Technical Report

NREL/TP-540-45908

June 2009

Impact of Sungate EP on PHEV 

Performance 

Results of a Simulated Solar Reflective 

Glass PHEV Dynamometer Test

John Rugh

Final Report in Support of Technical Services 

Agreement TSA-08-206

NREL Project Monitor: John Rugh

John.Rugh@nrel.gov, 303-275-4413

PGW Project Monitor: Mukesh Rustagi
National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393

303-275-3000 • www.nrel.gov

NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency and Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

Contract No. DE-AC36-08-GO28308

Technical Report

NREL/TP-540-45908

June 2009

Impact of Sungate EP on PHEV 

Performance 

Results of a Simulated Solar Reflective 

Glass PHEV Dynamometer Test

John Rugh

Final Report in Support of Technical Services 

Agreement TSA-08-206

NREL Project Monitor: John Rugh

PGW Project Monitor: Mukesh Rustagi

Prepared under Task No. WTF6.1000
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iii

Executive Summary

The objective of the project was to assess the impact of a solar reflective windshield and 

backlite on PHEV range and fuel economy. The effect of Sungate® EP on PHEV 

performance was evaluated on NREL’s PHEV test bed, a 2006 Toyota Prius modified 

with a 5 kWh Hymotion Li-ion Energy Storage System. The tests, performed at 

Environmental Testing Corporation in Aurora, Colorado, used portable electric heaters 

installed in the passenger compartment to simulate the solar heat gain through the 

glazings. A vehicle thermal analysis determined the thermal loads from the glazings 

(including transmitted, re-radiated, and convective loads) which were simulated with the 

electric heaters. The thermal load for Solargreen® glazings installed in all positions was 

1629 W. For Sungate EP in the windshield and backlite and Solargreen in the sidelites, 

the thermal load was 1264 W. 

Three configurations were run over a UDDS and a USO6 drive cycle. 

• A/C off

• A/C on with Solargreen heat load

• A/C on with Sungate EP heat load

The air conditioning system used automatic control with a temperature setpoint of 68oF 

and 100% recirculation. This resulted in maximum blower air flow rate. 

The test sequence was:

• Soak overnight at 100oF air temperature and charge ESS to 100% 

• Start interior heater 1.5 hours prior to start of drive cycle to approximate increased 

interior cabin temperatures due to a solar soak

• Initiate drive cycle and cabin cooldown

• Repeat drive cycles to the end of the drive cycle in which the vehicle was in 

charge-sustaining mode for the entire cycle. 

UDDS Drive Cycle

Over repeated UDDS drive cycles, the Sungate EP glazing reduced the A/C compressor 

power and resulted in an increase in fuel economy compared to Solargreen. The A/C 

compressor power dropped from 1509 W to 1403 W during charge-depletion mode and 

from 1431 W to 1236 W during charge-sustaining mode. The adjusted, utility factorweighted fuel economy increased from 36.8 to 42.9 mpg for the Sungate EP thermal load 

case while the adjusted, utility factor-weighted electrical energy consumption was 

roughly equivalent. The charge-depletion range turned out to be a poor metric because in 

some of the tests the current out of the ESS was limited due to temperature control limits 

of the power electronics and energy storage systems. When this situation occurred, the 

ESS provided power for a longer period of time and the charge-depletion range was 

greater. 

In addition to the lower A/C compressor power, the cabin air temperature was also lower 

for the Sungate EP case compared to the Solargreen case. The lower solar load (heater 
iv

power) due to the Sungate EP resulted in a 15oF reduction in cabin air temperature at the 

end of the soak. At the end of charge depletion, the cabin air temperature was 87.2oF for 

Solargreen and 82.7oF for Sungate EP. Although the time to charge depletion varied for 

each test, the temperature vs. time plots show the Sungate EP cabin air temperature is less 

than the Solargreen at all points during the test. 

USO6 Drive Cycle

Over USO6 drive cycles, the impact of the Sungate EP displayed similar trends compared 

to the UDDS drive cycles except for fuel economy. During charge depletion, the A/C 

power decreased from 1562 W to 1481 W due to Sungate EP. For charge-sustaining 

operation, the A/C power dropped from 1487 W to 1435 W. The adjusted, utility factorweighted fuel economy decreased from 40.4 to 40.0 mpg while the electrical energy 

consumption was the same. The < 1% reduction in fuel economy is thought to be due to 

test variation or differences in powertrain control strategy. In addition to the lower A/C 

compressor power, the cabin air temperature was also lower for the Sungate EP 

configuration compared to the Solargreen configuration. Prior to the cooldown, the cabin 

air temperature was 13oF cooler due to the reduced thermal load of the Sungate EP. At 

the end of charge depletion, the cabin air temperature was 93.2oF for Solargreen and 

84.0oF for Sungate EP. 

Conclusion

The UDDS/USO6 composite fuel economy increased 8% from 38.4 mpg to 41.6 mpg due 

to the reduction in thermal loads from Sungate EP glazings installed in the windshield 

and backlite. The electrical energy consumption was essentially equivalent with a less 

than 0.2% increase. 

In conclusion, Sungate EP resulted in lower A/C compressor power and lower interior 

cabin air temperature, which would result in improved occupant comfort. The lower A/C 

power resulted in improved UDDS/USO6 composite fuel economy. 
v 

TABLE OF CONTENTS

1.0 Introduction ................................................................................................................... 1

1.1 Background ............................................................................................................... 1

1.2 Objective ................................................................................................................... 1

1.3 Evaluation Approach ................................................................................................ 1

2.0 Test Setup ...................................................................................................................... 2

2.1 Vehicle ...................................................................................................................... 2

2.2 Test Location ............................................................................................................ 4

2.3 Data Acquisition ....................................................................................................... 4

2.4 Heater Configuration ................................................................................................ 5

2.5 Heater Power Analysis .............................................................................................. 7

2.5.1 Vehicle Solar Load Estimator ............................................................................ 7

2.5.2 Thermal Analysis to Determine Heater Power .................................................. 9

2.6 Calculation Procedure for mpg and Wh/mi ............................................................ 12

3.0 Results ......................................................................................................................... 14

3.1 UDDS Results ......................................................................................................... 14

3.2 USO6 Results .......................................................................................................... 18

3.3 UDDS/USO6 Composite Results ........................................................................... 23

4.0 Conclusions ................................................................................................................. 24
vi 

LIST OF FIGURES

Figure 1. Test Vehicle - NREL PHEV ............................................................................... 3

Figure 2. PHEV ESS SOC for 12/18/08 UDDS Solargreen Test ...................................... 3

Figure 3. NREL PHEV on 4-Wheel Dynamometer at ETC .............................................. 4

Figure 4. Temperature Measurement Locations for Hobo Data Acquisition System ........ 5

Figure 5. Passenger Compartment Portable Heaters on the Right Rear Seat .................... 6

Figure 6. Equipment Cart with Variable Transformers and Watt Meters .......................... 6

Figure 7. Sungate EP Spectral Properties .......................................................................... 7

Figure 8. Solargreen VSOLE Results ................................................................................ 8

Figure 9. Sungate EP VSOLE Results ............................................................................... 8

Figure 10. Vehicle from Sun's Perspective ......................................................................... 9

Figure 11. Thermal Analysis Network Diagram ............................................................... 10

Figure 12. Roadmap of mpg and Electrical Energy Consumption Calculations .............. 12

Figure 13. A/C Power vs time over UDDS Drive Cycles ................................................. 14

Figure 14. Average A/C Power – UDDS Drive Cycles .................................................... 15

Figure 15. Cabin Air Temperature vs Time over UDDS Drive Cycles ............................ 15

Figure 16. Average Cabin Air Temperature over UDDS Drive Cycles ........................... 16

Figure 17. Actual Fuel Economy, UDDS ......................................................................... 16

Figure 18. Actual Electrical Energy Consumption, UDDS .............................................. 17

Figure 19. Adjusted and UF-Weighted Fuel Economy, UDDS ........................................ 17

Figure 20. Adjusted and UF-Weighted Electrical Energy Consumption, UDDS ............. 18

Figure 21. A/C Compressor Power vs time over USO6 Drive Cycles ............................. 19

Figure 22. Average A/C Compressor Power over USO6 Drive Cycles ........................... 19

Figure 23. Cabin Air Temperature vs Time over USO6 Drive Cycles ............................. 20

Figure 24. Average Cabin Air Temperature over USO6 Drive Cycles ............................ 20

Figure 25. Actual Fuel Economy, USO6 .......................................................................... 21

Figure 26. Actual Electrical Energy Consumption, USO6 ............................................... 21

Figure 27. UF-Weighted Fuel Economy, USO6 ............................................................... 22

Figure 28. UF-Weighted Electrical Energy Consumption, USO6 .................................... 22

Figure 29. UDDS/USO6 Composite Fuel Economy ........................................................ 23

Figure 30. UDDS/USO6 Composite Electrical Energy Consumption ............................. 24

LIST OF TABLES

Table 1. Exterior Velocity and Ambient Temperature .................................................... 10

Table 2. Air properties and constants for thermal analysis .............................................. 11

Table 3. Heater Power Settings ........................................................................................ 12
1 

1.0 Introduction

1.1 Background

Fuel used for vehicle climate control significantly affects our nation’s energy security by 

decreasing the fuel economy of the 230 million light-duty conventional vehicles in the United 

States. To address this issue, NREL works closely with industry to develop techniques to reduce 

the ancillary loads, such as climate control, in vehicles. We are conducting research to improve 

vehicle efficiency and fuel economy by controlling the climate in the vehicle, while still keeping 

the passengers comfortable. As part of this effort, we are conducting research to reduce the 

thermal load on the vehicle interior. 

As powertrains become electrified, climate control loads reduce range or cause the gasoline 

engine to operate more frequently. The operation of the A/C system in a cooldown situation for 

a PHEV40 reduces the electric range 18% to 30% depending on the drive cycle. If the thermal 

loads of the vehicle can be reduced and subsequently the A/C usage and compressor power, the 

PHEV range with A/C on can be increased. If the battery is sized to account for the energy to 

operate the A/C system, reducing the thermal loads will decrease the battery size and cost. 

PGW has developed a technology, called Sungate® EP, that allows only 3% of the infrared (IR) 

energy to be transmitted through the glass. With this technology, only 33% of the total solar 

energy is transmitted through the glass, most of it in the visible spectrum. Since the federal 

requirements for visibility dictate a minimum of 70% visible light transmission, the Sungate EP 

glass is close to the highest performance possible within the constraints of the visibility 

requirements. 

1.2 Objective 

The objective of the test program was to determine the impact of solar reflective glass on PHEV 

range and fuel economy. 

1.3 Evaluation Approach

The approach of this test was to drive a PHEV over a drive cycle in a controlled environment 

with the A/C off and A/C on. Since the dynamometer cell did not have solar lamps, portable 

electric heaters were installed in the passenger compartment to simulate the solar heat gain

through the glazings. A vehicle thermal analysis determined the thermal loads from the glazings 

(including transmitted, re-radiated, and convective loads) which were simulated with the electric 

heaters. 

Three configurations were run over a UDDS and a USO6 drive cycle. 

• A/C off

• A/C on with Solargreen heat load

• A/C on with Sungate EP heat load 
2 

The air conditioning system used automatic control with a temperature setpoint of 68oF and 

100% recirculation. This resulted in maximum blower air flow rate. 

The test sequence was:

• Soak overnight at 100oF air temperature and charge ESS to 100% 

• Start interior heater 1.5 hours prior to start of drive cycle to approximate increased 

interior cabin temperatures due to a solar soak

• Initiate drive cycle and cabin cooldown

• Repeat drive cycles to the end of the drive cycle in which the vehicle was in chargesustaining mode for the entire cycle. 

Cabin air temperature, air conditioning power, and vehicle fuel use were measured during the 

test.

2.0 Test Setup

2.1 Vehicle

The test vehicle was NREL’s PHEV which is a 2006 Toyota Prius modified with a 5 kWh 

Hymotion Li-ion Energy Storage System (ESS or battery). The vehicle is shown in 

Figure 1. The OEM installed hybrid battery was still installed in the vehicle. The PHEV ESS 

was controlled to provide an electric assist during the initial portion of a trip. This is called the 

charge-depletion portion of the trip. Figure 2 shows the state of charge (SOC) of the PHEV ESS 

during one of the tests. Note the ESS starts fully charged and the SOC is 100%. When the SOC 

drops to ~5%, the ESS is discharged and the vehicle begins to operate like a regular hybrid Prius

(charge sustaining). The charge-depletion fuel economy and A/C compressor power are defined 

as the average of the data from cycle 1, cycle 2, and cycle 3 up to the point of SOC=5%. The 

charge-sustaining fuel economy and A/C compressor power are calculated using the data from 

cycle 4. The charge-depletion and charge-sustaining cabin air temperatures are defined as the

average of the 5 minutes before SOC reaches 5% and the end of cycle 4 respectively. 
3 

Figure 1. Test Vehicle - NREL PHEV

Figure 2. PHEV ESS SOC for 12/18/08 UDDS Solargreen Test

0

10

20

30

40

50

60

70

80

90

100

15:36:00 15:50:24 16:04:48 16:19:12 16:33:36 16:48:00 17:02:24 17:16:48 17:31:12

ess soc (%)

Cycle 1 Cycle 2 Cycle 3 Cycle 4

Charge Depletion Transition Charge Sustaining
4 

2.2 Test Location

The testing was performed at Environmental Testing Corporation (ETC) in Aurora Colorado. 

(http://www.etclab.com) The elevation of the facility is approximately 5437 feet above sea 

level. Since the Prius has regenerative breaking, the tests were performed using a 4-wheel 

dynamometer (Figure 3). The vehicle was either soaked overnight at 100oF in that chamber or a 

neighboring chamber and moved to the 4-wheel dynamometer chamber prior to the 1.5 hour soak 

with the heaters. 

Figure 3. NREL PHEV on 4-Wheel Dynamometer at ETC

 

2.3 Data Acquisition 

The bulk of the data from the test was recorded using a V2Green system that was installed with 

the Hymotion ESS. Data logged by this system included 

• Vehicle speed

• Distance

• Fuel consumption 

• Electrical energy consumption

• OEM hybrid battery (SOC, volts, current) 

• Hymotion ESS (SOC, volts, current)
5 

The data were automatically uploaded to the V2Green web site and manually downloaded after 

the test for processing. 

Additional temperature data were recorded using a small Hobo data acquisition system installed 

in the vehicle. The passenger compartment air temperature measurement location was at the left 

rear seat to the right and above the headrest. Resistance Temperature Detectors (RTD) were 

used at the locations shown in Figure 4. 

 

Figure 4. Temperature Measurement Locations for Hobo Data Acquisition System

 

In order to measure the air conditioning compressor power, an AVIT data logger was connected 

to the CAN bus and controlled using Snap-Master software.

2.4 Heater Configuration

Since the dynamometer cell did not have solar lamps, two portable 1500 W ceramic electric 

heaters were installed in the passenger compartment to simulate the solar heat gain through the 

glazings. The right rear seat was folded down and the heaters were placed on the resulting 

surface facing forward as shown in Figure 5. Each heater was plugged into a wattsup?Pro watt 

meter to measure and record the power usage. Each watt meter was plugged into a variable 

transformer to control the power. Figure 6 shows the variable transformers and watt meters on 

the equipment cart. 

The heater power had to be monitored closely and adjusted during the test since the heater 

resistance was a function of the passenger compartment air temperature. This was extremely 

important at the start of 1.5 hr soak and the start of cooldown. 
6 

Figure 5. Passenger Compartment Portable Heaters on the Right Rear Seat

Figure 6. Equipment Cart with Variable Transformers and Watt Meters
7 

2.5 Heater Power Analysis

2.5.1 Vehicle Solar Load Estimator

Prior to testing, a thermal analysis was conducted to determine the heater settings. The first step 

was to calculate the transmitted, absorbed, and reflective solar power at each glazing using 

NREL’s vehicle solar load estimator (VSOLE). The program takes into account the angle of 

incidence and calculates the transmitted, reflected, and absorbed power based on the radiation 

source, vehicle geometry, vehicle orientation, and glazing type. All glazing surfaces are 

assumed flat, and to have constant thickness, uniform properties, and regular shape. The 

calculation of the optical properties as a function of wavelength and angle uses a single-pane 

approximation for glass. 

The properties of Sungate EP were provided by PGW and are shown in Figure 7. 

Figure 7. Sungate EP Spectral Properties

The glazing areas and angles were measured on the NREL PHEV. A Phoenix incident solar 

radiation on July 6 at 12:30 pm was used. The VSOLE results for the Solargreen and Sungate 

EP configurations are shown in Figures 8 and 9 respectively. The sidelites were Solargreen in 

both cases. 
8 

Figure 8. Solargreen VSOLE Results

Figure 9. Sungate EP VSOLE Results
9 

2.5.2 Thermal Analysis to Determine Heater Power

Although the transmitted solar power can be obtained directly from VSOLE, the portion of the 

sun’s energy that would be absorbed and convected/reradiated to the interior adds to the heat 

load of the passenger compartment. 

A spreadsheet, included in Appendix B, was used to calculate the total heat load through the 

glazings. The heat transfer through opaque surfaces was not considered. For the analysis, the 

windshield and backlite were represented as a single glazing. The sidelites were also represented 

as a single piece of glazing with a uniform temperature. This seems reasonable since the sun is 

essentially overhead as shown in Figure 10. 

Figure 10. Vehicle from Sun's Perspective
10 

The simplified thermal network is shown in Figure 11. 

Figure 11. Thermal Analysis Network Diagram

The unknown in Figure 11 is Tglass and it is solved for iteratively. 

Qsolar, absorbed = Qconvection,interior + Qradiation, interior + Qconvection, exterior + Qradiation, exterior (1) 

where

Qsolar, absorbed = from VSOLE (2) 

Qconvection, exterior = hexterior (Tglass – Tambient) (3) 

Qradiation, exterior = ε σ (T4

glass – T4sky) (4) 

Qconvection, interior = hinterior (Tglass – Tinterior, air) (5) 

Qradiation, interior = ε σ (T4

glass – T4mean radiant temperature) (6) 

Table 1 includes the environmental assumptions. 

Table 1. Exterior Velocity and Ambient Temperature

Tglass

Tambient

Tsky

Tinterior, air

Tmean radiant temperature

Qconvection, exterior Qconvection, interior

Qradiation, exterior Qradiation, interior

Qsolar, absorbed

Measurement Value Units

UDDS average wind velocity (v) 8.76 m/s

USO6 average wind velocity (v) 21.64 m/s

Tambient 37.8 o

C
11 

The air properties were calculated at 315 K. The values used as well as other important 

parameters are identified in Table 2. 

Table 2. Air properties and constants for thermal analysis

Other equations used are 

Tsky = 0.0552 T1.5

ambient (7) 

l

kNu h = (8) 

The Reynolds number of the exterior flow was calculated and then the appropriate Nu correlation 

was selected based on comparing the Re to the Recritical. 

μ

ρ lV Re = (9) 

Nulaminar = 0.644 Re0.5 Pr0.33333 (10) 

Numixed = (0.037 Re0.8 – 871) Pr0.33333 (11) 

 

Parameter Value Units

density (ρ) 1.111 kg/m3

specific heat (cp) 1.007 kJ/kg K

thermal conductivity (k) 0.0274 W/m K

dynamic viscosity (μ) 1.9168E-05 Ns/m2

prandtl number (Pr) 0.705

thermal diffusivity (α) 2.47E-05 m

2

/s

characteristic length (l) 0.5 m

surface emissivity (ε) 0.9

Steph Boltz constant (σ) 5.67E-08 W/m2

K4

absorptivity baseline (α) 0.793

absorptivity SRF (α) 0.641

Interior Velocity 3 m/s

Interior Air Temperature 20 o

C

Area (windshield & backlite) 1.5663 m

2

Area (sidelites) 1.0484 m2
12 

The passenger compartment solar load from the glazings for the UDDS and USO6 drive cycles 

are shown in Table 3. 

Table 3. Heater Power Settings

For Solargreen glazings installed in the windshield and backlite, the solar load transmitted and 

reradiated/convected was 1629 W; therefore, the heaters were set to this level. An error was 

made adjusting the Sungate EP heaters during the test and they were 20 W low. In order to be 

consistent throughout the test, the heater setting was kept at 1264 W for Sungate EP.

2.6 Calculation Procedure for mpg and Wh/mi

The actual fuel economy and electrical energy consumption were adjusted to take into account 

how people drive and distance driven between charging events. The roadmap to the calculation 

is shown in Figure 12. 

Figure 12. Roadmap of mpg and Electrical Energy Consumption Calculations

 Heater Power (W)

Drive Cycle Solargreen Sungate EP

UDDS 1649 1270

USO6 1608 1298

aveage 1629 1284

CS 

UDDS

Adjusted 

CS Urban

CD 

UDDS

CS 

USO6

CD 

USO6

Adjusted 

CD Urban

[mpgequivalent]

[Wh/mi & 

mpgactual]

[mpgequivalent]

[Wh/mi & 

mpgactual]

[mpg]

[Wh/mi & mpg]

Adjusted & 

UF-Weighted 

Urban

UFWeighting 

(city)

UF-Weighted 

USO6

UFWeighting 

(hwy)

[Wh/mi & mpg]

[Wh/mi & mpg]

Composite 

PHEV 

Rating 

[mpg & 

Wh/mi] 

55%/45% 

City/USO6 

Weighting
13 

Since the SOCs during the charge-sustaining portion of the tests were not constant, the mpg was 

slightly adjusted using Equation 12. 

 (12) 

• D = Distance

• Vfuel = volume of fuel used

• Echarge = Battery energy used (OEM and Hymotion pack) 

• Egasoline = constant, 33.44 kWh/gal 

(13) 

 (14) 

 (15) 

The utility factors (UF) were calculated from SAE J 2841 using the CD mileage from the 

respective tests. Separate UF curves were used for the respective drive cycles.

 (16) 

 (17) 

 (18) 

 (19) 

gasoline

fuel

gasoline equivalent

E

E

V

D

mpg

charge +

=

gasoline equivalent

adjusted CS UDDS

mpg

mpg 1805.1 003259.0

1 ,,

+

=

adjusted CS UDDS gasoline equivalent CS UDDS

adjusted CS UDDS

mpg mpg

consumption

,, ,,

,,

1 1 ∆ = −

adjusted CS UDDS

actual CD UDDS

adjusted CD UDDS

consumption

mpg

mpg

,,

,,

,, 1

1

∆+

=

adjusted CS UDDS

UDDS

adjusted CD UDDS

UDDS

adjusted UF Weighted UDDS

mpg

UF

mpg

UF mpg

,, ,,

, , 1

1

− +

− =

( ) Eadjusted ,UF−Weighted ,UDDS = UFUDDS Eactual CD,, UDDS

6,, 6,,

6, 1

1

gasoline equivalent CS USO

HWFET

actual CD USO

HWFET

UF Weighted USO

mpg

UF

mpg

UF mpg − +

− =

( ) EUF−Weighted USO6, = UFHWFET Eactual CD USO6,,
14 

 (20) 

 (21) 

3.0 Results

3.1 UDDS Results

Figure 13 shows the A/C compressor power is lower for the Sungate EP case at all times during 

the test. Figure 14 shows the average A/C compressor power during charge depletion decreases 

from 1509 W to 1403 W due to Sungate EP. With the average charge-depletion time of 56 

minutes over repeated UDDS cycles, the reduction in A/C power equates to a 100 Wh increase in 

energy available for the powertrain. During charge sustaining, the A/C compressor power 

decreases from 1431 W to 1236 W for the Sungate EP case. 

Figure 13. A/C Power vs time over UDDS Drive Cycles

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Air Conditioning Compressor Power (kW), trailing one 

0 1000 2000 3000 4000 5000 6000

minute time average

Time from start of cooldown (sec)

 

Solargreen

Sungate EP

, , 6,

55.0 45.0

1

adjusted UF Weighted UDDS UF Weighted USO

composite

mpg mpg

mpg

− −

+

=

55.0 45.0 ) Ecomposite = Eadjusted ,UF−Weighted ,UDDS + EUF−Weighted USO6,
15 

Figure 14. Average A/C Power – UDDS Drive Cycles

The cabin air temperature vs time is shown in Figure 15. The lower simulated solar load of the 

Sungate EP results in lower cabin temperatures at every time point. During charge depletion, 

Figure 16 shows the cabin temperature for the Solargreen case is 87.2°F and 82.7°F for Sungate 

EP case. During charge sustaining, the cabin temperature is 82.7°F for Solargreen and 80.0°F 

for Sungate EP. 

Figure 15. Cabin Air Temperature vs Time over UDDS Drive Cycles

1509

1431 1403

1236

0

200

400

600

800

1000

1200

1400

1600

Charge Depletion Charge Sustaining

A/C Compressor Power (W)

 

A/C on, Solargreen

A/C on, Sungate EP

60

80

100

120

140

160

180

0 20 40 60 80 100 120

Cabin Air Temperature (oF)

Time from start of cooldown (min)

 

Solargreen

Sungate EP
16 

Figure 16. Average Cabin Air Temperature over UDDS Drive Cycles

The actual measured fuel economy and electrical energy consumption during the chargedepletion and charge-sustaining phases of the test are shown in Figures 17 and 18. These results 

need to be interpreted carefully because in-use performance will be different. For example, a 

driver will not get 233.7 mpg in city driving as implied by the UDDS A/C off test. Also a driver 

will not be start every trip fully charged and will sometimes drive beyond the charge-depletion 

range. 

Figure 17. Actual Fuel Economy, UDDS

87.2

82.7 82.7

80.0

76

78

80

82

84

86

88

Charge Depletion Charge Sustaining

Cabin Temperature (oF)

 

A/C on, Solargreen

A/C on, Sungate EP

233.7

64.9

86.8

37.1

117.9

42.5

0

50

100

150

200

250

Charge Depletion Charge Sustaining

Actual Fuel Economy (mpg)

 

A/C off

A/C on, Solargreen

A/C on, Sungate EP
17 

Figure 18. Actual Electrical Energy Consumption, UDDS

Using the equations in Section 2.6, the fuel economy and electrical energy consumption were 

adjusted to reflect real world usage. When the A/C is operated, the fuel economy drops from 

68.5 mpg to 36.8 mpg (Figure 19). Reducing the thermal load due to Sungate EP improves the 

A/C on fuel economy to 42.9 mpg which is a 17% increase. Figure 20 shows that the electrical 

energy consumption increases from 104.5 Wh/mi to 114.7 Wh/mi when the A/C is operated. 

The electrical energy consumption increased slightly (1%) to 115.7 Wh/mi for the Sungate EP 

thermal load.

Figure 19. Adjusted and UF-Weighted Fuel Economy, UDDS

168.5

3.3

220.5

8.1

226.9

5.2

0

50

100

150

200

250

Charge Depletion Charge Sustaining

Actual Electrical Consumption (Wh/mi)

 

A/C off

A/C on, Solargreen

A/C on, Sungate EP

68.5

36.8

42.9

0

10

20

30

40

50

60

70

80

A/C off A/C on, Solargreen A/C on, Sungate EP

Adjusted and UF-Weighted Fuel Economy (mpg)

 
18 

Figure 20. Adjusted and UF-Weighted Electrical Energy Consumption, UDDS

3.2 USO6 Results

Figure 21 shows the difference in A/C compressor power between the Solargreen and Sungate 

EP thermal loads was not as large over the USO6 drive cycles. In Figure 22, the average A/C 

compressor power during charge depletion is 1562 W for Solargreen and 1481 W for Sungate 

EP. During charge sustaining, the average A/C compressor power is 1487 W for Solargreen and 

1435 W for Sungate EP. The USO6 drive cycle has more aggressive accelerations than the 

UDDS. In the non-averaged A/C power data, it was noted the A/C compressor was clutched out 

during the hard accelerations. This did not happen during the UDDS drive cycles. 

104.5

114.7 115.7

0

20

40

60

80

100

120

140

A/C off A/C on, Solargreen A/C on, Sungate EP

Adjusted and UF-Weighted Electrical Energy Comsumption (Wh/mi)

 
19 

Figure 21. A/C Compressor Power vs time over USO6 Drive Cycles

Figure 22. Average A/C Compressor Power over USO6 Drive Cycles

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 1000 2000 3000 4000 5000 6000

Air Conditioning Compressor Power (kW), trailing one 

minute time average

Time from start of cooldown (sec)

 

Solargreen

Sungate EP

1562

1481 1487

1435

0

200

400

600

800

1000

1200

1400

1600

1800

Charge Depletion Charge Sustaining

Air Conditioning Compressor Power (W)

 

A/C on, Solargreen

A/C on, Sungate EP
20 

Figure 23 shows the Sungate EP cabin temperature was lower than the Solargreen cabin 

temperature at every time point. In Figure 24, the average cabin temperature is 93.2 °F for 

Solargreen and 84.0 °F for Sungate EP during charge depletion. During charge sustaining, the 

cabin temperatures are 93.6 °F and 84.7 °F for Solargreen and Sungate EP respectively. 

Figure 23. Cabin Air Temperature vs Time over USO6 Drive Cycles

Figure 24. Average Cabin Air Temperature over USO6 Drive Cycles

60

80

100

120

140

160

180

0 10 20 30 40 50 60 70 80 90 100

Cabin Air Temperature (oF)

Time from start of cooldown (min)

 

Solargreen

Sungate EP

1562

1481 1487

1435

0

200

400

600

800

1000

1200

1400

1600

1800

Charge Depletion Charge Sustaining

Air Conditioning Compressor Power (W)

 

A/C on, Solargreen

A/C on, Sungate EP
21 

The actual fuel economy and electrical energy consumption data are shown in Figures 25 and 26. 

Using a methodology similar to the UDDS, the raw data were adjusted to reflect real usage of a 

PHEV, and the results are shown in Figures 27 and 28. 

Figure 25. Actual Fuel Economy, USO6

Figure 26. Actual Electrical Energy Consumption, USO6

59.6

40.8

47.4

36.5

45.0

36.5

0

10

20

30

40

50

60

70

Charge Depletion Charge Sustaining

Actual Fuel Economy (mpg)

 

A/C off

A/C on, Solargreen

A/C on, Sungate EP

110

2.9

92.3

9.3

83.1

10.9

0

20

40

60

80

100

120

Charge Depletion Charge Sustaining

Actual Electrical Consumption (Wh/mi)

 

A/C off

A/C on, Solargreen

A/C on, Sungate EP
22 

When the A/C was not operated, the fuel economy was 46.3 mpg. The Solargreen thermal loads 

and A/C on resulted in 40.4 mpg. It was expected that the lower thermal loads for the Sungate 

EP would improve the fuel economy but that did not happen. Figure 27 shows the fuel economy 

dropped slightly to 40.0 mpg (1%) despite the lower A/C compressor power noted in Figure 22. 

Figure 28 shows that the electrical energy consumption increased slightly from 41.5 Wh/mi to 

41.6 Wh/mi (0.2% increase) when the Sungate EP thermal load was applied. While the exact 

reason for this is not known, it is probably within the test to test variation. 

Figure 27. UF-Weighted Fuel Economy, USO6

Figure 28. UF-Weighted Electrical Energy Consumption, USO6 

46.3

40.4 40.0

0

5

10

15

20

25

30

35

40

45

50

A/C off A/C on, Solargreen A/C on, Sungate EP

UF-Weighted Fuel Economy (mpg)

 

42.9

41.5 41.6

0

5

10

15

20

25

30

35

40

45

50

A/C off A/C on, Solargreen A/C on, Sungate EP

UF-Weighted Electrical Energy Comsumption (Wh/mi)

 
23 

3.3 UDDS/USO6 Composite Results

To combine the data from the two drive cycles into a composite value, the standard EPA split of 

55% city and 45% highway was used. Using equations 20 and 21 from Section 2.6, the fuel 

economy and electrical energy consumption were combined using the USO6 as a surrogate for 

the HWFET. Figure 29 shows the A/C off fuel economy is 56.4 mpg and the A/C on Solargreen 

fuel economy is 38.4 mpg. The Sungate EP thermal load results in an 8% increase in fuel 

economy to 41.6 mpg. The electrical consumption with A/C off is 76.8 Wh/mi while the A/C on 

and Solargreen thermal load electrical consumption is 81.8 Wh/mi. The electrical energy 

consumption for the Sungate EP thermal load increased < 1% to 82.3 Wh/mi which is probably 

within the test-to-test variation. 

Figure 29. UDDS/USO6 Composite Fuel Economy

56.4

38.4

41.6

0

10

20

30

40

50

60

A/C off A/C on, Solargreen A/C on, Sungate EP

UDDS/USO6 Composite Fuel Economy (mpg)

 
24 

Figure 30. UDDS/USO6 Composite Electrical Energy Consumption

4.0 Conclusions

Using Sungate EP solar reflective glazing in the windshield and backlite reduced the passenger 

compartment thermal load from 1629 W to 1264 W in a Toyota Prius. The reduced thermal load

due to Sungate EP in the windshield and backlite resulted in lower A/C compressor power and 

lower interior cabin air temperature (improved occupant comfort) compared to Solargreen. The 

lower compressor power yielded an 8% increase in the UDDS/USO6 composite fuel economy 

from 38.4 to 41.6 mpg while the UDDS/USO6 composite electrical energy consumption was 

equivalent. 

76.8

81.8 82.3

0

10

20

30

40

50

60

70

80

90

A/C off A/C on, Solargreen A/C on, Sungate EP

UDDS/USO6 Composite Electrical Energy Comsumption (Wh/mi)

 
F1147-E(10/2008) 

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1. REPORT DATE (DD-MM-YYYY)

June 2009

2. REPORT TYPE

Technical Report

3. DATES COVERED (From - To)

 

4. TITLE AND SUBTITLE

Impact of Sungate EP on PHEV Performance: Results of a 

Simulated Solar Reflective Glass PHEV Dynamometer Test

5a. CONTRACT NUMBER

DE-AC36-08-GO28308

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

J. Rugh 

5d. PROJECT NUMBER

NREL/TP-540-45908

5e. TASK NUMBER

WTF61000

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401-3393

8. PERFORMING ORGANIZATION

REPORT NUMBER

NREL/TP-540-45908

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)

NREL

11. SPONSORING/MONITORING

AGENCY REPORT NUMBER

12. DISTRIBUTION AVAILABILITY STATEMENT

National Technical Information Service

U.S. Department of Commerce

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Springfield, VA 22161

13. SUPPLEMENTARY NOTES

14. ABSTRACT (Maximum 200 Words)

The project assessed the impact of a solar reflective windshield and backlite on plug-in hybrid electric vehicle (PHEV) 

range and fuel economy. The effect of Sungate® EP on PHEV performance was evaluated on NREL’s PHEV test 

bed, a 2006 Toyota Prius modified with a 5 kWh Hymotion Li-ion Energy Storage System. The tests, performed at 

Environmental Testing Corporation in Colorado, used portable electric heaters installed in the passenger 

compartment to simulate the solar heat gain through the glazings.The UDDS/USO6 composite fuel economy 

increased 8% from 38.4 mpg to 41.6 mpg due to the reduction in thermal loads from Sungate EP glazings installed in 

the windshield and backlite. The electrical energy consumption was essentially equivalent with a less than 0.2% 

increase. Using the Sungate EP resulted in lower A/C compressor power and lower interior cabin air temperature, 

which would improve occupants' comfort. The lower A/C power improved UDDS/USO6 composite fuel economy. 

15. SUBJECT TERMS

advanced vehicle systems; fuel economy; plug-in hybrid electric vehicles; solar reflective glazings

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