Comparison of single axis trackers vs fixed tilt, and conditions where in it is economically justified.

1. Cost-Benefit Analysis (Single axis Tracker vs. Fixed-Tilt)
White Paper
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1. Introduction:-
The energy produced by the solar energy systems is directly proportional to the
incident radiation falling on the modules. As this is always changing at a particular
orientation, it would be an idea to move the modules is such a fashion that it captures
the maximum possible amount of radiation. It’s here when tracking solar structures
come into picture.
As of today, efficiency of most of the modules installed in a utility scale solar farm is
14% to 18%. This means that only 14-18% of the incident light is convertible to useful
energy. As we progress in time these numbers would surely follow an upward trend,
with a natural limitation of 26% for single junction c-Si modules.
Trackers are of 2 types: Single-axis & double axis. Single axis trackers are ones that
track the sun’s path in a day, which means it compensates for the variation in solar
radiation due to rotation. Double axis trackers, have the ability to move over 2 axes
and can hence compensate for the rotation & revolution of the earth. In this pursuit of
study of trackers, we are restricting ourselves to single axis trackers.
The ability of trackers to impact the IRR of a project depends on a number of factors
like spatial co-ordinates of the project, cost of land, cost of PV modules, cost of
tracking structures , actual gain in radiation, to name a few. Only after all these
factors are collated and financially analyzed, the decision could be taken.
This paper would try and link all the factors involved and come with a model which
will help in making this crucial choice. The real life data from plants on ground has
been taken for the analysis.
2. The evaluation model & key assumptions
The LCOE model employed for cost-benefit estimation is based on the LCOE model
as enunciated by Sunpower Corporation1. The major assumptions flowing into the
model were based on guidelines of CERC (Central Electricity Regulatory
Commission, India) and Lanco’s own on-field experiences. A debt-equity ratio of
80%, interest rate of 11%, return of equity of 16% for a system life of 25 years was
taken as assumptions for the financial aspects of the solar farm. For ensuring the
comfort of the techno-commercial analysis, the O&M costs were assumed to be Rs.9
Lakhs per MWp with 5% escalation annually for fixed tilt and Rs.9.9Lakhs per MWp
for single-axis trackers with 5% escalation annually.
System degradation in line with the performance of a multi-crystalline module was
taken. All PV farms were assumed to be setup on perfectly square plots to simplify

2. the costing behind fencing & civil costs alongside the employment of the central
inverters.
3. Factors affecting the decision :-
a) Yield: - The number of units (kWh) generated per kWp of installation is bound to
increase with the usage of single axis tracker(SAT). The quantum of increase in this
yield (kWh/kWp) is principally the benefit that a system derives from a technological
improvement. The kWh/kWp is affected by a number of factors, the important ones
of it being the latitude, distance from large water body & dust that can disperse
radiation in that location. For the purpose of study, the locations chosen in India are
Askandra(Rajasthan), Bhathrada (Gujarat), Gulbarga (Karnataka), Anantpur (Andhra
Pradesh), Pondicherry and Kovilpatti (Tamil Nadu). The increase in yield and the
comparison of yield of the systems (with & without trackers) are illustrated in the
graphs given below.
100.0 Yield gain by having tracker 1900
90.0 1876 1850
1856 1861
1843
80.0 1829 1821 1800
70.0 1750
60.0 1700
50.0 1650
% benefit of yield
40.0 1600
FT
30.0 1550 SAT
21.0 20.9 20.8
18.5
20.0 14.4 15.9 1500
10.0 1450
0.0 1400
Illustration 1: Gain in yield by employing single axis tracker
b) Land: - The land required to install a solar power plant is tremendous. To put it in
perspective the land required to produce enough energy, to light up a 100 watt
incandescent bulb for 24 hours is 8.7m2*. This is a big chunk to be spared for solar
power. As India adds on its installed solar capacity, the cost of land, even in the
remotest parts have seen a steep rise. For the purpose of the comparison
framework, the following land costs were assumed at the following locations.

3. Location Land cost (in Rs. Per
acre)
Askandra 200000
Bhathrada 500000
KA (Gulbarga) 350000
AP(Anantpur) 300000
TN(Kovilpatti) 500000
Pondicherry 3000000
The plant design should be such that the land could be used in the most efficient way
but there is a fundamental limit to it. When a fixed tilt system is installed on ground,
outmost care is taken so that shadows from a row of structures do not fall on the
adjacent rows. Shadow formation can ruin the generation figures and also damage
the modules. A specific inter row spacing is required to avoid any shadows; this in
turns depends on the latitude of the plant location. This means, for a fixed tilt system
at a location in Rajasthan, only 40 % of the land should actually be covered by the
panels to avoid any shadows. It is termed as the GCR (Ground Coverage Ratio).
This number increases as we move towards the equator. The GCR value at
Pondicherry in Southern India, for example is 90%.
For a Single Axis Tracking structure the GCR remains constant, regardless of the
latitude. The figure is 45% for the SAT. This means, at Pondicherry trackers would
take double the land to come up compared to fixed tilt systems. It would make sense
if the land there was very cheap.
Hence, even a small increase in the cost of the additional land employed for setting
up trackers should be compensated by a significant increase in yield for that location
by using SAT.
Location GCR-FT GCR-SAT % increase in yield
Askandra 39.90% 45.00% 14.36%
Bhathrada 60% 45.00% 15.88%
KA (Gulbarga) 63.20% 45.00% 18.52%
AP(Anantpur) 78.90% 45.00% 20.95%
Pondicherry 90.10% 45.00% 20.89%
TN(Kovilpatti) 92.30% 45.00% 20.76%
Illustration 2: Ground coverage ratio at different locations in India
c) Module Costs: - Earlier when the PV prices were high, the contribution of Module
Mounting Structure (MMS) costs in the overall EPC costs were lower compared to a
scenario of today when MMS forms a significant portion of the EPC costs, owing to
decreasing module prices.
This means that a 10% increase in price of a component that constitutes 40% of the
total cost has a greater impact on the overall cost, compared to a 10% increase in
cost of a component that constitutes 30% of the total cost.

4. Module costs trend
d) Module wattages:
The best cell efficiencies of about 33.7% is theoretical limit as enunciated by Shockley-
Queisser2 limit in 1961. Practically a cell-efficiency of 27% seems to be the upper limit for the
mass-scale manufacturing of cells globally.
At the time of writing this paper, 17% was the average module efficiency for p-type modules,
and hence the iteration was carried out for upto 21% module efficiency. With the increasing
module wattage, lesser number of modules are required to meet the required UMPP
capacity.
4. Analysis (Trackers vs. Fixed) :-
The analysis is carried out with respects to 2 variables, Land costs and Module
prices. This would try and see the viability of the trackers at various locations in India
with varying land costs and a given module price. Considering the given quantities,
erection costs, the yield, both the technologies have been subjected to the analysis.

5. % benefit vs $/Wp PV module price
10.0%
% benefit in LCOE for SAT 8.0%
6.0% 1.4
4.0% 1.2
2.0% 1
0.0% 0.8
0.6
-2.0%
-4.0%
Illustration 3: LCOE benefit with increasing module price
This curve shows the % benefit from the SAT vs. Fixed structures at different
locations in India. This comprehensively proves that with the decreasing module
price, the benefit of SAT is well negated because of the greater impact of the higher
structure costs. With the falling module prices, the portion of structure costs to the
overall cost increases, which means that any additional increase in structure costs at
low module price has a bigger impact on overall cost of the system.
To emphasize greater importance on the impact of module prices on the feasibility of
the SATs and lesser on the prices of land, the graph is also redrawn with same land
costs of Rs.2 lakhs per acre. The results are very much coherent with the logic of
higher module prices causing greater feasibility of SATs.
LCOE benefit with varying module price ($/Wp)
and land cost of Rs.2 lakhs per acre
10.0%
8.0%
6.0% 1.4
1.2
4.0%
1
2.0%
0.8
0.0% 0.6
Askandra Bhathrada KA (Gulbarga) AP(Anantpur) Pondicherry TN(Kovilpatti)
-2.0%
-4.0%
Illustration 4: LCOE Benefit for SATs with increasing module prices at land cost of Rs.2 lakhs per acre

6. The above graphs might lead us to the conclusion that SATs become more viable as
we move towards the equator, as the yield increase because of SAT is significant.
However, the second conclusion derived from the above graph holds good only in
case of constant land prices at each of the locations. After taking in to account the
above factors along with the yield the following chart can be arrived.
LCOE benefit of having SAT with increasing land
cost per acre @ module price of $0.6 per Wp
4.0%
Askandra
2.0% Bhathrada
0.0% KA (Gulbarga)
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 AP(Anantpur)
-2.0%
Pondicherry
-4.0%
Rs. lakhs per acre TN(Kovilpatti)
Illustration 5: LCOE benefit of tracker with increasing cost of land
Here the x-axis denotes land costs in Rs. / lakhs and the y axis signifies the %
benefit of tracker vs. fixed. Here the module price is kept constant at the present rate
$0.6 per Wp.
The following can be deduced from the above graph:-
 At Askandra, a location in Rajasthan, tracker would reap benefit with
increasing cost of the land as it is the only location where GCR for SAT is
greater than the GCR for fixed tilt. (Refer Illustration 2)
 For locations situated closer to the equator, the slope of the lines in
Illustration 5 increases. This is in accordance with the combination of the
highest GCR(as per Illustration 2) & fairly high yield(Illustration 1).
The impact of increasing module wattages is realised with the fact that lesser number of
modules will be required to achieve the same wattage at the plant level. Sample this, a
5MWp needs 20834 modules of 240Wp, where-as it needs only 16667 modules of 300Wp.
This 20% reduction in the number of modules for a 25% increase in wattage is only
theoretical. The benefit is mellowed to a certain extent by mismatch & transmission losses at
higher currents.
From a SAT perspective, higher module wattage implies lesser proportion of MMS costs in
the over-all EPC costs. A hike in the MMS costs by employing SATs is greatly diminished by
the lesser proportion that the MMS costs contribute to the total. To understand the issue, 2
graphs are plotted. One describes the LCOE benefit whilst land prices are assumed to be
same at Rs.2 lakhs per acre and the other when actual land prices are assumed.

7. LCOE Benefit with changing module wattage at
same land cost
6.0%
5.0%
4.0%
3.0%
2.0%
1.0%
0.0%
-1.0% Askandra Bhathrada KA (Gulbarga) AP(Anantpur) Pondicherry TN(Kovilpatti)
-2.0%
-3.0%
240 250 260 270 280 290 300
LCOE Benefit of Wattage/module at assumed
land cost
6.0%
5.0%
4.0%
240
3.0% 250
260
2.0%
270
1.0% 280
0.0% 290
Askandra Bhathrada KA (Gulbarga) AP(Anantpur) Pondicherry TN(Kovilpatti) 300
-1.0%
-2.0%
-3.0%
The benefit of higher module wattage is synonymous with the benefit of higher yield
from SATs. Higher the wattage, higher the benefit of using SATs.
5. Conclusions
 Economic sense to have SATs at latitudes presenting a higher GCR than the fixed
tilt, (that is north of Gujarat in the Indian context) would make sense when the land
costs are significantly higher.

8.  Benefit of SAT at lower land prices increases as we move towards the equator,
ignoring the aerosol effects of coastal locations (like Puducherry or Kovilpatti).
 Advantages of SAT are greatly diminished by the decreasing price of modules vis-à-
vis the increase in MMS costs for SATs.
 Increasing module wattages give an equivalent jump in the benefit received by
employing SATs.
 In sum, the viability of SAT depends on the cost of land that would be cheap enough
to make trackers financially successful at a given location for a given module cost for
a corresponding increase in yield.
References
1. The Drivers of the LCOE for utility-scale photovolatics by Sunpower Corporation,
14 August 2008
2. The Shockley-Quessier Limit (http://sjbyrnes.com/sq.pdf)