Brightsource and Bechtel Missed the Opportunity for Co-generation at Ivanpah Solar-Thermal Station
Less than two years ago, I wrote about the rush to industrialize the Mojave Desert with ever-larger solar thermal arrays. The most notable example was Brightsource Energy’s mega-solar plant in California’s Ivanpah Valley, near Primm, Nevada. Together, the three Brightsource units at Ivanpah obliterated 3,500 acres of fragile desert habitat, replacing it with 170,000 motorized, articulating mirrors and three massive receiving towers.
On September 24, 2012, Brightsource confirmed that it had synchronized their Unit 1 station with the existing electrical power grid. Although a photo on their website shows most, if not all of the Unit 1 mirrors in operation, no one other than the plants operators knows how many of the articulating mirrors pointed at the receiving tower during synchronization.
While testing prior to synchronization, operators focused many of the Unit 1 mirrors to either side of the receiving tower. Photos taken during the test procedures show an ominous “solar flux” to either side of the receiving tower. As additional heat for steam generation was required, operators quickly moved standby mirrors to focus directly on the receiving tower. Although it amounted to a “proof-of-concept” connection, in the months that have followed, Brightsource has yet to announce repetition of the synchronization process.
Since the Ivanpah project represents a quantum leap in solar thermal power generation, no one knows if it will work as planned. Will plant operators be able to point all 170,000 panels at the three receiving towers on any given day? Will the intensity of the reflected solar flux destroy the steam generators at the top of each tower? If Brightsource knows the answer to these questions, they are not talking. Their press releases featured platitudinous and self-congratulatory rhetoric about their first synchronization, but little else about testing protocols and procedures.
Maybe the Ivanpah mega-solar plant will succeed and maybe it will fail, but one mega-mistake is obvious. When Bechtel Corporation planned the facilities for Brightsource, they omitted any onsite thermal storage capability. If the plant ever works, it will produce power only when the sun is shining. When questioned, Brightsource said that they needed to get “several” plants working without onsite thermal storage prior adding that complexity to future projects. In other words, the technology is not yet ready to do it right.
As we know, the electrical grid is a complex and vulnerable infrastructure. Adding or subtracting too much power too quickly can cause cascading shutdowns of the adjacent grid. If Brightsource and Bechtel can simultaneously synchronize all three units with the grid, the lack of onsite thermal storage will limit electrical power production. If liquid-sodium thermal storage was present at Ivanpah, it could help balance and augment power generation at the site. With onsite thermal storage, co-generation could begin prior to sunrise and the mirrors could come online as the thermal storage dissipated. That would allow for a smooth ramp up of power entering the electrical grid. Without co-generation from onsite thermal storage, operators must bring each unit slowly up to power. Once operators achieve that elusive synchronization with the electrical grid, they can then focus additional mirrors on the receiving towers. At some point during the day, one would hope that all 170,000 mirrors would focus on the towers.
In the late afternoon, operators would refocus more mirrors away from the receiving towers. By sunset, the towers would go dark, steam generation would cease and the process of disconnecting each of the three units from the power grid would commence. The following morning, each unit would go through the delicate process of reheating and synchronization with the grid. The situation almost guarantees that the massive plant will rarely achieve maximum power output and will spend much of its time ramping up and ramping back down.
No one has said what would happen if a desert thunderstorm were to move rapidly over the solar array. What effect would so rapid a withdrawal of power do to power generation and synchronization to the electrical grid? What effect would a downpour have on the superheated receiving towers? If storms were in the forecast, the plant would have to operate at lower power, in anticipation of possible weather related shutdowns.
Like an old-fashioned steam locomotive, contemporary steam generators are more efficient and last longer when they operate continuously. Unlike a diesel electric locomotive, which can be brought up to operating temperature quite quickly, the firebox of a steam locomotive is kept hot until it is taken out of operation for maintenance or repair. Restarting these ancient “steam generators” is a time consuming and delicate process. Likewise, daily thermal cycling of the superheated steam generators at Ivanpah guarantees premature wear and increased operating costs.
In their haste to design and build the largest solar thermal energy station ever, Brightsource and Bechtel have made two potentially fatal errors. First was the aforementioned lack of onsite thermal storage and co-generation. Second was their use of single-sided mirrors for focusing sunlight on to the receiving towers. Had Bechtel taken a little more time in designing the systems, they could have designed the 170,000 articulating mirrors to flip over, thus exposing passive solar electrical panels affixed to their undersides.
If they had utilized this scheme, the majority of panels could start each day in passive solar mode, generating sufficient electrical energy to synchronize with the grid. Upon achieving synchronization, operators could begin flipping panels so that their mirrored sides would focus on a receiving tower. As sundown or a thunderstorm approached, operators could begin flipping panels from reflecting mode to passive reception mode, thus smoothing the ramping down of electrical generation and eventual disconnection from the grid.
The key to this plan is to switch quickly from solar reflecting mode to solar receiving mode. Before state and federal regulators approve construction of any additional solar thermal plants in our fragile desert environment, they should require both thermal storage and passive solar additions as part of any new plant construction.