This article is to help the solar rooftop installers to demonstrate the system performance test. The test should be conducted in a bright sunny day. THe steps followed are as follows:
1. _____________Check to make sure that the PV array is in full sun with no shading whatsoever. If it is impossible to find a time during the day when the whole array is in full sun, only that portion that is in full sun will be able to be accepted.
2. ___________If the system is not operating, turn the system on and allow it to run for 15 minutes before taking any performance measurements.
3.______________ Obtain solar irradiance measurement by one of two methods and record irradiance on this line: W/m2
. To obtain percentage of peak sun, divide irradiance by 1000 W/m2 and record the value on this line ___________. (example: 692 W/m2
÷ 1000 W/m2 = 0.692 or 69.2%.)
Method 1: Take measurement from calibrated solar meter or pyranometer.
Method 2: Place a single, properly operating PV module, of the same model found in the array, in full sun in the exact same orientation as the array being tested. After 15 minutes of full exposure, test the short circuit current with a digital multimeter and place that reading on this line: ________________Amps. Divide this number into the short circuit current (Isc) value printed on the back of the PV module and multiply this number by 1000 W/m2 and record the value on the line above. (example: Isc-measured = 3.6 Amps; Isc-printed on module = 5.2 Amps; Irradiance = 3.6 Amps/5.2 Amps * 1000 W/m)
4. ____________Sum the total of the module ratings and place that total on this line __________Watts = 692 W
Multiply this number by 0.7 to obtain expected peak AC output and record on this line Watts AC-estimated
5. _____________Record AC Watt output from the inverter or system meter and record on this line Watts AC-measured
6. _______________6. Divide Watts by percent peak irradiance and record on this line Watts AC-corrected. This “AC-corrected” value is the rated output of PV system. This number must be within 90% or higher of Watts AC-estimated
recorded in step 4. If it is less than 90%, the PV system is either shaded, dirty, miswired, fuses are blown, or the modules or inverter are not operating properly.
A PV system is made up of 20, 100 Watt STC
PV modules operating at an estimated irradiance of 692 W/m2
using method 2 shown above. The power output is measured to be 1000 Watts at the time of the test. Is this
system operating properly or not?
Sum of module ratings = 100 Watts STC
per module x 20 modules = 2,000 Watts
Estimated AC power output = 2,000 Watts STCx 0.7 = 1,400 Watts
Measured AC output = 1,000 Watts
.Corrected AC output = 1,020 WattsAC-measured
AC-corrected ÷ 0.692 = 1,474 Watts
Comparison of corrected and estimated outputs: 1,474 Watts ÷ 1,400 Watts
= 1.05 ≥ 0.9
Source: PV Installation guide: www.energy.ga.gov