Page 116 - Alternative Energy Systems in Building Design

92 SOLAR POWER SYSTEM PHYSICS AND TECHNOLOGIES

concealed, and underground conduits also must be reflected on the plans with distinct
design symbols and identification that segregate the regular and solar power system
from the electrical systems.
It should be noted that solar power cogeneration and electrical grounding should be
in a single location, preferably connected to a specially designed grounding bus, that
must be sited 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 EFFECT ON OUTDOOR EQUIPMENT

Lighting surges consist of two elements, namely, voltage and the quantity of charge
delivered by lightning. The high voltage delivered by lightning surges can cause seri-
ous damage to equipment because it can break down the insulation that isolates circuit
elements and the equipment chassis. The nature and amount of damage are directly
proportional to the amount of current resulting from the charge.
To protect equipment damage from lightning, devices know as surge protectors or
arrestors are deployed. The main function of a surge arrestor is to provide a direct con-
duction path for lightning charges to divert them from the exposed equipment 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 volt-
ages for a short time; however, the thresholds are so narrow that if charges are not
removed or isolated in time, the circuits will sustain an irreparable insulation breakdown.
The main purpose of a surge-arrestor device therefore is to conduct the maximum
amount of charge and reduce the voltage in the shortest possible time. Reduction of a
voltage surge is referred to as voltage clamping and in general depends on device char-
acteristics, such as internal resistance and the response speed of the arrestor and the
point in time at which the clamping voltage is measured. Figure 3.44 illustrates lighting
surge-arrestor spikes.
When specifying a lightning arrestor, it is necessary to take into account the clamping
voltage and the amount of current to be clamped. Figure 3.45 is a graphic diagram
showing deployment of a lightning surge arrestor in a rectifier circuit.

CENTRAL MONITORING AND LOGGING SYSTEM
REQUIREMENTS
In large commercial solar power cogeneration systems, power production from the PV
arrays is monitored by a central monitoring system that provides a log of operation