PAGE 1 | GREEN ENERGY HANDBOOK © 2 0 08- 2 0 1 8 M I C H A E L E T T E R S H A N K

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WORKSHOP 8.1 WHY MAKE PHOTOVOLTAIC [PV] SOLAR PANELS TRACK THE SUN?

Solar panels are most efficient [in other words make the most electricity from sunlight] when light strikes the

panel directly, because there is less reflection and resulting energy loss. If we look at the diagram below, the

panel on the left hand side captures less energy than the panel on the right.

While the easiest [and most cost effective option] involves placing the panels on the sunward side of a roof,

photovoltaic [PV] solar panels can also be made to ‘follow’ the sun across the sky.

Making solar panels track the sun is one of many examples of how engineers often copy clever ideas from

nature. ‘Heliotropism’ is a special word that describes the behaviour of young sunflowers, that follow the sun

all day until it sets in the West, then turning back towards the East waiting for sunrise.

If we look at the graph below the blue line represents output from a fixed solar panel. We can see how

maximum output is produced around midday. The yellow line shows output from a ‘heliotropic’ solar panel

that follows the sun to produce peak power in the morning, at midday and in the afternoon.

To track the sun across the sky with a solar panel, we can simply mount the panel on a pivoting base that

moves from east to west during the day. However, getting the most out of a solar panel is complicated by the

fact that in summer the sun rises higher in the sky than in winter. In winter the sun stays closer to the horizon

as per the illustration on the following page.

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To keep the solar panel facing the sun to produce the most electricity, it needs to be able to pivot moving

with the sun as the sun moves across the sky from East at sunrise to West at sunset, as well as following the

sun as it rises higher in the sky at midday in summer than in winter. In the diagram below we can see how

solar panels can be made to pivot in one axis, or two axes:

In the series of photographs below we can see what an actual sun tracking solar panel system looks like,

through various stages of the day from morning through midday and into the afternoon.