Page 127 - Alternative Energy Systems in Building Design

SOLAR TRACKING SYSTEMS 103

Solar Tracking Systems

Tracking systems are support platforms that orient solar PV module assemblies by
keeping track of the sun’s movement from down to dusk, thus maximizing solar energy
power-generation efficiency. Trackers are classified as passive or active and may be
constructed to track in single or dual axis. Single-axis trackers usually have a single-
axis tilt movement, whereas dual-axis systems trackers also move in regular intervals,
adjusting for an angular position.
In general, single-axis trackers, compared with fixed stationary tilted PV support
systems, increase solar power capture by about 20–25 percent. Dual-axis trackers, on
the other hand, can increase solar power production by 30–40 percent. Solar power
concentrators that use Fresnel lenses to focus the sun’s energy on a solar cell require
a high degree of tracking accuracy to ensure that the concentrated sunlight is focused
precisely on the PV cell.
Fixed-axis systems orient the PV modules to optimize power production for a limited
time and generally have a relatively low annual power production. On the other hand,
single-axis trackers, even though they are less accurate than dual-axis tracker applica-
tions, produce strong power in the afternoon hours and are deployed in applications
such as grid-connected solar power farms that enhance power production in morning
and afternoon hours.
Compared with the overall cost of PV systems, trackers are relatively inexpensive
devices that increase power output performance efficiency significantly. Even though
some tracker systems operate with good reliability, they usually require seasonal position
adjustments, inspection, and periodic lubrication.

PHYSICS OF SOLAR INTENSITY
The degree of solar intensity of the light that impinges on the surface of solar PV panels
is determined by an equation referred to as Lambert’s cosine law, which is I = k × cos A,
as depicted in Fig. 3.52. In words, the law states that the intensity of light falling
on a plane is directly proportional to the cosine of the angle of light source to the
normal of the plane. In other words, when in summer time the angle of the sun is

SUN
NORMAL LINE

A
SOLAR RAYS

PV PLANE
I = k cosine A
I = SOLAR INTENSITY
k = LAMBERT’S CONSTANT Figure 3.52 Solar intensity equation
A = SOLAR ANGLE diagram.