Page 142 - Alternative Energy Systems in Building Design

118 SOLAR POWER SYSTEM PHYSICS AND TECHNOLOGIES

To record shading, the platform is placed on level ground, and the Pathfinder is
adjusted for proper magnetic declination in order to orient the device toward the true
magnetic pole. A small brass lever, when pulled downward, allows the center triangle
to pivot or rotate the shading pattern toward the proper magnetic declination angle.
Magnetic declination is the deviation angle of the compass needle from the true mag-
netic pole. Global magnetic declination angle charts are available through magnetic
declination Web sites for all countries.

PHOTOVOLTAIC MAPPING AND CONFIGURATION ANALYSIS
On completion of the field evaluation and shading analysis, the solar power designer
must construct the topologic configuration of the solar power arrays and subarrays in
a fashion that allows for maximum harvest of solar energy. On choosing the most
appropriate or suitable type of PV product, the solar platform footprint must be popu-
lated or mapped with the specific dimensional mosaic of the PV modules. It should be
noted that the tilting angle of solar arrays must be weighed against the available solar
platform footprint. In some instances, performance efficiency resulting from tilting PV
support structures that cast shadows on adjacent arrays should be sacrificed for flat-
mounting configurations in order to increase total output power-generation capacity of
the overall solar system.
In certain other instances, climatic conditions may dictate specific PV array tilt-angle
requirements. For example, in northern territories, to avoid the accumulation of snow
and ice and to allow for natural self-cleaning, PV units must be mounted at the maxi-
mum latitude angle. However, in southern states, when summer electrical energy tariff
charges are high, it may be advisable to install PV arrays in a flat configuration because
in such a configuration, seasonal solar insolation will allow for harvest of the maxi-
mum amount of solar energy. In winter seasons, when electrical energy tariffs are low,
lower solar power harvesting may be justified because in the winter there is much less
use of air-conditioning systems, which in some instances represent 50–60 percent of
electrical energy use. Even though optimal titling of PV arrays results in superior average
yearly energy production for the same number of PV modules, lower efficiency resulting
from flat-array installation may constitute a reasonable alternative.

DC-TO-AC POWER-CONVERSION CALCULATIONS
On completion of the preceding steps, the designer must evaluate the PV module elec-
trical performance parameters and configure PV strings in a manner most appropriate
for use with a dc-to-ac inverter system. It should be noted that on preliminary config-
uration of the PV arrays and subarrays, the design engineer must coordinate solar
power dc and ac wiring details with the inverter manufacturer. In view of specific elec-
trical design performance characteristics of PV modules, inverter manufacturers provide
dc input boundary limitations for arrays in various types of configurations.
In general, the maximum allowable dc power voltages produced by a string of PV
modules for a specific type of an inverter may be limited within a 300- to 600-V dc