FlexBoss with parallel Hyperion panels, is it going to smoke?

[BcatV]

I'm building a system with the FlexBoss and 50 400w Hyperion panels. I selected the panels because they were cheap per watt and the array design should get the most out of the FlexBoss, if it doesn't smoke. The EG4 string sizer passes my planned array design, but with an MPPT Imp warning, as in third attachment. I discussed this question with SS when I purchased, and they were comfortable that it should be okay. Yesterday, getting closer to connecting the strings, I spoke with one of SS's tech support folks, had them look again at the panel sheets and plan to parallel, still comfortable.

So, my question for the assembled experience: What do you think? Reading about systems producing current spikes when cloud-edge effects deliver irradiance spikes has me concerned, but I have no experience, only scientific background and engineering caution.

If I don't parallel the strings, the best I can do is 38 panels, which won't get everything out of the FB, but will be safely away from any limits, as in second attachment. Hyperion panel spec in first attachment.

I like experiments, and I like getting full performance from a system, but it's a $4K inverter, so, seeking advice. If it were your money, would you turn it on?

Thanks

 

[rogerheflin]

Over paneling / excessive amps is unlikely to burn an inverter. The inverter will typically only draw the amount of current it needs.

I don't know about the flex but for the 18kpv it lists this:
MAX. USABLE INPUT CURRENT 25A (MPPT 1) | 15A (MPPT 2) | 15A (MPPT 3)
MAX. SHORT CIRCUIT INPUT CURRENT 31A (MPPT 1) | 19A (MPPT 2) | 19A (MPPT 3)

Given the flex has 26A/26A usable on the first 2, I would expect the Max Short circuit to be higher than the 18kpv and higher than what you are showing. check the manual.

 

[zanydroid]

Isc spec and prescriptive NEC conductor sizing is supposed to factor in weather spiking

Imp flags the potential for clipping

If you are super worried you can consider adding a separate SCC (though note this will require extra code homework for you since SCC aren’t really as product optimized for passing residential code requirements)

 

[timselectric]

Voltage is pushed, so that's a hard limit that should never be exceeded.
Amperage must be drawn. So, you can make as much as you want available. But the solar charge controller will only take what it can utilize.

 

[zanydroid]

13.8 A panel Isc is very common. Maybe a bit on the high side. If you get matching generation of SCC/hybrid you are fine. FB21 should be the same generation.

OP didn’t share screenshot of MPPT Isc spec and I don’t remember what it is for this.

I don’t think going over published Isc limit of the MPPT is a good idea. I’m speaking of fault conditions

 

[timselectric]

I don’t think going over published Isc limit of the MPPT is a good idea. I’m speaking of fault conditions

It would have to be an internal (SCC) fault.

 

[zanydroid]

There is also finger pointing during warranty issue

 

[sumpower]

There is also finger pointing during warranty issue

I wouldn't purchase a charge controller or all in one unless they had published specifications on max wattage array per charge controller.

 

[BcatV]

Attached is the FB manual page describing the PV input specs/limits. The warning in the string-sizer is for Imp over 26a, so if the inverter will only draw/allow the current that it needs, then having Imp 27a or more seems okay, and indeed the line in the manual "The array can have a higher Imp than the 26A/15A specified, but the MPPTs will not make full use of the extra current. Having an array that can produce more current than the MPPTs can utilize is useful for increasing morning, winter, or cloudy day solar production." is reassuring that it does behave that way. Isc doesn't produce a warning, and under normal conditions the panel spec doesn't go over 15a. But, with a lot of bifacial gain, the panels can go over 15a Isc. They won't have a lot of bifacial exposure as mounted, but will have some. So I guess I'm really trying to understand what exactly Isc means from the inverters point of view. If the inverter can always limit the current being sent through the electronics, then I don't see how it could ever be a problem, but it is clearly noted as a limitation, so, there must be circumstances where the current can go higher than the inverter electronics can handle. What are those circumstances?

 

[timselectric]

So I guess I'm really trying to understand what exactly Isc means from the inverters point of view.

It's the amount of current that it can protect itself from, in the case of reverse polarity. (Accidentally connecting + & - backwards)

 

[zanydroid]

If you supply a 100V stack of LFP batteries into a SCC , the “Isc” is at least 100-200A, and could be 10x higher before the breaker or BMS disconnects. Ain’t no way the SCC was engineered to eat that if a fault occurs

 

[BcatV]

Thanks Tim. Still, for a system with no hookup faults and no failures, with string voltage within MPPT limits, how does the potential current from the string cause damage to the inverter? If the panels got a real boost of bifacial energy (or presumably way over STC irradiance from cloud lensing) and pumped out 470 watts, the operating current would still only be 15a, but Isc would be 16a. How would that situation damage the inverter?

 

[BcatV]

So is the potential problem from Isc over the MPPT Isc limit only going to become an actual problem if a fault occurs somewhere? The language in the manual "An Isc higher than 31A/19A will cause damage to the inverter." made me think that if the panels reached a state, due to high irradiance, that would have an Isc > 15.5a, that the inverter would be damaged. Not true?

 

[zanydroid]

There’s some posts on this forum about how some SCCs present a very low impedance during some operations.

I didn’t ask someone to walk through the circuitry. I don’t think this forum is super sophisticated, beyond “reverse polarity protection” and “I done heard Victron clubs in a near dead short”. May need to ask an EE or power engineering forum.

Also, IMO one could maybe argue that maybe bifacial spikes are not that high probability of a problem, given that prescriptive NEC code doesn’t force you to make specific adjustments

 

[BcatV]

While I wouldn't want to assume that the FB and Victron MPPTs are reliably similar, some Victron guys gave a clear explanation of the current limitation due to the reverse-polarity protection circuit limits, and assert that for Victron, overcurrent capability should almost never be a problem if not hooked up in reverse polarity while also delivering overmax Isc. I think I can avoid that. I'm going to hook it up and see what happens.

Oversizing a PV Array (within max Voc and Isc) can do any damage to MPPT ? - VictronEnergy

communityarchive.victronenergy.com

 

[Brucey]

While I wouldn't want to assume that the FB and Victron MPPTs are reliably similar, some Victron guys gave a clear explanation of the current limitation due to the reverse-polarity protection circuit limits, and assert that for Victron, overcurrent capability should almost never be a problem if not hooked up in reverse polarity while also delivering overmax Isc. I think I can avoid that. I'm going to hook it up and see what happens.

Oversizing a PV Array (within max Voc and Isc) can do any damage to MPPT ? - VictronEnergy

communityarchive.victronenergy.com

For what its worth I have forty panels on a Victron 450/100 (heavy overpanelling). Two strings of ten in parallel to each tracker. Ten aptos 370W and 30 vikram 375s all bifacials. So around 15kW of panels on a 5600W scc. The current limit is 18A but that's the limit of the reverse polarity protection. But that's Victrons premier controller, I wouldn't necessarily expect the same from an eg4 device, but the 18kpv seems relatively competent despite firmware bugs.

 

[EatonPV]

I'm not sure what you are using for racking but for my case the mounts were more expensive than the panels. I was looking at the Solar Space 535w and you can use 8 fewer panels and get around 1500 more Watts out of the system! Plus no warnings on the calculator.

 

[timselectric]

Thanks Tim. Still, for a system with no hookup faults and no failures, with string voltage within MPPT limits, how does the potential current from the string cause damage to the inverter? If the panels got a real boost of bifacial energy (or presumably way over STC irradiance from cloud lensing) and pumped out 470 watts, the operating current would still only be 15a, but Isc would be 16a. How would that situation damage the inverter?

The panels are just a current source. Current isn't pushed, it must be drawn.

Just like a receptacle in your house. If it's on a 15a circuit, you can plug in devices that pull up to 15a.
It doesn't matter if you plug in a microwave or a cell phone charger. They will only draw the amount of current that they can use.

 

[zanydroid]

Just like a receptacle in your house. If it's on a 15a circuit, you can plug in devices that pull up to 15a.
It doesn't matter if you plug in a microwave or a cell phone charger. They will only draw the amount of current that they can use.

With respect this is a bad example to put out online because it indirectly perpetuates the notion that NEC doesn’t care about the max OCPD (and therefore limit to fault current) you put upstream of an appliance. Unless otherwise marked a 15A appliance is either limited to 20A or 25A by the set of rules on this in NEC

 

[timselectric]

With respect this is a bad example to put out online because it indirectly perpetuates the notion that NEC doesn’t care about the max OCPD (and therefore limit to fault current) you put upstream of an appliance. Unless otherwise marked a 15A appliance is either limited to 20A or 25A by the set of rules on this in NEC

OCP is for the conductors. Not the plug in appliances connected to them.
NEC doesn't apply to appliances. That falls under UL listing.

 

[Quattrohead]

Yes weirdly the USA regulations protect the wires, the rest of the world protects the appliance.

 

[timselectric]

Yes weirdly the USA regulations protect the wires, the rest of the world protects the appliance.

I do like how other countries have fuses in the male cord ends.
I wish we had that. It would avoid a lot of house fires.

 

[BcatV]

Eaton, that panel is a good fit for the FB, if it had been on sale when I was buying might have been the choice. The Hypes were/are 22c/w vs 25c/w for the Luminas, and the power/area is the same, so for the area I have I don't think I could have fit any more power, I worked the drafting tools/permitting rules pretty hard to fit what I have
I'm using Unirac Solarmount for racking, and my racking costs are only about 1/3 of my panel costs, after finding a good sale. Of course, I'm not expecting Montana snow loads...

 

[BcatV]

Tim, you/Zany/others have convinced me that the language in the FB manual is broader than the problem its covering, probably in simple CYA/don't encourage the ignorant to do stupid things mode, which is fine. I'll try to not hook anything up in reverse polarity and trust that the electronics won't allow more current to flow than they can handle. And if there are transient behaviors (when a big load drops off, or others) that expose the electronics to fatal overcurrent, then we'll know the design should have been a little better...

By the way, that thought about fuses at the receptacle end seems very logical, are there plug-in pass-throughs that incorporate the fusing?

 

[timselectric]

I'll try to not hook anything up in reverse polarity

Always test before connecting.

and trust that the electronics won't allow more current to flow than they can handle.

Since the MPPT is in charge of the current. It will only draw what it can use.
Things like cloud edging only make more available at the panels. It doesn't change what the MPPT can draw.