NREL | 1

Effect of Torque-Tube Parameters on Rear-Irradiance and Rear-Shading Loss

for Bifacial PV Performance on 1-Axis Tracking Systems

Silvana Ayala Peláez, Chris Deline, Joshua S. Stein (Sandia National Labs), Bill Marion, Kevin Anderson (Cypress Creek Renewables), and Matthew Muller

46th IEEE PVSC, June 16-21, 2019, Chicago, IllinoisNREL/PR-5K00-74236

NREL | 2NREL | 2

Hourly BGE

© Dr. Andrew J. Marsh, 2014.http://andrewmarsh.com/apps/staging/sunpath3d.html

Yearly BGEJune 21st

Bifacial modules boost energy yield by 4% to 15%

Ayala Pelaez, Silvana, et al. "Model and Validation of Single-Axis Tracking With Bifacial PV." IEEE Journal of Photovoltaics(2019).

NREL | 3NREL | 3

Effect of torque tube on rear-irradiance

Repercussions on energy loss

Ideal location of sensors?

NREL | 4

Tracking and Torque tubeHourly annual simulations

NREL | 5

bifacial_radiance program (raytrace)

https://github.com/NREL/bifacial_radiance/Open Source! (a.k.a. free!)

Cairo, Egypt. 20 modules per row, 7 rows.

200 points per hour modeled across center module’s collector width

Albedo of 0.28, GCR of 0.25

NREL | 6

2 m

CW = 2 m

zgap 5 cm

diam 10 cm

Comparing to a case with no torquetube,This base case has a 5.7% Shading Factor

Grear Shading Factor = 1 −∑t=08760 𝐺𝐺𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 𝑟𝑟𝑎𝑎𝑟𝑟𝑟𝑟𝑟𝑟𝑎𝑎𝑟𝑟 (𝑤𝑤ith 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡)

�∑t=08760 𝐺𝐺𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 𝑟𝑟𝑎𝑎𝑟𝑟𝑟𝑟𝑟𝑟𝑎𝑎𝑟𝑟 (no 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡

NREL | 7

+ ygap 0 to 30 cm

5 to 20 cm

zgap

Compared to various scenarios

Shading Factor: 5% - 7.5%

Shading Factor:6% 2%

CW = 2 m

Grear Shading Factor = 1 −∑t=08760 𝐺𝐺𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 𝑟𝑟𝑎𝑎𝑟𝑟𝑟𝑟𝑟𝑟𝑎𝑎𝑟𝑟 (𝑤𝑤ith 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡)

�∑t=08760 𝐺𝐺𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 𝑟𝑟𝑎𝑎𝑟𝑟𝑟𝑟𝑟𝑟𝑎𝑎𝑟𝑟 (no 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡

NREL | 8NREL | 8

Varying torquetube reflectivity

7.8% Shading Factor

5.7%Shading Factor

Grear Shading Factor = 1 −∑t=08760 𝐺𝐺𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 𝑟𝑟𝑎𝑎𝑟𝑟𝑟𝑟𝑟𝑟𝑎𝑎𝑟𝑟 (𝑤𝑤ith 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡)

�∑t=08760 𝐺𝐺𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 𝑟𝑟𝑎𝑎𝑟𝑟𝑟𝑟𝑟𝑟𝑎𝑎𝑟𝑟 (no 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡

Panel A Panel B

NREL | 9NREL | 9

Varying torquetube reflectivity

8.5% Shading Factor

-1.7%Shading Factor

NREL | 10NREL | 10https://solarbuildermag.com/featured/bifacial-gains-how-much-will-bifacial-modules-add-to-solar-tracker-value-we-are-about-to-find-out/

Torque tube reflections

NREL | 11NREL | 11

Varying Y-gap 2 pm GRear Shading Factor (Annual) %

5.7

0

-0.2

0.4

Sunny dayYGAP [cm]

0

5

10

15

Cloudy day

NREL | 12NREL | 12

Cairo, June 21st at 2 PM

Detailed Irradiance valuew. torque tube

Averaging Irradiancefor the module

w.o torque tube~1031 W/m2

P0

P1

𝐿𝐿𝐷𝐷𝐷𝐷 = 1 −𝑃𝑃1𝑃𝑃0PVMismatch OpenSource!: https://github.com/SunPower/PVMismatch

Shading plus Electrical Mismatch

~1%

NREL | 13NREL | 13

Total Loss DC %

1.2

0.5

0.6

1.1

2 pm GRear Shading Factor (Annual) %

5.7

0

-0.2

0.4

Sunny dayYGAP [cm]

0

5

10

15

Cloudy dayVarying Y-gap

NREL | 14NREL | 14

LossDC to parameters in PVSyst?

• Structure shading factor, a.k.a. Rear shading factor gets put directly into the loss diagram as “Shading loss on rear side”.

• Mismatch loss factor a.k.a. rear mismatch loss, affects the Mismatch for back irradiance in the loss diagram

NREL | 15NREL | 15

NREL | 16NREL | 16

𝑃𝑃0 = 𝐺𝐺𝐹𝐹0 + 𝐺𝐺𝑅𝑅0 � φ � η0

𝑃𝑃1 = 𝐺𝐺𝐹𝐹0 + 𝐺𝐺𝑅𝑅0 � φ � η0 � (1 − 𝐿𝐿𝐷𝐷𝐷𝐷)

𝑃𝑃1 = 𝐺𝐺𝐹𝐹0 + (1 − 𝑋𝑋)𝐺𝐺𝑅𝑅0 � φ � η0

𝑋𝑋 = 𝐿𝐿𝐼𝐼𝐼𝐼𝐼𝑡𝑡𝐼𝐼𝑡𝑡𝐼𝐼𝑡𝑡 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑡𝑡𝑀𝑀𝐼 + 𝐿𝐿𝑆𝑆𝑡𝑡𝐼𝐼𝑡𝑡𝑀𝑀𝑡𝑡𝑡𝑡𝐼𝐼𝑀𝑀𝑆𝑆 𝑆𝑆𝐼𝑀𝑀𝑆𝑆𝑀𝑀𝐼𝐼𝑆𝑆

𝑋𝑋 =𝐿𝐿𝐷𝐷𝐷𝐷𝐵𝐵𝐺𝐺

+ 𝐿𝐿𝐷𝐷𝐷𝐷

Shading Factor and Rear Electrical Mismatch Factors

1%

11%

10%

P0

P1

NREL | 17NREL | 17

Grear Shading Factor: -0.1 to 8.1 % metallic 7.8 – 8.5 % black

0

4

8

12

16

20

0 0.1 0.2 0.3

G rea

rTo

tal L

oss %

Y-gap

Loss X (total)

Black TT

Metallic TT

-2

1

4

7

10

0 0.1 0.2 0.3

Gre

arSh

adin

g Fa

ctor

%

Y-gap (m)

GRear Shading Factor

Black TT

Metallic TT

NREL | 18

Sensor Position Study

NREL | 19NREL | 19

Rear-Irradiance Modeling at different locations in the tracker

• Single row of HSAT, N-S oriented on Jackson, Michigan• Data collected for 4 months, Dec. 2018 to April 2019.• 45.9% DHI to DNI ratio for location• Albedo measured on location.

NREL | 20NREL | 20

MBE and RMSE of Sensor location modeled value vs. average modeled value of north-part of the array for 1 day

Position on Module E-W

Posit

ion

on M

odul

e N

-S

Position on CW

Non-Uniformity [%]

NREL | 21NREL | 21

Non-Uniformity [%]

MBE and RMSE of Sensor location modeled value vs. average modeled value of north-part of the array for 1 day

Position on Module E-W

Posit

ion

on M

odul

e N

-SMBE2.5-8W/m2

RMSE~20 W/m2

NREL | 22NREL | 22

Conclusions

• Shading optical loss for modeled systems is between 2-8%

• Gap + torquetube reflections equal potential energy gains

• System mismatch loss (Dc losses) are around 1%, but must be propagated backwards to reflect the losses at the Grear irradiance level for implementation in current softwares.

• Grear irradiance measurements must account for non-uniformities and equipment shading. Avoid ends and middles of the modules for sensor placements.

NREL | 23

www.nrel.gov

Thank you

A portion of this research was performed using computational resources sponsored by the Department of Energy's Office of Energy Efficiency and Renewable Energy and located at the National Renewable Energy Laboratory.

This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. 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 30286, 34910, and Award Number DE-EE0008564. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government.

Silvana.Ayala@nrel.gov

NREL | 24NREL | 24

Measured vs. modeled Rear Irradiances, overall modeling accuracy at any position

NREL | 25NREL | 25

Sensor location for sensors located at torque tube

In-plane torque-tube shading.

In-plane torque-tube causes a different shading profile

Position on CW

NREL | 26NREL | 26

Measured vs. modeled Rear Irradiances, overall modeling accuracy at any position

Modify Average Measured to be dotted line