600V AC Inverters For Building Mounted Systems

[cyriousn]

We've run into a situation where we made the mistake of specifying 1500V DC equipment for a rooftop system on one of those metal storage building facilitates. Luckily the buildings aren't considered habitable so we don't need to have 4/6 foot perimeter pathways but I was wondering if anyone knew of a reliable inverter that would have a 600V AC output. We are currently looking at a Solar Edge unit that has a 480V output but I'd like to try and keep the project transformer secondary voltage the same since the utility has already studied the project.... Thanks all in advance for any help on this.

 

[ggunn]

We've run into a situation where we made the mistake of specifying 1500V DC equipment for a rooftop system on one of those metal storage building facilitates. Luckily the buildings aren't considered habitable so we don't need to have 4/6 foot perimeter pathways but I was wondering if anyone knew of a reliable inverter that would have a 600V AC output. We are currently looking at a Solar Edge unit that has a 480V output but I'd like to try and keep the project transformer secondary voltage the same since the utility has already studied the project.... Thanks all in advance for any help on this.

Whatever 1500VDC inverter you have specified should be capable of running at 1000VDC, shouldn't it? Can you redistribute the stringing to run at 1000VDC without busting the per MPPT input current limit?

 

[solarken]

Whatever 1500VDC inverter you have specified should be capable of running at 1000VDC, shouldn't it? Can you redistribute the stringing to run at 1000VDC without busting the per MPPT input current limit?

Not really, usually the min rated MPPT and startup voltage ranges are too high to run at 1000VDC.

 

[solarken]

We've run into a situation where we made the mistake of specifying 1500V DC equipment for a rooftop system on one of those metal storage building facilitates. Luckily the buildings aren't considered habitable so we don't need to have 4/6 foot perimeter pathways but I was wondering if anyone knew of a reliable inverter that would have a 600V AC output. We are currently looking at a Solar Edge unit that has a 480V output but I'd like to try and keep the project transformer secondary voltage the same since the utility has already studied the project.... Thanks all in advance for any help on this.

I have had success with 480VAC SMA Core 1 Tripower 62.5kW inverters on metal buildings. Somewhat flexible on string lengths and simplifies the rooftop wiring and only two conduits needed from the inverter, the AC output and the ethernet. They have built-in Sunspec PLC transmitter for Rapid Shutdown.

 

[ggunn]

Not really, usually the min rated MPPT and startup voltage ranges are too high to run at 1000VDC.

I haven't looked at the specs on the inverter he is considering because I don't know which one it is, but for most of the modern inverters I have experience with the operational voltage ranges are pretty wide. For example, for the SMA Core 1 62.5kW 1000VDC inverter the MPPT operating voltage range is 150V - 1000V, the MPP tracking range is 550V - 800V, and the minimum startup voltage is 188V.

 

[solarken]

I haven't looked at the specs on the inverter he is considering because I don't know which one it is, but for most of the modern inverters I have experience with the operational voltage ranges are pretty wide. For example, for the SMA Core 1 62.5kW 1000VDC inverter the MPPT operating voltage range is 150V - 1000V, the MPP tracking range is 550V - 800V, and the minimum startup voltage is 188V.

I see the wide range for 1000VDC inverters too, but usually when I look at 1500VDC inverters for use in 1000VDC applications I find the voltages are just too high. The SMA Highpeak3 MPPT range starts at 684V for the 125kW 480VAC model and 855V for the 150kW 600VAC model. The Chint CPS 100kW inverter MPPT starts at 870V. Also, the 1500VDC inverters generally do not have rapid shutdown features which I assume would be required on the storage building.

 

[cyriousn]

I see the wide range for 1000VDC inverters too, but usually when I look at 1500VDC inverters for use in 1000VDC applications I find the voltages are just too high. The SMA Highpeak3 MPPT range starts at 684V for the 125kW 480VAC model and 855V for the 150kW 600VAC model. The Chint CPS 100kW inverter MPPT starts at 870V. Also, the 1500VDC inverters generally do not have rapid shutdown features which I assume would be required on the storage building.

Yes the rapid shutdown requirement was something we were having a difficult time finding for a 1500V inverter.

 

[cyriousn]

I think we may be in a position of needing to submit a modification request to the utility either way since we are going from (4) 125kw Sungrow SG125's to (5) of the Solar Edge 100kw units. Less than ideal mistake that we made on this one...

 

[ggunn]

I see the wide range for 1000VDC inverters too, but usually when I look at 1500VDC inverters for use in 1000VDC applications I find the voltages are just too high. The SMA Highpeak3 MPPT range starts at 684V for the 125kW 480VAC model and 855V for the 150kW 600VAC model. The Chint CPS 100kW inverter MPPT starts at 870V. Also, the 1500VDC inverters generally do not have rapid shutdown features which I assume would be required on the storage building.

Yeah, the RSD requirement is probably the killer, but why would a 855V lower bound for MPPT tracking be a major issue? DCV doesn't vary much with insolation and temperature variation is usually just a few volts per module, so fitting into the 855V to 1000V (145V) window could be doable with an appropriate string length. It's academic now, of course.

 

[solarken]

Yeah, the RSD requirement is probably the killer, but why would a 855V lower bound for MPPT tracking be a major issue? DCV doesn't vary much with insolation and temperature variation is usually just a few volts per module, so fitting into the 855V to 1000V (145V) window could be doable with an appropriate string length. It's academic now, of course.

I know this is an old thread, but just wanted to add one more comment for those who find it during a search. I still believe nearly all 1500Vdc inverters are unsuitable for rooftop applications that limit DC to 1000V, even without regards to RSD. The reason is the MPPT operating voltage is not low enough or is just too narrow for 1000V applications. I disagree that 855V to 1000V is doable. When string lengths are sized for worst case using temperature corrected Voc at record low temps, the operating voltage of a string designed for 1000V is generally much lower than 855V. As an example, here is the operating voltage of three strings connected to three different SMA Core1 62.5kW inverters for a rooftop system limited to 1000Vdc max. The string length is 18 modules and was designed for 985V max at record low Voc. The operating string voltage is generally between 600V and 700V as shown. In addition, the modules are REC mono panels with a -0.28% Temp coefficient of Voc, which is lower than many modules out there. I think calculations will be similar for other modules and string lengths, in most areas of the country that have any significant seasonal temp variation.

 

[ggunn]

I know this is an old thread, but just wanted to add one more comment for those who find it during a search. I still believe nearly all 1500Vdc inverters are unsuitable for rooftop applications that limit DC to 1000V, even without regards to RSD.

But it's a moot point, isn't it? An inverter for a PV system should be selected by considering all the details of where it will be installed. Even if it could be made to work, a 1500VDC 600VAC inverter is a bad choice for a rooftop system in the US. Square peg, round hole.

 

[pv_n00b]

I ran this down a few years ago and in talking to several inverter engineers and standards engineers I found out that the MPPT tracking works over the whole DC operational range. When the inverter manufacturer selects the MPPT range to publish that window is selected to give a reasonable range while maximizing the inverter efficiency number for better marketing. Inverter efficiency only represents the efficiency in the MPPT operating window and efficiency above and below the MPPT window will be lower. Operate outside the MPPT window and MPPT still works but the inverter efficiency will be lower than the published number.
The numbers that ultimately matter are turn on voltage, minimum operating voltage, and maximum operating voltage. As long as you don't mind lower efficiency.

 

[solarken]

An inverter for a PV system should be selected by considering all the details of where it will be installed. Even if it could be made to work, a 1500VDC 600VAC inverter is a bad choice for a rooftop system in the US. Square peg, round hole.

I agree. The OP said they made a mistake in specifying the 1500V inverter, didn't intentionally specify the square peg for the round hole. I was just responding to the posted comments that suggested he should consider keeping the 1500V inverter and making it work at 1000V.

 

[solarken]

Operate outside the MPPT window and MPPT still works but the inverter efficiency will be lower than the published number.
The numbers that ultimately matter are turn on voltage, minimum operating voltage, and maximum operating voltage. As long as you don't mind lower efficiency.

Good point. Would need to look at efficiency curves to see how severe the efficiency drop is over the range.

 

[ggunn]

I agree. The OP said they made a mistake in specifying the 1500V inverter, didn't intentionally specify the square peg for the round hole. I was just responding to the posted comments that suggested he should consider keeping the 1500V inverter and making it work at 1000V.

I get that. It could be made to work, but it would not be optimum. At the very least it would require a transformer to interconnect to the service, with the attendant power losses and expense. I say return it and get the correct inverter for the job.