multi-year study of bifacial energy gains under various ... · 2 sites currently operation...

Prism Solar Technologies – 2015 (All Rights Reserved)

Multi-Year Study of Bifacial Energy Gains Under Various

Field Conditionsby Jose Castillo-Aguilella

[email protected]

4Th PV Performance Modelling and Monitoring WorkshopCologne, Germany

mailto:[email protected]


Prism Solar Technologies

• Prism Solar founded in 2005.

• Researched bifacial technology and applications since 2008.

• Manufacturing of bifacial modules since 2012.


Presentation Topics

• Bifacial module field data related to the Bifacial Gain in Energy over similarly rated monofacial modules.

• What is the true rating of a bifacial module: Issues with standard STC module ratings when they are applied to bifacial modules.


Traditional Bifacial Module Applications


Modules Used in the Study

Bifacial Modules: Prism Solar B245 Front STC = 245W (w/ black background); typ = 245-248W

Pmax Temp coefficient = -0.465%/C

Bifacial Ratio (BR) [%] = 95%*

*Bifacial Ratio [%] = 100*(REAR/FRONT) = 100*(PREAR@STC/PFRONT@STC)

Reference Module: Canadian Solar CS6P-245MFront STC = 245W (+0-5W Positive Tolerance)

Pmax Temp coefficient = -0.45%/C

Bifacial Gain in Energy:BGE [%] = (Total[kwh]-Front[kwh])/Front[kwh]


Test Conditions

Test Condition

Date RangeTilt Angle (deg.)

Min Height

Ratio h(m)

Albedo (%)

Azimuth

(deg)BGE(%)

110/1/2012 to

4/28/201530 0.63 10% 180 17.7

25/10/2013 to 10/04/2013

30 0.76 77% 180 36.8

35/10/2013

to10/04/201330 0.2 77% 180 27.3

410/06/2013 to

01/14/201520 0.2 70% 180 18.41

510-31-2013 to 12/31/2014

20 0.2 68% 180 19.57

610-31-2013 to 12/31/2014

20 0.2 22% 180 12.31

71/1/2014 to 08/01/2015

10 0.3 75% 180 17.85

Vertical configurations pointing South, East and 45 deg from South will also be shown


Prism Solar Central Hudson Test Yard

Location: Highland, NYLatitude: ~41.6°NSystem Tilt: 30°Azimuth: 180° (South)Ground Reflectance: ≤10%

Test Condition Date RangeTilt Angle (deg.)

Min Height Ratio h(m)

Albedo (%)Orientation

(P/L)Azimuth (deg)

Bifacial Gain in Energy (%)

110/1/2012 to

4/28/201530 0.63 10% L 180 17.7

0%

5%

10%

15%

20%

25%

30%

35%

40%

0

1

2

3

4

5

6

O-1

2

D-1

2

F-13

A-1

3

J-13

A-1

3

O-1

3

D-1

3

F-14

A-1

4

J-14

A-1

4

O-1

4

D-1

4

F-15

A-1

5

Bif

acia

l Gai

n in

En

ergy

(%

)

Ave

rage

Dai

ly [

kWh

/kW

]

Bifacial [kWh/kW_dc]/day Monofacial [kWh/kW_dc]/day



Prism Solar Tucson, AZ Test Yard

C6SP

CS6P

CS6P

CS6P

B245

B245

B245

B245

Location: Tucson, AZLatitude: ~32.18°NSystem Tilt: ~30°Azimuth: 180° (South)Ground Reflectance: 77%

CS6P-245M

Reference Array

B245 Bifacial

Array @ 0.76m

B245 Bifacial

Array @ 0.2m

Module Maximum Power

Rating of the (Pmax)245 W 245 W 245 W

Inverter Model

PowerOne

Micro-0.3-I

OUTD-US

PowerOne

Micro-0.3-I

OUTD-US

PowerOne

Micro-0.3-I

OUTD-US

Inverter max AC power

output300 W 300 W 300 W

Number of Modules 4 2 2

Mounting Angle 30 30 30

Data Range5/10/2013 -

10/04/2013

5/10/2013 -

10/04/2013

5/10/2013 -

10/04/2013

Days 144 144 144

Normalized Energy

Generated

[kWh/kW_STC/day]

5.03 6.88 6.42

Gain - 36.8% 27.3%


0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

0

2

4

6

8

10

12

14

16

18

20

5/1

15

/18

5/2

56

/16

/86

/15

6/22

6/2

97

/67

/13

7/2

07

/27

8/3

8/1

08

/17

8/2

48

/31

9/7

9/1

49

/21

9/2

81

0/5

Dai

ly B

ifac

ial G

ain

in E

ner

gy (

%)

kWh

/kW

per

day

AVG Energy B245 30" [kWh/kW]AVG Energy B245 8" [kWh/kW]AVG Energy CS6P [kWh/kW]Daily Bifacial Energy Gain 8" (%)Daily Bifacial Energy Gain 30" (%)


100

120

140

160

180

200

220

240

260

280

300

5/1

15

/18

5/2

56

/16

/86

/15

6/2

26

/29

7/6

7/1

37

/20

7/2

78

/38

/10

8/1

78

/24

8/3

19

/79

/14

9/2

19

/281

0/5

Pea

k M

od

ule

Po

wer

(W

)

Peak Daily Power 30" Bifacial (Watts)

Peak Daily Power 8" Bifacial (Watts)

Peak Daily Power CS6P 245 (Watts)




(P/L)Azimuth (deg)


25/10/2013 to 10/04/2013

30 0.76 77% L 180 36.8

35/10/2013

to10/04/201330 0.2 77% L 180 27.3



020406080

100120140160180200220240260280

5 7 9 11 13 15 17 19

Ave

rage

Mo

du

le P

ow

er

[W]

5/11/2013 - Time of day

CS6P-245M Average

B245 Average

0%

25%

50%

75%

100%

125%

150%

5 7 9 11 13 15 17 19

BG

E (%

)

5/11/2013 - Time of day

5 min BGE (%)Daily BGE (%)Annual BGE (%)

Test Condition 2 values for (LEFT) 5 minutes average power values for the B245 modules, set at =77%, h=0.76m, =30 , and CS6P-245M modules on 5/11/2013. (RIGHT) Average BGE values for 5 minute, daily and annual average for 5/11/2013 – Please note the large variation of the BGE in relation to the time of study.

BGE [%]] = (Total[kwh]-Front[kwh])/Front[kwh]


B245

B245CS6P

CS6P

CS6P




(P/L)Azimuth (deg)


4OCT 2013 to

JAN 201520 0.2 70% L 180 18.41

0%

5%

10%

15%

20%

25%

30%

0

1

2

3

4

5

6

7

8

O-1

3

N-1

3

D-1

3

J-1

4

F-1

4

M-1

4

A-1

4

M-1

4

J-1

4

J-1

4

A-1

4

S-1

4

O-1

4

N-1

4

D-1

4

Bif

acia

l Gai

n in

en

erg

y B

GE

(%)

Dai

ly A

vera

ge k

Wh

/kW

Bifacial (kWh/kW) Mono (kWh/kW) BGE (%)







(P/L)Azimuth (deg)


510-31-2013 to 12/31/2014

20 0.2 68% P 180 19.57

610-31-2013 to 12/31/2014

20 0.2 22% P 180 12.31

Location: TucsonLatitude: ~32.18°N

System Tilt: 20° PortraitAzimuth: 180° (South)

Ground Reflectance: 68% and 22%

0%

5%

10%

15%

20%

25%

30%

35%

0

1.5

3

4.5

6

7.5

O-1

3

N-1

3

D-1

3

J-1

4

F-1

4

M-1

4

A-1

4

M-1

4

J-1

4

J-1

4

A-1

4

S-1

4

O-1

4

N-1

4

D-1

4

Bif

acia

l Gai

n in

En

erg

y (%

)

Dai

ly A

vera

ge k

Wh

/kW

0.68 Bifacial (kWh/kW) 0.22 Bifacial (kWh/kW)

Monofacial (kWh/kW) 0.68 Bifacial Gain in Energy (%)

0.22 Bifacial Gain in Energy (%)



B245

B245

CS6PCS6P

CS6P

CS6P

Test Condition

Date Range

Tilt Angle (deg.)


Albedo (%)

Orientation (P/L)

Azimuth (deg)

Bifacial Gain in Energy

(%)

7

JAN1/2014 to

AUG01/2015

10 0.3 75% P 180 17.85

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

0

1

2

3

4

5

6

7

8

J-14 F-14 M-14 A-14 M-14 J-14 J-14 A-14 S-14 O-14 N-14 D-14 J-15 F-15 M-15 A-15 M-15 J-15 J-15 A-15

BG

E(%

)

Ave

rage

Dai

ly [

kWh

/kW

]

Bifacial [kWh/kW] Monofacial [kWh/kW] BGE(%)


Vertical Testing - Prism Solar Tucson, AZ

0

1

2

3

4

5

6

7

8

J-1

3

F-1

3

M-1

3

A-1

3

M-1

3

J-1

3

J-1

3

A-1

3

S-1

3

O-1

3

N-1

3

D-1

3

J-1

4

F-1

4

M-1

4

A-1

4

M-1

4

J-1

4

J-1

4

S-1

4

O-1

4

N-1

4

D-1

4

J-1

5

Ave

rage

Dai

ly k

Wh

/kw

C6SPSouth(Wh)B245South(Wh)C6SP East(Wh)

B245 East(Wh)

B245 -45(Wh)

Vertical C6SP South (REF)

Vertical B245 South

Vertical C6SP East Vertical B245 East Vertical B245 -45

Average Annual Energy (kWh/kW) 1186 1555 854 1796 1737

Energy Gain Jan 2013 – Jan 2015 31.34% -27.93% 51.55% 46.54%

For an additional comparison, the 10 degree tilt monofacial reference system of Test Condition 7 produced an annual yield 1744 kWh/kW


Notes on Bifacial Testing for Tucson, AZ

• Dry and hot environment at an elevation of 730m above sea level, and therefore less air mass.

• The observed results would tend to understate the bifacial gain in locations with a higher proportion of diffuse light, under similar conditions.


Additional Independent Testing

TÜV/GTM Comparative Energy Yield (CEY) program which is deploying systems at 4 sites world-wide, each with 10 module manufacturer’s products in a direct comparison of various PV commercially available technologies, each manufacturer with 2kW-2.5kW.

2 sites currently operation (Phoenix, Arizona and Davis, California). For both sites, Prism Solar bifacial modules have reported a higher monthly energy (kWh/kW) yield than any other system including other bifacial modules, since testing started in May 2015.

All systems were deployed over low albedo surfaces and with partial racking obstructions of the rear of some of the bifacial modules in the array


Bifacial Energy Estimation –Prism Solar Design Guide

A simplified annual yield model based on these experiments is presented as the Prism Solar Bifacial Design Guide.

http://www.prismsolar.com/pdf/Design_guide.pdf

Customers can estimate the additional annual backside energy performance of Prism Solar modules (Bifacial Ratio ~0.90) under some of the most common field installation conditions.

http://www.prismsolar.com/pdf/Design_guide.pdf


What is the True Rating of a Bifacial Module?


What is the True Rating of a Bifacial?

UL, IEC and other standards only account for the front side at STC conditions to rate the modules, bifacial or not. The background and angular illumination for a bifacial STC test conditions are not defined.

• Fails to address the true energy generation potential of bifacial modules. Wiring, fuses/protection and inverter may be undersized as a consequence of STC sizing.

• Customers cannot compare bifacial manufacturers.

Prism Solar modules are IV-tested using a collimated light source and black material behind the module, as to not add opposite-side power contribution to the side being tested. This produces a lower STC flash than someone using a white background or/and an un-collimated flash tester.


Rating of Bifacial Modules is Generally Left to Manufacturers

Most manufacturers only present the STC rating and the performance of the module when it achieves 10%, 20% or 30% of additional power from the backside. None describe the background or illumination conditions for their STC flash.

Unfortunately, this method doesn’t address the issue of how much light it takes to reach that additional power.


What is the True Rating of a Bifacial Module?

ManufacturerParameter A B C D E

STC Rating (W) 270 270 270 270 270

Equivalent Rating at +30% Power (W) 351 351 351 351 351

Backside Efficiency Ratio (Rear/Front) 10% 50% 75% 90% 100%Rear Illumination Needed for +30% in (W/m^2) 3000 600 400 333 300

Field Average Illumination Level (W/m^2) 300 300 300 300 300Power at Field illumination Level (W) 278.1 310.5 330.8 342.9 351

Although all these manufactures would have equal STC ratings and equal +30% bifacial ratings, the performance under equal rear illumination conditions would be different among them.


BSTC = Bifacial STC

Prism used a BSTC rating for protection and wire sizing since 2013, and certified its modules with the independently developed bifacial TÜV guidelines at TÜV PTL (Phoenix, AZ) in 2015.

BSTC conditions (TÜV guidelines) =

Cell temp 25°C, AM1.5, 1000W/m2 (front) + 300W/m2 (rear)

Prism Solar modules tested with TÜV underwent full UL, IEC and NREL’s Qualification Plus testing at BSTC amperage levels to fully certify the safety aspects of the bifacial design.


BSTC = Bifacial STC

BSTC provides additional relevant information about the bifacial performance of a module.

By comparing the BSTC and Front STC ratings, the rear STC module efficiency can be estimated.

Alternatively, if the Front STC and Rear STC is given, the BSTC can be determined.

Bifacial ratings, safety protections and wiring sizing should account for bifacial effects.


Conclusions• The field performance of bifacial modules under a variety of field

conditions was shown.

• Under standard mounting conditions, bifacial modules exceeded annual energy yield of monofacial reference modules by at least 12% and up to +30%.

• Vertically mounted bifacial modules have the potential to generate as much energy as traditionally mounted monofacial modules.

• We have shown how the current lack of bifacial standards makes a direct comparison between bifacial manufacturers difficult, based both on IV flash test conditions and rear side efficiency.

• In the case of protection of bifacial systems, safety issues could arise from the additional current and power not being accounted for under STC conditions.


Future Work

• Add data set from TÜV/GTM Comparative Energy Yield program to bifacial model.

• Joint bifacial work with Sandia National Labs with 3 sites in the US with multiple installation configurations at each site and add data set to model.

• Work with Sandia/NREL on bifacial standards.


Thank You

Additional questions:[email protected]

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