solar pv technologies

Solar PV Technologies: A Few Key Issues

CONFIDENTIALADITYA BIRLA GROUP

Amitabh Verma, Ph.D

Vice President- Technology

Solar Power Business

Outline

• Technology as profitability driver

• Importance of meteorological data

• Selection of modules for power plants

• Pros and cons of thin film modules

• Inverter choices for power plants

• Module layout options

• Concentration photovoltaic

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• Concentration photovoltaic

• Operation and Maintenance

1

Profitability Through Design

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Comparison of Satellite and Ground Based Data

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MOS is Model Output Statistics which takes into account

ground based data and satellite data

3

How Predictable is Year-To-Year Radiation Data?

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Brightening Dimming Brightening

Very few weather stations in the world have 40-50 years radiation data

4

Measurement Uncertainty

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3

4

5

6

7

8G

HI

(kW

h/m

2/d

ay

)

MNRE NASA Meteonorm

Global Horizontal Incidence (GHI) for Jodhpur

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0

1

2

Jan Feb Mar Apl May Jun Jul Aug Sep Oct Nov Dec

Months

� NASA data is based on Satellite Imaging

� Meteonorm is based on Satellite Imaging and weather station� MNRE is based on weather station� NASA was different than MNRE and Meteonorm in ANOVA analysis

6

20

25

30

35

40

Am

bie

nt

tem

p.

(oC

)

MNRE 24 h average MNRE day time average NASA 24 h average Meteonorm 24 h average

Ambient Temperature for Jodhpur

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0

5

10

15

20

Jan Feb Mar Apl May Jun Jul Aug Sep Oct Nov Dec

Am

bie

nt

tem

p.

(

Months

7

Variation of Plant Output with GHI and Ambient Temp.

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1694

1678

1709

1620

1640

1660

1680

1700

1720E

ne

rgy

Ou

tpu

t (M

Wh

)

Plant Output per MWp Using Different Weather Data

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1593

1520

1540

1560

1580

1600

MNRE-24 h MNRE-Day Temp NASA Meteonorm

En

erg

y O

utp

ut

(MW

h)

Weather Data

9

18.5 18.3

17.2

18.7

26.4 26

23.4

26.9

20

25

30

IRR

(%

)

Project IRR (Pre-tax) Equity IRR (Pre-tax)

Project Return

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0

5

10

15

MNRE-24 h MNRE-Day Temp NASA Meteonorm

IRR

(%

)

Weather data

10

Uncertainty in Yield Calculation

Parameters % Uncertainties Remarks

Year-to-Year climate variability 4%

Solar resource estimation in the

horizontal plane5%

This is due to variation in irradiance and

temperature data

Radiation in the plane of array 3%

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Power rating of modules 3% Variability due to manufacturing

Losses due to dirt 2%

Other sources of error 5%The losses in inverter, cable and transformers

have uncertainty

Annual Uncertainty 8.4%

Monte Carlo Simulation has to be done to calculate the probabilistic generation value

11

Inverters

Grid

Schematic of MW Solar Park

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AC Panel

Inverters

Combiner box with string monitoring ,

DC switch and Surge Protector

AC Switch AC Ckt BreakerStep up

Transformer

Data Monitoring

Power Socket

Sensor

12

4.00%

5.00%

6.00%

7.00%

Total Loss Pareto

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Near

Shading

on

Global

IAM

Factor on

Global

Non-STC

Operatio

n

Soiling

DC Array

Variabilit

y

Module

Mismatc

h

DC Cable

Loss

Inverter

Efficiency

Inverter

Limitatio

n

Inverter

Cooling

Data

Acquisiti

on & Aux

MV

Transfor

mers

AC Cable

Loss

HV

Transfor

mer

Series1 1.60% 1.90% 6.10% 3.00% 2.00% 1.50% 1.00% 1.62% 0.09% 0.41% 0.12% 1.06% 1.00% 0.47%

0.00%

1.00%

2.00%

3.00%

Total loss to the tune of 22%

13

Effect of Temperature on the Output

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Module Type Temp. Coeff.Module

Efficiency (%)Tolerance

Relative Module

Price

Mono-crystalline Silicon -0.41%/0C 14-20 3% 1.1

Multi-crystalline silicon -0.46%/0C 13-18 3% 1.0

Increasing

Area

Crystalline or Thin Film Module

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Cadmium Telluride Thin

Film-0.30%/0C 10-11 5% 0.90

Micromorph Silicon -0.25%/0 C 6-7 5% 0.75

Amorphous Silicon Thin

Film (Single Junction)-0.18%/0 C 5-6 5% 0.70

15

Cd-Te Module

Multi-crystalline Module

I-V Characteristic of Modules

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Mono-crystalline Module Amorphous Silicon Module

16

Visual Identification of Different Modules

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Mono-Crystalline Multi-Crystalline Amorphous Si Cadmium Telluride

17

Module Type

Module

Wattage

(Wp)

No. of

Modules

No. of

Modules in

series

No. of

Strings

Total Module

Area

Annual

Energy

(kWh)

Excess

Energy

Compared

to Multi-

crystalline Si

PR

SunPower 210 23184 18 1323 29627 8847762 0.88% 77.7

Mono-

Crystalline 210 23805 15 1587 39629 8806077 0.40% 77.4

5 MWp Plant Design with Different Modules

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Crystalline

silicon

210 23805 15 1587 39629 8806077 0.40% 77.4

Multi-

Crystalline

Silicon

21023805 23 1035 38025 8770840 0 77.1

Cd-Te 80 62946 9 6944 44997 8954308 2.1% 78.7

Micromorph

Silicon445 11235 3 3745 64264 9033976 3.0% 79.4

Location: Rajasthan and Central Inverter. All other parameters being same

18

� Degradation rate

� Reliability� Area available

� O&M cost

� Bankability� Installation cost

� BoS cost such as structure,

Module TypeDegradation

Rate (%/Year)Exposure Year

Mono-crystalline

Silicon0.30 8

Multi-Crystalline

Miscellaneous Considerations for Module Selection

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� BoS cost such as structure, cable and string monitor

� As per a study by Sandia lab

the module replacement ratefor crystalline module is 0.05%

and for thin films approx. 1%

Multi-Crystalline

Silicon0.5 9

Amorphous

Silicon0.7-1.4 7-12

Cd-Te 0.70 10

19

Around 65% of Non-Module Costs Scale with Module Efficiency

65%

35%100%

(Rs.40/Wp)

Halving efficiency

increases non-module costs by 65% and module costs must decrease correspondingly to

maintain competitiveness on a systems level

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systems level

Efficiency

dependent non-

module

costs

Efficiency

independent non-module

costs

Total non-

module cost

20

c-Si reference

module12.8%

Nominal module

efficiency (%)“Normalized” module

efficiency (%)Yield at

Rajasthan(kWh/kWp)

176212.8%

Thin Film Vs Crystalline Silicon

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Micromorph Si thin

film module 7.8% 1807 8.0%

Taking into account Rajasthan irradiation and

temperature statistics, the „normalized“ efficiency of a micromorph thin film module is 8% vs.

12.8.0% for a c-Si module

21

Entitlement of Thin Film Module Cost TakingCrystalline Silicon System Cost as Reference

Rs.120/Wp Rs.14/Wp

Rs.41.6/Wp

26x(12.8/8.0)

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Rs.64.4/Wp

Efficiency

dependent non-

module costs

Deduced thin

film Si module

price

Efficiency

independent

non-module

costs

Total systems

cost

Thin film module shall be20% cheaper than

Crystalline silicon moduleso as to meet the system

level cost.

22

Choice of Inverters

� Maximize efficiency and performance

� Maximize reliability and durability� Leverage scale of mass produced AC components� Easy to install� Special training not required for installation� Less risk/hazard

Inverter CTQs

+ A large number of power pointtrackers improve the yield

+ High DC system voltage range

+ Inverter integrated withmodule

+ Module level MPPT

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Central Inverter String Inverter Micro-inverter

and Three phase is now possible

in string inverters.

+ Reduced losses in both AC andDC cable and hence higher output

+ Dispense with junction box

+ Less skilled manpower needed

+ Inverters can be placed among the

modules+ No string monitor is needed

+ Module level MPPT

+ Module level monitoring

is possible

+ DC cabling not required+ More modular

-More expensive at present

- Bankability?

23

Central String

Less Inverters of High

Capacity

More Inverters of Less

capacity

For 1 MW:

2 No of 500kVA each

For 1 MW:

91 No of 11kVA each

++ Standard

composite Unit of

Inverter,

Transformer Station,

Switchgears as a

++ Separate Units

as Inverters, AC

Combiner Boxes,

Communication

Cables, Transformer

Comparison of Central and String for 1 MWp Plant

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Switchgears as a

package including

Communications

Cables, Transformer

Station, Switchgears

++ Easy

for Planning and

Installation

- - Complex

and a lot of

engineering reqd.

++ Easy

to Maintain due to less

components

++ Easy

to Maintain due to

higher reliability

24

Layout of Central Inverter Plant of 1 MWp

28 x SMA string-monitor

7 – 8 per Main Box

8 strings per combiner box8 contacts per string monitor,

Module Power: 180 Wp

26 modules per string

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Transformer 1000 MVA

Inverter 500 HE-11

Inverter 500 HE-11

SMA concrete

station 1000 MV

including 2 inverters

including transformer

TransferStation

2 x SMA DC main box2 per Inverter

25

Layout of String Inverter 1 MWp Plant

. . .

96 x SMC 11000TL

1 String is 20 modules

3 strings per inverter

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Transformer 1000 MVA

AC Combiners AC Combiners

AC Combiners for Phase

Balancing, Transformer

Station Transfer

Station

2 x SMA Web box

96 x SMC 11000TL

……………

26

Module Mounting Configuration

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Landscape Portrait

Which is Preferred?

27

Portrait layoutLandscape layout

Implications

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Shadow or Snow

Shadow or Snow

One string bypassed

Both strings bypassed

28

Concentration PV (CPV)

Salient Features of CPV� Concentration 500x� Dual axis tracking

� Uses direct radiation

� High efficiency III-V cells

Positives� Higher energy harvesting because of

• Tracking

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• Tracking

• Lower temp. coeff. (-0.16%/deg. C)

Negatives� Not a static system

� Reliability?

� Bankability� Cost

� Area efficiency

29

Frequency of Outages and Impact on Energy Loss

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O & M Cost (Fixed Crystalline Si as Reference)

Relative CostRelative CostRelative CostRelative Cost

O&M Activity

Fixed Crystalline

Si as the benchmark

Cd-Te Amorphous Si

Single Axis

Tracked Crystalline Si

Schedule

maintenance 1 1.2 1.4 1.5

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maintenance and cleaning

1 1.2 1.4 1.5

Unscheduled

maintenance1 1 1 2.5

Inverter

Maintenance1 1 1 1

Civil structure

and ground maintenance

1 1.5 2 1.5

32

Summary

• Generation over life time, capital cost and O&M are critical for economic

viability of project

• Design of Solar Power Plant is key to profitability

• Solar installation has to last for 25 years and negligence in component

selection and design may hurt in future

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selection and design may hurt in future

• Meteorological data are not accurately known nor can be predicted

with high certainty. Probabilistic approach to yield calculation is more prudent.

• One size does not fit all or a single design is not optimally suited for all

locations. An optimum solution for each location has to be designed.

33

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