Energy Optimizer for Roof with two directions

[dmkjr]

Looking for assistance in understanding if a power optimizer is needed or warranted here.

I have an EG4 6500ex (two MPPT inputs). I have one string running at 5kw (300v / 16a). I have another string I'm looking to install but can only install 15 panels on the southwest facing side of my house. I have the ability to install 4-8 panels on the other side of the peak to capture some of the morning sun. However, because I do not have another MPPT input available, I would like to use the 15 panel string but am worried about the shading on those 4-8 (probably will be 5) panels since the sun will set on the other side of the peak.

Would a power optimizer help on those panels? In a little research it looks like it will optimize the string to assist those panels that may be shaded?

Thanks!

 

[400bird]

What is the VOC in those panels? Many are around 40 volts, which at 15 panels is 600 volts.
You're talking a out running 21 in series to the second MPPT? Your going to blow it up.

 

[dmkjr]

What is the VOC in those panels? Many are around 40 volts, which at 15 panels is 600 volts.
You're talking a out running 21 in series to the second MPPT? Your going to blow it up.

Maybe I did not explain it correctly.

2S2P.... so about 300v per "side" and paralleled before the MPPT. I have this setup now.

But I still want to understand the power optimizers and if they will help here.

 

[400bird]

Ok, so two parallel strings per MPPT. I don't think they are 2s (2 panels in series)

Optimizers would help your set up sure. You'd probably be better off installing a complete string on each side of the ridge. I can't find the documentation, but Tigo has reported their optimizers can only account for a 25% production difference between panels.

 

[Hedges]

Up to 15 panels on one face, up to 8 on the other.

How about three strings of 7 panels. If you had two MPPT then 7s2p into one and 7s into the other.

If only one MPPT, 7s3p. OK that one string is oriented different. Some shade when off-angle won't cause harm (avoid shade with other panels that are in series getting full sun, overloads bypass diodes.)

When string are paralleled, a small percentage of one shaded doesn't cause significant loss, but large percentage shaded would.

I'm disinclined to use optimizers but have no experience with them.

You may be required to have RSD, in which case optimizers may be small additional cost. I've bought RSD for a future install.

If an optimizer is a buck converter then I think optimizer on panels of unshaded string would be needed to better match to voltage of partially shaded string. On the other hand, boost converter on panels of shaded string would also match voltages.

 

[zanydroid]

Tigo is a buck optimizer.

Tigo has pictures in a technical document showing how many you need for different kinds of string matching.

 

[dmkjr]

I think I would rather just get an EG4 MPPT Charge Controller to be able to add another string to the mix so I don't need to mix the two.

 

[Solar Guppy]

Honestly, putting panels in known shade is a very expensive way to add marginal net harvest increases ( even with optimizers ), looking at your loads / efficiency improvements could be a better way to address things?

 

[dmkjr]

Honestly, putting panels in known shade is a very expensive way to add marginal net harvest increases ( even with optimizers ), looking at your loads / efficiency improvements could be a better way to address things?

Not putting panels in known shade. Just putting panels on a different orientation so will be "shaded" at a different time of the day. But the panels aren't shaded by any object.

 

[zanydroid]

Extra SCC seems to make sense here. The ratio difference was too big for TIGOs and anyway would have required at least 8 for their partial matching capability, and the SCC is easier to install than reconfiguring the existing string.

 

[dmkjr]

After talking to Signature Solar, I changed my order and added another 6500ex. The SCC wouldn’t be able to communicate with the inverter and would be fighting the output of both on a charge. They believed it would lower the effective output of the SCC. The EG4 SCC is intended for those without an EG4 inverter or non lithium batteries.

 

[zanydroid]

Hmm, but people parallel SCCs all the time. That advice is not consistent with the forum consensus.

 

[Hedges]

If a BMS tells inverter/charger to reduce current allowing time for balance, an open-loop SCC would defeat that.

For lead-acid batteries, it could be useful for inverter and SCC to agree on charge phase Absorb, Float, Equalize. Some systems offer that.

Extra inverter for additional MPPT gives more AC power or is available as a spare. But how much no-load power loss? Or can it operate as SCC while inverter function is off or in a sleep mode?

 

[zanydroid]

If a BMS tells inverter/charger to reduce current allowing time for balance, an open-loop SCC would defeat that.

Yeah, this makes sense. But you could go open loop and then manually configure both sides to match.

Agree on the other points. Doesn’t the extra inverter decrease reliability from the extra complexity of stacking? Both from firmware going bonkers or the stacking setup (software and wiring) being botched up. I guess you can also botch an SCC but there are a couple fewer wires involved

 

[Hedges]

Reliability would depend on how they fail. Software of course can do anything.
For my Sunny Island, at least for 3-phase, I can tell them if I want them to keep running or shut off for lost phase.
There is a relay in grid connection, but AC output I think is transformer connected to H-bridge. Shorted FETs there would fight any paralleled inverters. HF design could similarly fail open or fail shorted. Breakers able to carry full power couldn't be cleared by an inverter - maybe 5 or 6 in parallel would clear one.

I think Midnight is doing something with hot swappable bank of inverters. Would hope they considered failure modes to ensure system stays up.

DC systems, including SCC, could generally get paralleled. And in case of a short, battery provides current to clear OCP. Or burn up a higher impedance fault. Just avoid polarized breakers.

A nice thing with my Sunny Island Charger is it has lead-acid voltage settings if no one is talking to it, gets voltage (although not current) levels from Sunny Island when connected, so cooperates with phases of charging. Midnight Classic with interface does the same. Both Midnight and Victron have communication/regulation of chargers. Lead-acid you want a particular current. Lithium can generally take whatever you have to give, except when colder (don't think amps vs. temperature is a function of the equipment we see available.)

 

[dmkjr]

I have use for the second inverter. Today, I just have 120v loads. Originally I thought "this is all I will ever do" and then I bought another 8kw in panels. I don't have enough MPPT inputs to put the strings in one 6500ex, so I needed more. SCC was the cheaper way to go, but I want to be able to visually see how much PV I'm generating as well as ensure I'm putting as much to the batteries as possible. Voltage and not SOC just doesn't seem like the best way. Another inverter gives me 240v.

Curious though, what does a third, fourth, etc. inverter give you? More capacity on each leg?

 

[zanydroid]

I have use for the second inverter. Today, I just have 120v loads. Originally I thought "this is all I will ever do" and then I bought another 8kw in panels. I don't have enough MPPT inputs to put the strings in one 6500ex, so I needed more. SCC was the cheaper way to go, but I want to be able to visually see how much PV I'm generating as well as ensure I'm putting as much to the batteries as possible. Voltage and not SOC just doesn't seem like the best way. Another inverter gives me 240v.

Curious though, what does a third, fourth, etc. inverter give you? More capacity on each leg?

Yes more capacity. But at the penalty of idle consumption.

 

[dmkjr]

Yes more capacity. But at the penalty of idle consumption.

Adding 8kw in panels. It was needed anyway. Haven’t played with any energy savings or standby modes. Not even sure if they are available on those inverters.

 

[zanydroid]

Adding 8kw in panels. It was needed anyway. Haven’t played with any energy savings or standby modes. Not even sure if they are available on those inverters.

I think with these high idle power inverters you just have to add more batteries to make it through winter nights. Lame.

 

[dmkjr]

I think with these high idle power inverters you just have to add more batteries to make it through winter nights. Lame.

I have a lot of battery capacity. But when you say “high idle”, what is that number exactly? I haven’t experienced anything that appears to be abnormal.

I have lower self consumption on my Victron unit in my RV. But the RV runs refrigerators and that’s it when I’m not there.

My home runs on battery most of the night. We aren’t “off grid”, we still take power from the grid. But also runs servers from my house for business use. I’m not trying to get completely off grid, even if that ends up being the end result.