Posted by *JS* on October 20, 2008, 1:42 am

: quoted-printable

I have few home made solar panels. I would like to ask you experts here

in this forum about accurately determine rated output power of the =

panels.

Can I just simply multiply open circuit voltage by short circuit =

current?

My open-circuit-voltage is about 18V at full sun and short circuit =

current

is 3.2A. Does that mean the rated power (P=VxI) is about 57 watts?

If it does not, how I am going about determine the rated power?

Thanks in advance.

JIMMY

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*<DIV><FONT face=Arial size=2>I have few home made solar panels. I would like to *

ask you experts here</FONT></DIV>
*<DIV><FONT face=Arial size=2>in this forum about accurately determine rated *

output power of the panels.</FONT></DIV>
*<DIV><FONT face=Arial size=2>Can I just simply multiply open circuit voltage by *

short circuit current?</FONT></DIV>
*<DIV><FONT face=Arial size=2>My open-circuit-voltage is about 18V at full *

sun and short circuit current</FONT></DIV>
*<DIV><FONT face=Arial size=2>is 3.2A. Does that mean the rated *

power (P=VxI) is about 57 watts?</FONT></DIV>
*<DIV><FONT face=Arial size=2>If it does not, how I am going about determine the *

rated power?</FONT></DIV>
*<DIV><FONT face=Arial size=2></FONT> </DIV>*
*<DIV><FONT face=Arial size=2>Thanks in advance.</FONT></DIV>*
*<DIV><FONT face=Arial size=2></FONT> </DIV>*
*<DIV><FONT face=Arial size=2></FONT> </DIV>*
*<DIV><FONT face=Arial size=2>JIMMY</FONT></DIV>*
*<DIV><FONT face=Arial size=2></FONT> </DIV></BODY></HTML>*
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Posted by *Martin Riddle* on October 20, 2008, 2:46 am

I have few home made solar panels. I would like to ask you experts here

in this forum about accurately determine rated output power of the

panels.

Can I just simply multiply open circuit voltage by short circuit

current?

My open-circuit-voltage is about 18V at full sun and short circuit

current

is 3.2A. Does that mean the rated power (P=VxI) is about 57 watts?

If it does not, how I am going about determine the rated power?

Thanks in advance.

JIMMY

No its not Isc * Voc.

You need to charaterize the panel, by creating a I V curve.

Start with the open circuit voltage then add resistance and record I and

V.

ex:

I V I*V

0 18 0

0.5 17 8.5

1 16 16

1.5 15 22.5

2 14 28

2.5 13 32.5

3 12 36 Max power

3.2 11 35.2

Or you can just measure I and V under the load you run.

Cheers

Posted by *Bruce Harvey* on October 20, 2008, 3:49 am

I have few home made solar panels. I would like to ask you experts here

in this forum about accurately determine rated output power of the panels.

Can I just simply multiply open circuit voltage by short circuit current?

My open-circuit-voltage is about 18V at full sun and short circuit current

is 3.2A. Does that mean the rated power (P=VxI) is about 57 watts?

If it does not, how I am going about determine the rated power?

Thanks in advance.

JIMMY

Jimmy,

This is not correct. The Voltage and Current must be measured at the same

point to get the Maximum Power Point of your panel. I will use your example,

of 18Voc and 3.2A Isc.

As you will realise, when the voltage open circuit (Voc), i.e. no load, the

current (Ioc) is 0.0A, and when the current (Amps) is measured in short

circuit (Isc) the voltage short circuit (Vsc) should be 0.0 V Therefore:

18 Voc x 0.0 Ioc = 0.0Watts i.e. there is no usable power produced by the

panel at this voltage.

0.0 Vsc x 3.2A Isc = 0.0Watts i.e. there is no usable power produced by the

panel at this Current.

What you need to do is connect a measurable load across the terminals to

graph the output of the panel at different loads. For example using a load

of some kind big enough to handle the panel, you need to measure the current

in amps at different voltages and work out by multiplying the figures

together what the maximum power output is.

For example, you measure these at 1V intervals from say 6V to 15V and come

up with a table of outputs similar to the following table:

06V 1.0A = 6W

07V 1.1A = 7.7W

08V 1.2A = 9.6W

09V 1.4A = 12.6W

10V 1.7A = 17.0W

etc., etc.

15V 1.0A = 15W

From this you should be able to get a pretty good idea of the maximum output

of the panel. Keep in mind that other factors will effect the results like

the insolation (sun power) during the test and the temperature of the panel

among others, but this basic test will give you some idea of the actual

output of your panel.

Hope this helps.

Posted by *Bill Kaszeta / Photovoltaic Re* on October 20, 2008, 4:34 am

*>I have few home made solar panels. I would like to ask you experts here*

*>in this forum about accurately determine rated output power of the panels.*

*>Can I just simply multiply open circuit voltage by short circuit current?*

*>My open-circuit-voltage is about 18V at full sun and short circuit current*

*>is 3.2A. Does that mean the rated power (P=VxI) is about 57 watts?*

*>If it does not, how I am going about determine the rated power?*

*>Thanks in advance.*

*>JIMMY*

*>Jimmy,*

*>This is not correct. The Voltage and Current must be measured at the same *

*>point to get the Maximum Power Point of your panel. I will use your example, *

*>of 18Voc and 3.2A Isc.*

*>As you will realise, when the voltage open circuit (Voc), i.e. no load, the *

*>current (Ioc) is 0.0A, and when the current (Amps) is measured in short *

*>circuit (Isc) the voltage short circuit (Vsc) should be 0.0 V Therefore:*

*>18 Voc x 0.0 Ioc = 0.0Watts i.e. there is no usable power produced by the *

*>panel at this voltage.*

*>0.0 Vsc x 3.2A Isc = 0.0Watts i.e. there is no usable power produced by the *

*>panel at this Current.*

*>What you need to do is connect a measurable load across the terminals to *

*>graph the output of the panel at different loads. For example using a load *

*>of some kind big enough to handle the panel, you need to measure the current *

*>in amps at different voltages and work out by multiplying the figures *

*>together what the maximum power output is.*

*>For example, you measure these at 1V intervals from say 6V to 15V and come *

*>up with a table of outputs similar to the following table:*

*>06V 1.0A = 6W*

*>07V 1.1A = 7.7W*

*>08V 1.2A = 9.6W*

*>09V 1.4A = 12.6W*

*>10V 1.7A = 17.0W*

*>etc., etc.*

*>15V 1.0A = 15W*

*>From this you should be able to get a pretty good idea of the maximum output *

*>of the panel. Keep in mind that other factors will effect the results like *

*>the insolation (sun power) during the test and the temperature of the panel *

*>among others, but this basic test will give you some idea of the actual *

*>output of your panel.*

*>Hope this helps. *

The concept is correct, but the example is not correct.

Maximun current is always at zero volts (Isc).

Current decreases as voltage increases, the maximum voltage is at zero current

(Voc).

At both of these points the power (product of volts x amps) is zero.

It is not likely that you have a variable load that you can attach so that you

can

measure the current at other voltages. Try a 12-volt battery, it will start at

about

12.5 volts and increase to about 14 volts. 14 volts will be about the maximum

power voltage for a silicon solar cell panel with a Voc of 17 volts. If you have

rather good solar cells, and no weak ones in the circuit, you could get a

maximum power of about 40 watts (clear day, noon, pointed at the sun).

Bill Kaszeta

Photovoltaic Resources Int'l

Tempe Arizona USA

bill@pvri-removethis.biz

Posted by *Bruce Harvey* on October 20, 2008, 2:21 pm

*> wrote:*

*>>I have few home made solar panels. I would like to ask you experts here*

*>>in this forum about accurately determine rated output power of the panels.*

*>>Can I just simply multiply open circuit voltage by short circuit current?*

*>>My open-circuit-voltage is about 18V at full sun and short circuit *

*>>current*

*>>is 3.2A. Does that mean the rated power (P=VxI) is about 57 watts?*

*>>If it does not, how I am going about determine the rated power?*

*>>*

*>>Thanks in advance.*

*>>*

*>>*

*>>JIMMY*

*>>*

*>>Jimmy,*

*>>This is not correct. The Voltage and Current must be measured at the same*

*>>point to get the Maximum Power Point of your panel. I will use your *

*>>example,*

*>>of 18Voc and 3.2A Isc.*

*>>As you will realise, when the voltage open circuit (Voc), i.e. no load, *

*>>the*

*>>current (Ioc) is 0.0A, and when the current (Amps) is measured in short*

*>>circuit (Isc) the voltage short circuit (Vsc) should be 0.0 V Therefore:*

*>>18 Voc x 0.0 Ioc = 0.0Watts i.e. there is no usable power produced by the*

*>>panel at this voltage.*

*>>0.0 Vsc x 3.2A Isc = 0.0Watts i.e. there is no usable power produced by *

*>>the*

*>>panel at this Current.*

*>>What you need to do is connect a measurable load across the terminals to*

*>>graph the output of the panel at different loads. For example using a load*

*>>of some kind big enough to handle the panel, you need to measure the *

*>>current*

*>>in amps at different voltages and work out by multiplying the figures*

*>>together what the maximum power output is.*

*>>For example, you measure these at 1V intervals from say 6V to 15V and come*

*>>up with a table of outputs similar to the following table:*

*>>06V 1.0A = 6W*

*>>07V 1.1A = 7.7W*

*>>08V 1.2A = 9.6W*

*>>09V 1.4A = 12.6W*

*>>10V 1.7A = 17.0W*

*>>etc., etc.*

*>>15V 1.0A = 15W*

*>>From this you should be able to get a pretty good idea of the maximum *

*>>output*

*>>of the panel. Keep in mind that other factors will effect the results like*

*>>the insolation (sun power) during the test and the temperature of the *

*>>panel*

*>>among others, but this basic test will give you some idea of the actual*

*>>output of your panel.*

*>>Hope this helps.*

*>>*

*> The concept is correct, but the example is not correct.*

Please show me where the error is.

*> Maximun current is always at zero volts (Isc).*

*> Current decreases as voltage increases, the maximum voltage is at zero *

*> current (Voc).*

*> At both of these points the power (product of volts x amps) is zero.*

That is what my example says.

*> It is not likely that you have a variable load that you can attach so that *

*> you can*

*> measure the current at other voltages. Try a 12-volt battery, it will *

*> start at about*

*> 12.5 volts and increase to about 14 volts. 14 volts will be about the *

*> maximum*

*> power voltage for a silicon solar cell panel with a Voc of 17 volts. If *

*> you have*

*> rather good solar cells, and no weak ones in the circuit, you could get a*

*> maximum power of about 40 watts (clear day, noon, pointed at the sun).*

The OP just wanted to know how to do it. I just gave an example of how he

could. I suspect that it is possible that he may have a potentiometer that

would handle the job.

*> Bill Kaszeta*

*> Photovoltaic Resources Int'l*

*> Tempe Arizona USA*

*> bill@pvri-removethis.biz*

>I have few home made solar panels. I would like to ask you experts here>in this forum about accurately determine rated output power of the panels.>Can I just simply multiply open circuit voltage by short circuit current?>My open-circuit-voltage is about 18V at full sun and short circuit current>is 3.2A. Does that mean the rated power (P=VxI) is about 57 watts?>If it does not, how I am going about determine the rated power?>Thanks in advance.>JIMMY>Jimmy,>This is not correct. The Voltage and Current must be measured at the same>point to get the Maximum Power Point of your panel. I will use your example,>of 18Voc and 3.2A Isc.>As you will realise, when the voltage open circuit (Voc), i.e. no load, the>current (Ioc) is 0.0A, and when the current (Amps) is measured in short>circuit (Isc) the voltage short circuit (Vsc) should be 0.0 V Therefore:>18 Voc x 0.0 Ioc = 0.0Watts i.e. there is no usable power produced by the>panel at this voltage.>0.0 Vsc x 3.2A Isc = 0.0Watts i.e. there is no usable power produced by the>panel at this Current.>What you need to do is connect a measurable load across the terminals to>graph the output of the panel at different loads. For example using a load>of some kind big enough to handle the panel, you need to measure the current>in amps at different voltages and work out by multiplying the figures>together what the maximum power output is.>For example, you measure these at 1V intervals from say 6V to 15V and come>up with a table of outputs similar to the following table:>06V 1.0A = 6W>07V 1.1A = 7.7W>08V 1.2A = 9.6W>09V 1.4A = 12.6W>10V 1.7A = 17.0W>etc., etc.>15V 1.0A = 15W>From this you should be able to get a pretty good idea of the maximum output>of the panel. Keep in mind that other factors will effect the results like>the insolation (sun power) during the test and the temperature of the panel>among others, but this basic test will give you some idea of the actual>output of your panel.>Hope this helps.