PV Performance
Daily PV Summaries for the WHEDA Bldg, Madison, WI
The following data types are collected by the WHEDA datalogger on a 15-minute basis:
- year, date, and 15-minute period (e.g., 6:45, 7:00, 7:15 ...)
- air temperature in Deg C
- power on array in W/m2 (solar irradiation in the plane of the array)
- wind speed in m/s
- volts +, volts -, current +, current - Note: the Omnion inverter employs a bipolar DC input
- inverter output in kWac
The following graph shows the monthly measured and simulated energy production from September 1997 through December 1999.
Why is there a difference between the measured and simulated energy output?
There are several factors that contribute to the less than predicted performance of the WHEDA PV system. First, there is shading from several nearby building structures. A church spire casts a significant shadow across the array around 10:30 a.m. each morning. Parapet walls, around the roof of the WHEDA building, partially shade the array in early morning and late afternoon - of most significance in winter. Second, an inverter failure in July 1999 decreased the system availability. Third, the pyranometer, watt transducers, and temperature sensor may require calibration. Fourth, the model used for simulating the PV system output probably has a certain level of inaccuracy. All of these and other factors probably contribute to the discrepancy.
Links to Daily PV Summaries by Month for 2000:
January February March April May June July August September October November December
