I have some PV's to evaluate. They are:
Solarwatt P12 AK GET AK
BP Solar BP212SR
Siemens SM20
Intersolar Phoenix Gold.
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 14°C/W heatsink is not adequate, but the effect is more impressive!
What were you doing in week 8 1974?
 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.
|
| 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 |
 |
| Current / Voltage |
 |
| Power / load |
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
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%.
 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 |
Max. power transfer at 33R.
 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 |
|
Yellow - overcast sky, sun facing. Red - overcast sky, north facing. Optimum voltage falls to 12.5V Blue from 13.5V Red
|
| Power / voltage |
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.
 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. |
| 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 |
|
Yellow - overcast sky, sun facing. Red - overcast sky, north facing.
|
| Power / voltage |
Not sure that the panel is in current production.
The self regulation works!
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?
Blue
- 10:00am sunshine (20/5/2001)
Blue
- 10:00am sunshine (20/5/2001)