Doubt in a Solar Panel?

[Electroenthusiast]

I have a solar panel that was being used for charging emergency lamp.
Right no, it is not being used... I measured the Voltage and Current across its terminals ;and found it to be 8.7 V and 60-70 mA...
My question is why is the voltage across it 8.7V, i mean on what factors does the voltage depend?
Since i'm using it to charge a battery, i feel that " Voltage does'nt play an important role, instead the current."
WHY VOLTAGE IS 8.7V ?

 

[colin55]

What is the voltage of the battery?

 

[Birdman Adam]

I'd guess your panel is rated at 9VDC. The voltage depends (mostly) on the amount of light hitting it.

If you have a 9VDC battery, that 8.7, or even 9 volts won't be enough to charge it. Your voltage must be higher than the batteries to charge it. After that, the amount of current determines how fast the battery will charge.

 

[RCinFLA]

Solar cells are illumination based current source, clamped in voltage by an inherent diode. There is a series resistance associated with connecting to the silicon but a good quality cell will have a very flat current output from near zero volts loading to point where inherent diode conducts.

In full sun, measure the short circuit current and open circuit voltage. At no load on panel (open circuit voltage, Voc) all the generated current is shunted down the inherent diode. There is a negative temperature coefficient to diode so hotter panel gets the lower the diode conduction voltage gets.

A panel comprises cells wired in series. Maximum power point is about 0.5 vdc per cell at 25 deg C where loading on panel is such that inherent diode shunts about 3% of illumination current. Open circuit voltage is about 0.63 vdc per cell at 25 deg C.

 

[Simple Simon]

r.vittalkiran

If you took the reading as a open voltage "no load" and it was 8.7 volts 60 ma, that would charge a 6 volt battery.

Charging voltage has to be highter than the battery voltage for charging to take place.

S. Simon

 

[Electroenthusiast]

Solar cells are illumination based current source, clamped in voltage by an inherent diode......................************.

Can i get a diagram?
That which is relevant to the explaination?

 

[RCinFLA]

**broken link removed**