Page 286 - Solar Power in Building Design The Engineer's Complete Design Resource

METEOROLOGICAL DATA 253

The California Energy Commission (CEC) rates each manufacturer-approved PV
unit by a special power output performance factor referred to as the power test condi-
tion (PTC). This figure of merit is derived for each manufacturer and PV unit model
by extensive performance testing under various climatic conditions. These tests are
performed in a specially certified laboratory environment. Design parameters that
affect the system efficiency are as follows:

■ Geographic location (PV units work more efficiently under sunny but cool
temperatures)
■ Latitude and longitude
■ Associated yearly average insolation
■ Temperature variations
■ Building orientation (north, south, etc.)
■ Roof or support structure tilt
■ Inverter efficiency
■ Isolation transformer efficiency
■ DC and ac wiring losses resulting from the density of wires in conduits
■ Solar power exposure
■ Long wire and cable runs
■ Poor, loose, or corroded wire connections
■ AC power transmission losses to the isolation transformers
■ Poor maintenance and dust and grime collection on the PV modules

Meteorological Data

When the design is planned for floor-mount solar power systems, designers must
investigate natural calamities such as extreme wind gusts, periodic or seasonal flood-
ing, and snow precipitation. For meteorological data contact the NASA Surface
Meteorology and Solar Energy Data Set Web site at http://eosweb.larc.nasa.gov/sse/.
To search for meteorological information on this Web site, the inquirer must provide
the latitude and longitude for each geographic location. For example, to obtain data for
Los Angeles, California, at latitude 34.09 and longitude 118.4, the statistical data
provided will include the following recorded information for each month of the year
for the past 10 years:
2
■ Average daily radiation on horizontal surface [kWh/(m ⋅ day)]
■ Average temperature (°C)
■ Average wind speed (m/s)

To obtain longitude and latitude information for a geographic area refer to the
Web site www.census.gov/cgi-bin/gazetter. For complete listings of latitude and lon-
gitude data please refer to Appendix A. The following page lists a few examples for
North American metropolitan area locations.