Page 141 - Alternative Energy Systems in Building Design

SOLAR POWER SYSTEM DESIGN CONSIDERATIONS 117

A 180-degree opening on the lower side of the dome allows the viewer to mark the
shading on the solar pattern by means of an erasable pen. To determine the total yearly
percentage shading multiplier, all the portions of the 12 monthly curves not exposed
to shading are totaled. When taking the mean average percentage of all 12 months, a
representative solar-shading multiplier is derived, which is applied in dc-to-ac conver-
sion calculations, as discussed in the section on PV system power output rating.
It also should be noted that a number of rebate disbursement agencies, such as the
Los Angeles Department of Water and Power, require the inclusion of solar perform-
ance multipliers in ac output power calculations.
The Solar Pathfinder dome and shading pattern assembly are mounted on a tripod,
as shown in Fig. 3.60. For leveling purposes, the base of the assembly has a fixed lev-
eling bubble at its center that serves to position the platform assembly on a horizontal
level. At the lower part of the platform, which holds the pattern plate, a fixed compass
indicates the geographic orientation of the unit (shown in Fig. 3.63). The pattern plate,
in turn, is secured to the platform by a raised triangular notch.

Figure 3.63 Solar Pathfinder platform showing the removable
shading graph, the leveling bubble at the center, the triangular holder,
and the compass. Photo courtesy of Solar Pathfinder.