Crescent Dunes is the world’s first utility-scale facility to feature advanced molten salt power tower energy storage capabilities
Photo courtesy of SolarReserve

Bright idea: The Crescent Dunes plant powers 75,000 homes with no emissions

Sun on a Stick

Desert Companion

A new solar plant outside Tonopah is sparking a debate about the relationship of big renewable energy projects to the environment 

Tonopah, Nevada

It’s so bright it’s hard to look at. But it’s also very hard not to look at. On a sunny, breezy Friday afternoon, the Crescent Dunes solar thermal plant is at full thrum, the receiver on its signature tower glowing a surreal, angelic, otherworldly white.

“It’s mesmerizing, isn’t it?” says plant manager Brian Painter, peering up at the 640-foot tower. “In a lot of ways, 80 percent of this is a conventional energy plant. But it’s the 20 percent that makes all the difference.”

Plant Manager Brian Painter

Plant Manager Brian Painter. Photography by Christopher Smith.

The 20 percent he’s referring to is that unearthly glowing tower. But it’s actually quite earthly, in a very literal sense. Heated by sunlight reflected by more than 10,000 mirrors, the receiver contains molten salt, which flows down the concrete tower and through a process that creates steam that drives a turbine that generates energy. About 10 miles outside sleepy Tonopah, SolarReserve’s Crescent Dunes power plant represents the latest and greatest in renewable energy technology. The 110-megawatt plant swung into full operation in November 2015; it powers 75,000 homes without any carbon emissions, preventing 279,000 metric tons of CO2 annually from polluting the atmosphere. The molten salt is nontoxic and is expected to last for the plant’s anticipated life span of 30 years.

Its exotic footprint on the landscape — the gleaming mirrors amassed like a saluting robot army, the top of the tower glowing like a miniature sun on a stick — suggests this is a dramatic departure from a classic photovoltaic solar plant. It is. The Crescent Dunes plant has a few tricks up its sleeve that conventional photovoltaic (PV) solar doesn’t. For instance, it has the ability to store the energy it produces, keeping the 1,050-degree Fahrenheit molten salt in a storage tank, allowing the plant to produce power at night and in bad weather. No wonder that future solar projects in this “power tower” style are, for many, a beacon of hope for the next wave of renewable energy.

As cutting-edge as it may seem, the idea of concentrating, capturing and transferring sunlight like this to generate power has been around for a while.

Crescent Dunes' heliostats reflect sunlight

Crescent Dunes' heliostats reflect sunlight.  Photography by Christopher Smith

“It’s literally rocket science,” Painter says as we walk amid the alien forest of mirrors (also called heliostats) during an April 1 tour of the plant. “They came up with this idea in the ’80s, but it took some time to get it to work at an efficiency that could exist on a commercial scale.”

The actual molten salt storage technology was developed by scientists at Aerojet Rocketdyne over two decades. With seed capital from investment firm U.S. Renewables Group, SolarReserve formed in 2008 to commercialize solar thermal power with storage and, ultimately, bought Rocketdyne’s technology. With the help of a $737 million federal loan guarantee, it built Crescent Dunes on 1,600 acres leased from the Bureau of Land Management. To be sure, there are other power tower projects in the world — just over the border in California is BrightSource’s Ivanpah Solar Electric Generating System, whose receivers are filled with water. But as of now, Crescent Dunes is the world’s largest solar thermal plant of the molten-salt storage type.

Steam is created by the plant's molten salt.

Steam is created by the plant's molten salt. Photography by Christopher Smith.

Kevin Smith, CEO of SolarReserve — a mechanical engineer before he became an energy executive — has watched as renewable energy sources from wind to photovoltaic solar have become more efficient and affordable, but his money is on concentrated solar power.

“Wind projects have advanced considerably, with bigger turbines making the price come down substantially. Photovoltaic really picked up in 2006-2008, with the pricing coming down dramatically to be comparable with conventional energy,” he says. “The problem with both of them is they’re intermittent. When the wind blows, when the sun shines, you get power. When the wind stops, when the sun goes down, you don’t. Our big benefit to the customers and the power markets is that our energy source is reliable. We’ve got a whole day’s worth of energy. If we get cloud cover for 45 minutes at two o’clock in the afternoon, with molten salt storage, it’s not an issue.”

But not everyone is so quick to sing the praises of solar thermal. Another key word in “utility-scale solar power” is “utility.” Skeptics say it’s important to keep in mind that the industrial footprint created by these sites isn’t completely without consequence, and the technology that’s so promising for humans and the planet may have some downsides. One Nevada environmental watchdog group, Basin and Range Watch, has raised the same concerns about Crescent Dunes that have beset other solar thermal plants: their possible effect on birds.

Even asking questions about bird deaths caused by a solar plant is to enter into a debate that requires some dizzying moral calculus.  How many bird deaths are justified by how many megawatts of clean energy.

“They put these very large-scale solar plants in the middle of remote areas that may be in bird migratory flyways, so there are going to be bird deaths,” says Laura Cunningham, co-founder of Basin and Range Watch, based in Beatty. “What we’re seeking is a lot more information, study and research on how many birds are dying, and what kind, and an open dialogue so we can figure out a way to avoid or at least mitigate those deaths.” Basin and Range Watch has filed a Freedom of Information Act lawsuit against the BLM to see uncensored monitoring reports and emails about those reports between SolarReserve, its contracted environmental monitoring company, Stantec, and the BLM.


The flux of the matter

Collisions with the mirrors, which birds may mistake for water, and “solar flux,” the plant’s pool of concentrated sunlight that converts to heat when there’s an object present (such as a bird) to absorb it, are thought to be the two main killers of birds.

But how many birds? What kinds of birds? Those are the big questions. The answers you get depend on whom you ask. According to a document provided by SolarReserve, Stantec reported that a total of 54 birds died at the Crescent Dunes solar project between January 15 and October 27, 2015, including those found dead in a two-mile buffer zone outside the plant’s boundary. (The document doesn’t list what types of birds.) SolarReserve’s methodology for monitoring and preventing bird deaths includes a systematic search for bird carcasses. This search has several components, including environmental consultants watching the tower each day with binoculars, and another group performing a monthly site search for dead birds; the monthly search takes seven days and covers one-eighth of the site. In other words, in increments of one week a month, the entire 1,600-acre Crescent Dunes plant site is completely surveyed for dead birds every eight months. The Great Basin Bird Observatory also helps oversee the surveys and performs its own surveys, too.

It sounds like a good plan. But some scientists say getting a more accurate picture of bird deaths at renewable energy plants requires you to account for a big X factor: what those surveyors aren’t
finding and aren’t seeing. Ornithologist Shawn Smallwood, a veteran at conducting bird death surveys for wind power projects in California, says large time gaps between surveys and old-fashioned human error means searchers will never see the dead birds that blend in with the landscape, never see the bird carcasses carried off by predators, never see the birds that are fatally injured but die later, far away from the plant. Smallwood doesn’t necessarily doubt SolarReserve’s good intentions, but he questions the thoroughness of their search methods, particularly the fact that only a fraction of the site is searched at a time, with several weeks between searches.

His take on their methods: “Incredibly, the fatality search interval is eight months, meaning that any given site is visited by the searchers every 8 months. This is by far the longest fatality search interval I have ever seen at any site. ... No wonder the fatality list is small.” His conclusion: “There’s no way to tell how many birds are being killed by this project. The monitoring will be unable to inform of project impacts because the design appears to be hopelessly ill-suited for deriving estimates of fatalities.”

SolarReserve’s Smith stands by the numbers, and is eager to put them in perspective. “The amount of fatalities represented by third-party biologists are very low,” says Smith. “But even if they were triple what they are, from a biological standpoint, it’s still an incredibly small amount compared to (birds killed by) fossil fuels.”

But no one knows how many for sure. Part of the problem is that there has been only one peer-reviewed research project that attempted to establish a clear picture of how many bird deaths are caused by solar power-tower plants — and that’s practically ancient history: It was published in 1986 in the Journal of Field Ornithology, about the small, 10-megawatt Solar One project near Daggett, Calif. And yet, that study has been used as the basis for estimating bird death figures at much larger projects. For instance, extrapolating from that, ornithologist Smallwood testified in 2014 to the California Energy Commission that the 377-megawatt BrightSource solar thermal project in Ivanpah could be killing up to 28,000 birds a year, though he cautioned that this was based on “quick calculations and my unverified assumptions.” (To the contrary, on its website, BrightSource reports 321 bird deaths at Ivanpah between January and June 2014). Smallwood was testifying about plans for the Palen Solar Electric Generating System, a 500-megawatt solar project proposed for 2,800 acres in Riverside County, near Joshua Tree National Park. The commission essentially killed Palen by denying a permit extension for the project, which had become mired in bankruptcies, ownership changes, and design modifications (indeed, what began as a solar trough design morphed into an ambitious power-tower plan, which is part of what moved Smallwood to get involved). While Palen’s troubled finances dealt a major blow to the project, the concerns of Smallwood and others about solar thermal’s possible effect on birds grabbed headlines.


Moral calculus in flight

How do you reconcile such wildly different figures about bird deaths? You really don’t, except to acknowledge that surprise and uncertainty reign in our early understanding of this new technology’s possible side effects on wildlife and the environment.

Case in point: Well after the BLM and other federal agencies approved SolarReserve’s Avian and Bat Protection Plan for Crescent Dunes in 2011, there were unforeseen events. For instance, according to an email from a Stantec worker to a BLM official, on January 14, 2015, 130 birds died at Crescent Dunes over a four-hour period. The worker wrote: “During Tonopah Solar’s testing today there were about 1/3 of the heliostats pointed above the power tower, which formed a halo that is about 1,200 feet off the ground. Our CIC (compliance inspection contractor) and mortality biologists observed approximately 130 birds fly into the flux halo above the power tower and become white flashes with a small smoke cloud immediately following. ... There were no carcasses that they could find on the ground below the tower, but it is clear that these are bird mortalities.” SolarReserve says it’s since altered the “standby” position of the heliostats to avoid creating this lethal halo of solar flux, and that bird deaths have dropped dramatically since, according to Stantec’s numbers.

Even asking questions about bird deaths caused by a solar plant is to enter into a heated discussion that requires some dizzying moral calculus. How many bird deaths are justified by how many megawatts of emissions-free energy produced? And does it matter what kinds of birds die? What if a solar plant kills a relatively small number of sensitive regional birds, but ostensibly replaces a fossil fuel plant that, both directly and indirectly, kills a vastly larger number of birds? Is it morally meaningful to compare the impacts of these two types of energy production, or is it intellectually dishonest?

“It’s exasperating to me that our critics look at conventional energy and say, ‘Well, there’s nothing we can do about it.’ That’s where the focus should be. Look at the tremendous impact conventional energy has on birds — not just the structures and the wastewater ponds on coal sites, but the emissions,” says SolarReserve CEO Smith. “(Solar thermal) is having more than zero effect on birds, I’ll agree, but on a scale of one to 100, if coal is 100 and we’re a two, three, four or 10, we’re still 10 times better, a dramatic improvement from fossil fuel’s effect.”

But, says Cunningham of Basin and Range Watch, a bird is not a bird is not a bird.

“We get it a lot: ‘Well, cats kill millions of birds a year compared to solar plants,’” she says. “But when you have a giant solar plant in the middle of the Great Basin desert, we’re talking about Swainson’s hawks, a sensitive species in Nevada, or desert birds like horned larks being impacted. We’re not talking doves and rock sparrows, we’re talking about a sensitive desert ecosystem that has a giant bird-catcher plopped in the middle of it.” She adds: “And none of this is to say we’re against renewable energy. Instead, we’re in favor of the nuances of making renewable energy safer for the environment.” Cunningham also rejects the frequent charge that Basin and Range Watch is opposed to any kind of industrial solar development.

What if, with better monitoring methods, it’s discovered that more birds than previously thought are dying at the plant? It would be untenable to shut the plant down; more realistic, says Cunningham, would be to ask for SolarReserve to compensate by paying to preserve bird habitat somewhere else, or consider modifying plant operations during bird migrations.

The plant's molten salt is stored in tanks to provide energy well after dark.

The plant's molten salt is stored in tanks to provide energy well after dark.  Photography by Christopher Smith.

The questions aren’t going away. With the U.S. government having extended federal tax credits for solar projects through 2022, the industry is hitting its stride. SolarReserve has several more projects planned using its signature molten salt tech. One, Redstone, is a 100-megawatt CSP plant in South Africa that will start construction in the next few months. Another, Copiapo, is a planned hybrid PV/CSP plant in Chile that has received all its environmental permits. SolarReserve also made bids to build three other CSPs in South Africa and submitted environmental permits for a second one in Chile. Crescent Dunes looks like it’s here for the long haul, too: It has a 25-year contract to sell the energy it produces to NV Energy.

“Crescent Dunes has a worldwide reputation already,” says CEO Smith. “When I’m traveling to Santiago, or Johannesburg, or Hong Kong, I must say ‘Tonopah’ 500 times. If you’ve never heard of Tonopah, you’d never know it existed. But it’s the center of the universe for concentrated solar power with storage.”

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