Bifacial PV System Performance · Bifacial PV System Performance: Separating Fact from Fiction Chris Deline, Silvana Ayala Peláez, Bill Marion, Bill Sekulic, Michael Woodhouse,

Bifacial PV System Performance: Separating Fact from Fiction

Chris Deline, Silvana Ayala Peláez, Bill Marion, Bill Sekulic, Michael Woodhouse, and Josh Stein (Sandia National Labs)

PVSC-46, Chicago, IL 2019

NREL/PR-5K00-74090

NREL | 2NREL | 2

Bifacial PV in the news

NREL | 3NREL | 3

Status of Bifacial Installations 2019

R. Kopecek, Photonics North 2019, May 22nd Quebec

NREL | 4NREL | 4ITRPV 2018, PV Celltech Conference March 10-11th 2019 Penang Malaysia

Historic & projected PV market

Al-BSF

PERCSHJ

Different cell technology Bifacial cell in world market

NNRRELEL | | 5 Thorsten Dullweber et al. PERC+: industrial PERC solar cells with rear Al grid enabling bifaciality and reduced Al paste consumption, Prog. Photovolt: Res. Appl. (2015)

PERC cell technology – easily bifacial

Module bifaciality 𝜙𝜙 = 𝑃𝑃𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑃𝑃𝐹𝐹𝑅𝑅𝐹𝐹𝐹𝐹𝐹𝐹

= 0.65-0.80 (p-PERC)

0.75-0.90 (n-PERT)

0.85 – 0.95 (Si Heterojunction)

Reduced screen-print metallization

NREL | 6NREL | 6

PERC PERC+ n-PERT SHJ

Additional details given in: (1) M Woodhouse, B Smith, A Ramdas, and R Margolis “Economic Factors of Production Affecting Current and Future Crystalline Silicon Photovoltaic Module Manufacturing Costs and Sustainable Pricing”, In preparation. (2) A Faes, C Ballif, M Despeisse, et al, “Metallization and interconnection for high efficiency bifacial silicon heterojunction solar cells and modules”, Photovoltaics International, 3, 1—12 (2018) (3) A Louwen, W van Sark, R Schropp, and A Faaij, “A Cost Roadmap for silicon heterojunction solar cells”, Solar Energy Materials and Solar Cells, 147, 295—314 (2016)

Monofacial vs Bifacial module manuf. cost

Calculated Minimum Sustainable Price

R&D, Sales, Administrative

Module Assembly

BOM Materials

Stringing and tabbing consumables

Other Cell direct costs

Cell Metallization

April 2019 Wafer pricing

BifacialMonofacial

Bifacial PerformanceModeling

Photo credit: Prism Solar

NREL | 8

𝑮𝑮𝑻𝑻𝑻𝑻𝑻𝑻𝑻𝑻𝑻𝑻 = 𝑮𝑮𝑭𝑭𝑭𝑭𝑻𝑻𝑭𝑭𝑻𝑻 + 𝑮𝑮𝑹𝑹𝑹𝑹𝑻𝑻𝑭𝑭) × (𝒃𝒃𝒃𝒃𝒃𝒃𝑻𝑻𝒃𝒃𝒃𝒃𝑻𝑻𝑻𝑻𝒃𝒃𝑻𝑻𝒃𝒃) × (𝟏𝟏 − η𝑳𝑳𝑻𝑻𝑳𝑳𝑳𝑳

Bifacial total irradiance

Gfront

Grear * φ_𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵

Module bifaciality φ_𝑩𝑩𝒃𝒃𝒃𝒃𝒃𝒃 =𝑃𝑃𝑃𝑃𝑝𝑝0 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑃𝑃𝑃𝑃𝑝𝑝0 𝐵𝐵𝑟𝑟𝑓𝑓𝑓𝑓𝑓𝑓

NREL | 9

Modeling Rear Irradiance

Grear = Gdiffuse,r + Greflected,r + Gbeam,r

NREL | 10


Grear = Gdiffuse,r + Greflected,r + Gbeam,r

NREL | 11

Bifacial energy gain BGE= 𝐸𝐸𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵/𝐸𝐸𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 − 1= ??

What bifacial gain can be expected?

NREL | 12NREL | 12

0

100

200

300

400

500

0 0.2 0.4 0.6 0.8 1

Gre

arW

m-2

Ground reflectance (R)

Asphalt

Soil Concrete

Built-up roof

White EPDM

NASA Earth Observations, https://neo.sci.gsfc.nasa.gov/view.php?datasetId=MCD43C3_M_BSAR. Kopecek and J. Libal, Bifacial Photovoltaics: Technology, applications and economics, IET publishing, 2019

Rear irradiance, single module at STC (1kWm-2 frontside)

Surface Albedo has a big effect

https://neo.sci.gsfc.nasa.gov/view.php?datasetId=MCD43C3_M_BSA

NREL | 13NREL | 13

0

30

60

90

120

150

0 5 10 15 20

Gre

ar(W

m-2

)

Modules per row

Single row

Front row

Interior row

System GRear experiences self-shading

C. Deline et al., Assessment of Bifacial Photovoltaic Module Power Rating Methodologies – Inside and Out, J. Photovoltaics 7, 2017

Grear: -50%

Bifacial PerformanceModels

Photo credit: C.Deline

NREL | 15NREL | 15

Complicated geometries possible, including racking and terrain.Radiance uses backward ray-trace to evaluate the irradiance (W/m2) at the modules

Open-source software freely available at http://www.github.com/NREL/bifacial_radiance

Bifacial_Radiance Model for Rear Irradiance

S. Ayala Pelaez, C. Deline, S. MacAlpine, B. Marion, J. Stein, R. Kostuk, "Comparison of bifacial solar irradiance model predictions with field validation" IEEE Journal of Photovoltaics, 2019, vol 9 no. 1, pp. 82-88.

Field validation shows good agreement with close-mount rooftop mockup

Open-source software freely available at http://www.github.com/NREL/bifacial_radiance

0

50

100

150

200

250

300

50 150 250 350 450 550

Gre

ar[W

m-2

]

Back Sensor Position (mm)

MeasuredView FactorRadiance

h = 0.6

h = 0.15

Bifacial_Radiance Model for Rear Irradiance

http://www.github.com/NREL/bifacial_radiance

NREL | 17

View Factor Model for Rear Irradiance

basicgeometry

Simple

computationallyinexpensive

Fast

BehindSAM, Pvsyst, and others

Common

PVSyst v6.75

NREL | 18

View Factor Model for Rear Irradiance

Grear is summed over 180° field-of-view:

Grear = 𝐺𝐺𝐷𝐷𝐷𝐷𝐷𝐷,𝑟𝑟𝑟𝑟𝐵𝐵𝑟𝑟 + �𝐵𝐵=1°

180°

𝑉𝑉𝑉𝑉𝐵𝐵 � 𝑉𝑉𝐵𝐵 � 𝐺𝐺𝐵𝐵 ;

B. Marion et al., A Practical Irradiance Model for Bifacial PV Modules, 2017B. Marion, Numerical method for angle-of-incidence correction factors for diffuse radiation incident photovoltaic modules, 2017

𝑉𝑉𝑉𝑉𝐵𝐵 = 12� cos 𝐵𝐵 − 1 − cos 𝐵𝐵 ;

𝑉𝑉𝐵𝐵 = 𝐼𝐼𝑓𝑓𝐼𝐼𝐵𝐵𝐼𝐼𝑟𝑟𝑓𝑓𝐼𝐼𝑟𝑟 𝑟𝑟𝑓𝑓𝑎𝑎𝑎𝑎𝑟𝑟 𝑃𝑃𝑓𝑓𝐼𝐼𝐵𝐵𝐵𝐵𝐵𝐵𝑟𝑟𝑟𝑟(ϴ)

𝐺𝐺𝐵𝐵 = 𝐼𝐼𝑟𝑟𝑟𝑟𝑟𝑟𝐼𝐼𝐵𝐵𝑟𝑟𝑓𝑓𝐼𝐼𝑟𝑟 𝐺𝐺𝑠𝑠𝑠𝑠𝑠𝑠,𝐺𝐺ℎ𝑀𝑀𝑟𝑟 , ρ·𝐺𝐺𝑔𝑔𝑟𝑟𝑀𝑀𝑔𝑔𝑀𝑀𝑔𝑔 ;

Irradiance sources: sky, ground (shaded or unshaded)

NREL | 19

N. DiOrio, C. Deline, “Bifacial simulation in SAM”, presented at 5th BifiPV in Denver, CO 2018.S. Ayala Pelaez, C. Deline, S. MacAlpine, B. Marion, J. Stein, R. Kostuk, "Comparison of bifacial solar irradiance model predictions with field validation" IEEE Journal of Photovoltaics, 2019, vol 9 no. 1, pp. 82-88.

NREL SAM Model

8

9

10

11

12

13

14

0.3 0.35 0.4 0.45 0.5

GRe

ar\

GFr

ont

[%]

Ground Coverage Ratio

1-axis tracking model comparison

PVSyst 6.75

Bifacial_Radiance

SAM0.3 albedo

SAM v2018.11

Bifacial trackers, 75 kW5 bifacial technologies

NREL | 21

20 modules (7.5 kW) / row

4 PERC, 1 SHJ Bifacial strings

3 PERC monofacial strings

Module electronics / monitoring

String kWhDC monitoring

Front, rear POA irradiance

Bifacial system configuration

NREL | 22








NREL | 23








NREL | 24








NREL | 25








NREL | 26








= Front POA

= Rear POA

NREL | 27NREL | 27

Initial field results – bifacial trackers

Bifacial gain: 5%

Bifacial gain: 15%

BGE = 𝐸𝐸𝑏𝑏𝑏𝑏𝑏𝑏𝑅𝑅𝑏𝑏𝑏𝑏𝑅𝑅𝑏𝑏𝐸𝐸𝑚𝑚𝐹𝐹𝐹𝐹𝐹𝐹

− 1

NREL | 28NREL | 28


Bifacial gain: 5%

Bifacial gain: 15%


− 1

NREL | 29NREL | 29

More diffuse = higher BGE


− 1


NREL | 30NREL | 30


− 1


Annual power histogram

50% energy production

NREL | 31NREL | 31

Modeled vs Measured kWDC Power

BifacialMonofacial

*SAM v2018.11 using 15-minute measured DNI, DHI, albedo from SRRL BMS. Andreas, A.; Stoffel, T.; (1981). NREL Solar Radiation Research Laboratory (SRRL): BaselineMeasurement System (BMS); Golden, Colorado (Data); NREL Report No. DA-5500-56488. Bifacial systems assume 5% shading loss, 5% mismatch loss, 0% transmission factor

NREL | 32NREL | 32

Bifacial modeling sensitivity

6%

9%

PERC bifacial gain 4-8%

Si-HJT bifacial gain 6.5-11%

8%

4%

6.5%

11%

Field testresults to date


− 1

3 sensitivity cases:

Ground albedo

PERC φBifi

Si-HJT φBifi

High case 0.30 0.75 0.95Average case 0.20 0.7 0.90Low case 0.15 0.65 0.85

*SAM v2018.11 using 15-minute measured DNI, DHI, albedo from SRRL BMS. Andreas, A.; Stoffel, T.; (1981). NREL Solar Radiation Research Laboratory (SRRL): BaselineMeasurement System (BMS); Golden, Colorado (Data); NREL Report No. DA-5500-56488. Bifacial systems assume 5% shading loss, 5% mismatch loss, 0% transmission factor

Market Analysis

NREL | 34

$25

$30

$35

$40

$45

1,200 1,450 1,700 1,950 2,200 2,450

LCO

E (2

019

USD

/MW

h)

Site kWh/kW annual

Bifacial vs Monofacial LCOE at various US sites6% Nominal Discount Rate. Single Owner and Unlevered Pro Forma with 30% ITC

Monofacial LCOE Bifacial LCOESeattle, WA

Kansas City, MO

Miami, FL

Daggett, CA

$1.05/W $1.10/W

Pre-Tariff situation illustration based on R. Fu, D. Feldman, R. Margolis, M. Woodhouse, K. Ardani, “U.S. Solar Photovoltaic System Cost Benchmark: Q1 2017” NREL/TP-6A20-68925, 2017 And Solar Energy Industries Association. US Solar Market Insight: 2018 Year in Review. Washington, DC March. 2019. Assumptions: 100MW system, 1.2 DC-AC ratio, 0.35 GCR

LCOE Analysis for Monofacial and Bifacial PV Systems

https://www.nrel.gov/docs/fy17osti/68925.pdf

NREL | 35

$25

$30

$35

$40

$45

1,200 1,450 1,700 1,950 2,200 2,450

LCO

E (2

019

USD

/MW

h)

Site kWh/kW annual



Kansas City, MO

Miami, FL

Daggett, CA

$1.05/W $1.10/W

Pre-Tariff situation illustration based on R. Fu, D. Feldman, R. Margolis, M. Woodhouse, K. Ardani, “U.S. Solar Photovoltaic System Cost Benchmark: Q1 2017” NREL/TP-6A20-68925, 2017 And Solar Energy Industries Association. US Solar Market Insight: 2018 Year in Review. Washington, DC March. 2019. Assumptions: 100MW system, 1.2 DC-AC ratio, 0.35 GCR

$30.0

$30.5

$31.0

$31.5

$32.0

$32.5

$33.0

2,180 2,200 2,220 2,240 2,260 2,280

LCO

E (2

019

USD

/MW

h)

Site kWh/kW annual

PRE-TARIFF Situation LCOE - Miami, FL

High case+8% BGE

Avg. case+6% BGE

Low case+4% BGE

+1¢/w

-1¢/wMonofacial reference$1.05/W

Bifacial PERC$1.10/W

Bifacial



NREL | 36

$25

$30

$35

$40

$45

1,200 1,450 1,700 1,950 2,200 2,450

LCO

E (2

019

USD

/MW

h)

Site kWh/kW annual (monofacial)

POST-TARIFF Bifacial vs Monofacial LCOE at various US sites6% Nominal Discount Rate. Single Owner and Unlevered Pro Forma with 30% ITC

Monofacial LCOE PERC Bifacial SHJ Bifacial

Seattle, WA

Kansas City, MO

Miami, FL

Daggett, CA

$1.05/W $1.05/W $1.09/W

Post-Tariff illustration: -5¢/W bifacial based on R. Fu, D. Feldman, R. Margolis, M. Woodhouse, K. Ardani, “U.S. Solar Photovoltaic System Cost Benchmark: Q1 2017” NREL/TP-6A20-68925, 2017 And Solar Energy Industries Association. US Solar Market Insight: 2018 Year in Review. Washington, DC March. 2019. Assumptions: 100MW system, 1.2 DC-AC ratio, 0.35 GCR


$29.5

$30.5

$31.5

$32.5

2,210 2,220 2,230 2,240 2,250 2,260 2,270 2,280 2,290

LCO

E (2

019

USD

/MW

h)

Site kWh/kW annual

POST-TARIFF LCOE - Miami, FL

Monofacial reference$1.05/W


Bifacial SHJ$1.09/W


Conclusions:

• Bifacial PV is becoming mainstream with GW’s of installed projects

• Energy gain depends on the site configuration and surface albedo. Models like SAM, PVSyst and Bifacial_Radiance can assist with system design and power estimation.

• 1-axis tracker validation is underway at NREL, showing good initial match with model, and energy gain of 6% and 9% annually for PERC and Si-HJT.

• LCOE of bifacial systems is competitive with monofacial systems now, even with initial cost adder of 5-6 ¢/W. Post-tariff, bifacial is a clear winner.

June20

Sept12-17

June19

WEDNESDAY, 10:30A: (Sheraton 4-5)• B. Lee, J. Wu: Bifacial PERC cells. 11A & 11:30A

THURSDAY, 8:30A: (Chicago 8)• A. Asgharzadeh: Benchmarking models. 8:30A• M. Waters: Bifacial Capacity Testing. 8:45A• K. McIntosh: Bifacial mismatch loss 9:00ATHURSDAY 10:30A: (Sheraton 1)• M. Patel, R. Bailey: Albedo. 10:30 & 10:45A• S. Ayala: Shading effects on bifacial trackers. 11A

36th EU PVSEC (Marseille)6th Bifi PV Workshop (Amsterdam)• S. Ayala: Electrical mismatch and shading• B. Marion: Ground albedo measurements• J. Stein: HPC Optimization of Bifacial Systems

Look for more

Acknowledg-ments

This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-08-GO28308 with the National Renewable Energy Laboratory (NREL). Funding provided by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under Solar Energy Technologies Office (SETO) Agreement Number 34910. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government.

Backup Slides

NREL | 40NREL | 40

Clearance

Tilt

Albedo

Others:Spacing between cells#rows, #panelsMounting Structure Other scene elements

Irradiance ModelLocation WeatherSky Diffuse Model

Image: http://opsun.com/mounting-solutions/flat-roof/bifacial-pv-racking/


NREL | 41

$25

$30

$35

$40

$45

1,200 1,450 1,700 1,950 2,200 2,450

Real

LCO

E (U

SD/M

Wh)

Site kWh/kW annual



Kansas City, MO

Miami, FL

Daggett, CA

$1.05/W $1.10/W


Illustrative example based on R. Fu, D. Feldman, R. Margolis, M. Woodhouse, K. Ardani, “U.S. Solar Photovoltaic System Cost Benchmark: Q1 2017” NREL/TP-6A20-68925, 2017And Solar Energy Industries Association. US Solar Market Insight: 2018 Year in Review. Washington, DC March. 2019. Assumptions: 100MW system, 1.2 DC-AC ratio, 0.35 GCR

$44.0

$44.5

$45.0

$45.5

$46.0

$46.5

$47.0

1,465 1,467 1,469 1,471 1,473 1,475

Nom

inal

LCO

E (U

SD/M

Wh)

Site kWh/kW annual

LCOE detail - Seattle, WA

High case+8% BGE

BifacialAvg. case+6% BGE

Low case+4% BGE


Monofacialreference$1.05/W


NREL | 42

$25

$30

$35

$40

$45

1,200 1,450 1,700 1,950 2,200 2,450

LCO

E (2

019

USD

/MW

h)

Site kWh/kW annual (monofacial)

POST-TARIFF Bifacial vs Monofacial LCOE at various US sites6% Nominal Discount Rate. Single Owner and Unlevered Pro Forma with 30% ITC

Monofacial LCOE PERC Bifacial SHJ BifacialSeattle, WA

Kansas City, MO

Miami, FL

Daggett, CA

$1.05/W $1.02/W $1.06/W

Post-Tariff illustration: -8¢/W bifacial based on R. Fu, D. Feldman, R. Margolis, M. Woodhouse, K. Ardani, “U.S. Solar Photovoltaic System Cost Benchmark: Q1 2017” NREL/TP-6A20-68925, 2017 And Solar Energy Industries Association. US Solar Market Insight: 2018 Year in Review. Washington, DC March. 2019. Assumptions: 100MW system, 1.2 DC-AC ratio, 0.35 GCR

$28.0

$29.0

$30.0

$31.0

$32.0

$33.0

2,210 2,220 2,230 2,240 2,250 2,260 2,270 2,280 2,290

LCO

E (2

019

USD

/MW

h)

Site kWh/kW annual

POST-TARIFF LCOE - Miami, FL

Monofacialreference$1.05/W


Bifacial SHJ$1.06/W



Bifacial PV System Performance · Bifacial PV System Performance: Separating Fact from Fiction Chris Deline, Silvana Ayala Peláez, Bill Marion, Bill Sekulic, Michael Woodhouse,

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