is on time and moving along smoothly. “The team continues to push ahead with heliostat assemblies, regularly completing over 500 heliostats each day. More than 14,000 assemblies were completed in November alone!,” BrightSource said. “In early December, the team hit an impressive milestone – 100,000 heliostats installed in the solar fields. Only 73,500 more to go.”

Even as construction workers continue to install the heliostats, other workers are busy commissioning them. “During commissioning, project electricians wire heliostats together and connect them to the communication and power distribution units,” BrightSource said. After that each heliostat is calibrated with the company’s Solar Field Integrated Control System software. The calibration ensures that each heliostat in the field of 10‘s of thousands is aimed at the boiler unit atop the tower, ensuring the sun’s thermal rays are appropriately reflected on the tower. Now, construction on the power block area, where the steam turbine will generate electricity underway.

Currently, the three units are in various stages of completion, with Unit 1 being the furtherest along. Workers are commissioning pumps, feed water systems, the fuel gas system and auxiliary boiler to support the main boiler system. Then it will clean the boiler’s evaporator section and conduct the first steam blow. And test the air cooled condenser to test the integrity of piping and checking for leaks. Unit 2 is slightly behind the first unit, with work on Unit 3 bringing up the rear.