Reinstall, upgrade, or replace

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AgingInOctal
Forum Expert
Posts: 64
Joined: Thu Jan 24, 2008 5:07 pm
My RE system: Garage roof 2008
-27 (9x3) Day4Energy 180W
-2 GVFX3648, 2 FM80, FNDC, Mate
-8 PVX 2580 12V 258AH AGM
Location: Tualatin, OR

Reinstall, upgrade, or replace

Post by AgingInOctal »

Way back in 2008, I had the system described in my signature installed at my home. Now the roof needs to be replaced. A couple of years ago, I called a few places and was told it would cost about $3000 to remove the PV panels and reinstall them after the roof was done. I checked again recently and was told the cost for remove/reinstall was priced by the panel plus the cost of replacing most, or all, of the mounting hardware. One company said $200 per panel. The other said $300. With 27 panels this can get a bit costly for a 14+ year old system. I will mention that the panels are in a single 9 wide by 3 high array on a South facing garage roof with a 4/12 pitch. It doesn't get any easier than that.

I believe that my FM80s and inverters will handle a fair amount more power than my current PV panels put out.

Which would you choose:
A) Remove/reinstall existing panels
B) Replace existing panels with new higher power panels to max out other existing components.
C) Replace everything.

What do you think?
User avatar
Mike Curran
Forum Emperor
Posts: 2966
Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback - Garage roof (2007/2017):
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters

Battery systems operate in grid-tied, net metering w/backup mode
All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Reinstall, upgrade, or replace

Post by Mike Curran »

Someday I will have a similar situation on my garage roof, which is about 15 years old. When the time comes...

I would replace my 180W modules with higher power panels and keep my 300W modules. Problem is, the tiltable frames on the 180s are undersized for today's panel offerings so I'd have to redo them. Lower panels are mounted on rails with L brackets bolted to roof flashing mounts, so could keep all the hardware but the flashing mounts. Bottom line is not looking forward to it.

Part of my rationale for increasing power is that my array is undersized for my battery, and even though I'm grid-tied I'd still like more solar charging capacity. Also helps with sales to grid.

Don't know if this helps or not but at least you know you're not alone.
FB_IMG_1496760253740.jpg
Edited to correct age of roof.
https://ei.tigoenergy.com/p/pZXn7SZQyO45
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
AgingInOctal
Forum Expert
Posts: 64
Joined: Thu Jan 24, 2008 5:07 pm
My RE system: Garage roof 2008
-27 (9x3) Day4Energy 180W
-2 GVFX3648, 2 FM80, FNDC, Mate
-8 PVX 2580 12V 258AH AGM
Location: Tualatin, OR

Re: Reinstall, upgrade, or replace

Post by AgingInOctal »

Thanks for the reply.
It looks like you replaced your GVFXs in 2020. Did they fail or did the VFXR3524A have improvements you needed?

I suspect you originally had a Mate and switched to the Mate3s when you upgraded the inverters. Is that correct or was there another reason?

Are your FM80s still original?

It looks like my best option is replacing my 180s with more powerful panels. The next big question is how long the other components are likely to last.

I designed my system originally, but it was installed by a utility approved electrician because that got me an additional $9000 rebate. If this was still 2008, I would probably make the changes myself, but my wife and son don't want me on the roof anymore. :sad: They're right (Parkinson's Disease).
User avatar
Mike Curran
Forum Emperor
Posts: 2966
Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback - Garage roof (2007/2017):
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters

Battery systems operate in grid-tied, net metering w/backup mode
All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Reinstall, upgrade, or replace

Post by Mike Curran »

AgingInOctal wrote: Wed Jan 18, 2023 11:14 am Thanks for the reply.
It looks like you replaced your GVFXs in 2020. Did they fail or did the VFXR3524A have improvements you needed?
Did not fail, just wanted to replace before they did.
AgingInOctal wrote: Wed Jan 18, 2023 11:14 amI suspect you originally had a Mate and switched to the Mate3s when you upgraded the inverters. Is that correct or was there another reason?
Mate, then Mate3, then Mate3s when Mate3 failed under warranty. Can't remember why the Mate upgrade, but it was done before getting the new inverters.
AgingInOctal wrote: Wed Jan 18, 2023 11:14 amAre your FM80s still original?
Started with 1 MX60, added an FM80 with the 6×300W array, then replaced the MX60 with FM80.
AgingInOctal wrote: Wed Jan 18, 2023 11:14 amIt looks like my best option is replacing my 180s with more powerful panels. The next big question is how long the other components are likely to last.

I designed my system originally, but it was installed by a utility approved electrician because that got me an additional $9000 rebate. If this was still 2008, I would probably make the changes myself, but my wife and son don't want me on the roof anymore. :sad: They're right (Parkinson's Disease).
https://ei.tigoenergy.com/p/pZXn7SZQyO45
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
pss
Forum Emperor
Posts: 1191
Joined: Mon Jul 24, 2017 8:40 am
My RE system: 8330 watts in three strings, Flexmax 60 x 3, Radian 8048A, GSLC load center, Mate 3S, Hub 10.3, FN-DC and 900 Amp, 48V Trojan T105-RE battery bank.

Re: Reinstall, upgrade, or replace

Post by pss »

Here are some ideas. Since these are 180's, you may be able to shop around like on craigslist and locate some used panels in the 240-280 watt range that are perfectly good and may fit all of your existing rails. If I was having the roof replaced and the mounting rails and lags had to come out, then I would research exactly how the holes should be plugged up so as not to leak in the future. Maybe when the wood underlayment is bare and before the waterproof membrane is laid over, you may want to brush on or mop on a roof sealant of some kind. Also, there may be a CED greentech (now greentech renewables) location near you that you can purchase products from directly at the will call counter that you will use in your update and save some money and just find a handy person to install the railings and panels. Also, remember that solar specific mounting rails are not always required. You may be able, since it is a garage roof to simply use galvanized strut attached to the roof as rails, giving you flexibility on the size of the array. Our biggest array is built on strut. Just some thoughts.
AgingInOctal
Forum Expert
Posts: 64
Joined: Thu Jan 24, 2008 5:07 pm
My RE system: Garage roof 2008
-27 (9x3) Day4Energy 180W
-2 GVFX3648, 2 FM80, FNDC, Mate
-8 PVX 2580 12V 258AH AGM
Location: Tualatin, OR

Re: Reinstall, upgrade, or replace

Post by AgingInOctal »

Mike Curran wrote: Wed Jan 18, 2023 1:32 pm
AgingInOctal wrote: Wed Jan 18, 2023 11:14 am Thanks for the reply.
It looks like you replaced your GVFXs in 2020. Did they fail or did the VFXR3524A have improvements you needed?
Did not fail, just wanted to replace before they did.
Since you replaced your GVFXs at 13 years, it might make sense for me to replace my 14 year old ones.
Mike Curran wrote: Wed Jan 18, 2023 1:32 pm
AgingInOctal wrote: Wed Jan 18, 2023 11:14 amI suspect you originally had a Mate and switched to the Mate3s when you upgraded the inverters. Is that correct or was there another reason?
Mate, then Mate3, then Mate3s when Mate3 failed under warranty. Can't remember why the Mate upgrade, but it was done before getting the new inverters.
If I replace the inverters, I'll need a new mate3s. If I don't replace the inverters, will a mate3s work with the old GVFXs?
Mike Curran wrote: Wed Jan 18, 2023 1:32 pm
AgingInOctal wrote: Wed Jan 18, 2023 11:14 amAre your FM80s still original?
Started with 1 MX60, added an FM80 with the 6×300W array, then replaced the MX60 with FM80.
If my inverters are old, the charge controllers are too.
Mike Curran wrote: Wed Jan 18, 2023 1:32 pm
AgingInOctal wrote: Wed Jan 18, 2023 11:14 amIt looks like my best option is replacing my 180s with more powerful panels. The next big question is how long the other components are likely to last.
Well, I'm pretty sure I want to replace the 27 old 180W panels with at least 18-20 400W panels using the existing GVFXs and FM80s. I think I could fit 30 400s with a little creative racking and a third FM80. A mate3s, if it will work with the old stuff, will give me a access to Optics RE which should be useful. Keeping the GVFXs and FM80s until they start to fail might provide a useful longevity data point. I'll probably stick with the old AGM batteries unless they start to go bad because battery tech seems to be improving rapidly.

I see 2 potential problems with updating as needed:
1) I may lose out on rebates and tax credits this way.
2) If Key components may fail after the killer earthquake hits off the Oregon coast or the zombie apocalypse happens, I'll be out of electricity, water, and luck.

My suspicion is that a new 10KW system would cost less than the old 4860W system. The old system has already paid for itself anyway. Not in the value of the energy generated, of course, but in the market the purchase helped create/grow.
raysun
Forum Emperor
Posts: 9378
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
Off-Grid

Re: Reinstall, upgrade, or replace

Post by raysun »

If I replace the inverters, I'll need a new mate3s. If I don't replace the inverters, will a mate3s work with the old GVFXs?
viewtopic.php?t=13855

The question in the post was regarding a GVFX -E (Export) model, but the considerations should apply to the North American units too.
Last edited by raysun on Thu Jan 19, 2023 8:41 pm, edited 2 times in total.
AgingInOctal
Forum Expert
Posts: 64
Joined: Thu Jan 24, 2008 5:07 pm
My RE system: Garage roof 2008
-27 (9x3) Day4Energy 180W
-2 GVFX3648, 2 FM80, FNDC, Mate
-8 PVX 2580 12V 258AH AGM
Location: Tualatin, OR

Re: Reinstall, upgrade, or replace

Post by AgingInOctal »

raysun wrote: Thu Jan 19, 2023 8:05 pm
If I replace the inverters, I'll need a new mate3s. If I don't replace the inverters, will a mate3s work with the old GVFXs?
viewtopic.php?t=13855

The question in the post was regarding a GVFX -E (Export) model, but the considerations should apply to the North American units too.
Thanks, my original system documentation includes serial numbers and I know that the firmware has not been updated since installation in 2008. I'll contact Outback tomorrow to see what my options are.
AgingInOctal
Forum Expert
Posts: 64
Joined: Thu Jan 24, 2008 5:07 pm
My RE system: Garage roof 2008
-27 (9x3) Day4Energy 180W
-2 GVFX3648, 2 FM80, FNDC, Mate
-8 PVX 2580 12V 258AH AGM
Location: Tualatin, OR

Re: Reinstall, upgrade, or replace

Post by AgingInOctal »

pss wrote: Wed Jan 18, 2023 1:52 pm Here are some ideas. Since these are 180's, you may be able to shop around like on craigslist and locate some used panels in the 240-280 watt range that are perfectly good and may fit all of your existing rails. If I was having the roof replaced and the mounting rails and lags had to come out, then I would research exactly how the holes should be plugged up so as not to leak in the future. Maybe when the wood underlayment is bare and before the waterproof membrane is laid over, you may want to brush on or mop on a roof sealant of some kind. Also, there may be a CED greentech (now greentech renewables) location near you that you can purchase products from directly at the will call counter that you will use in your update and save some money and just find a handy person to install the railings and panels. Also, remember that solar specific mounting rails are not always required. You may be able, since it is a garage roof to simply use galvanized strut attached to the roof as rails, giving you flexibility on the size of the array. Our biggest array is built on strut. Just some thoughts.
Thanks for the ideas. I wasn't aware of Greentech Renewables, but since they have a location 15 miles away they should be very useful.
raysun
Forum Emperor
Posts: 9378
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
Off-Grid

Re: Reinstall, upgrade, or replace

Post by raysun »

AgingInOctal wrote: Thu Jan 19, 2023 8:25 pm
raysun wrote: Thu Jan 19, 2023 8:05 pm
If I replace the inverters, I'll need a new mate3s. If I don't replace the inverters, will a mate3s work with the old GVFXs?
viewtopic.php?t=13855

The question in the post was regarding a GVFX -E (Export) model, but the considerations should apply to the North American units too.
Thanks, my original system documentation includes serial numbers and I know that the firmware has not been updated since installation in 2008. I'll contact Outback tomorrow to see what my options are.
It's unlikely a firmware upgrade is available, other than the last iteration of your unit's control board. A 3rd party supplier, Zonna Energy, may be a good option to see if there is a board available.
User avatar
Mike Curran
Forum Emperor
Posts: 2966
Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback - Garage roof (2007/2017):
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters

Battery systems operate in grid-tied, net metering w/backup mode
All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Reinstall, upgrade, or replace

Post by Mike Curran »

FWIW, I sold my old GVFXs on eBay for about a third of their original cost, so not a complete loss. But if you keep them, mine worked fine with the Mate3 (from 2016) and then 3s (from 2019) until I replaced them in 2020. Mine also had the original firmware from 2007, I think it was version 66 or something like that, so I don't think fw should be a concern.
https://ei.tigoenergy.com/p/pZXn7SZQyO45
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
AgingInOctal
Forum Expert
Posts: 64
Joined: Thu Jan 24, 2008 5:07 pm
My RE system: Garage roof 2008
-27 (9x3) Day4Energy 180W
-2 GVFX3648, 2 FM80, FNDC, Mate
-8 PVX 2580 12V 258AH AGM
Location: Tualatin, OR

Re: Reinstall, upgrade, or replace

Post by AgingInOctal »

My original question was "Should I reinstall, upgrade, or replace?" My answer to that seems to be upgrade and replace, leaving me with a new question "Should I do replace it in stages or all at once?" To answer that, I'll need to research the incentives from Energy Trust of Oregon (funded by local utilities), State of Oregon, and the feds. Of course, the other unknown is whether it will be easier to find new owners for the old components individually or together.

Thanks for your help.
provo
Forum Emperor
Posts: 1283
Joined: Thu Jul 27, 2006 4:34 pm
My RE system: 16 Evergreen EC-120 (4 strings, total 1920W)
2 SimpliPhi 3.8-m-24V (150Ah each)
One FM80
One VFXR3524A
Hub 10
Mate3s
FNDC
Honda EU3000is generator
Grid connection, no selling back
Location: Sierra foothills

Re: Reinstall, upgrade, or replace

Post by provo »

AgingInOctal wrote: Tue Jan 17, 2023 12:50 pm Way back in 2008, I had the system described in my signature installed at my home.
...
I believe that my FM80s and inverters will handle a fair amount more power than my current PV panels put out.

Which would you choose:
A) Remove/reinstall existing panels
B) Replace existing panels with new higher power panels to max out other existing components.
C) Replace everything.

What do you think?
Hopefully those AGM batteries don't go all the way back to 2008! If your array is undersized, the batteries (even if newish) are probably suffering from chronic undercharging. As long as you're even considering option C above, here's my two cents:

1) Get a whole new integrated system, like a Flexpower 2 or a Flexpower Radian.

2) Get some high quality Li-ion batteries (I couldn't be happier with my SimpliPhi's.)
AgingInOctal
Forum Expert
Posts: 64
Joined: Thu Jan 24, 2008 5:07 pm
My RE system: Garage roof 2008
-27 (9x3) Day4Energy 180W
-2 GVFX3648, 2 FM80, FNDC, Mate
-8 PVX 2580 12V 258AH AGM
Location: Tualatin, OR

Re: Reinstall, upgrade, or replace

Post by AgingInOctal »

provo wrote: Sat Jan 21, 2023 6:25 am
Hopefully those AGM batteries don't go all the way back to 2008! If your array is undersized, the batteries (even if newish) are probably suffering from chronic undercharging. As long as you're even considering option C above, here's my two cents:
Oops. Yes, the AGM batteries are from 2008. The only exercise they get is when the grid goes down, maybe once every year or two. Otherwise they stay at 100%. Last year, the grid was down for a day and a half (after a storm) and my son, who is the only person currently living at the house, didn't notice until the second evening that he was the only one in the neighborhood with electricity.

When I calculated the storage capacity, I measured all the house loads, including start up surges, using a Brultech energy monitor, calculated 3 days estimated usage on the circuits that would be on the backup subpanel, and doubled it. The goal was backup storage for 3 days, with no PV, without going below 50% SOC. I don't remember considering array size. Did I buy too much battery? I do remember being happy that contractors were the ones lifting those 8 165lb batteries into place.

How do you size the array to the batteries?
provo wrote: Sat Jan 21, 2023 6:25 am 1) Get a whole new integrated system, like a Flexpower 2 or a Flexpower Radian.
I'll have to compare the specs on these 2 systems. I'm sure there have been several discussions comparing them. I'll see what I can find.
provo wrote: Sat Jan 21, 2023 6:25 am 2) Get some high quality Li-ion batteries (I couldn't be happier with my SimpliPhi's.)
I imagine they would be a huge improvement.
User avatar
Mike Curran
Forum Emperor
Posts: 2966
Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback - Garage roof (2007/2017):
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters

Battery systems operate in grid-tied, net metering w/backup mode
All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Reinstall, upgrade, or replace

Post by Mike Curran »

I do remember being happy that contractors were the ones lifting those 8 165lb batteries into place.
207# each x 12, pallet to battery boxes via engine hoist:
Hoisting them in.jpg
https://ei.tigoenergy.com/p/pZXn7SZQyO45
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
provo
Forum Emperor
Posts: 1283
Joined: Thu Jul 27, 2006 4:34 pm
My RE system: 16 Evergreen EC-120 (4 strings, total 1920W)
2 SimpliPhi 3.8-m-24V (150Ah each)
One FM80
One VFXR3524A
Hub 10
Mate3s
FNDC
Honda EU3000is generator
Grid connection, no selling back
Location: Sierra foothills

Re: Reinstall, upgrade, or replace

Post by provo »

AgingInOctal wrote: Sat Jan 21, 2023 12:01 pm
The only exercise they get is when the grid goes down, maybe once every year or two. Otherwise they stay at 100%. Last year, the grid was down for a day and a half (after a storm) and my son, who is the only person currently living at the house, didn't notice until the second evening that he was the only one in the neighborhood with electricity.
...
How do you size the array to the batteries?
Well that's pretty good! -- maybe the loads are very light (?) Others on the forum know more than me about AGM's. I had flooded and was off-grid for 11 years (no longer), so no comparison there. AGM's being used and recharged frequently would be unlikely to last the 15 years you've had them, but if it works in your situation, great!

As to sizing the array to the batteries, it all comes down to how often and how much you need to recharge them. Obviously it would be nice if the array could put back what was needed in all but the worst weather -- you have to run the numbers. Your system may be fine, though, in a 100% float application. In fact, Li-ion might not do well in that case.
raysun
Forum Emperor
Posts: 9378
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
Off-Grid

Re: Reinstall, upgrade, or replace

Post by raysun »

How do you size the array to the batteries?
This is an interesting question. There's a few considerations:
• Energy consumption, battery chemistry and charging efficiency.
Energy drawn from the battery must be replaced. The larger the typical consumption, the proportionately larger the array must be. Certain battery chemistries charge more efficiently than others - requiring less time and energy to charge fully. The array should be sized to accommodate the charging requirements of the battery.
• Maximum acceptable charge current.
The battery chemistry and capacity will dictate the maximum charge rate. E.g.; If the battery will accept 80A charge current maximum, then the array should be sized to deliver at or near the maximum at full array output.
• Variability of solar harvest.
PV arrays vary quite dramatically in output power with variations in solar power (insolation.) On clear, sunny days, an array may produce a good deal of power. On cloudy days with little sun exposure, an array may produce relatively little power. On partly cloudy days, or seasonal "low solar exposure", modest solar harvests are seen. In order to the maximuize number of days the solar array provides enough power to fully charge the battery, it should be sized for the "worst practical case". If summer solar peaks can charge the battery fully at array wattage of N, and the system is to fully charge the battery at 50% solar power in the off-peak seasons, then the array should be N * 2 watts.
If the larger array would exceed maximum charge current limits, the charge controller must be capable of limiting the current to a safe maximum.
• Maximum power handling of the charge controller.
The "overpaneling" strategy described above has a limit defined by the maximum safe power handling capacity of the charge controller. Overdriving the controller can lead to premature failure. E.g.: An Outback FlexMax 80 can safely deliver 80A of charge current to the battery. The maximum array power will be a product of battery voltage * charge current. For a 48V nominal battery, that's 50V * 80A = 4000 Watt array. If more array power is needed to meet energy consumption needs, multiple charge controllers, each with a separate array, will be required.
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