16.32KW System Requires 2 Inverters?

[wwhitney]

OK, I'm no PVWatts expert (I don't know if there is a way to enter two different arrays simultaneously), but with those panel orientations, clipping appears to be a non-issue for you. I just looked at the two orientations separately, and compared the program results with DC/AC of 1.0 to DC/AC of 1.5, leaving everything else at default. No difference at all.

[If there had been a difference, treating the two orientations separately would have been a definite underestimate, because it ignores that one orientation might be using less than its proportional share of inverter capacity, allowing the other orientation to use more that its proportional share and avoid clipping.]

Basically, your panel orientations are so far from optimal, your panels are never going to produce close enough to their nameplate values that you'll have any significant clipping at all. Go ahead with 15.5 kW DC and a 10 kW inverter. [With a more sophisticated analysis, you could probably justify going to 16+ kW, based on your panel orientations, but I don't have the ability to do that analysis easily.]

Cheers, Wayne

 

[VslavZman]

Thanks Wayne. That's really very helpful... I'll play around in PVWatts, but that's exactly what I anticipated. One last question for everyone - is there a panel separation limit by which they would have to recommend a second inverter? As you can see in the proposed layout, I have 3 banks of panels. Will it be an issue to connect all 3 banks to one inverter just based on how far apart they are?

 

[TORQU3]

I have a MA National Grid net metering cap exemption question. I'm in the process of getting a solar/power wall system with Tesla. Current design is 39 panels, 10kw inverter, and 4 power walls.

I specifically discussed with the project manager about the 10kw net metering cap and wanting to stay under it to get the full retail rate for over production. I have the 10kW inverter specified in the system and 13.26kW of panels. The panels will be on a 30 degree roof pointing just south of east at about 110 degrees or so. I've run the numbers in PV watts and I'll lose very little to clipping. It seems worth it to stay under the cap, since I'd be just over.

They just started to apply for permits today and I got a bunch of notifications to sign paperwork online. I saw on a few documents for SMART and the interconnection stuff for National Grid that they show the AC capacity of my system at 12.157 kW, which obviously puts me over the net metering exemption cap. I've emailed to see what's going on, if it's a mistake or something else going on. Even in that paperwork it has the 10kW solar edge inverter specified. I didn't sign the national grid items until this is clarified. There was one discussing selling at the p-rate tariff.

I can't figure why the AC capacity would be listed as higher than the inverter rated output. Anything I'm missing?

 

[DrSmile]

I can tell you that my Solaredge 11.4 KW inverter has never exceeded its rated output. It maxes out at about 11.3.

 

[h2ofun]

I can tell you that my Solaredge 11.4 KW inverter has never exceeded its rated output. It maxes out at about 11.3.

Yep, that is what I have seen

 

[TORQU3]

I'm hoping to hear from Tesla today about this. It seems like a big disadvantage to be slightly over the net metering cap exemption, especially if it's because of a paperwork error. I want to be sure to get full retail (well very close) during potential overproduction in the summer months.

 

[wjgjr]

I'm hoping to hear from Tesla today about this. It seems like a big disadvantage to be slightly over the net metering cap exemption, especially if it's because of a paperwork error. I want to be sure to get full retail (well very close) during potential overproduction in the summer months.

Is it possible Tesla just took your DC number and multiplied it by some efficiency factor to get the AC number, forgetting that it would also be limited by the inverter? I also don't know what the rules are for whether the system size must be based on the installed capacity of the panels even when the inverter would limit it to a lower maximum.

 

[TORQU3]

Is it possible Tesla just took your DC number and multiplied it by some efficiency factor to get the AC number, forgetting that it would also be limited by the inverter? I also don't know what the rules are for whether the system size must be based on the installed capacity of the panels even when the inverter would limit it to a lower maximum.

It's certainly possible that's the error, I had the same thought. I wasn't sure if there was some obscure National Grid rule that I couldn't find on AC output calculation. I assumed it was determined by the limiting factor of the system, weather that be the DC size * efficiency, or the maximum inverter output when have a DC/AC ratio greater than 1.

 

[TORQU3]

Still nothing from Tesla. I spoke with the MA ACA Contact & Support - MassACA which does a lot of things related to net metering regulation in Mass. It looks like my understanding that it's only the nameplate AC nominal output capacity of the inverter that matters and the SE10000H-US definitely would qualify me for the net metering cap exemption. The 1.3:1 DC oversize isn't considered and he confirmed that it's a typical oversize amount, also that the battery storage isn't considered in the AC output capacity since it's an AC coupled storage system and only charged from solar. MA ACA guy said that I shouldn't be needing to sign any qualified facility paperwork either, since I would be under net metering, not QF rules and rates.

I emailed my project manager at Tesla, just waiting for a follow up and correction.

 

[adspguy]

Still nothing from Tesla. I spoke with the MA ACA Contact & Support - MassACA which does a lot of things related to net metering regulation in Mass. It looks like my understanding that it's only the nameplate AC nominal output capacity of the inverter that matters and the SE10000H-US definitely would qualify me for the net metering cap exemption. The 1.3:1 DC oversize isn't considered and he confirmed that it's a typical oversize amount, also that the battery storage isn't considered in the AC output capacity since it's an AC coupled storage system and only charged from solar. MA ACA guy said that I shouldn't be needing to sign any qualified facility paperwork either, since I would be under net metering, not QF rules and rates.

I emailed my project manager at Tesla, just waiting for a follow up and correction.

I’m in MA as well. I have a 36 panel 12.24kW 3 pw system with a se10000 inverter. My eversource paperwork has me qualified for regular net metering cap exemption. At the moment I am still awaiting PTO but Eversource put in the net metering meter and the solar production meter for SMART. Although you have a couple more panels, you have the same inverter and it’s ac output is all that matters. My paperwork for eversource lists both the dc and ac values and uses the 10kW dc number as the power output limit for net metering. With an se10000 inverter they should be listing your power as 10kW.

 

[TORQU3]

I heard back from Tesla, they reviewed the paperwork verified that 10kW AC was in the spots it needed to be and I would be under the net metering cap. The 12.157 AC noted elsewhere needed to be based on the DC size for whatever reason.

The next thing I'm chasing down is sales tax. PV installs are sales tax exempt in MA, but I have sales tax applied to the power wall part of the system. It's not trivial, $1750 on 4 power walls. The Federal ITC incentive considers energy storage part of the PV system and eligible if it can only charge from PV output. I called the Massachusetts Department of Revenue to see if they follow the same approach. The woman I spoke with on the phone said she is fairly certain that the energy storage would be sales tax exempt but needed to verify. I'm waiting to hear back.

For refence, I found this about PV and energy storage sales tax in Massachusetts. While it looks to be for a grid scale project, I don't see why it would be any different for residential. Letter Ruling 18-3: Energy Storage System used at Photovoltaic Electricity Generation Facility

 

[adspguy]

I paid 1125 ma tax on 3 powerwalls. Please keep me posted on your progress on this.

 

[TORQU3]

I paid 1125 ma tax on 3 powerwalls. Please keep me posted on your progress on this.

I'll post again when I hear. They haven't called me back. I'll try the MA DOR again tomorrow if I have a few minutes.

 

[TORQU3]

Update, I heard back from Mass Department of Revenue. The power walls, when paired with a PV system are sales tax exempt in Mass.

The next step will be getting Tesla to realize this and not charge me (or others) sales tax. I will likely need to get a document from the rules and regs department of the DOR.

If you have paid the sales tax already, log into MA Tax Connect and file a dispute.

 

[TORQU3]

Another update. I let my solar project coordinator/manager know what the MA DOR said about the power walls being sales tax exempt. She prepared a MA sales tax exempt form for me to e-sign and removed all sales tax from the invoice. I'm not sure if this will be stand practice or just due to my request. It essentially shifts liability from Tesla to me, which is ok. I confirmed with the department of revenue that it's correct.

 

[adspguy]

That’s great news. Time to file some paperwork! Thanks @TORQU3

 

[TORQU3]

That’s great news. Time to file some paperwork! Thanks @TORQU3

Let us know how you make out with the disputed sales tax.

When I get a response from the DOR Rules and Reg's team, which should be an official statement I can post it here for others to reference if needed.

 

[adspguy]

Let us know how you make out with the disputed sales tax.

When I get a response from the DOR Rules and Reg's team, which should be an official statement I can post it here for others to reference if needed.

Will do on keeping folks posted. Also, I did get a Xmas present and got PTO on xmas eve. Contacting the eversource rep listed on the massaca website got me turned on a couple days after.

 

[TORQU3]

Excellent! I'm not sure when mine will be installed yet. I'm having the 20 year old roofing shingles replaced on that section of roof tomorrow in preparation. They are in great shape but I don't want to have issues 5 years down the road.

Permits have been issued for the solar and PW's. I figure sometime in the next 30-60 days it should be installed, but who knows. I still need to get a corner of my basement cleared out for the equipment.