Different types of inverters mixed?

[Miguel Sousa]

Hello, SolarPanelTalk comunity.

For a grid-connected solar system, would it be possible to mix different types of inverters into the same photovoltaic system, more precisely string inverters with microinverters?

Since, for economic reasons, a string inverter is preferable on non-shading scenarios, I was wondering if in a string of 7 solar panels, with only one being partially shade from 4pm forward, if it would be posible to connect a string inverter to the 6 irradiated PVs, while leaving a microinverter on the other one, and then connect them in paralel.


Best regards, and thanks for any insights!

[ButchDeal]

Yes and no.
String inverters are not necisarily prferabke either, cheaper maybe.

few if any string inverters are going to operate with 6 pv modules on it.
You can do a solardge with otimizers for all 7 ( new optimizers have a minimum string length of 6)
or you could do all micros.

[TAZ427]

Technically what you would have would be two separate solar panel systems connected to the grid.

1.) Single panel w/ MicroInverter - Microinverter outputs AC directly
2.) Multi-panel DC String -> Inverter -> AC

They would only be 'connected in parallel' from an AC perspective.

I'd first ask my AHJ if it's permissible to do so. Also make sure you've got the breaker spaces to support this in your panel as each will require a separate breaker to disconnect them.

Personally, I'd doubt that the microinverter for the single panel is going to gain you a lot. I'd recommend using PVWatts and calculate what percentage would even be produced if it was un-shaded and multiply that to the percentage you think you can extract from it while shaded (and how long) is that 10% - 20% of the time and 20% of output -> 2-4% of that single panel in extra production?

I've got a similar situation, 24 panels with 4 panels of mostly west facing start get shading after 4:30pm in Summer, I used power optimizers. 2 Shutting off at ~4:30pm, and the other two somewhere around 5pm. For me that's about 1/6 of 20% sun production or 3.3% that I could possible get 10-20% of back if I had microinverters or 0.33 - 0.66% of total production lost. That said, I'm not a fan of microinverter reliability and when Power Optimizers w/ single inverter. If I really want that 3.3% back, I'll trim the top of the tree out that's causing the shading. I want to say that the microinverter efficiency is about 97.5% rated and my SolarEdge inverter is 99% efficient, there's some DC line loss as well, but I believe that should be below 1%, so this still leaves one asking if it's worth going microinverters or single inverter. Arguments can be made for both sides, but I'd personal make a choice of one or the other.

[Miguel Sousa]

Thanks for all the insights!

The question was really more for academic purposes and self-knowledge than to any installation (at least, for the time being).

Just to be sure, the use of optimizers benefits the system by denying any module mismatch, correct?

And about the AC connection, since the system is grid-connected, they should be in the same phase and frequency, so there should not be any problem, correct?

Again, thank you for all the insights!

[ButchDeal]

Thanks for all the insights!

The question was really more for academic purposes and self-knowledge than to any installation (at least, for the time being).

Just to be sure, the use of optimizers benefits the system by denying any module mismatch, correct?

And about the AC connection, since the system is grid-connected, they should be in the same phase and frequency, so there should not be any problem, correct?

Again, thank you for all the insights!

TAZ427 has simplified things a bit.

Technically you would need an AC combiner so that there is a single AC disconnect on your install. You can mix any number of different inverters from different manufacturers if you want but would have to be combined in an AC combiner. This of course would greatly complicate any monitoring.

EDIT: Not the combiner but the fact that there are multiple vendors monitoring solutions.

Micro inverters AND optimizers would prevent module miss-match as well as shadow differences from effecting the other modules.
All systems have their own limitations for design in the number that can be in a string (both minimum and maximum) as well as string voltages (min and max), string wattage limits (max). These different limits effect the design along with the local weather patterns and PV modules chosen to limit the configurations. Sometimes making many specific inverters impossible to configure a viable setup. Micros and optimizers are more flexible in this regard but micros also come up on another limitation where the inverter often can't handle all the power provided: called clipping, This is a design style and limits production when done well very little, when designed poorly more so.

[TAZ427]

Good point on the AC combiner - Hadn't thought of that since I'm a Single Inverter user personally and I'm still learning things.

[Miguel Sousa]

TAZ427 has simplified things a bit.

Technically you would need an AC combiner so that there is a single AC disconnect on your install. You can mix any number of different inverters from different manufacturers if you want but would have to be combined in an AC combiner. This of course would greatly complicate any monitoring.

EDIT: Not the combiner but the fact that there are multiple vendors monitoring solutions.

Micro inverters AND optimizers would prevent module miss-match as well as shadow differences from effecting the other modules.
All systems have their own limitations for design in the number that can be in a string (both minimum and maximum) as well as string voltages (min and max), string wattage limits (max). These different limits effect the design along with the local weather patterns and PV modules chosen to limit the configurations. Sometimes making many specific inverters impossible to configure a viable setup. Micros and optimizers are more flexible in this regard but micros also come up on another limitation where the inverter often can't handle all the power provided: called clipping, This is a design style and limits production when done well very little, when designed poorly more so.

I see. So, if I was also to have more than one string inverter, I would also need an AC combiner, correct?

And I realize now how important it is to consider optimizers, I didn't have any knowledge in that field before.
And speaking of which, maybe this is a dull question but, in cases of shading and with a DC optimizer/microinverter, if it is only partial shading on one group of cells., the current will pass through the bypass diode, decreasing production to around 66%. In case of 2 groups, 33%. But if full shading is applied, all the cells will produce energy, since they all suffer the same irradiation. Could this ever be higher than the 33%? Or since it's only diffuse, it's not nearly as much?

[TAZ427]

Yes for multiple string inverters you will need an AC combiner.

For both Microinverters and Power Optimizers if working correctly. No panel will impact another panels output period. If 1-6 are sunny and 7 is shaded - 1-6 are still producing at that sunny rate.

The Shaded one gets a bit better output with the Microinverter, while the PO will try to work a voltage level that will enable power output, but it will shut it down and bypass if needed.

That said, one needs to consider how much shading it gets, is it every day, what percentage of the power is impacted, is it worth going microinverter with a slightly lower efficiency than say the aggregated efficiency of PO and Inverter? To attempt play catchup on a small percentage of panels, for a small percentage of time? Or a mixed system, with some additional HW cost.

I'd go back and do some analysis. That said, you're limited to smaller panel output with a microinverter (or suffer clipping), you could go slightly larger panel output, use 6 of them and PO w/ String Inverter and be done with it. Or if they're never shaded, simply go straight string inverter and forget the cost of POs.

[Miguel Sousa]

Yes for multiple string inverters you will need an AC combiner.

For both Microinverters and Power Optimizers if working correctly. No panel will impact another panels output period. If 1-6 are sunny and 7 is shaded - 1-6 are still producing at that sunny rate.

The Shaded one gets a bit better output with the Microinverter, while the PO will try to work a voltage level that will enable power output, but it will shut it down and bypass if needed.

That said, one needs to consider how much shading it gets, is it every day, what percentage of the power is impacted, is it worth going microinverter with a slightly lower efficiency than say the aggregated efficiency of PO and Inverter? To attempt play catchup on a small percentage of panels, for a small percentage of time? Or a mixed system, with some additional HW cost.

I'd go back and do some analysis. That said, you're limited to smaller panel output with a microinverter (or suffer clipping), you could go slightly larger panel output, use 6 of them and PO w/ String Inverter and be done with it. Or if they're never shaded, simply go straight string inverter and forget the cost of POs.

Yes, I understood that! Maybe I asked the question wrongly: I meant to ask how the performance of the single panel is with the "evolution" of the shading.

I'm trying to study a case with a roof divided in 2 areas, but one of them has shadow from 2pm foward, and another one has shadow until 10am, so I'm considering to introduce solar panels only on the 2nd area, with optimizers / microinverters to help out the morning loads

[Mike90250]

Just remember - as you add inverters, and dump more power into the grid, the line resistance from your inverter to the PoCo transformer, will slightly raise your AC voltage, Some folks have had troubles with high AC line voltage shutting inverters down, because their wiring was inadequate.

[Miguel Sousa]

Just remember - as you add inverters, and dump more power into the grid, the line resistance from your inverter to the PoCo transformer, will slightly raise your AC voltage, Some folks have had troubles with high AC line voltage shutting inverters down, because their wiring was inadequate.

Wouldn't the AC combiner protect it from any overvoltage?

[ButchDeal]

The Shaded one gets a bit better output with the Microinverter, while the PO will try to work a voltage level that will enable power output, but it will shut it down and bypass if needed.

This is true of Tigo optimizers but not true for solaredge. For solaredge the optimizers have built in MPPT and buck/boost.

[TAZ427]

This is true of Tigo optimizers but not true for solaredge. For solaredge the optimizers have built in MPPT and buck/boost.

Yes, I was oversimplifying things. The reality is that all the PO's work together to try to maintain a string voltage level while maximizing the power, current must be the same through them all since they're in series of course (EE 101.) The reality is other PO's in the string will raise their voltage, and the highly shaded lower, not quite to zero, but a small voltage level (I see mine getting down to about 3.5V and the panels are outputing about 18W -> close to 5A current - with other panels jumping up to 50ish volt range - by end of day all of them are at 60V with the setting sun.)

[ButchDeal]

Yes, I was oversimplifying things. The reality is that all the PO's work together to try to maintain a string voltage level while maximizing the power, current must be the same through them all since they're in series of course (EE 101.) The reality is other PO's in the string will raise their voltage, and the highly shaded lower, not quite to zero, but a small voltage level (I see mine getting down to about 3.5V and the panels are outputing about 18W -> close to 5A current - with other panels jumping up to 50ish volt range - by end of day all of them are at 60V with the setting sun.)

not really; the SolarEdge each has its own MPPT and with buck boost they then separately manage the string voltage independent of the output of the PV module.

Also NOT all SolarEdge optimizers are limited to 60V. See the specs for the P405 and P505 for example which can boost to 85V, and thus their minimum string length is recommended to be 6 optimizers where the others is recommended to be 8 (in reality you only need 6 older optimizers to get to 360V or 4 of the P405/P505 )

Tigo does not have MPPT and can only buck the voltage down, thus your statements are true for it only.

SolarEdge will in almost ALL cases be more efficient and produce more power than micro inverters.

https://www.solaredge.com/sites/default/files/se-P5-series-add-on-power-optimizer-datasheet-na.pdf