April 15, 2013

Solar Project Could Have Significant Effect on Desert Views

A portion of the area from which the Palen solar project's glowing collectors could be visible, overlain in red. (Google Earth screen capture by KCET ReWire)

by Chris Clarke
KCET Rewire

The proposed Palen Solar Electric Generating System east of Desert Center could be visible from as far away as the Mojave National Preserve, Mount San Jacinto, and the Kofa National Wildlife Refuge in Arizona, according to preliminary calculations by ReWire. The project, proposed by BrightSource Energy and Abengoa, is currently being evaluated by the California Energy Commission.

The project, which would include two solar receiver steam generators (SRSGs) each surrounded by 80,000 mirrored heliostats, would be built just north of Interstate 10 near the Corn Springs Road exit east of Desert Center. The SRSGs, each 130 feet tall, would sit atop 620-foot pedestals, so that the top of each SRSG would be approximately 750 feet above the ground.

The location of the Palen site in the eastern Chuckwalla Valley has one of the most expansive viewsheds in the western United States, even at ground level. Atop a 750-foot tower, line-of-sight distances to the horizon are even longer. And if one can see a spot on the horizon from Palen's SRSGs, it's safe to assume that an observer on that spot on the horizon would be able to see the SRSG.

ReWire used a publicly available web-based line-of-sight generator to calculate the viewshed from each of Palen's SRSGs, and the results are rather surprising. Given a clear day, Palen's SRSGs could well have uninterrupted lines-of-sight to high peaks in the Mojave National Preserve including Table Top, the Providence Mountains, and perhaps even the highest peaks in the New York Mountains, 110 miles north of the Palen site. Wide swaths of the Trigo Mountains, 45 miles distant in Arizona just across the Colorado River from Blythe, and even some western slopes in Arizona's Kofa Mountains 70 miles from Palen, could view Palen's SRSGs. And surprisingly, even a spot in the southern reaches of Mount San Jacinto, about 80 miles from Palen, might well enjoy a direct view of the SRSG atop Palen Unit 1's power tower.

Visibility of the SRSGs at such great distances would depend on a number of factors, including air quality. Though the SRSGs are intensely bright, the perceived intensity of light drops dramatically with increasing distance, following a mathematical relationship called the "inverse square law": if you increase the distance between you and a bright light, the apparent intensity of that light will diminish by an amount proportional to the square of the increase in distance.

Or perhaps more simply: if the Palen Unit 1 SRSG is indeed visible from the eastern slopes of Pine Mountain in the San Jacintos near Idylwilld, it would appear one one-hundredth as bright from that vantage point 80 miles distant as it would from the eastern outskirts of Desert Center, eight miles from the plant.

From 80 or a hundred miles away, on a clear day with no wind-driven dust, even a brightly lit SRSG may well appear only as a glint on the horizon, roughly as bright as a sunglint on a distant window. The noticeability of an SRSG at significant distance will depend in large part on contrast: if the light source is backed by bright midday sky, it may be only marginally visible at best, while the same unit might be clearly visible at the same distance from a vantage point where the SRSG is backdropped by a dark desert mountain range.

Of much greater importance (at least to those of us for whom unspoiled desert vistas are not our primary concern) is the effect of those brightly illuminated SRSGs on observers closer at hand.

Palen's power tower design would be substantially similar to that of BrightSource's now-mothballed project at Hidden Hills in Inyo County. In the Final Staff Assessment for that earlier project, California Energy Commission staff noted that glare from Hidden Hills' SRSGs "would produce a distinct visual distraction effect and be significant in perceived brightness and discomfort/disruption glare effects for a nominal viewing distance of 8.5 miles."

Assuming that Palen's power towers put out the same amount of light -- which seems a sound assumption -- that means drivers on I-10 would be subject to that level of glare discomfort and distraction along a stretch of a bit more than 17 miles between Desert Center and Wiley's Well Road, that distraction accentuated by the towers' placement less than two miles from the highway. For a considerable distance in that stretch, the power towers would be nearly impossible for drivers to exclude from their fields of vision without impeding their view of the highway.

By way of comparison for readers who've driven the section of Interstate 15 that runs past BrightSource's Ivanpah Solar Electric Generating System just south of Primm, NV and may have the mental image of those nearly 460-foot towers in mind, Palen's power towers will be nearly 300 feet taller.

At 8.5 miles distance, based on the CEC's Hidden Hills assessment, the SRSGs would appear to be a third the width of the sun. At 2.8 miles, each SRSG would appear to equal the sun in width. Unit 2 is approximately one mile from the Interstate, and Unit 1 about 2 miles. The potential for visual interference with safe driving on this high-speed desert highway seems considerable.

Also potentially considerable: the plant's effect on the visual resources of wilderness areas of Joshua Tree National Park. Though the more trammelled parts of the park are shielded from the plant by the Eagle Mountains and other ranges, park visitors who stray well off the pavement in the park's eastern section may well get a good view of the facility from the valley floor in the Pinto Basin just south of Clarks Pass along Highway 62. Wilderness areas in the Coxcomb and Eagle Mountains that happen to face east and south may well be afforded an unobstructed view of the facility as well.

If you have a copy of Google Earth and you'd like to explore the Palen project's possible viewshed, we've created two .kmz files that detail the viewshed from a somewhat arbitrarily chosen point a bit more than a third of the way from the top of each of the SRSGs. The files are here for Unit 1 and here for Unit 2. It's important to note that our calculations are preliminary; though the line-of-sight calculating app we used -- "Hey, What's That -- relies on reasonably accurate data from both Google Maps and the U.S. Geological Survey, the USGS digital elevation models used to calculate these viewsheds are accurate only to 100 feet. A 50-foot hill in the real world that's not accounted for in the digital elevation models might well turn out to obstruct a line of sight charted here.

Still, due to the facility's proposed location and the immense height of the power towers (more than twice the height of the Statue of Liberty) it seems certain that Palen will be clearly visible over hundreds of square miles of desert, and from surprising distances. It's worth noting that BrightSource is asking the CEC to grant an amendment to a previously approved project that lacked the power towers, which would certainly not have been visible from outside the Chuckwalla Valley. As previously designed by the now-bankrupt Solar Millennium, Palen would have used horizontal parabolic trough mirrors to heat a transfer fluid, and the mirror arrays would have reached no more than 30 feet or so above the ground. A difference in impact that large would seem to merit restarting the permitting process from square one.