Misaligned mirrors at the Ivanpah Solar Electric Generating System in California caused electrical cables to catch fire about two-thirds of the way up the Unit 3 tower on May 19, according to several media reports of statements attributed to fire department personnel.

The San Bernardino County (Calif.) Fire Department (SBCFD) reported on its Facebook page that it received the call just after 9:30 a.m. of a “commercial structure fire at the NRG Solar Generating Station” (Figure 1). The initial report suggested that there were “visible flames from the unit 3 tower near the 9th floor.” The Clark County (Nev.) Fire Department also responded to the call.



1. Smoke appears to be visible coming from the tower on the left in this image. Courtesy: SBCFD

According to SBCFD, when the first fire department personnel arrived onsite, plant workers led them to a staging area, but shortly thereafter the fire was reported to be smoldering with flames no longer visible. The teams then accessed “the upper stories of the tower to check for fire extension and ensure the fire was completely extinguished.”

David Knox, senior director of external communications for NRG Energy, told POWER via email that no personnel were injured as a result of the incident. He said the company is “currently assessing damage, investigating the cause and developing and implementing” its repair plan (Figure 2).



2. This image shows some steam line insulation that was damaged during the incident. Courtesy: SBCFD

In a followup email received on May 25, Knox told POWER that the Ivanpah Unit 3 fire “was caused by the heliostats (mirrors) being locked in place in preparation for a maintenance activity (maintenance mode), causing the solar flux to briefly move over a portion of the boiler tower. The mirrors were unlocked and moved to remove the solar flux from the tower.” He also said that new safeguards have been implemented to prevent similar incidents in the future.

Knox said the damage to Unit 3 was primarily limited to the aluminum covering of the insulation around pipes, as well as wiring and some valves, which he said could be repaired “relatively easily.” NRG anticipates having the unit back online within three weeks.

In March, the California Public Utilities Commission approved a forebearance agreement between Pacific Gas and Electric Co. and plant investors NRG Energy, Google, and BrightSource Energy. The agreement was necessary because the concentrating solar power plant—POWER’s 2014 Plant of the Year—is not meeting the guaranteed energy production (GEP) stipulated in its power purchase agreement. The GEP is measured over a rolling 24-month period starting with the first calendar month following the initial energy delivery date, which was mid- to late-January 2014 depending on the unit.

Performance in the past year has been better than in the first year, which is not uncommon when first-of-a-kind technology is deployed, but has not been good enough to overcome the previous year’s deficiency. The forebearance agreement extends the time to achieve the required GEP by six months. It is currently unclear how long Unit 3 will be offline as a result of the fire and how that might affect the plant’s ability to meet its GEP.

Aaron Larson, associate editor (@AaronL_Power, @POWERmagazine)

Updated (May 26 at 8:05 a.m. CDT): Added new information received from David Knox following NRG’s incident investigation.