PV Solar Cell Equivelent Circuit Model

[philly]

If anyone is familiar with the equivelent circuit model for a PV solar cell can someone please explain to me the function of the shunt diode in the circuit? Is this diode intentionally placed in the circuit to shunt the cell/module in the event that the modle is not recieving sunlight? Or is the diode part of the physical makeup of the cell related to the physics of how sunlight is converted into current?

Also is the output voltage of PV module determined by the current from the current source that is passes across the shunt resistance in the circuit model? If not what circuit elements determine the output voltage of the cell since the cell source is a current source and not a voltage source?

 

[G._S._Ohm]

If anyone is familiar with the equivelent circuit model for a PV solar cell can someone please explain to me the function of the shunt diode in the circuit? Is this diode intentionally placed in the circuit to shunt the cell/module in the event that the modle is not recieving sunlight? Or is the diode part of the physical makeup of the cell related to the physics of how sunlight is converted into current?

Also is the output voltage of PV module determined by the current from the current source that is passes across the shunt resistance in the circuit model? If not what circuit elements determine the output voltage of the cell since the cell source is a current source and not a voltage source?

Post the equivalent circuit you are using. The one on Wikipedia seems to have disappeared.

 

[philly]

Post the equivalent circuit you are using. The one on Wikipedia seems to have disappeared.

I am using the one shown on the following link:

http://www.google.com/imgres?imgurl...a=X&ei=nvRBTYrPCYr3gAew2O3BAQ&ved=0CCYQ9QEwAg

 

[gar]

110127-2005 EST

philly:

See http://zone.ni.com/devzone/cda/tut/p/id/7230

The diode is inherent to the solar cell. The cell is essentially a photosensitive diode operated in its forward biased quadrant.

.

 

[G._S._Ohm]

what circuit elements determine the output voltage of the cell since the cell source is a current source and not a voltage source?

According to your schematic and neglecting Rs for the moment, the output voltage at low current [low illumination] is determined by the value of Rsh and is Il x Rsh.
At high current the output voltage levels off at the forward drop across the shunt diode. For most discrete diodes this voltage is about 1 v, but for LEDs it can go to 3 or 4 volts.
Diode drop is the sum of the junction voltage and the bulk resistance of the semiconductor material.

If the load draws current then there will be an additional voltage drop across Rs.

Plus all of this stuff is temperature sensitive.


With a light source, voltmeter and a load resistor you can probably determine Il, Rsh, Rs and the forward diode drop.

Maximum power is transferred when the load resistance is equal to the apparent source resistance looking back into the cell.
There are electronic convertor circuits that track this max. power point and adjust the load resistance presented to the cell to stay at this maximum.

 

[ggunn]

If anyone is familiar with the equivelent circuit model for a PV solar cell can someone please explain to me the function of the shunt diode in the circuit? Is this diode intentionally placed in the circuit to shunt the cell/module in the event that the modle is not recieving sunlight?

Yes. I am assuming that what you are talking about is what we in the PV industry know of as a bypass diode. If you open the junction box on the back of a typical crystalline Si solar module, you will see the bypass diodes. What they do is allow current to bypass a dead element in a series circuit. When the element is producing voltage, the diode is reverse biased and does not conduct. When the element shuts off, the diode becomes forward biased and shunts the current around the failed element.

 

[gar]

110128-2146 EST

ggunn:

I believe what philly was asking about the equivalent circuit diode of the photovoltaic cell itself. This was discussed in the reference I provided above.

The reverse biased diode you referred to I would classify as an external diode to the basic photo cell.

The equivalent circuit that I believe philly was presenting is a way of describing the V-I characteristics of the photo cell. With this circuit then you can analyze how the device will work in the external circuit consuming power from the photo cell.

Under no load and constant light excitation the output voltage vs temperature will vary as the change you would expect with an ordinary semiconductor diode. When a sufficient load is applied to the photo cell, then output is approximately a constant current.

.

 

[ggunn]

110128-2146 EST

ggunn:

I believe what philly was asking about the equivalent circuit diode of the photovoltaic cell itself. This was discussed in the reference I provided above.

The reverse biased diode you referred to I would classify as an external diode to the basic photo cell.

The equivalent circuit that I believe philly was presenting is a way of describing the V-I characteristics of the photo cell. With this circuit then you can analyze how the device will work in the external circuit consuming power from the photo cell.

Under no load and constant light excitation the output voltage vs temperature will vary as the change you would expect with an ordinary semiconductor diode. When a sufficient load is applied to the photo cell, then output is approximately a constant current.

I'm confident that between the two of us we got him what he wanted. ;^)