New 20kw Solar Install - just interconnected - Did we get screwed?

[LCF]

Good morning forum!

We have a farm in Rhode Island and just spent the last year and a half planning a 20kw solar panel install on our property. The system is set up on 2 rooftops and uses Panasonic panels with SolarEdge inverters and optimizers.

As we are a farm we took advantage of 3 separate grant opportunities which helped offset the cost of our system. We just got interconnected 2 days ago and were starting to fill out our grant reimbursement paperwork when we noticed a problem.

I was looking in our SolarEdge app and saw energy flat lining at 15kw. The system is designed as 19,175 watts (DC)/23,815 kwH annually, and the solar company we used guaranteed in our contract we would produce at least 17.8 KWH annually in our first year. I was concerned seeing it being limited at 15kw, so I emailed the installer and got a pretty swift response saying we are capped at 15kw.

After some research I am starting to believe that we are capped at 15kw due to being single phase? Am I correct? If this is the case, why did they sell us a 20kw system? Additionally, as a condition of our grants we need to show that the system can generate the 20kw we got approved for. If these conditions are not met then our grants will not be paid. I am very nervous about this and looking for some advice.

Thanks in advance for any help you can give. I look forward to being here on this forum going forward as we grow and expand our solar system.

[bcroe]

It sounds like your inverters have a 15KW AC output capability, which will set your
maximum possible energy to the grid. Its not uncommon to have DC/AC ratios
on the order of 18KW/15KW, depending on your situation. Though you are apparently
clipping at 15KW, the available power might be only slightly higher, and for a short
time each day. Bruce Roe

[LCF]

Thanks for the response Bruce. Why would a company install a 20kw system if there was a limit of 15kw with the inverters? Its not making much sense to us.

[peakbagger]

Solar panels are rated at specific set of conditions that are rarely met in the field. They are illuminated with a standardized light source at specific brightness at an angle perpendicular to the surface of the panel. Unless you have tracking solar panels the vast majority of time the sun is not perpendicular to the panels so the 20KW rated array is only capable of putting out less power. Even though the sun is at an angle and the sun may not be as bright as the standard light source a 20kw array is going to generate more power than 15kw array as it has more surface area to collect what there is of the sun. The trick is to optimize the amount of panels to maximize year round power production (KWH) by going oversized on the number of panels while balancing the costs taking into account that most incentive programs are based on total KW capacity installed (not yearly KWH). Since the panels rarely put out the rated output, installers undersize the inverter to save a few bucks, realizing the during some times of the year the inverter will waste (clip) the input KW to keep the inverter at or below the rated output.

I personally am not a fan of undersizing inverters as I would rather slightly oversize them so they are not running at 100% for extended periods. I have an "ancient" grid tied inverter that is oversized and installed in a cool area and it just keeps on running despite many of its contemporary units that were undersized long since relegated to the junkyard.

[LCF]

PeakBagger. So to understand what you are saying, they put more panels on in order to get more coverage. Our goal was to be 100% solar powered. Since this system was designed a year and a half ago we have built another commercial building on the farm and our energy usage is much higher now. When they sold us the system they said that the panels would produce more than our previous energy consumption so the new building usage would likely be offset. If they installed inverters that are capping the output to 15kw, then what does that mean for our ability to actually offset all of our electrical usage? Our contract with the installer says they garauntee that in the first year we will produce a minimum of 17.8KWH. How is this possible with inverters capped at 15?

[J.P.M.]

1.) Did the response from the installer say why the output is "capped" at 15 kW ?

2.) Further to Bruce's comment, what is/are the inverter sizes ? Sounds like you may very possibly have 15 kW of inverter capacity. Still, depending on max. possible array output at your location and at your orientation, that 15 kW may not be all that undersized compared to max. likely array output. That is, max. actual system output may well be close to 15 kW, with max. system output to the inverter(S) only happening a few times/yr. and only for a few minutes or less per occurrence.

3.) In addition sharing most of Peakbagger's opinions about inverter sizing, I'd comment further to his post with respect to STC rated system sizes and max. output. Depending on array orientation(s), 15kW power output/19.175 STC kW system size doesn't sound all that far out of line, particularly with what sounds (reads) like a partially malfunctioning system. BTW, how many panels, and what's the STC wattage rating on each panel ?

4.) Did/have you modeled the system with PVWatts to verify the vendor's numbers ?

Before I went further, I'd make sure I understood the in/outs of the monitoring system, and while the vendor is fixing the failed equipment, have the monitoring system checked as well and any questions about monitoring system operation you may have addressed at that time.

If you haven't done so already, buy/download a copy of "Solar Power Your Home for Dummies". You need information about the basics and that's a decent primer.

Sounds (reads) to me like your situation is pretty typical of many/most folks who get PV systems but didn't/don't understand the basics of PV with respect to system potentials and limitations. If you got screwed, that might be where some of some of it got enabled.

Welcome to the neighborhood and the forum of few(er) illusions.

[LCF]

Thanks for the response, JPM. I'll try to take each point in order:

1 - The installer did not provide an explanation as to why output was capped. After a bit of digging in the past 24 hours I think it may be a limitation put on the system by the utility for connections to properties within single-phase power (and, because of that limitation, the inverter was sized accordingly). This is still unconfirmed.

2- The contract had two inverters: SolarEdge SE 10000H and Solar Edge SE 5000H. At 240V I believe that's a nominal AC output of 10,000 and 5,000, respectively. However, we noticed the cap almost immediately after the system was turned on (just two days ago). We hit it pretty early in the morning and stayed pushing up against it for most of the day. We're hitting it now, even with overcast skies. That gives us the impression that the max actual system output is well in excess of the inverter capacity.

3- The panels were placed on south-facing roofs with no shade. It's 59 panels (model number: VBHN3256SA17 - rated wattage of 325 watts).

4- We did not model the system with PVWatts to verify their numbers originally, but just ran it all now and it matches the installers numbers pretty closely.

I think what it comes down to is that we aren't overly concerned about the cap if it still means we're offsetting 100% of our electricity usage (and we're not straining the inverters). But if the inverter size (and, possibly, lack of 3-phase power) is limiting the system then we'd like to know if that's going to prevent us from hitting the 23,815 kwH annually (or, optimistically, more) that we were supposed to be able to offset. If it means we need to bring 3-phase power and have the inverters replaced we'd like to know, as it's seeming to us like the lack of 3-phase power is what drove the inverter size, not the number of panels or annual offset targets. Does that sound accurate?

If that's the case, it seems like something we'll have to resolve with the installer, as we think it should have been communicated to us. If, because of the inverter size, we're producing the same amount of power that we would be producing with fewer panels, then we were sold more panels than we feasibly could have used.

I just got the public link so you can see the system. The smaller building on the right is the one with the broken panel and it looks like the panels are producing less than the building on the left. Is this normal? https://monitoringpublic.solaredge.c...LCF#/dashboard

[J.P.M.]

Thanks for the response, JPM. I'll try to take each point in order:

1 - The installer did not provide an explanation as to why output was capped. After a bit of digging in the past 24 hours I think it may be a limitation put on the system by the utility for connections to properties within single-phase power (and, because of that limitation, the inverter was sized accordingly). This is still unconfirmed.

2- The contract had two inverters: SolarEdge SE 10000H and Solar Edge SE 5000H. At 240V I believe that's a nominal AC output of 10,000 and 5,000, respectively. However, we noticed the cap almost immediately after the system was turned on (just two days ago). We hit it pretty early in the morning and stayed pushing up against it for most of the day. We're hitting it now, even with overcast skies. That gives us the impression that the max actual system output is well in excess of the inverter capacity.

3- The panels were placed on south-facing roofs with no shade. It's 59 panels (model number: VBHN3256SA17 - rated wattage of 325 watts).

4- We did not model the system with PVWatts to verify their numbers.

I think what it comes down to is that we aren't overly concerned about the cap if it still means we're offsetting 100% of our electricity usage (and we're not straining the inverters). But if the inverter size (and, possibly, lack of 3-phase power) is limiting the system then we'd like to know if that's going to prevent us from hitting the 23,815 kwH annually (or, optimistically, more) that we were supposed to be able to offset. If it means we need to bring 3-phase power and have the inverters replaced we'd like to know, as it's seeming to us like the lack of 3-phase power is what drove the inverter size, not the number of panels or annual offset targets. Does that sound accurate?

If that's the case, it seems like something we'll have to resolve with the installer, as we think it should have been communicated to us. If, because of the inverter size, we're producing the same amount of power that we would be producing with fewer panels, then we were sold more panels than we feasibly could have used.

Thank you for the timely and informative response. More later.

BTW: What's the array orientation(s), i.e., tilt and azimuth ? Also, what's your zip ? After you read the book, download and run PVWatts after reading all the help/info screens a couple of times. That'll give you a fair dart throw of likely annual output +/- 10 % or so, maybe a bit better. Biggest variable is annual weather variation.

[neweclipse]

Is 3 phase just now entering into the conversasion? Upgrading to 3 phase farm wide would be wise if loads justify 3 phase. Common mistake not doing 3 phase sooner rather then later.

[LCF]

J.P.M I updated the above response to show that we just ran the PVwatts numbers and they match pretty closely. Also here is the public link to our system https://monitoringpublic.solaredge.c...LCF#/dashboard zipcode is 02825

[LCF]

Is 3 phase just now entering into the conversasion? Upgrading to 3 phase farm wide would be wise if loads justify 3 phase. Common mistake not doing 3 phase sooner rather then later.

The town inspector has been encouraging us to upgrade to 3 phase for years and we were hoping to in the next year or so. The solar installer never asked or even mentioned the phase upgrade to us. Also, wouldn't we then have to upgrade the inverters?

[neweclipse]

The town inspector has been encouraging us to upgrade to 3 phase for years and we were hoping to in the next year or so. The solar installer never asked or even mentioned the phase upgrade to us. Also, wouldn't we then have to upgrade the inverters?

Inverters some depending on maker, can be 'stacked' to wired to 3 phase...others would need replaced, so it depends...

[ButchDeal]

Thanks for the response, JPM. I'll try to take each point in order:

1 - The installer did not provide an explanation as to why output was capped. After a bit of digging in the past 24 hours I think it may be a limitation put on the system by the utility for connections to properties within single-phase power (and, because of that limitation, the inverter was sized accordingly). This is still unconfirmed.

2- The contract had two inverters: SolarEdge SE 10000H and Solar Edge SE 5000H. At 240V I believe that's a nominal AC output of 10,000 and 5,000, respectively. However, we noticed the cap almost immediately after the system was turned on (just two days ago). We hit it pretty early in the morning and stayed pushing up against it for most of the day. We're hitting it now, even with overcast skies. That gives us the impression that the max actual system output is well in excess of the inverter capacity.

3- The panels were placed on south-facing roofs with no shade. It's 59 panels (model number: VBHN3256SA17 - rated wattage of 325 watts).

4- We did not model the system with PVWatts to verify their numbers originally, but just ran it all now and it matches the installers numbers pretty closely.

I think what it comes down to is that we aren't overly concerned about the cap if it still means we're offsetting 100% of our electricity usage (and we're not straining the inverters). But if the inverter size (and, possibly, lack of 3-phase power) is limiting the system then we'd like to know if that's going to prevent us from hitting the 23,815 kwH annually (or, optimistically, more) that we were supposed to be able to offset. If it means we need to bring 3-phase power and have the inverters replaced we'd like to know, as it's seeming to us like the lack of 3-phase power is what drove the inverter size, not the number of panels or annual offset targets. Does that sound accurate?

If that's the case, it seems like something we'll have to resolve with the installer, as we think it should have been communicated to us. If, because of the inverter size, we're producing the same amount of power that we would be producing with fewer panels, then we were sold more panels than we feasibly could have used.

I just got the public link so you can see the system. The smaller building on the right is the one with the broken panel and it looks like the panels are producing less than the building on the left. Is this normal? https://monitoringpublic.solaredge.c...LCF#/dashboard

You keep referring to it as a 20kW array but it is only 19kW

It is limited to 15kW total output because strictly speaking you have a 10kW inverter and a 5kW inverter.
Also those are specifically NOT 3 phase capable inverters. It should be the SE11400h and the SE6000h for 3 phase compatibility which would also make it capable of 17.4kW AC instead of 15kW AC.


You also mention 23.8MWh/ year but that the installer only guarantied 17.8MWh/ year

It does not seem like 3 phase had ANYTHING at all to do with the inverter sizing but just poor choice by the installer.

The smaller building has 7.15kW on a 5kW ( ratio of 1.43) inverter and is clearly clipping more than the other with 12.35kW on a 10kW inverter (ratio of 1.235)

If you have full access you can graph the DC voltage on the two inverters and see the clipping

[ButchDeal]

The town inspector has been encouraging us to upgrade to 3 phase for years and we were hoping to in the next year or so. The solar installer never asked or even mentioned the phase upgrade to us. Also, wouldn't we then have to upgrade the inverters?

you would as is. If they had used SE6000h and SE11400h then no as these inverters are 3 phase capable. they would only feed in on 2 legs at 208V but the ones used are not supported on 208V

https://www.solaredge.com/sites/default/files/se-hd-wave-single-phase-inverter-with-setapp-datasheet-na.pdf

[LCF]

Thanks for the detail butch. I was rounding up to 20kw as we paid for a 19.175kw system and they are clipping us at 15. I don't know what the benefit was for them to undersize the inverters unless there is some sort of limitation set by National Grid in our state. If this is the case we were not made aware of it. We are going to ask that they replace these inverters and allow us to actually sell the excess to the grid like they told us we would be doing rather than clipping us without our consent.