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PV panels output


h_1985
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Hello,

i need to know about somthing confusing me about PV panels

the question about pv panel output, some people say that pv panel output can reach OR exceed peak power shown on nameplate and then oversize inverter to be able to override increase in output

other people said that pv output power cannot goes to rated peak power OR exceed this value

what is the right concept :? :? ??

any help

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Usually the PV array very rarely reachs its nominal power during operation.

Except under special partial cloudy conditions (transitory conditions), or at high altitudes, the irradiance perpendicular to the PV module doesn't exceed about 1000 W/m2.

But in these conditions the PV array temperature is at its higher values. A PV cell temperature of 55°C, with a temperature coefficient muPmpp of -0.42%/°C, will induce a loss of 12.6° with respect to STC (1000 W/m2 and 25°C).

Now the inverter sizing is not really dependent on this: you can accept some hours of overload without loosing much energy.

PVsyst offers an explicit tool for the sizing of the inverter. You can see that a PnomRatio (= PnomPV / PNomInverter) of 1.25 to 1.3 is quite acceptable in most cases.

 

Sizing_Conditions.png.bc2144e44c09030d59543555021a4061.png

Inverter sizing conditions

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Usually the PV array very rarely reachs its nominal power during operation.

Except under special partial cloudy conditions (transitory conditions), or at high altitudes, the irradiance perpendicular to the PV module doesn't exceed about 1000 W/m2.

But in these conditions the PV array temperature is at its higher values. A PV cell temperature of 55°C, with a temperature coefficient muPmpp of -0.42%/°C, will induce a loss of 12.6° with respect to STC (1000 W/m2 and 25°C).

Now the inverter sizing is not really dependent on this: you can accept some hours of overload without loosing much energy.

PVsyst offers an explicit tool for the sizing of the inverter. You can see that a PnomRatio (= PnomPV / PNomInverter) of 1.25 to 1.3 is quite acceptable in most cases.

 

[attachment=0]Sizing_Conditions.png[/attachment]

 

Thanks for reply

But in all pv panels data sheets a term called power tolerance usually is (-0/+5), this term means panel output can exceed peak power by 5 watts or what?

:?:

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Usually the PV array very rarely reachs its nominal power during operation.

Except under special partial cloudy conditions (transitory conditions), or at high altitudes, the irradiance perpendicular to the PV module doesn't exceed about 1000 W/m2.

But in these conditions the PV array temperature is at its higher values. A PV cell temperature of 55°C, with a temperature coefficient muPmpp of -0.42%/°C, will induce a loss of 12.6° with respect to STC (1000 W/m2 and 25°C).

Now the inverter sizing is not really dependent on this: you can accept some hours of overload without loosing much energy.

PVsyst offers an explicit tool for the sizing of the inverter. You can see that a PnomRatio (= PnomPV / PNomInverter) of 1.25 to 1.3 is quite acceptable in most cases.

 

[attachment=0]Sizing_Conditions.png[/attachment]

 

Thanks for reply

But in all pv panels data sheets a term called power tolerance usually is (-0/+5), this term means panel output can exceed peak power by 5 watts or what?

:?:

 

There is a manufacture tolerance.

The peak value in the datasheet it´s the "average" of the electrical parameters of the same PV modules model. In facts, each manufactured module have different electrical characteristic (slight difference). The "power tolerance" in manufactorer datasheet menas that your PV module, for characteristic of the manufacturing process, can exceed the peak power in +5%.

For example, you have 3 modules of 300Wp with -0/+5 (identical brand and model) , according to manufacturer, you can have:

- 1 module 300Wp (+0% power tolerance)

- 1 module 303Wp (+1% power tolerance)

- 1 module 315Wp (+5% power tolerance)

.....

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Usually the PV array very rarely reachs its nominal power during operation.

Except under special partial cloudy conditions (transitory conditions), or at high altitudes, the irradiance perpendicular to the PV module doesn't exceed about 1000 W/m2.

But in these conditions the PV array temperature is at its higher values. A PV cell temperature of 55°C, with a temperature coefficient muPmpp of -0.42%/°C, will induce a loss of 12.6° with respect to STC (1000 W/m2 and 25°C).

Now the inverter sizing is not really dependent on this: you can accept some hours of overload without loosing much energy.

PVsyst offers an explicit tool for the sizing of the inverter. You can see that a PnomRatio (= PnomPV / PNomInverter) of 1.25 to 1.3 is quite acceptable in most cases.

 

very rarely [/b] so we don't need to oversize inverter but array must be oversized

that is the rule right??

Another question please >>> 1000 w/m2 mentioned always in pv panels data sheets in STC condition means only Direct (perpendicular) irradiance only OR all global Irradiance???

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You usually size your installation based on the STC peak power, the power tolerance is a range of power(statistical), maybe all your modules will be in the 0% or all in the 5%...you will never know before the making the engineering, so size the installation based on the statistical maximun power tolerance, will be more expensive.

The inverter can operate over the "maximun power input", symply limit the input (modify MPPT) and output power.

"Direct" does not neccesarily mean "perpendicular". The STC test is with a Artificial ligth, thats include the Direct and Diffuse component

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