By Dave Levitan:
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The vast and glittering Ivanpah solar facility in California will soon start sending electrons to the grid, likely by the end of the summer. When all three of its units are operating by the end of the year, its 392-megawatt output will make it the largest concentrating solar power plant in the world, providing enough energy to power 140,000 homes. And it is pretty much smack in the middle of nowhere.
The appeal of building solar power plants in deserts like Ivanpah’s Mojave is obvious, especially when the mind-blowing statistics get thrown around, such as: The world’s deserts receive more energy beamed down from the sun in six hours than humankind uses in a year. Or, try this one: Cover around 4 percent of all deserts with solar panels, and you generate enough electricity to power the world. In other words, if we’re looking for energy—and of course, we are—those sandy sunny spots are a good place to start.
But statistics are one thing, building a few thousand gigawatts of solar power is quite another. Deserts are dusty, windblown and remote. So far, only a few hundred megawatts of utility-scale desert solar power have been built. Most projects are in the American Southwest, with a few in the Middle East and north Africa as well. Though progress has been slow and significant technical challenges remain, experts and industry leaders seem to agree that engineering difficulties alone are not holding us back from a big desert solar build-out. “From the technical side, I think we can do it. In fact, I know we can do it,” says Seth Darling, a solar researcher at Argonne National Laboratory near Chicago. “I don’t know that we can do it from a policy side, but I sure hope we can.”
Water and dust
On the engineering side, though, Darling says that there are one or two challenges that still could be “deal breakers,” at least for some technologies. The big one is water. Concentrating solar power (CSP) plants, like traditional power plants, need to be cooled to run, and cooling takes water—lots of it. And of course, if water were abundant in the desert, it wouldn’t be the desert. At Ivanpah, on-site wells supply the plant with water, but that solution won’t always be feasible. “I can’t think of any technical way around that unless a dry cooling technology that’s effective and affordable is developed,” Darling says. “No one has really come up with a way to do that.”
For photovoltaics (PV), water is only needed to clean the panels, which brings up the second large problem with desert solar: dust. Solar panels and mirrors need to be cleaned almost daily if efficiencies are to stay where they need to be. Dust is not transparent, so even just one gram of dust per square meter of solar panel area can reduce efficiency by around 40 percent. At that rate, it doesn’t take long in a dusty desert for the problem to become intractable.
In the desert near Abu Dhabi in the United Arab Emirates the Middle East’s first large CSP plant recently faced down the dust issue. In order to reach the 100-megawatt-capacity goal of the Shams 1 plant, developers had to add substantially more mirrors to the plant than planned due to dust in the atmosphere. Scott Burger, an analyst at Greentech Media’s GTM Research who focuses on the region, said the plant probably ended up costing three times the initial estimate, thanks in part to dealing with that dust. And now that it is built, Shams 1 sends a series of trucks up and down the lines of 250,000 mirrors every day, using robot arms to spray that precious water and clean away the dust.
The good news on the dust front, though, is that some water-free ideas exist for cleaning PV panels—they just haven’t been produced at large scale yet. The best possibilities are electrostatic cleaning, where a charge flowing over a panel can essentially push the dust out of the way (the technology was developed initially by NASA for lunar and Mars missions) or mechanical systems that would just brush off a panel once a day. For CSP plants where windblown dust and sand can permanently erode the mirrors, tilting them down out of an oncoming sandstorm is one way to keep the plants viable.
From deserts to market
And then there’s transmission, which Randy Hickok, the senior vice president of asset management at Ivanpah co-owner NRG Solar, says could be the biggest hurdle. “Traditionally power plants haven’t been in deserts, so you don’t have a lot of high-voltage transmission running to these out-of-the-way locations,” he says. “For a lot of your best solar resource, you don’t have available transmission, and siting transmission is not an easy task.” High-voltage lines can cost millions of dollars per mile.
But again, the technical side of this is not the deal breaker. Darling says we are perfectly capable of building long lines to remote locales, and with high-voltage direct current (HVDC) the efficiency losses are quite low, on the order of only a few percent every thousand kilometers.
Hickok says that developers have rushed to build new facilities in locations where few upgrades to a transmission system are needed, but those “low-hanging fruit” possibilities get exhausted relatively quickly. The really big desert-solar ideas, like DESERTEC’s plan to power all of Europe with HVDC lines across the Mediterranean from north Africa, would require such a massive investment in transmission lines that they’re unlikely to move forward on meaningful timescales.
And even DESERTEC—which had led the calls for massive desert renewables development—has scaled back its planet-saving rhetoric in recent years as the challenge of getting started has grown. Thiemmo Gropp, director of DESERTEC, says the foundation’s main goal now is to help build some impressive pilot projects that will illustrate to the rest of the world that building big in the desert is doable. The group has partnered with Saudi Arabia, which hopes by 2030 to build an astonishing 54 gigawatts of renewable energy (41 GW from solar, essentially all of it in the vast Saudi desert) and is also on board with some initial projects in Morocco. Gropp agrees that the engineering challenges are not the primary obstacle, although of course the technology will continue to improve. “There are no serious hurdles,” he says. “Right now we have a car like in the 1920s or 1930s, we don’t have mass production of 2013; but it’s got an engine, it’s got 4 wheels, it works. I don’t see any technical principle hurdles.”
Out in the Mojave, Ivanpah is clearly a desert success story, but it can’t obscure the ongoing struggles that accompany it. BrightSource Energy, co-owner of the plant along with NRG Solar, has this year shelved a full gigawatt of other desert solar ideas. Many CSP plants have either been canceled or switched to more modest PV designs as panel prices have plummeted in recent years, showing again that the effort remains at the whims of fickle market dynamics. It is good to know, though, that whereas other planetary saviors (like, say, carbon capture and storage) languish in technological and cost purgatory, building solar power where the sun shines brightest doesn’t seem to worry those who are doing the building.