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Author Topic: matching panels and inverter  (Read 1473 times)
chasfromnorfolk
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« on: January 26, 2016, 04:43:34 PM »

I know so little about electrickery, and yet even so occasionally something happens to call into doubt whether I know anything at all: when 'matching' panels to an inverter (or the other way round) what is paramount; wattage or voltage? Or both?

I ask because I now have some newly acquired  37v /  250w panels and was contemplating adding one to the system - currently 4x 250w / 37v running through an inverter that is clearly badged as coping with 1250w / 500v.

The guy who dropped them off, supposedly in the know, said it was only important that the combined voltage wasn't exceeded, not the wattage - and that I could put 10 (ie combined 370v) 'comfortably' through the inverter, and that the resultant combined 2500w would be coped with.

Can't be right, surely?

Chas
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Iain
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« Reply #1 on: January 26, 2016, 05:04:48 PM »

Hi
Most inverters have a max wattage they should cope with however the max voltage is the important one. Max O/C voltage of the panels should not exceed the max voltage of the inverter. If the wattage is too high, within certain limits the inverter will just restrict to its max output.
Iain
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JohnS
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« Reply #2 on: January 26, 2016, 11:03:19 PM »

It is more important to match the current than the voltage or watts.  All panels on the same string will have the same current flowing through them. 

Check the panel specs and make sure that the current is similar at different irradiation levels.
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Iain
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« Reply #3 on: January 26, 2016, 11:16:19 PM »

Hi
But the max voltage is more important for the inverter.
Iain
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nowty
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« Reply #4 on: January 26, 2016, 11:34:51 PM »

The guy who dropped them off, supposedly in the know, said it was only important that the combined voltage wasn't exceeded, not the wattage - and that I could put 10 (ie combined 370v) 'comfortably' through the inverter, and that the resultant combined 2500w would be coped with.

The guy is mostly right, exceeding the max voltage with even very low power will kill an inverter.

Adding more panels, even more than the inverter can handle in power usually just results in the inverter power limiting by chocking off the current flowing. Saying that I would not put anymore than 6 on such an inverter.

What is the make and model of the inverter ?

Also if your claiming FITs then you can no longer extend systems, even with an MCS installation.
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oliver90owner
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« Reply #5 on: January 26, 2016, 11:41:55 PM »

I would be guessing that the 37V is max power voltage?  But it may be open circuit volts.

I know most panels are 72 cells and I have at least one with 48.  If yours are 60 cells, that voltage could be open circuit voltage.

If the inverter sees more than its rated string voltage it should never restart, if reconnected, or it may let the smoke out due to exceeeding the voltage for components (likely capacitors).

Extra panels added to a string should operate at the same current as the existing string or the performance will be dragged down towards the lower value

So all are important.  String voltage - for security of the inverter; operational current - for performance of string; and the total power presented to the inverter if the inverter is unable to reject the excess power without damage (some can and some may not).

So all the panel parameters need to be known before deciding yes or no.  It is usually quite easy by comparing output and cell numbers, or the panel data.

Panels of the same power but different cell counts will not perform well and it is never ideal to mix old and new panels - although an acceptable compromise on occasions.
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chasfromnorfolk
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« Reply #6 on: January 28, 2016, 09:14:04 AM »

Thanks, everyone, for the info. It would seem my cautious approach - to offer the max wattage to the inverter while not exceeding the stated max volts DC - is the way to go. All the panels 'match' (well, to within a volt and a watt) so there seems no reason not to add the final fifth one.

Cheers, Chas.
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