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Asking Tesla for a second inverter
- Thread starter flatroofer
- Start date
The short answer is you can ask, but they will almost certainly not give you one for free, and probably wouldn't install one at all.
You are experiencing clipping, and some amount is not necessarily uncommon (and, if you take a look through threads on this forum, there is a lot of discussion around clipping and why it is often not a major issue) - and right around now, with nearly the longest days and relatively cooler temps than the summer - is when it is most likely to happen. Tesla likely took that into account in the estimates it provided you for annual production, and as long as you get that, you would likely not have any reason to expect Tesla to modify the install.
It might be helpful if you want a more detailed discussion of your clipping, and how significant it is, is to post a screenshot of the app for a day to illustrate for how long the clipping is occurring. Also, an image or description of your layout (is it all south-facing, half east/west, etc.) can help with understanding the choice of inverter, but the ~21% oversizing of your system rating to the inverter is not out of the ordinary.
You are experiencing clipping, and some amount is not necessarily uncommon (and, if you take a look through threads on this forum, there is a lot of discussion around clipping and why it is often not a major issue) - and right around now, with nearly the longest days and relatively cooler temps than the summer - is when it is most likely to happen. Tesla likely took that into account in the estimates it provided you for annual production, and as long as you get that, you would likely not have any reason to expect Tesla to modify the install.
It might be helpful if you want a more detailed discussion of your clipping, and how significant it is, is to post a screenshot of the app for a day to illustrate for how long the clipping is occurring. Also, an image or description of your layout (is it all south-facing, half east/west, etc.) can help with understanding the choice of inverter, but the ~21% oversizing of your system rating to the inverter is not out of the ordinary.
You could ask, they will almost assuredly say either "no" or if you buy it from us for $ X,XXX we will put it in, where X,XXX is way more than the value of the amount of electricity you are "losing" by clipping, over the life of the system.
Perhaps read through the following thread for more information:
SE7600H clipping at 7.9KW
Anyones else's SE7600 clipping at 7.9 KW. Today I had a ton of cloud reflection resulting in output going up to and pegging at 7.9 KW and it stayed there even when the brightness climbed well above that. I then looked back on the historical data for all the other partly cloudy days and each time...
teslamotorsclub.com
Can you post a screen shot graph of your highest production without cloud reflection? A small amount of clipping will more than be offset by the higher efficiency of the smaller inverter at all other times.
can you help me understand why a smaller inverter is more efficient in certain cases?
The key point is that both PV panels and inverters cost money. So the ratio of the two that optimizes (energy production / cost) will both "waste" some inverter capacity (i.e. not include enough PV so that the inverter is maxed out most of the day) and "waste" some PV capacity (i.e. not include enough inverter capacity so that you never have clipping).
In other words, if you don't have any clipping, the system was probably not designed in an economically optimal way. Now you might have other goals, e.g. maximizing production in a certain fixed space, and you could communicate those to Tesla to hopefully get a different design. But as Tesla is in the business of making money, their default design will typically be based on economics.
Oh, and lastly, a 7.6 kW inverter is often the sweet spot of what is easy to add to an existing wiring system. Often going up in size would require more extensive changes to the existing house wiring, so a larger inverter would cost disproportionately more.
Cheers, Wayne
In other words, if you don't have any clipping, the system was probably not designed in an economically optimal way. Now you might have other goals, e.g. maximizing production in a certain fixed space, and you could communicate those to Tesla to hopefully get a different design. But as Tesla is in the business of making money, their default design will typically be based on economics.
Oh, and lastly, a 7.6 kW inverter is often the sweet spot of what is easy to add to an existing wiring system. Often going up in size would require more extensive changes to the existing house wiring, so a larger inverter would cost disproportionately more.
Cheers, Wayne
charlesj
Active Member
What specs was the design based on?
Does your power company limits the amount of PV generation with respect to the previous year's home usage before solar?
If so, perhaps that is the reason.
Did you try to order a larger system?
Does your power company limits the amount of PV generation with respect to the previous year's home usage before solar?
If so, perhaps that is the reason.
Did you try to order a larger system?
I read the article but I still don't understand why an undersized inverter would have energy gains in the morning and afternoon.
It has to do with the efficiency curve of the inverter, efficiency (AC power out/DC power in) vs AC power out. A typical curve will be much lower below, say, 40% power versus above 40% power, and will be fairly flat above, say, 60% power. So an oversized inverter will spend more of the day in the less efficient band; if that effect is larger than clipping with a smaller inverter, then the smaller inverter would produce more energy during the day.
However, I expect this effect would be very sensitive to the details of the efficiency curve, and with the discreteness of inverter sizes, I don't this actually happens very often in practice. The main reason to have a DC/AC ratio above 1.0 is that even if at a starting point of a DC/AC ratio of 1.2, if you want to spend a little more money to make a little more power, you'll get a greater bang for your buck by adding more panels and increasing the DC/AC ratio than you will by spending more on a bigger inverter and decreasing the DC/AC ratio.
Cheers, Wayne
The only reason I have seen to add a larger inverter is adding more panels in the future. But based on code changes, etc. doing it all at the beginning, IMO, is the smarter thing to do. I am now trying to add more panels and I might not get approved, where if I had done this last year, I would have been fine.
Let's take an actual pair of inverters. I have the data for the Delta M series, and it shows that the efficiency is nearly flat down to 10% power, and that a 10kW inverter has slightly higher efficiency than the 8kW version. So there is effectively no power gain to be had in taking the DC/AC ratio above 1 unless the the money saved in buying a smaller inverter is put into more panels. Or, a utility company may have rules that restrict the power capability of an inverter.
In the below plot, you can see the efficiciencies of 8 and 10kW inverters. You can also see the loss of power: about 7kWh for these south facing panels over the course of 5 hours. There is no gain in the morning or evening for this pair of inverters, but even if the 8kW inverter were more efficient, the gains would only occur when the power generation is low, so the effect would be much smaller than the 5 hours of loss at near peak generation.
In the below plot, you can see the efficiciencies of 8 and 10kW inverters. You can also see the loss of power: about 7kWh for these south facing panels over the course of 5 hours. There is no gain in the morning or evening for this pair of inverters, but even if the 8kW inverter were more efficient, the gains would only occur when the power generation is low, so the effect would be much smaller than the 5 hours of loss at near peak generation.
The Tesla inverter is quite similar: See the Excel Spreadsheet compiled by the CEC. Every inverter approved for grid tie use in CA has to provide this kind of data.
For nominal voltage (375V):
10% 20% 30% 50% 75% 100%
96.8 97.9 98.2 98.6 98.2 97.7
For IQ7+
94.2 95.6 96.8 97.5 97.4 97.2
I don't know how to find the efficiencies at the various power levels for the SolarEdge power optimizers, but the inverters themselves are quite high
96.9 98.5 98.8 98.9 98.9 99.0
For nominal voltage (375V):
10% 20% 30% 50% 75% 100%
96.8 97.9 98.2 98.6 98.2 97.7
For IQ7+
94.2 95.6 96.8 97.5 97.4 97.2
I don't know how to find the efficiencies at the various power levels for the SolarEdge power optimizers, but the inverters themselves are quite high
96.9 98.5 98.8 98.9 98.9 99.0
I'm looking for some advise on this thread as well. I have a 25.16 Kw system. I'm being clipped now at 15.4. This wasn't explained to me at the start but from what I read, its only supposed to be a small amount. In my case I feel like I'm being clipped for a lot and it feels like Tesla did not design my system correctly if they are making me pay for a 72 panel system at 25.16 Kw then clipping me for 10+ Kw. Does this seem normal? I originally bought 3 powerwalls and opted to get a 4th which they approved post install based on the amount I was generating (prior to the clipping). I sort of feel like I'm getting ripped off now because it used to generate 24.x Kw frequently so I'm not sure why they started to clip my system now.
