Wednesday, May 6, 2009

Solar PV Trackers Can Boost Power Bigtime

They're getting better...

When I was cutting my teeth in the PV industry, I sold nothing but UniSolar panels and laminates. UniSolar works well in diffuse light because of its triple-junction technology which is more responsive to the sun's light spectrum. Therefore, directly tracking the sun's path was not as important and, because thin-film PV requires more area, tracking becomes cost prohibitive.

I was also conditioned to think why anyone would add something mechanical--requiring maintenance and susceptible to breakdown--to something that works well statically, the solar panel. In fact, when researching trackers earlier this decade I read one PV system owner using a tracker say "if you have enough time on your hands and like to tinker, use a tracker. Otherwise, I don't advise it." But since then I've become more accepting of tracking.

Single-axis tracking (SAT), which pivot panels along the sun's path from east to west throughout the day can increase electricity production over fixed flat panels by as much as 38%. SAT panels produce 23% more power than arrays fix tilted at 15 degrees south. Obviously, this is significant if one's rebate or feed-in tariff is based on monthly kilowatt-hour output. Power purchase investment groups also came to require single- or dual-axis trackers to make the numbers work for a viable power purchase agreement.

So in order for trackers to go from novelty to mainstream, they had to become better overall at what they do particularly for large-scale projects. And they did. The apparent next phase of large-scale (sometimes called utility scale) PV systems is in concentrated PV arrays utilizing dual-axis tracking. CPV panels use less silicon and maximize that silicon's output with mirrors or Fresnel lenses sometimes requiring less area than flat plate panels, less mounting hardware, less labor to install. One company, Opel Inc., in Shelton, Connecticut, says its Mk-Id high concentration photovoltaic module (at right) with its dual-axis tracker will require 25% less gross DC wattage than a flat-plate array to get the same kWh production. The Mk-Id design has sunlight shining through a 11"x11" fresnel lens which concentrates rays on a tiny 10mm x 10mm silicon chip. The module with dual axis tracking surpasses output of fixed-flat panels by 40% and 15-degree fixed panels by 35%.

So who needs PV tracking? Anyone who needs to eke out as much performance from the panels as they can. Trackers by nature are more appropriate for ground-mounted systems but there are exceptions.

It's suggested readers conduct their own online research on trackers for residential scale projects. For large-scale projects some other major tracker manufacturers besides Opel, include the RayTracker (photo at top), Wattsun Tracker, APS Tracking (developed by Arizona Public Service) and ET Trackers.


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