An oil donkey, cycling every 7 or 8 seconds, dips into the well 11,500 times per day. (The math is pretty simple.) A solar tracker, over a 30-year lifetime, making one cycle per day, makes 11,000 trips in its career. System failure for these devices, therefore, should not be a concern. The metric that matters is cost, so if you spend 10 percent more to track the sun, and get 25 percent more light (and revenue), that would be considered a good trade, and a step worth taking. On your roof, this is problematic; on the ground it is highly recommended, and it helps to explain why utility scale arrays, outstanding in their field, can provide power at a much lower cost.
Most photos of PV arrays show them to be fixed, either to a roof or to the ground. The trouble is that most of the light bounces off the surface and is lost. “Direct normal insolation” (aka, DNI) is what engineers call the phenomenon of having the sun directly overhead, beaming its signal straight to whatever device is collecting it. Fixed arrays, even if they are tilted in the right direction, attain this happy state only for a short time, and so the efficiency of a stationary PV panel is pretty low. It stands to reason that you would get a much higher yield if you could point the array at the sun all day long.
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The solar tracker business is no longer small potatoes. In January of this year, Soltec, the Spanish maker of single-axis trackers, began installing them at Piaui, a power plant in Brazil owned by Enel; it is a 292 MW array. “This is the second large-scale solar power tracker installation taken by Soltec in Brazil. After completion of this project Soltec would have installed trackers at 450 megawatts of projects in the South American country.”
“Overall, the Spain-headquartered tracker giant has installed 1.4GW of trackers in the Americas, and also has several large-scale projects underway in the US.”
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You may have noticed the phrase “single-axis tracker,” and wondered what other kind is there? Single axis tracking means that the array tilts from pointing east in the morning to west as the sun sets. You may recall from your first year Latin class that the word oriental refers to the ‘rising’ sun. The word occidental refers to the ‘setting’ sun. Every morning, these arrays automatically ‘orient’ themselves to greet the rising disk. Related: This Supermajor Is Leading The Charge On Renewables
Dual-axis tracking means that the array not only tracks the sun from east to west, but also follows it as it rises then falls above the horizon, a measurement known as the azimuth. In order for a PV array to follow the sun on both axes, it would be limited in width; tipping up the northern end of a 100-meter long array is rather prohibitive in terms of too much structure. (In Australia or Chile, you would have to tip up the Southern end.)
The only solar technology that benefits from using dual axis tracking is a dish concentrator. The upside of dishes is that they, and only they, collect 100 percent of the signal, ie, the available sunlight, so they always maintain a “direct normal” position relative to the sun. The downside is, you don’t need a thousand suns to boil water, and in order to make power in a dish, the engineering necessary to overcome the steel-melting heat makes it cost prohibitive. (Believe me, I’ve tried, and was far more successful melting steel at the focus than making cheap electricity. By the way, do not try this at home without welding goggles. The brightness will ruin your eyes. Now where did I put that keyboard.)
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How green is my solar?
The leader in the field, NEXTracker, recently announced that it has sold over 1 GW of trackers in India alone. (In my view, India is the world’s best solar market, though China will give them a run for their money.) GTM Research noted that NEXTracker remained the leading solar power tracker for a second consecutive year in 2016, and increased its global share in trackers market from 24 percent to 30 percent. NEXTracker also recently shipped trackers to the largest solar power project in the western hemisphere. Related: The Biggest Threat To Renewables Is Not What You Think
The project, located in Northern Mexico, “will have an installed capacity of 752 megawatts and is owned by a subsidiary of Enel Green Power.”
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Source: GTM Research report The Global PV Tracker Landscape 2016
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NEXTracker is also now working with a battery company to store the output. Though it is extremely sunny in much of India, the sun doesn’t shine all the time. But when it does we might as well make the most of it, and that is why trackers matter.
This is not a niche application or an experiment that may or may not work out. Trackers are here to stay, and a mean-time-between-failure (MTBF) expectation of 30 years is not unreasonable. In fact, that may be second only to the ongoing record of the local fusion reactor that feeds them which has gone four billion years so far without a shortage.
What’s not to like?
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By Henry Hewitt for Oilprice.com
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