Page 102 - Solar Power in Building Design The Engineer's Complete Design Resource

72 SOLAR POWER SYSTEM DESIGN CONSIDERATIONS

current output capacity of the solar system. For example, if we were to add a 200-A
solar power cogeneration to the switchgear, the bus rating of the switchgear must in fact
be augmented by an extra 250 A. The additional 50 A represents an 80 percent safety
margin for the solar power output current. Therefore, the service entrance switchgear
bus must be changed from 600 to 1000 A or at a minimum to 800 A.
As suggested earlier, the design engineer must be fully familiar with the NEC 690
articles related to solar power design and ensure that solar power cogeneration system
electrical design documents become an integral part of the electrical plan check sub-
mittal documents.
The integrated solar power cogeneration electrical documents must incorporate the
solar power system components such as the PV array systems, solar collector distri-
bution panels, overcurrent protection devices, inverters, isolation transformers, fused
service disconnect switches, and net metering within the plans and must be considered
as part of the basic electrical system design.
Electrical plans should incorporate the solar power system configuration in the
electrical single-line diagrams, panel schedule, and demand load calculations. All
exposed, concealed, and underground conduits must also be reflected on the plans with
distinct design symbols and identification that segregate the regular and solar power
system from the electrical systems.
Note that the solar power cogeneration and electrical grounding should be in a single
location, preferably connected to a specially designed grounding bus, which must be
located within the vicinity of the main service switchgear.

Lightning Protection

In geographic locations, such as Florida, where lightning is a common occurrence, the
entire PV system and outdoor-mounted equipment must be protected with appropriate
lightning arrestor devices and special grounding that could provide a practical mitiga-
tion and a measure of protection from equipment damage and burnout.

LIGHTNING’S EFFECT ON OUTDOOR EQUIPMENT
Lightning surges are comprised of two elements, namely voltage and the quantity of
charge delivered by lightning. The high voltage delivered by lightning surges can cause
serious damage to equipment since it can break down the insulation that isolates circuit
elements and the equipment chassis. The nature and the amount of damage are directly
proportional to the amount of current resulting from the charge.
In order to protect equipment damage from lightning, devices known as surge protec-
tors or arrestors are deployed. The main function of a surge arrestor is to provide
a direct conduction path for lightning charges to divert them from the exposed equip-
ment chassis to the ground. A good surge protector must be able to conduct a sufficient
current charge from the stricken location and lower the surge voltage to a safe level
quickly enough to prevent insulation breakdown or damage.
In most instances all circuits have a capacity to withstand certain levels of high
voltages for a short time; however, the thresholds are so narrow that if charges are