PV panels limiting to 15A

[niksloter]

Hi guys, i am not sure if i am posting in the right theme, however, can anyone explain why the pv modules can withstand 15A backfeed current? (for example). What determines these 15 A, what part of the pv module blocks the current to 15 amps?

 

[Worcester]

I think you might have some confusion.

It is (generally) permissible to connect a Solar PV system to the UK grid on a single phase, so long as the output is limited to 16A (at 230V = 3.68kWp) - this is done by various parameters in the inverter that manage the grid connection and synchrisation (actual grid voltage and actual grid frequency)

Solar Panels are DC generators and as such will always generate current in one direction, fit two panels back to back and they will cancel each other out based on voltage.

The chemical and physical nature of the way a PV silicon wafer panels generates electricity means that they are inherently a current llimiting device. see here : Theory of solar cells - Wikipedia, the free encyclopedia here Solar cell - Wikipedia, the free encyclopedia and here: Photovoltaics - Wikipedia, the free encyclopedia

The physical construction of the PV panels is why they usually have a recommended maximum voltage rating of 1000V, else the insulation may break down. In theory you could connect lots together to make 2000V however there then may be a signifcant DC leakage due to the various levels of insulation.

So I think you got the '15' Amps from somewhere else.

 

[SibertSolar]

I think the OP may be referring to the maximum series fuse rating?

 

[SibertSolar]

See also "bypass diodes"

 

[SibertSolar]

Also check out the modified wording regarding DC string fuses in the latest PV Install Guide in relation to max series fuse rating....I'm a small bit inebriated so I'll leave it there before spellcheck gets the better of me

 

[niksloter]

I think you might have some confusion.

It is (generally) permissible to connect a Solar PV system to the UK grid on a single phase, so long as the output is limited to 16A (at 230V = 3.68kWp) - this is done by various parameters in the inverter that manage the grid connection and synchrisation (actual grid voltage and actual grid frequency)

Solar Panels are DC generators and as such will always generate current in one direction, fit two panels back to back and they will cancel each other out based on voltage.

The chemical and physical nature of the way a PV silicon wafer panels generates electricity means that they are inherently a current llimiting device. see here : Theory of solar cells - Wikipedia, the free encyclopedia here Solar cell - Wikipedia, the free encyclopedia and here: Photovoltaics - Wikipedia, the free encyclopedia

The physical construction of the PV panels is why they usually have a recommended maximum voltage rating of 1000V, else the insulation may break down. In theory you could connect lots together to make 2000V however there then may be a signifcant DC leakage due to the various levels of insulation.

So I think you got the '15' Amps from somewhere else.

No buddy, as the guy below your answer said, i am referring to maximum series fusing, 15 amps, that is on the back of the module. So my question again, what determines these 15 amps? Why 16 amps would break the PV module. What will break? If that is the blocking diode, where are they located in the PV module?

 

[Meggerman]

No buddy, as the guy below your answer said, i am referring to maximum series fusing, 15 amps, that is on the back of the module. So my question again, what determines these 15 amps? Why 16 amps would break the PV module. What will break? If that is the blocking diode, where are they located in the PV module?

The design. The panels are given their current rating based on performance under standard test conditions (STC). If they are all wired in series then it is not an issue as current remains same. If you have them series - parallel then 2 strings of 8A panels would be 16A when the two series strings are then put in parallel back to inverter.

 

[SibertSolar]

@niksloter - you mention blocking diodes so I'll assume you're coming from an off-grid/battery type PV background. OCPD/current rating considerations differ between on-grid and off-grid applications but, fundamentally, the max series fuse rating reflects the amount of reverse current a singular module can cope with before the diodes (remember than PV cells are effectively diodes) will fail/break down. In off-grid scenarios, it's more common to parallel modules together, and the battery bank is considered an external source of current that can potentially back feed into the module array. This is not the case with an on-grid/inverter setup, where the main consideration is the potential fault current that may be passed back through a series string by other strings connected to it in parallel (hence my comment about what the latest PV install guide sggests when considering DC string fuses, and the importance of understanding the module's series fuse rating when doing so...)

Most crystalline silicon PV modules are made up of 3 or more sub-strings of cells connected in series. These sub strings are then connected in parallel with a BYPASS (not BLOCKING) diode to provide a reverse current path should part of the sub string's series cells be shaded or malfunction.

If you really want to get into the nitty gritty of it then you should look at the electrical characteristics of a single typical PV cell and the overall structure of a typical module and then do some simple DC electronics maths - it's not rocket science but, as I mentioned earlier, considerations do differ between on and off-grid scenarios

Hope this helps, writing from my mobile so apologies if it's a little haphazard...

 

[oldsalty]

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