Question regarding FWPV6-FH600-SDA.

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marckeez
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Posts: 8
Joined: Thu Jun 11, 2020 7:51 am
My RE system: VFXR3648A with a Flex Max 80 Mate 3s, FlexNet DC, all came pre-wired from Wholesale solar. Batteries are Fullriver 6 VDC in a 48 VDC bank. Solar panels are Astronegy 280watt and have a total of 12 for 3360 total watts using a Outback combiner with Rapid shut-down UL1741.

Question regarding FWPV6-FH600-SDA.

Post by marckeez »

Can someone please explain how the FWPV6-FH600-SDA works when connected to 4 PV strings and lets say 3 are covered with snow. The retailer has explained it 2 totally different ways to me. When I purchased the system it was explained that the PV array strings would still produce power to the charge controller & inverter under this condition. Then another representative said it would not produce power due to the 3 having 0 volts and the system is only good as lowest power producer in the complete PV string. My solar panels are on a roof and difficult to clean snow off of. I have room in my combiner for another PV string and was thinking about mounting a new PV array where it will be shielded from snow. If this is possible does it need to be the same watts as the other PV strings?

Thank you,
Marc
raysun
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Posts: 8601
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A-01 - Parallel 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
Off-Grid

Re: Question regarding FWPV6-FH600-SDA.

Post by raysun »

The combiner permits feeding parallel PV panel strings the charge controller. The charge controller "sees" the whole array as a single entity, and its MPPT function "sweeps" the entire array to find the optimum voltage/current combination, maximizing the harvested power.
The dynamics within the array are a bit more complex. Each series string is impacted by the individual panel performance at any given moment. The rule of thumb: string voltage is set by the lowest voltage panel. The panel in the string that receives the least sunlight has the highest resistance, which limits the overall string current. The combination of lowest voltage and current limit sets the boundary for amount of power the string can generate. Each string can have a different ratio of voltage and current. A shaded string will have reduced performance within the string. It will have less of an impact on the other strings in the array.
In the scenario described in the OP, strings that have panels covered in snow may produce little power, while the strings without snow cover will produce more. Since the MPPT function is seeking to optimize power, it will "favor" the voltage/current of the producing strings and "disregard" the poorer producing strings. (That's oversimplification, but the net effect.)
When snow covers part of the array, power output will be reduced, but will be greater than zero. Whether the amount produced is sufficient for consumption demands cannot be determined until the conditions are in effect.
was explained that the PV array strings would still produce power to the charge controller & inverter under this condition.
This is true. It could be little under a cover of snow and leaden skies, but power can be produced.
Then another representative said it would not produce power due to the 3 having 0 volts and the system is only good as lowest power producer in the complete PV string.
This is not exactly true - the individual string may produce no power, but the entire array will. Power will be produced, the question will be how much.
I have room in my combiner for another PV string and was thinking about mounting a new PV array where it will be shielded from snow. If this is possible does it need to be the same watts as the other PV strings?
The panels don't need to be the same wattage, but the string voltage should be as close as possible. The array should be kept at or below 4000 watts.
How is the array configured currently? (# panels per string, # of strings.)
marckeez
Forum Member
Posts: 8
Joined: Thu Jun 11, 2020 7:51 am
My RE system: VFXR3648A with a Flex Max 80 Mate 3s, FlexNet DC, all came pre-wired from Wholesale solar. Batteries are Fullriver 6 VDC in a 48 VDC bank. Solar panels are Astronegy 280watt and have a total of 12 for 3360 total watts using a Outback combiner with Rapid shut-down UL1741.

Re: Question regarding FWPV6-FH600-SDA.

Post by marckeez »

I have 3 panels per string and 4 stings. 12 panels @ 280 watts per panel currently for a total of 3,360 watts. If I was to max my system (components are in my profile) for a 5th string (shielded from snow) what do you recommend in the max wattage for new string? Thanks for your help.
raysun
Forum Emperor
Posts: 8601
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A-01 - Parallel 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
Off-Grid

Re: Question regarding FWPV6-FH600-SDA.

Post by raysun »

The existing panels have a couple of specifications that will help guide the selection of additional panels:
V(oc) - Open Circuit Voltage
V(mp) - Maximum Power Voltage

The V(oc) of each string should match as closely as possible. It will be 3xV(oc) of a single panel. It will take a 3 panel string to match the current strings' V(oc).
The V(mp) of each string should match as closely as possible, however different panel wattage will likely result in a different M(mp) for the additional string.

The FM80 rated input = 4000W @ 48V. The current array leaves 640W "headroom" for an additional string, which likely will be around 750 - 900W. Depending on location and conditions, a small excess is not likely to cause overload. If the current array reaches peaks approaching 4000W during "production high season", the 5th string can be switched off, and used during "low season".
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