Solar panel voltage

[Fraser32]

Hi all, I do alot of camping and may be able to get my hands on some solar panels from a house and want to use it to charge 12v battery.

My question is what is the voltage straight out of the panel?

Its my understanding that the voltage from a solar panel generally used in camping applications is 17v which then goes through a regulator to get the voltage to around 13v for charging applications. However i believe the voltage is a bit higher from home solar panels?

 

[MikeMl]

Depends on the specific panel. You will need a part number and a data sheet...

Most nominal 12V panels have an open circuit voltage between ~18V and 22V.

 

[Ian Rogers]

Normally panels are Watt rated

ie.. 80 watt panel will give a maximum output of 5A.. So on a nice sunny day you could get 16v at 5A.. On a bad day the voltage will be lower.

I have a small solar panel I removed from a garden light... Really sunny 2,8v ~ 3.0v, Cloudy 0.8v ~ 1.2v.. It varies too much that's why they rate them in watts....

Not cheap though this panel for the top of a motor home is £399 ( comes with all the attachments..)

 

[Fraser32]

Hi guys thanks for your response, i realise that they are power rated but i still need to know the output voltage of the panel to ensure i dont fry my regulator, will try get a part number

 

[Colin]

You can directly couple a 12v panel to a 12v battery via a diode.
It will automatically adjust and deliver the maximum current according to the strength of the sun.
If you are using the battery each night you don't need any other regulator if the panel takes about 10 hours to fully charge the battery.
We need to know a few more parameters before giving a complete answer.

 

[Pommie]

Here in Australia, the normal house roof panels are rated at 250W and therefore, at 12V they will deliver 20A in full sun.

Mike.

 

[bryan1]

Here in Australia, the normal house roof panels are rated at 250W and therefore, at 12V they will deliver 20A in full sun.

Mike.

Also one will find roof top solar panels are 24 volt and not 12 volt when the wattage is above 80 watts.

 

[large_ghostman]

You can directly couple a 12v panel to a 12v battery via a diode.
It will automatically adjust and deliver the maximum current according to the strength of the sun.
If you are using the battery each night you don't need any other regulator if the panel takes about 10 hours to fully charge the battery.
We need to know a few more parameters before giving a complete answer.

Personally I prefer the idea of a regulator, a battery that is trickle charged lasts longer than one that you dumnp alot of current into like when on fast charge. I didnt know over 250W they were 24V, its not sunny enough here to measure that from a solar panel lol. I have a small solar panel from an energy harvesting kit, its total rubbish even in full sun, the one I dug out of a garden light is smaller and better

 

[bryan1]

With the advent of grid tie solar came the 72 cell panel suited for the high voltage for the grid tie, the standard 60 cell panels above 80 watts are generally 24 volt panels. The 24 volt panels have a nominal 38 volts open circuit too with doesn't make them good for 12 volt operations.

 

[Nigel Goodwin]

Also one will find roof top solar panels are 24 volt and not 12 volt when the wattage is above 80 watts.

The 145W ones we have at work (not connected to anything yet) are 12V ones - funnily enough from Electus Distribution Pty in Australia.

 

[large_ghostman]

I checked ours as we have 4 panels, 3 are 12V and 1 is 24V. Makes me wonder if the 12V ones are a older type as the 24V one is newer, I dont know the wattage of them though. We have them on an out building and not connected to the grid

 

[rumpfy]

Fraser,
I have a small 12Volt panel (10 watt), which I use for keeping my tractor battery topped up. I checked its characteristics by measuring the cell voltage with varying loads on the cell. At no load, the cell voltage was about 21 volts. As the load increased, the cell voltage reduced. For each step of load current, I calculated the cell power by multiplying the load current by the cell voltage. As the load increased, the cell power increased. However, to charge a 12 volt battery, you need about 14 volts. With the cell, I found that the maximum power from the cell occurred at a cell voltage of 14 volts. This was done in bright sunlight. It seems that solar panels for charging 12 volt batteries, are designed so that they can be directly connected to a battery without the need for an extra regulator. Of course, in my case the application is to keep the battery topped up while the tractor is not in use; whereas you are looking for a more serious battery charging setup. To effectively charge 12 volt batteries, you really need to select the cell and the regulator.