T
wo small photovoltaic (PV) panels measuring 100 X 90 mm
were to hand. The Techlyn office is located at approximately
26 degrees South and 28 degrees East. We decided to mount
one panel on a fixed bracket so that it would be normal (90 degrees)
to the sun’s rays at 12:08.
The other would be mounted on an equatorial mount (parallel
to the earth’s axis) and coupled to a one revolution per day (siderial)
drive. This method would enable the PV panel to track the diurnal
movement of the sun.
A data logger would record the two panels’ outputs for a full day.
The total energy absorbed would be graphed and compared.
The mechanism
The principle of a diurnal equatorial mount is shown in
Figure 1
. The
panel is spun on a shaft that is
parallel to the earth’s axis. The
panel is mounted at an adjustable
angle such that it is normal to
the sun’s rays. The (siderial) drive
motor (one revolution per day)
keeps the panel facing the sun’s
rays. This method is used for
astronomical telescopes.
An alternative method would
be to use sensors to track the
sun’s position and steer the PV
panel with a servomotor. The prob-
lem is that cloud cover diffuses the
sun’s rays, rendering this method
useless under cloud cover. One
could defeat this condition and
keep the panel stationary until
the clouds passed. This seemed
unnecessarily complicated, as well
violating the (K)eep (I)t (S)imple
(S)tupid (KISS) principle.
Experimental efficiency comparison
between fixed and tracked photovoltaic
solar panels
G Craig,Techlyn
As a company with vast experience in measurement work as well
as mechatronics, this project presented an opportunity to use both
competencies on an energy related project. The experiment was
carried out specifically as a report for ‘Energy Efficiency Made
Simple, Vol IV’.
Figure 2: Test unit.
The sun’s elevation at midday does not remain constant, but varies (in
Johannesburg) from 88 degrees above the horizon on 21 December
(Summer Solstice) to 40 degrees on 21 June (Winter Solstice).
If the pane elevation were set to 64 degrees which corresponds
to the equinoxes (21 September and 21 March), the maximum error
Figure 1: Principle of a diurnal equatorial mount.
1
Photovoltaic solar panels are wonderful devices that provide an energy
source that should be a vital part of any exposed roof. They are most
efficient at a perpendicular angle for the sun’s rays. It is perfectly
viable to track the diurnal movement of the sun, optimise the solar
energy captured – and convert it to electric energy.
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ENERGY EFFICIENCY MADE SIMPLE 2015