Danish tests

The tests at DTI were done outdoors on a side by side configuration with three test panels of 3.5 m2 each and a single PV reference module. PV modules were each 190 Watt from Evergreen.

image004

System 1: SolarWall with two PV modules on top, variable flow (high)

System 2: SolarWall with two PV modules on top, variable flow (low)

System 3: SolarWall alone, variable flow (thermal reference)

System 4: PV module alone, natural ventilation (electrical reference)

The tests were carried out in open air at variable insolation and wind speed. Side-by-side testing was done to eliminate errors due to different ambient conditions. Nominal flow rates were:

PVT #1: 140 m[3]/h pr m2 PVT #2: 75 m3/h pr m2 T #3: 75 m3/h pr m2

Подпись: Figure 5. PV/T outdoor tests with 190 Watt Evergreen PV modules

The last PV panel #4 had an open back surface, typical of NOCT test conditions but not typical of an ordinary roof system.

Table 2 indicates the difference in air temperature between ambient and the air leaving the transpired solar panel. Irradiance, wind speed and flow rates are shown to all have an effect on the thermal gain.

Table 1. Test Conditions

Designated #

Test Type

Irradiance [W/m2]

Wind Speed [m/s]

1

PV — NOCT

810

1

2

Thermal

910

3

Table 2. Air Temperature Rise for various flow rates and PV modules.

Collector Type

108 m3/h. m2 6 CFM/FT2

108 m3/h. m2 6 CFM/FT2

36 m3/h. m2 2 CFM/FT2

36 m3/h. m2 2 CFM/FT2

1

2

1

2

[°C]

[°C]

[°C]

[°C]

BP PV/T

9

7

15

9

Evergreen PV/T

9

6

14

10

UniSolar PV/T

11

9

20

15

Bare SolarWall

16

13

28

20

Table 3. Electrical and thermal efficiencies and temperatures

Air

PV

PV n

PV n

T

Thermal

Thermal

Total

Test

Flow

Power

rated

Actual

avg

Power

n

T rise

n

Watts

C

Watts

C

EG

1

2

746

11.4%

10.3%

1878

23.2

14.41

32.4

EG

2

2

858

11.4%

10.5%

1276

14

9.74

23.4

BP

2

2

720

11.9%

10.5%

1220

13.4

9.36

21.3

BP

1

2

637

11.9%

10.4%

1954

24.1

15.12

31.9

US

1

2

477

6.1%

6.6%

2542

31.4

19.68

37.3

US

2

2

1962

21.5

15.06

N/A

US

2

6

557

6.1%

6.8%

41

3573

39.3

9.46

45.4

US

1

6

487

6.1%

6.7%

48

4076

50.4

10.8

56.4

BP

1

6

627

11.9%

10.3%

46

3545

43.8

9.42

51.6

BP

2

6

726

11.9%

10.5%

37

2534

27.8

6.72

35.8

EG

1

6

753

11.4%

10.3%

47

3229

39.6

8.56

48.8

EG

2

6

866

11.4%

10.6%

41

2443

26.7

6.43

36.2

The thermal results are interesting in that they clearly show reasonable heat gains and reasonable solar efficiencies. For comparison purposes, the thermal gains of the bare transpired SolarWall panel are shown in Table 2 from the previous certification test data on the same 10 m2 test panel.

Transpired collectors are installed for heating or preheating the ventilation air required in buildings. Most applications are designed to preheat air with a temperature rise in the 5°C to 20°C range. The test data shows that the temperature gain from the PV modules is between 6°C to 20°C or within the typical range for transpired collectors.

It was expected that the bare transpired collector would perform better than with PV modules mounted above it (PV/T). What is surprising is that by resizing the transpired collector or adjusting

the air flow rate, the same thermal design target with PV/T is possible as is currently produced in many transpired collector installations.

The NOCT tests are conducted with an open back and PV suppliers typically list a PV panel temperature in the 47°C range. The PV/T tests, (with a closed back) as listed in Table 3, which is typical of a BIPV configuration, show temperatures similar to or lower than the NOCT data.

The efficiency data for the PV portion of PV/T in Table 3 is based on the dimensions of the PV modules. The thermal efficiency data is based on the transpired collector area of 10 m2. Since the PV modules do not cover 100% of the transpired collector, the column showing Total n (efficiency) is not a straight addition of the PV and thermal numbers but is based on the gross test panel area of 10 m2.

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