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3..Tracking
or a fixed setting for the array? 

One
alternative to elevating your PV array to suit the season is to have your array's
horizontal angle set at the midangle, that is, at an angle midway between the
sunray paths for December the 21st and June the 21st. The horizontal angle for
the midangle in the Cairns region is 17 degrees. Local
PV installer, Marcus Axton of Platypus Power, is doing this. An example of his
work can be seen to the left. The face of the array is facing true north and at
the midangle. Also note that the array is well off the roof to allow breezes
to flow through under the array helping to keep its temperature down. 

To
make a comparison of the effectiveness of an array set at the midangle and a
single axis tracker we must first look at the angle of incidence of the sunrays
and the resultant electrical output.
Neil
Clarke is an electrical, electronic and communications engineer from
Melbourne. Neil has produced a graph, this can be seen below, and it
shows the angle of incidence versus power loss.
(See
the NOTE at the bottom of this page).

Using
the information above, it is possible to make a comparison between a
single axis tracker and an array set at the midangle for a period of
one year in the Cairns region.
Note that the readings shown below are for midday only.
ARRAY
WITH TWO SETTINGS PER YEAR A geometric calculation of the sun's rays hitting
this array over a year indicates the following: four times per year the angle
of incidence is 12 degrees. Using Neil's graph this converts to a power loss of
2%. Also, four times per year the array directly faces the sun giving a power
loss of zero. So overall, at midday an array with two settings per year would
average a power loss of 1%.
See below:

ARRAY
SET AT THE MIDANGLE A geometric calculation
of the sun's rays hitting this array over a year indicates the following: twice
per year the angle of incidence is 25 degrees. Using Neil's graph this converts
to a power loss of 9%. Also, twice per year the array directly faces the sun giving
a power loss of zero. So overall, at midday an array set at the midangle would
average a power loss of 4.5% over a year.
See below:

Therefore
(roughly speaking because the readings are for midday only) in the Cairns region,
a single axis tracker elevated twice per year would have a 3.5% greater efficiency
than an array system that is fixed at the midangle.
Even if a resident does choose a midangle array rather than a single
axis tracker, a problem still exists with the array's exposure to
strong winds and its highly visible appearance from the street.
(Oh dear, what will the neighbours think!) But is there another
option? Go to the next section to
find out.
NOTE

For
people who prefer a table layout rather than a graph, please
see the table shown on the left.
The
angles of incidence are at intervals of five degrees and the
power loss is shown as a percentage.
This
table can be handy for situations when solar panels are to
be placed and a more general calculation of the power loss
is required.

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