SolarEdge HD Wave has 'PWR Limit' set 20% below system capacity

[MowAlon]

I recently turned on my Tesla-installed solar system. It's got 30 Panasonic 325w panels for a total system size of 9.75Kw. Of course, my total purchase price is a measure of the total watts produced...

So I was upset when I flipped through the screens of my SolarEdge HD Wave inverter to see that it has a setting called 'PWR Limit' with a value of 7.6Kw (about 20% less than my total system's potential output). It seems this is a setting in the inverter to limit the total output of the system, even if my panels are generating more energy at any given moment.

One Tesla support rep told me they intentionally set this limit below the total system output level to increase longevity of the system. I haven't been able to find any discussion about this, and when I mentioned this to someone else at Tesla (a solar project manager), she had never heard such a thing. I dug in and found some documentation for the inverter which mentions the PWR Limit feature:

Page 51 - https://www.solaredge.com/sites/default/files/se_hd_wave_inverter_installation_guide_na.pdf
... which links to:
Page 5 - https://www.solaredge.com/sites/default/files/application_note_power_control_configuration.pdf

I realize this would only impact production at peak production times, so overall production wouldn't be drastically different if there wasn't this artificial limit, but if this capping isn't actually necessary, I could get the same output from a system with the same physical footprint and lower output per panel... 30 260w panels, for example.

I'm not an electrical engineer, so I'm sure there are some pieces of the calculation that I'm not factoring in, but the bottom line is that I paid for a 9.75Kw system, and the current setup prevents me from producing any more than a 7.6Kw system (as far as I know).

Does anyone know if this is standard practice? Should I be upset about this, or is Tesla doing the right thing here? Does anyone else have a similar setup installed by Tesla with such a cap in place?

Thanks in advance for any insight.

 

[MowAlon]

OK... really important update. I just checked the stats on the inverter. I just went on this big rant about artificially limiting the inverter, and it's not true at all (despite what the guy on the phone told me). The inverters Max output is actually 7.6Kw, so it must be set to 100%.

So my general concern is the same, that I have a system bigger than my inverter is outputting, but it's not because of an artificial limit.

I've read in other posts here that an inverter can handle 125% of its rating... is that theoretical or real? If it's real, should I expect to see output beyond the 7.6Kw of the inverter at peak times? Thus far, I have not, but I certainly haven't been watching it like a hawk. I did check a couple days ago at 1pm when it was perfectly sunny, and it was outputting almost exactly 7.6Kw. Given that, I don't understand what I've read about this 125% business.

 

[JohnRatsey]

Look at it differently: Having the higher capacity array means proportionally greater output when not in the peak situation. In the long term, the reduction in the panel efficiency (1%/year?) will reduce the mis-match. Also, the inverter efficiency reduces as the power drops so, if you have a higher rated inverter, it will spend more time at lower efficiencies.

 

[MorrisonHiker]

Do you happen to have more than one array, such as one array facing east and another facing west? If so, your system probably wouldn't be generating the full 9.75 kW at once and maybe that would allow them to use the smaller inverter.

 

[wwhitney]

The inverter limitation should have been spelled out and explained up front.

But, cost-wise, it makes sense to install more PV panels than the inverter rating, even though you get some clipping at peak production times. The lost value of the reduction in energy, over the life of the inverter, is typically less than the cost increase for the next size up inverter. A ratio of 125% is within the usual range.

Another way of looking at it, say the cost of the inverter size bump equals the cost of about two of your PV panels. (I think that's about right). So which will produce more power of the course of the year: your current system, or a system with the larger inverter and 2 fewer panels?

Cheers, Wayne

 

[Wubbles]

I'm getting my Tesla system installed next Weds. 26 325W panels. 8.450 kw sized system with estimated yearly production at 10,756 kWh according to Tesla estimates. My rep sent me the full list of equipment being installed and I also see SolarEdge 7600H as the inverter.

Going to reach out to my rep for more info on the inverter choice and see what he says.

 

[emoore33]

If your panels are in different planes (east, west, south) then it probably won’t matter since you aren’t producing over 7600 watts at the same time.

 

[Wubbles]

If your panels are in different planes (east, west, south) then it probably won’t matter since you aren’t producing over 7600 watts at the same time.

All of my panels are going to be facing south west. Same direction and orientation. Zero shade too

 

[MowAlon]

Do you happen to have more than one array, such as one array facing east and another facing west? If so, your system probably wouldn't be generating the full 9.75 kW at once and maybe that would allow them to use the smaller inverter.

I have two groups of panels on different roofs of the house, but they have virtually identical orientations.

 

[MowAlon]

The inverter limitation should have been spelled out and explained up front.

But, cost-wise, it makes sense to install more PV panels than the inverter rating, even though you get some clipping at peak production times. The lost value of the reduction in energy, over the life of the inverter, is typically less than the cost increase for the next size up inverter. A ratio of 125% is within the usual range.

Another way of looking at it, say the cost of the inverter size bump equals the cost of about two of your PV panels. (I think that's about right). So which will produce more power of the course of the year: your current system, or a system with the larger inverter and 2 fewer panels?

Cheers, Wayne

This would be a reasonable concern if I was involved in the decision making for the inverter and the price was dependent on that choice. It was not. I simply negotiated my price per watt (by price matching a better deal from a local provider)... after that, Tesla did everything. If I was given a different inverter, my price would have been the same.

 

[nwdiver]

This would be a reasonable concern if I was involved in the decision making for the inverter and the price was dependent on that choice. It was not. I simply negotiated my price per watt (by price matching a better deal from a local provider)... after that, Tesla did everything. If I was given a different inverter, my price would have been the same.

This subject has been discussed a lot.

... also here...

One other important thing to note... 7.6kW is a 'magic' size for most residential service. 40A is the largest Solar breaker you can add to a common 200A residential panel. 32A is the max continuous current on a 40A breaker. 32A * 240v = 7680w; So a larger inverter would have required a more costly install with very little benefit. I've modeled a 1 vs 1.2 ratio for a ~10kW system...the difference is <200kWh/yr... I also have an ~8kW inverter and 10.7kW of solar.

7 Reasons Why You Should Oversize Your PV Array

 

[Dan123]

OK... really important update. I just checked the stats on the inverter. I just went on this big rant about artificially limiting the inverter, and it's not true at all (despite what the guy on the phone told me). The inverters Max output is actually 7.6Kw, so it must be set to 100%.

So my general concern is the same, that I have a system bigger than my inverter is outputting, but it's not because of an artificial limit.

I've read in other posts here that an inverter can handle 125% of its rating... is that theoretical or real? If it's real, should I expect to see output beyond the 7.6Kw of the inverter at peak times? Thus far, I have not, but I certainly haven't been watching it like a hawk. I did check a couple days ago at 1pm when it was perfectly sunny, and it was outputting almost exactly 7.6Kw. Given that, I don't understand what I've read about this 125% business.

Undersizing the inverter is normal and common. 7.6 inverter for 9.7kw system seems normal. It also depends on how the panels are positioned. In general, you shouldn't have too much clipping with this configuration. And as time goes buy, the panels will degrade slightly, and will get a little dirt on them, so you will have even less clipping.

 

[Dan123]

All of my panels are going to be facing south west. Same direction and orientation. Zero shade too

If you are in NJ, then 8.4 kw of panels will almost never produce 7.6 kw of AC of energy.

You can model it on pvwatts.com by the hour.

 

[Dan123]

This would be a reasonable concern if I was involved in the decision making for the inverter and the price was dependent on that choice. It was not. I simply negotiated my price per watt (by price matching a better deal from a local provider)... after that, Tesla did everything. If I was given a different inverter, my price would have been the same.

They obviously should have communicated it to you. But their design choice was reasonable, and that's what most systems have. The difference in annual production is going to be like 1% in the first year, and less after that. So we are talking about $10-$20 per year of electricity.

 

[3laine]

According to my customer service person, they try to avoid clipping.

"If you were to receive the SolarEdge 5000 for an 11kW system one inverter would clip slightly at 104% and the other at 99%. We try not to go over 100% to avoid loss of production."

Or maybe they just change their position based on what suits them best... like trying to justify installing Delta inverters instead of SolarEdge, in this case.