Energy Efficiency Made Simple Vol IV

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.

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.

ENERGY EFFICIENCY MADE SIMPLE 2015