Page 132 - Solar Power in Building Design The Engineer's Complete Design Resource

102 INTRODUCTION TO SOLAR POWER SYSTEM DESIGN

The total sum of percentage points shown on the monthly solar energy curves repre-
sent the maximum percent of solar insolation (100 percent) on the platform. For instance,
the total energy percent shading multiplier for the month of December or January, or any
other month when summed up, totals to a 100 percent multiplier. For example, according
to the 31 to 37 north latitude chart, the percent multiplier for the month of December
when summed up equals.

Efficiency multiplier % = 2 + 2 + 3 + 4 + 6 + 7 + 7 + 8 + 8 + 8 + 8 + 7 + 7 + 6 + 5
+ 4 + 3 + 2 + 2 + 1 = 100%

The same summation for the month of June equals.

Efficiency multiplier % = 1 + 1 + 1 + 2 + 2 + 3 + 4 + 5 + 5 + 6 + 6 + 7 + 7 + 7 + 7
+ 7 + 6 + 6 + 5 + 5 + 4 + 3 + 2 + 2 + 1 + 1 + 1 = 100%

Note that the insolation angle of the sum increases and decreases for each latitude;
hence, each plate is designed to cover specific bands of latitudes for the northern and
southern hemispheres.
When the plastic dome is placed on top of the platform that holds the curved solar
energy pattern, the shadows cast by the surrounding trees, buildings, and objects are
reflected in the plastic dome, clearly showing the shading patterns at the site which are
in turn cast on the pattern. The reflected shade on the solar pattern distinctly defines
the jagged pattern of shading that covers the plate throughout the 12 months of the
year.
A 180-degree opening on the lower side of the dome allows the viewer to mark the
shading on the pattern by means of an erasable pen. To determine the total yearly per-
cent shading multiplier, each portion of the 12 monthly curves not exposed to shading
are totaled. When taking the mean average percent from all 12 months, a representa-
tive solar shading multiplier is derived that is applied in dc-to-ac conversion
calculations.
Note that a number of rebate disbursement agencies such as the Los Angeles
Department of Water and Power require inclusion of the solar performance multiplier
in ac output power calculations and some do not.

USING THE SOLAR PATHFINDER INSTRUMENT
SETTING AND MAGNETIC DECLINATION
The Solar Pathfinder dome and shading pattern assembly are mounted on a tripod as
shown in Figure 4.10. For leveling purposes, the base of the assembly at its center has
a fixed leveling bubble that serves to position the platform assembly on a horizontal
level. At the lower part of the platform, which holds the pattern plate, is a fixed com-
pass that indicates the geographic orientation of the unit. The pattern plate is in turn
secured to the platform by a raised triangular notch.
To record the shading, place the platform on level ground and adjust the pathfinder
for the proper magnetic declination (the deviation angle of the compass needle from