Solar panel open circuit voltage

[rubbishman]

Hi all,
Thinking of buying a cheap 50 watt panel,the other ones I have now and in the past state an open circuit voltage voltage of 20-22but this one states 18v only.Does this matter ?

 

[RichardS]

Are you going to use the 18V panel in series/parallel with your existing 22V panels?

Richard

 

[rubbishman]

No, but that is a option I hadn't considered,any problems doing that?

 

[rubbishman]

Hmmm,got a better WiFi network ( I'm in Philippines). Not as simple as I thought any tips you've got mate would be greatly appreciated,
C.

 

[RichardS]

Hmmm,got a better WiFi network ( I'm in Philippines). Not as simple as I thought any tips you've got mate would be greatly appreciated,
C.

I'm not sure what tips you are looking for as it all depends upon what you intend to do with the new panel and whether it will be connected through a controller.

In general, if it's going to be a free-standing panel, with or without a controller, then the lower voltage will not be a problem, although some controllers have a minimum trigger voltage so 18v might be slightly limiting.

If you are going to connect the new panel in series or parallel with existing panels, then it is best to have panels with the same voltage and current rating. This is usually more important where the panels are to be connected in parallel.

Richard

 

[noelex]

There are two voltages listed on solar panels. The open circuit voltage which is usually listed as Voc. The second is the maximum power point voltage which is usually listed as Vmp.

If the Voc is listed as 18v as you have indicated this suggests it 32 cell rather than a 36 cell panel. You can usually count the cells on the front surface yourself to check.

A Voc of 18v sounds plenty, but in practice, while these panels will charge a 12v battery, the voltage is not quite enough for efficient charging. A 36 cell panel which will have a Voc of around 22v would be a better choice.

If you are going to add this panel in parallel with an existing panel with an MPPT controller the general rule of thumb is the voltages should be within 0.5v (although matching Vmp of both panels is more important than matchingthe Voc) so you cannot mix a 22v and 18v without loosing a reasonable amount of efficiency. With a non MPPT controller (sometimes called a PWM controller) matching the voltages does not matter, but the panel with a Voc of 18v will still be less effecient in some (especially hot) conditions.

 

[matthewriches]

I'd keep them the same personally.

 

[William_H]

As said the OC voltage indicates the number of cells in series in the panel. Now if you are charging a 12v battery directly or with a PWM controller then in full sunlight no problem. In effect the voltage of the panel above your 14v needed to charge the battery is wasted. Except as said under load that voltage falls anyway. Not a problem until you get to less than ideal light on the panel so less cells means charging will cease at a light level greater than that for one with more cells.
So perhaps if you lived in Scotland more cells would be worth having but if you live on the equator less would be OK.
I don't however think you would have problem paralleling anb 18v with a 20v ol'will