ECONOMIC EVALUATION OF ENERGY PRODUCED BY A BIFACIAL PHOTOVOLTAIC ARRAY IN THE ERA OF TIME-OF-USE PRICING

J. Johnson, K. Hurayb, Y. Baghzouz

Electrical & Computer Engineering Department

University of Nevada, Las Vegas, NV (USA)

International Conference on Clean Electric Power

Alghero, Sardinia – Italy June 11th-13th, 2013

Overview

Background/Introduction Bifacial-Photovoltaic Power System Electrical

Characteristics. Bifacial PV Power Generation Curve under

Different Orientations Local Utility Load Characteristics Local Utility Tariffs Bifacial PV Performance under Different

Orientations Economic Analysis Conclusions

Introduction

Bifacial photovoltaic modules are designed to produce power from light striking their front as well as light incident on their rear side.

Introduction

Bifacial modules are often installed as sound barriers in fence-integrated systems in motorways and railways. Other applications include architectural awnings, partial patio and parking lot covers.

Bifacial PV panels are typically two to 3 times more expensive than their mono-facial counterparts because of their “added ornamental value” that allows some of the light to pass though, thus resulting in a pleasing environment.

Introduction

With the Time-Of-Use (TOU) pricing of electricity becoming an option to electricity customers, a bi-facial array is expected to provide an advantage over conventional mono-facial arrays as it receives more sunlight .

This article analyzes the performance of a 1 kW, grid-connected, bifacial PV array that is installed on the roof of a local building over a one-year period. Two orientations are considered:

West orientation with 90o tilt angle (vertical)

South orientation with 30o tilt angle (equal to latitude angle)

Description of Bifacial PV Array

Array Composition: 5 series bifacial PV modules.

Module Model: Sanyo HIP-195DA3 Array Electrical Characteristics:

Peak Power: Pmax = 975 W,

Voltage at Pmax: Vm = 275 V,

Current at Pmax: Im = 3.5 A,

Open Circuit Voltage: Voc = 343 V,

Short circuit Current: Isc = 3.73 A,

Power Temp. Coef: TP=-0.35%/oC, Module Efficiency: η =16.1%.

What is the efficiency of the back side?

The figure below shows the measured power-voltage curve of each panel side (with the back covered). The back side is nearly 15% less efficient than the front side of the

panel.

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

Voltage (V)

Po

wer

(W

)Back Side Front Side

Test Conditions:Solar irradiance: 950 W/m2 Cell operating temp: 57o C

Circuit Model

Circuit parameter values (best fit): IL = 4.45 A,

Io = 1 x 10-10 A,

Rs = 12 mΩ,

Rsh = 6 Ω.

Bifacial PV Power Generation Orientation: Vertical East/West

Mismatch due to shade of frame

Bifacial PV Power Generation Orientation: South with 30o tilt

Utility Load Characteristics

The load is dominated by summer (June - September) and winter (November - April) patterns, with May and October being the transition months.

Utility Load Characteristics

The peak demand period is defined from 1:00 pm to 7:00 pm during the four summer months.

Utility Tariffs

Historically, residential customers are charged a fixed rate of

$0.113/kWh for the electric energy consumed throughout the year. More recently, the company installed an Advanced Metering

Infrastructure (AMI) which allowed it to provide variable rates that

depend on time. The Time-Of-Use (TOU) rate rewards the customer for reducing the

consumption during the peak summer period. Current TOU rates for single-family homes are as follows:

During peak demand period (1:00 pm – 7:00 pm), 6/ - 9/30:

$0.329/kWh. During summer off-peak period (7:00 pm – 1:00 pm), 6/1 - 9/30:

$0.071/kWh. During rest of the time of the year, 10/1 - 5/31: $0.049/kWh.

Utility Tariffs

Note that relative to the flat standard rate of $0.113/kWh, the TOU rate is Increased by nearly 300% during peak demand period:

720 hrs or 8% of the time,

Reduced by nearly 37% during off-peak summer hours: 2,160 hrs or 26% of the time,

Reduced by nearly 57% during the rest of the year: 5,760 hrs or 66% of the time.

Bifacial PV Power Generation Comparison of two orientations during peak demand

The vertical East-West orientation generates significantly more energy during the latter half, but less energy during the first half of the peak demand period when compared to the south-facing orientation.

Bifacial PV Power Generation Comparison of two orientations during the summer months

The vertical east/west orientation generates more energy in June & July, but

less energy in August and September.

Bifacial PV Power Generation Comparison of two orientations during entire year

The South-facing orientation outperforms the vertical East/West orientation except during the months of May, June and July.

ANNUAL ENERGY COST PRODUCED BY PV ARRAY

ARRAY ORIENTATION COST(FIXED RATE)

COST(TOU RATE)

South with 30o Tilt all Year $259.22 $237.43

West with 90o Tilt all Year $226.90 $220.85

South with 30o Tilt (Oct – May), and West with 90o Tilt (June – Sept.)

$257.30 $234.03

Conclusions

The vertical East/West orientation produces significantly more energy during the late afternoon hours of the summer months, but less energy during the early afternoon hours.

The total amount of energy produced by the vertical East/West orientation during the 4 summer months in nearly the same as that of south-facing orientation.

For obvious reasons, the south-facing orientation produces significantly more energy during the winter and shoulder months.

The fixed South-facing orientation performs best under both fixed and TOU energy rates.

A slight improvement can be made by re-orienting the array to a vertical East/West orientation during the months of May, June and July, but this is not worth the effort.

The recessed frame design caused significant shading in the late morning hours, thus not suitable for vertical east-west orientation.

Acknowledgement

The work presented in this paper is sponsored by the National Renewable Energy Laboratory (NREL), Golden, CO, (USA).

Questions and Comments?