solar energy
Learning from Others’ Mistakes by Robert Dally
AS A LONGTIME INSTALLER AND SOLAR ENGINEER,
I’ve seen many single-axis tracker failures over the last two decades. Failures from wind, bad designs, wrong materials, poor planning, and EPC errors (root cause usually a bad design). Tracker trend was to reduce steel to lower cost, thinning out to excess only to encounter wind failures; the knee-jerk reaction was to apply shock absorbers, springs, multi-faceted torque tubes (e.g., complexity, cost, and uncertainty). When those ideas fell short, the second knee-jerk reaction was to replace simple steel with complicated steel (e.g., transmissions with gears, oil, and seals, driveshafts with U-Joints, hangers for spinning driveshafts). Thanks to an underabundance of forethought and an overabundance of after-the-fact fixits, a GW solar farm that used to have 20,000 drives (1/row) now has 180,000 (9/row). I’ve seen contractors beat on the U-joints with a hammer because the HDG on the two mating splines was too thick. Many U-joints’ bearing cups broke open to become a latent defect had I not noticed it as an Owner’s Engineer on a 21 MW tracking solar farm. Simplicity, not complexity, will deliver true cost savings in CAPEX, EPC, and OPEX. Single-Axis Trackers for PV Solar Farms are valuable in all markets. In sun-rich areas, they deliver 20 percent more annual energy compared to fixed tilt, and around 35 percent more in the summer months (air conditioning); the 20 percent more energy (revenue) for perhaps 5 percent more up-front cost to a solar farm (compared to fix tilt) is a net gain of 15 percent on ROI (e.g., 10 percent ROI becomes 11.5 percent). Another way to look at
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the financial gain is that, compared to fixed tilt solar farm in MENA, it can be 20 percent smaller (in less PV, mounting, inverter, transmission, etc.) and net 15 percent cheaper to deliver the same energy/year as a fixed tilt system. Single-axis tracking in high latitudes, such as the UK and northern Europe, yields a dismal 12 percent more energy than fixed tilt, barely justifying the extra expense for a single-axis tracker mounting system. However, a 4-meter chord tracker (or larger) allows ample access underneath for weed abatement and ground maintenance, an otherwise difficult and costly (OPEX) task with fixed tilt mounting. Restricted access underneath is also an issue with small trackers (~2m chord) which have relatively low tilting tables of PV. Unwittingly, the single axis tracker expanded its own geographical market simply by going to a 4m chord to support bifacial PV in a 2P configuration. A 4m chord in England will have 4m wide aisles (at 50 percent GCR), allowing ample access during construction (assuming no linkages or drive shafts blocking thru-access) and for OPEX (O&M, panel cleaning with water trucks, etc.), but most importantly for agriculture activity. A low laying crop such as clover, carrots, roses, grape vines, in the aisles with drivethru tractor access is possible with single axis tracking of the appropriate size. Single-
