SolarPro Magazine.pdf - Contractors Institute

performance measurement period. Theeasiest tool to use for this purpose is anIR thermometer. Use this instrument tomeasure a few cell temperatures in differentplaces on a module and in a varietyof locations throughout the array. Writedown the average cell temperature indegrees Celsius.Irradiance and inverter ac output mustbe measured simultaneously. Even on a relativelyclear day, high clouds or haze canquickly change irradiance. Remember tolook up at the sky periodically during testing.In one case, I was so focused on jumpingback and forth between reading theinverter displays and getting the pyranometer lined up withthe modules, I was surprised when I looked at the measurementsI had written down over a period of about 2 minutes.One irradiance value was much higher than the other two. Atfirst, I thought I must have written it down wrong or held thepyranometer at the wrong angle—pointing directly at the sun,for example—but then I noticed that the inverter output wasalso much higher. Finally, I looked up at the sky and noticedOur system DOES NOT search forthe sun, it FOLLOWS the arc of thesun, returns at midnight, and adjustselevation for the changing seasons.SIt is imperative to getreliable irradiancethat what had been a completelyclear sky now had a couple of hardedgedcumulous clouds. I had justmeasured about a 10% increase inirradiance and production fromthe elusive edge-of-cloud effect.With a full monitoring systemor portable datalogger, 15minutes’ worth of averaged irradianceand ac output provide anexcellent simultaneous reading.However, even with a simple $150pyranometer and the inverter display,you can obtain good resultswith the following method:Find a good location to place the pyranometer so thatit has exactly the same azimuth and tilt angle as the modules.Ideally, the instrument has a square edge or bracketand can be clamped or held in place on the corner of a moduleto ensure alignment. Make sure the pyranometer doesnot shade the modules. Alternatively, set the pyranometerup on a tripod and carefully align it to match the azimuthand tilt angle of the modules. The tripod method requiresmeasurements;otherwise, the powerestimate will haveso much uncertaintythat all other factorsbecome meaningless.Building Large Commercial Tracking Systems ForOver 28 Years!• Standard 16-panelsystem is designedfor 90 mph winds!• For huricane zones,we have a 12-panelsystem rated for150-mph winds!Tracking systemPrice:$4,980.00(Designed to tyour solar panels.)We also make a single-pole xedsystem with a safe, easy winter/summeradjustment. (Sept 21: loosen 2 bolts &adjust crank to winter & tighten bolts.March 21 reverse.)System cost: $3,200(Designed to t your solar panels.)The advantages of a pole-mountedsystem over a roof-mount:• Less Expensive ~ No Roof Leaks• Operates Cooler & More Ef ciently• Winter/Summer Adjustment For More GainThe Future Is Now!20KW system with(6) 3.36KW tracking panels.SOLAR(A Division of DH Satellite)600 N Marquette Rd, Prairie du Chien WI 53821608-326-8406 ~ 608-326-4233 (fax)www.dhsolar.net ~ 800-627-9443solarprofessional.com | SolarPro 49