PV Evaluation - some notes...

I have some PV's to evaluate. They are:

Active Load

The panels need to be loaded. Maximum power is transferred when source and load impedances match. 

The correct matching is what interests me - I not interested in sticking PV's across batteries with a blocking diode. ( I will be playing with buck converters soon ....)

For testing I needed an adjustable load that could dissipate the anticipated 20W power. 

A power rheostat was not to hand - so I cobbled together the adjustable load shown above. The 14C/W heatsink is not adequate, but the effect is more impressive!

What were you doing in week 8 1974?

Solarwatt P12 AK GET AK

Rating plate: 12W, Uoc 21.7, Isc 0.72A, 

Dimensions 575, 250, 20mm (Face area 0.144 m2)

Rated Power / Area 83W m-2

At 12:51p.m. ( 12th May 2001) it was local noon.  This is when the sunlight path through the atmosphere is the shortest. 

Directed at the sun, the panel only acquiesced to providing an Isc of 0.67A. 

3 hours earlier I read an Isc of 0.60A.  The difference is due to the path length through the atmosphere.

 

The measurements

V I  mA R P
20 100 200 2
19 300 63 5.7
18 500 36 9
17 600 28 10.2
16.5 620 26 10.23
16 640 25 10.24
15.5 640 24 9.92
15 650 23 9.75
14 650 21 9.1
13 650 20 8.45
12 650 18 7.8
11 650 16 7.15
10 660 15 6.6

The plots

Current / Voltage
 
Power / load

Obscuring the panel

Peak power measurements were taken with the panel partially obscured.

Blocking one cell. 8V, 60mA, 0.48W, 133R

Film (bubble wrap) over entire panel: 16V, 0.4A, 6.4W, 40R

Film + cloth: 16V, 50mA, 0.8W, 320R

Conclusion

Max. power transfer during the midday tests was into a 25R load.  As the light fades, the optimum load resistance increases. 

The panel only produced a peak of 10.24W, less than rated 12W. The date code was 1998 - so it had aged 3 years. The tolerance is quoted at 15%.

Intersolar Phoenix Gold Thin Film Panel

This was tested on the same day as the Solarwatt. At local noon this provided a mere Isc of 0.52A.

http://www.thesolarcompany.com

The enclosed leaflet rated the panel at 14W, 15.8V, 0.94A

Uoc 24, Isc 1.2A

Dimensions 475, 340, 29mm (ID 33511W) (Face area 0.16 m2

Rated Power / Area 31W m-2 (Assumes 5W panel rating)

But the label on the box quoted 5W! (This is part of the Intersolar Flexi Lite Kit available from CAT.)

V mA R P
20 70 285.7 1.4
19 160 118.8 3.0
18 190 94.7 3.4
17 260 65.4 4.4
16 290 55.2 4.6
15 330 45.5 5.0
14 360 38.9 5.0
13 390 33.3 5.1
12 410 29.3 4.9
11 430 25.6 4.7
10 440 22.7 4.4
Current / Voltage
 
Power / load

Conclusion

Max. power transfer at 33R.

Siemens SM20

Ratings plate: SM20, Max Power 20W Uoc 18.0, Isc 1.6A. Rated at 14.5V 1.38A,  
(14.5V * 1.38A = W = 20W) 

Rated Power / Area 108W m-2

Dimensions  328 * 566 * 35 mm (Face area 0.185 m2)

V mA R P
16 270 59.3 4.3
15 790 19.0 11.9
14 1070 13.1 15.0
13 1250 10.4 16.3
12 1370 8.8 16.4
11 1420 7.7 15.6
10 1450 6.9 14.5
9 1470 6.1 13.2
Current / Voltage
 
Power / load

Blue - 10:00am sunshine (20/5/2001)

Yellow - overcast sky, sun facing.

Red - overcast sky, north facing.

Optimum voltage falls to 12.5V Blue from 13.5V Red

 

 

Power / voltage

Conclusion

Very sensitive to cells being obscured from sunlight. Placing a couple fingers over the panel, and the output drops dramatically. ( 1.4A -> 30mA)

The above plots were measured 3 hours before local noon. The Isc 1.51A was measured at this time. 

At noon a brief reading of Isc 1.87A was measured  This higher than rated output can be put down to cloud lensing - direct sunlight and plenty of bright cloud.

BP Solar BP212SR

Ratings plate:  Max Power 12W Uoc 18.9, Isc 0.8A. 
Rated at 15.2V 0.72A,  

Dimensions  231 * 561 * 38.5 mm. (Face area 0.13 m2)

Rated Power / Area 92W m-2

This monocrystalline panel has 32 cells in an anodised aluminium frame.

The suffix SR denotes Self Regulation. These panels useful for direct connection and charging of 12 volt batteries. 
Minimum battery capacity is 2.5 times the module wattage, e.g. 30 Amp hour battery minimum for a 12 watt panel.

V mA R P
16 370 43.2 5.9
15 550 27.3 8.3
14 640 21.9 9.0
13 680 19.1 8.8
12 700 17.1 8.4
11 710 15.5 7.8
10 715 14.0 7.2
9 720 12.5 6.5
Current / Voltage
 
Power / load

Blue - 10:00am sunshine (20/5/2001)

Yellow - overcast sky, sun facing.

Red - overcast sky, north facing.

 

Power / voltage

Conclusion

Not sure that the panel is in current production. 

The self regulation works!

Evaluation notes

England is not that sunny, especially when evaluating solar panels. 

The Watt peak figures are never reached. Examine manufacturer's data for normal dull average murky weather. Does the max power transfer voltage change with different levels of irradiance? (I'm not mixing units here! The impedance will change - clouds are series resistors - but does the terminal voltage change when matched to the optimum load?

Mixing panels in an array is not a good idea - their characteristics are different. All of the above deliver peak power at different voltages.

The BP Solar BP212SR keeps its maximum power transfer point at the same voltage - 14 V i.e. with differing levels of irradiance the optimum load changes, but the terminal voltage remains at 14V.

The Siemens SM20 has the best power per area figure.

The power / voltage / irradiance graphs are key. 

What load will be driven? Bound to be rechargeable cells... what are their characteristics?