If the label is gone or unreadable, electrical measurements and the frame size usually settle the question. Measure the open-circuit voltage (Voc) with a multimeter across the disconnected module output in bright sun, optionally the short-circuit current (Isc) with a DC clamp or ammeter, and the outer frame length and width. The tool ranks the 16 Siemens modules by how close they are.
Reading the model name
Siemens used a letter pair for the series and a number for the approximate power in watts: SM (single-crystal silicon, for example SM55), SP and SR (silicon modules in the 18 to 100 W range) and ST (copper indium diselenide thin film). Order codes add the voltage and the construction: SM11012F is the 110 W module for 12 V in a frame and SM11024L the 24 V laminate without a frame. A trailing -24 in a model name such as SM110-24 also marks the 24 V version.
Clues beyond the numbers
Outline sizes
| Model | Length × width (mm) | Cells | Voc (V, 12 V variant) |
|---|---|---|---|
| SR100 / SR90 | 1498 × 594 | 36 | 22 |
| SM110 / SM100 | 1316 × 660 | 72 | 21.7 |
| SM55 / SM50 | 1293 × 329 | 36 | 21.7 |
| SM50-H | 1219 × 329 | 33 | 19.8 |
| SP75 / SP70 | 1200 × 527 | 36 | 21.7 |
| SM46 | 1083 × 329 | 30 | 18 |
| SR50 / SR50Z | 783 × 594 | 36 | 21.6 |
| SP18 | 633 × 275 | 36 | 21.7 |
| SP36 | 633 × 527 | 36 | 21.7 |
| SM20 | 567 × 328 | 30 | 18 |
| SM10 | 360 × 330 | 34 | 19.9 |
| SM6 | 330 × 175 | 33 | 19.5 |
Once you have a candidate, open its page for the full datasheet and replacement notes, then use the array calculator to see how it behaves with a modern charge controller. If your module is not on the list, it may be an earlier M-series module from the same company: the case notes call these M50, M55, M65 and M75.