Upgrading PV Array

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Posts: 1
Joined: Mon Oct 23, 2023 7:18 am
My RE system: Outback FlexPower One 3KW/48V

Upgrading PV Array

Post by saulmahoney »

Hi there,
I have a FlexPower One, 3KW 48v version. It is connected to 6 x 250W panels (1500W) and is not grid tied. Data over 5 years suggests I have a 20% shortfall over 12 months, but in December and January the PV vs generator is about 50/50. I think the best way to reduce the need for the generator is to upgrade the panels to 6 x 400W giving an new PV input of (2400W). My question is - what are the steps/setting adjustments required to perform the swap out? I am fairly competent with this stuff, but if this solution I'm looking at requires a professional installer to do it, fair enough I'll do it, but I'd prefer to do this myself if I can. Any help or suggestions would be welcome.
Many thanks.
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Posts: 10391
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A-01 - Series Stacked, (2) FM80, MATE3s, FlexNetDC
6 SimpliPhi 3.8-48 (48v @ 75AH. 450AH total)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
2 Midnite Solar MNPV6 combiners w/20A DC disconnects.
Honda EU7000is gas fuel generator

Re: Upgrading PV Array

Post by raysun »

A FlexPower One generally has a FlexMax 80 charge controller installed. The FM80 will support up to 4kW of solar panels in a 48V system. 6 400W panels 2.4kW is certainly within its capability.
When configuring the new array, an important consideration is to make sure the string open circuit voltage does not exceed the FM80's 150V maximum input. What is all that exactly?
If you look at the panel's specifications, there will be a parameter:V(oc), the open circuit voltage at 75°F. A 400W panel will have a V(oc) between 38 - 45V depending on model. The 150V maximum comes into play when the panels are wired into an array. If the 6 panels are wired as 2 parallel strings of 3 panels in series (as the current array may be), then the V(oc) may be as high as 135V. That's below 150V so should be OK, except V(oc) rises as ambient temperature falls. V(oc) must be calculated for the lowest possible temperature.
A safe method when using higher power panels is to make the strings 2 panels instead of 3. That leaves a very wide safety margin for V(oc). You may wish to wire the array as 3 parallel strings of 2 panels in series.
In terms of charging adjustments, the higher power array should deliver higher charge current. (2400W / 48V = 50A). Check that the battery is capable of accepting the new current rate. If it needs to be adjusted, the FM80 Current Limit parameter can be set to a value matching what the battery will accept.
Outside that, everything else should remain the same.
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