Cost-Benefit Analysis (Single axis Tracker vs. Fixed-Tilt)

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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

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.

Askandra

Bhathrad

a

KA (Gulbarg

a)

AP(Anan

tpur)

Pondicherr

y

TN(Kovil

patti)

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14.4 15.9 18.5 21.0 20.9 20.8

1856 18611843

1876

1829 1821

Yield gain by having tracker

% benefit of yieldFTSAT

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.

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.

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.

Askandra

Bhathrad

a

KA (Gulbarg

a)

AP(Anan

tpur)

Pondicherr

y

TN(Kovil

patti)

-4.0%

-2.0%

0.0%

2.0%

4.0%

6.0%

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% benefit vs $/Wp PV module price

1.41.210.80.6

% b

enefi

t in

LCO

E fo

r SAT

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.

Askandra Bhathrada KA (Gulbarga) AP(Anantpur) Pondicherry TN(Kovilpatti)

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LCOE benefit with varying module price ($/Wp) and land cost of Rs.2 lakhs per acre

1.41.210.80.6

Illustration 4: LCOE Benefit for SATs with increasing module prices at land cost of Rs.2 lakhs per acre

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.

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

-4.0%

-2.0%

0.0%

2.0%

4.0%

LCOE benefit of having SAT with increasing land cost per acre @ module price of $0.6 per

Wp AskandraBhathradaKA (Gulbarga)AP(Anantpur)PondicherryTN(Kovilpatti)

Rs. lakhs per acre

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.

Askandra Bhathrada KA (Gulbarga) AP(Anantpur) Pondicherry TN(Kovilpatti)

-3.0%-2.0%-1.0%0.0%1.0%2.0%3.0%4.0%5.0%6.0%7.0%

LCOE Benefit with changing module wattage at same land cost

240 250 260 270 280 290 300

Askandra Bhathrada KA (Gulbarga) AP(Anantpur) Pondicherry TN(Kovilpatti)

-3.0%

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LCOE Benefit of Wattage/module at assumed land cost

240250260270280290300

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.

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)