Comprehensive coverage of solar tracking system basics

4. Why do we need Solar tracking systems
Let us compare a power generation curve for a fixed PV module
and a dual axis tracked SPV system. We observe there are
certain advantages when using dual axis tracked modules:
1. Higher energy generation during sunrise and sunset.
2. Uniform generation during peak collection hours
3. Higher energy generation over the course of day.

5.  A solar tracker is a devise that orients a
solar panel in the direction of incident
sunlight.

6.  Solar trackers minimize the angle of
incidence between the incoming sunlight and
a photovoltaic panel, and increase power
generation.
 Ideally the sun rays should fall at an angle
of 90˚ to the plane of the photovoltaic
panel.

9.  By sun angles.
 We split the movement of the sun along the
solar ecliptic into a horizontal component
and a vertical component.
 The measure of the horizontal angle from the
true north meridian is called the solar
azimuth angle and the measure of the
vertical angle with respect to the ground is
called the elevation angle.

12.  Peak collection time is taken as the time
between 9am and 3pm, when the sun is highest
in the sky.
 Shading due to distant objects is minimal
during this time.
 Collection(or generation) is highest during
these hours.
 Hence fixed SPVs are usually oriented
anticipating sun rays to be coming from that
direction.

13.  Firstly due to the nature of the shape of the
earth (spherical), the rotation about a central
axis, this axis being tilted(i.e. not
perpendicular with respect to the plane of
rotation) and finally due to revolution about
sun.
 The first two causes namely spherical shape and
rotation about a central axis cause most of the
daily variation.
 The last two namely a tilted axis and revolution
about the sun cause seasonal variation.

16.  In summer the sun remains in the sky for a
longer time. Thus, solar azimuth variation
is greater during summer.
 In winter the sun stays in the sky for a
shorter time hence, solar azimuth variation
is smaller during winter.

24.  Solar declination is the latitude at which
the direct rays of the sun fall for a
particular day of the year.
 Solar declination changes over the course of
the year.
 It is shown in a curve known as the
analemma. It shows the sun position at a
particular time of day from a specific place
throughout the year.

25. Cause for change in solar declination
The reason for change in solar declination is as that which causes change
in lengths of day and night over the year and seasons, namely change in
orientation of earth’s rotation axis with respect to the sun.

26.  Solar declination = α
 Latitude = γ
 Solar elevation = [90˚ -(γ - α)]

27.  For the month of June in Calcutta,
 α=23.5 ˚North, γ=23.5 ˚North
 Therefore, solar elevation = [90 ˚-(23.5-
23.5)]=90 ˚.

29.  The change in solar declination over the
year causes change in the elevation angle of
sun as observed from a particular point at a
particular time.
 Thus the path of the sun as observed from
the point shifts up or down by a total of 47˚
over the course of the year.
 This creates the concept of solar window.

30. Table showing variation in optimum tilt angle of fixed
SPV in Calcutta.The values given below can also be interpreted as the
maximum sun elevation observed in the given months.. The
total variation in sun elevation over the course of the
year is approximately 47 degrees for any place on earth.

31.  From the table we observe the optimum tilt
angle for fixed SPVs in winter,
spring/autumn and summer and calculate the
average value:
 (0+23+23+46)/4 = 23˚ tilt angle with
respect to the horizontal is optimum for
fixed SPVs in Calcutta.

34.  As the angle of incidence of the incident
sunlight on the PV panel increases, the
power generated by the PV panel decreases
drastically.
 Fixed SPVs face oblique sun rays during
sunrise and sunset.
 Fixed SPVs are incapable of adjusting
position with respect to change in sun path
over the year.

35.  Single tracked SPV modules have east to west
rotation capabilities, i.e. they track the
sun’s azimuth angle and are capable of
generating 25% more power than fixed SPVs if
the proper tilt angle is provided.

38.  Dual axis tracking SPV modules can track the
sun’s elevation because they have North-
South rotation capabilities. They generate
around 8.3% more power than single axis
tracked SPV systems.

44.  Single axis trackers have one degree of
freedom that acts as an axis of rotation.
 The axis of rotation of single axis
trackers is typically aligned along a true
North meridian.

45.  The different types of single axis trackers
are:
i. Horizontal Single Axis Tracker(HSAT)
ii. Horizontal Single Axis Tracker with Tilted
Module(HTSAT)
iii. Vertical Single Axis Tracker(VSAT)
iv. Tilted Single Axis Tracker(TSAT)

46.  The axis of rotation for horizontal single axis
tracker is horizontal with respect to the
ground. The posts at either end of the axis of
rotation of a horizontal single axis tracker can
be shared between trackers to lower the
installation cost.
 Horizontal trackers typically have the face of
the module oriented parallel to the axis of
rotation. As a module tracks, it sweeps a
cylinder that is rotationally symmetric around
the axis of rotation.
 The axis of the tube is on a north–south line.

48.  In HSAT, the modules are mounted flat at 0
degrees, while in HTSAT, the modules are
installed at a certain tilt.
 These trackers are suitable in high latitude
locations but does not take as much land
space as consumed by Vertical single axis
tracker (VSAT).

50.  The axis of rotation for vertical single
axis trackers is vertical with respect to
the ground.
 Such trackers are more effective at high
latitudes than are horizontal axis trackers.
 As a module tracks, it sweeps a cone that is
rotationally symmetric around the axis of
rotation.

52.  These trackers have an axis of rotation
between horizontal and vertical.
 The face of the module is oriented parallel
to the axis of rotation.

54.  Dual axis trackers have two degrees of
freedom that act as axes of rotation.
 These axes are typically normal to one
another.
 The axis that is fixed with respect to the
ground can be considered a primary axis.
 Dual axis trackers typically have modules
oriented parallel to the secondary axis of
rotation.

58.  Two common implementations are :
1. tip-tilt dual axis trackers (TTDAT)
2. azimuth-altitude dual axis trackers
(AADAT).

59.  A tip–tilt dual axis tracker (TTDAT) is so-
named because the panel array is mounted on
the top of a pole.
 East–west movement is driven by rotating
the array around the top of the pole.
 On top of the rotating bearing is a T- or H-
shaped mechanism that provides vertical
rotation of the panels and provides the main
mounting points for the array.

61.  An azimuth–altitude dual axis tracker (AADAT)
has its primary axis (the azimuth axis) vertical
to the ground. The secondary axis, often called
elevation axis, is then typically normal to the
primary axis.
 AADAT systems can use a large ring mounted on
the ground with the array mounted on a series of
rollers. The main advantage of this arrangement
is the weight of the array is distributed over a
portion of the ring, as opposed to the single
loading point of the pole in the TTDAT.

64. Type of tracker % gain in generation
Latitude tilt fixed 23%
Horizontal tracked 37%
Horizontal tracked with tilted axis 64%
Dual axis tracked 71%

67.  Solar trackers require actuators to move the
tracker around either a single or dual axis.
 In order to control and manage the movement
of these massive structures special slewing
drives are designed.
 Linear actuators control movement in single
axis solar tracker or control elevation of a
dual-axis solar tracker.

69.  Slew drives are
used for the
rotation of a dual
axis tracker about
the vertical axis.

70.  There are two methods commonly employed for the
control of solar trackers. One is to use an
optical sensing system, and the other is to use
a mathematical equation. Both types of systems
usually employ a microprocessor based
controller which directs a motor to operate one
way or the other.
 The optical sensing system works better in
clear skies.

71.  Sun sensor is a device to measure the
incident angle of the sun rays when they
go through a small window. This allows,
the sensor to measure the Sun position or
other light sources regarding to the
sensor position.
 The sun sensors are designed over MEMS
technology (Micro-Electro Mechanical
Systems).

73.  Solar PV trackers do not require a position
accuracy of much better than a few degrees.
In that case, the motor-move-frequency can
be reduced to a move per degree or two,
which equates to one start/stop per 5-10
minutes.

75.  Trackers include moving parts and sophisticated
hardware, hence come at an added cost relative
to fixed tilt systems.
 Tracking systems tend to use additional land
space because they must be spaced out in order
to avoid shading one another.
 Operational and maintenance costs tend to be
higher for this type of system.
 In order for a tracker to make economic sense,
the increased energy harvest must exceed the
added cost of installing and maintaining
trackers over the lifetime of the system.

76.  Land area required for fixed tilt array<
Land area required for single axis tracked
array< land area required for dual axis
tracked array.
 This happens because of the movement of
structure and alignment of PV array
perpendicular to the direction of sunlight,
which tends to cause longer shadows around
the structure.

77.  Most Solar power plant employing trackers
adopt the backtracking algorithm to avoid
the shading effects which happen during
morning and late afternoons when sun height
is low.
 Backtracking algorithms help arrays to
position themselves such that inter shading
between different arrays do not happen.

78.  No, while solar trackers do involve moving
parts and might hence require some
maintenance. Note that the tracker movements
are slow and gradual and hence are not
subject to the same wear and tear that a
fast moving motor would.

79.  CUF=(Actual output of the solar plant over
the year)/(maximum possible output from it
in one year).
 Solar power plants with fixed tilt arrays
have CUF in the range 16-18% and if single
axis tracking is installed then CUF may go
up to 21-23%.

80.  Trackers usually add an extra cost for setup
extra O&M cost per year.
 They also require larger land area to
because tracking PV panels tend to generate
longer shadows around them.
 But the extra generation that is achieved
due to tracker implementation can recover
all these cost overturn the fortunes of a
power company.

81. Parameters Without Trackers With Trackers
Capital Cost(Rs,lakh) 5.75 6.15
CUF 18% 21%(couldgo up to
23%)
Plant Output(kWh,000) 16 19(could go up to 21)
Land Area 2178 2613.6
O&M
costs(000/MW/year)
5 7

82.  Added capital cost if using trackers
= (6.15 – 5.75)lakh rupees
= 0.4lakh rupees = 40,000 rupees
 Increase in plant output = (19,000 – 16,000)kWh
= 3,000 kWh
 Assuming PPA Tariff of Rs. 7/kWh,
Extra revenue generated per year
= (3,000X7) rupees = 21,000 rupees.
 The additional expense of Rs 40,000 usually pays
back within 2 years owing to extra generation.

83.  The ROI (Return on Investment ) for a PV
plant of 10kW capacity is quite good, as the
plant that employs a tracker will be
generating 19000 rupees worth of extra
revenue each year.
 Considering the lifetime of the plant to be
25 years. And expecting initial capital
costs to be recovered by 5 years, total
extra revenue generated per 10kW comes out
to be around 4lakh rupees for the entire
lifetime of the plant.

85.  If a shadow is cast on even just part of one
solar panel in a solar array, it can
compromise the output of the whole system.

86.  Depending on the voltage requirements of the
system’s inverters, solar arrays are
divided into ‘strings’ of solar panels.

87.  You can think of a string of panels as
something like a piece of pipe, and the
solar power is like water flowing through
that pipe. In conventional solar panel
strings, shade is something that blocks that
flow.

88.  Site your solar panel array where there will
be no regular shading.
 Using a string inverter with MPPT tracking
capabilities.
 Get a system with micro inverters or power
optimizers.

89.  MPPT is based on the principle of maximizing
power output from solar panels by varying
the resistance in the circuit.
 Example: When a cloud covers only a few PV
panels, then those panels receive less solar
radiation and operate under different
circuit conditions — they have a different
MPP.

91.  An MPP Tracker helps to minimize losses in
output associated with partial shading and other
panel output mismatches.
 An inverter equipped with an MPP Tracker (or
several of them) is able squeeze the most usable
energy possible out of a string of solar panels
(even when shaded) by adjusting the voltage to
always suit the inverter’s preferred input
range
 Inverters without MPPT capability simply lose
the output from the weaker string once it passes
below the required output threshold.

93.  Micro Inverters perform panel level MPPT
tracking.
 There is one micro inverter per SPV panel.
 The output from several micro inverters is
combined and fed to the electrical grid.

94.  Each micro inverter performs MPPT tracking
for its connected module and hence, small
amount of shading , or even complete module
failure does not drastically reduce the
output of the entire array.
 Simple construction.
 Lower amperage wires.

96.  Higher initial equipment cost since each
inverter needs to be installed adjacent to a
panel (usually on a roof).
 This also makes them harder to maintain and
more costly to remove and replace (O&M).

98.  Power optimizer employs similar technology
as that of micro inverter but it does not
convert to AC per module.
 Power Optimizers are provided with a
simplified version of string inverter for DC
to AC conversion.

100. String Inverter Micro Inverter
 String inverter
converts power from
all modules from DC to
AC(shading problem).
 Good for ground mount
or large roof.
 Difficult to expand.
 Cheap.
 Easy to maintain.
 Micro inverters work
at the module level –
converts power from
each module.
 Good for roof made of
many small areas.
 Easy to expand.
 Costly .
 Difficult to maintain.

101.  http://solarelectricityhandbook.com/solar-
angle-calculator.html
 https://en.wikipedia.org/wiki/Solar_tracker
 https://www.solarchoice.net.au/blog/partial-
shading-is-bad-for-solar-panels-power-
systems
 https://www.youtube.com/