Energy Efficiency Made Simple Vol IV 2015

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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Experimental efficiency comparison between fixed and tracked photovoltaic solar panels G Craig,Techlyn

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 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’.

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.

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.

Figure 2: Test unit.

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ENERGY EFFICIENCY MADE SIMPLE 2015