Rough guide to Solar Panel Output
There is currently a lot of solar panel's available on fleabay and from other sources. Some are good and some aren't so good. One aspect that I've come across is some poetic license on panel output power.
A lot of the panels offered are a bit light on with specifications so it can be hard to see what it is you are getting for your money. Provided you can obtain the physical size of the panel, the Voc, the Isc and the panel power rating you can get a rough comparison for the panel output.
With some assumptions made, 1kW/m2 radiation and 17% conversion efficiency you can get a fair idea of how the panel compares to other similar products.
Utopia would be having the actual VmaxP and ImaxP but they aren't allways provided.
What we calculate is the theoretical maximum power that can be extracted from a physical panel size. So if the claimed rating is greater than or close to this then we've got reason to be doubtful of the claims.
Here is some calculations I've done for a few panels.
| efficiency | w/sqm | max w/m2 | ||||||||
| 17% | 1000 | 170 | ||||||||
| Claimed | Voc(V) | Isc(A) | P(W) | Vmp(V) | Imp(A) | Pmax(W) | H(mm) | W(mm) | theory W | |
| 80 | 22.1 | 4.8 | 106.08 | 17.6 | 4.55 | 80.08 | 534 | 1209 | 110 | actual 80W |
| 80 | 21.6 | 5.17 | 111.672 | 17.2 | 4.65 | 79.98 | 534 | 1220 | 111 | actual 80W |
| 80 | 21.6 | 4.8 | 103.68 | 18 | 4.44 | 79.92 | 534 | 1220 | 111 | actual 80w |
| 80 | 20.5 | 2.9 | 59.45 | 534 | 840 | 76 | claimed 80W | |||
| 80 | 19.5 | 5 | 97.5 | 534 | 1220 | 111 | Replacement for above | |||
| 60 | 21.6 | 3.6 | 77.76 | 18 | 3.33 | 59.94 | 534 | 840 | 76 | for comp with claimed 80W |
The first three panels are 80W, similar size and similar Voc, Isc and powers. Note the relationship with the power between multiplying Voc x Isc and the theoretical power
( theoretical power = efficiency * W/m2 * m2 of panel ), they are roughly the same.
The actual output power is ~70% of the theoretical.
Panel 4 was what i was sent when I ordered and paid for an 80W panel. It arrived with a specification sticker claiming to be an 80W panel. Obviously it wasn't :( After discussions with the seller and the proof above a replacement panel was sent ( #5 above ).
And for comparison panel 6 is a 60W panel.
My original panel didn't really pass the laughter test ;)