Page 134 - Solar Power in Building Design The Engineer's Complete Design Resource

104 INTRODUCTION TO SOLAR POWER SYSTEM DESIGN

or any object that may cast a shadow. Solar design engineers must familiarize themselves
with the use of the Pathfinder shading evaluation and calculation methods described ear-
lier in this chapter.
Roofs, whether made of wood or concrete, require a structural integrity evaluation.
The decision as to the choice of PV support structures must be made to meet specific
requirements of the roof structure. In some instances, spacing of wooden roof rafters
would necessitate special footing support reinforcement and structural engineering
intervention. In other instances, existing old roof-covering material such as asphalt
fiber or shingles must be completely replaced since the life expectancy of the PV sys-
tem installation will significantly outlast the expected life of the roofing material. In
order to prevent water penetration, PV support platforms and stanchion anchors must
be covered by specially designed waterproof boots.
Regardless of the type of roof structure, a registered professional engineer must
evaluate the solar power support structure for roof loading, penetration, and wind
shear calculations.

Ground-mount solar power systems For ground-mount solar power systems
(more specifically for solar farm type installations), in addition to the site evaluation
measures described previously, the designer must evaluate the site conditions for soil
erosion, earthquake fault lines, and periodic floods.

Shading analysis As discussed earlier in this chapter, sites that are susceptible to
shading must be evaluated for the seasonal performance multiplier as per the proce-
dure described in the shading calculation example.

Photovoltaic mapping or configuration analysis After completing the field
evaluation and shading analysis, the solar power designer must construct the topo-
logical configuration of the solar power arrays and subarrays in a fashion that would
allow maximum harvest of solar energy. Upon choosing the most appropriate or suit-
able type of PV product, the solar platform footprint must be populated or mapped
with the specific dimensional mosaic of the PV modules. Note that the tilting angle
of solar arrays must be weighed against the available solar platform footprint. In
some instances, the performance efficiency resulting from tilting a PV support struc-
ture that casts a shadow on adjacent arrays should be sacrificed for a flat-mounting
configuration to increase the total output power generation capacity of the overall
solar system.
In some other instances, climatic conditions may dictate the specific PV array tilt
angle requirement. For example, in northern territories, to avoid accumulation of snow
or ice and to allow natural self-cleaning, PV units must be mounted at the maximum
latitude angle. However, in southern states, when summer electric energy tariff
charges are high, it may be perhaps advisable to install the PV arrays in a flat config-
uration since in such a configuration seasonal solar insolation will allow harvesting of
the maximum amount of solar energy. In the winter season, when electric energy
tariffs are low, lower solar power harvesting may be justified, since there is much less
air-conditioning system use, which in some instances represents 50 to 60 percent of