I was told inverters can overdrive. I have one 7.7 tesla powerwall plus inverter with 9.8 panels and in Feb I have a big plateau.
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11.6kw Solar Roof, but only one Inverter?
- Thread starter ericl
- Start date
Just chiming in on this thread as I have had a similar experience to others here who are experiencing solar clipping despite being told the PW+ had an overdrive function that would cover solar generation of my 10.54Kw system. Put simply, my installation and experience prior to PTO was nothing short of a nightmare: water intrusion in the inverter, two inverters blown and replaced with no explanation, crews that were overworked and never met scheduled installation timelines - and yet, let the system believe all was satisfactory.
But more germane to this issue, I actually called off my installation in Aug. 2021 because nobody could explain to me why I had an inverter rated for 7.6kw but a solar system rated for 10.54. It didn't help that my PA was completely absent during the entire installation period despite reaching out directly for assistance multiple times. I did call the generic support line where a different PA gave me similar advice to several of you.... essentially not to worry, that the PW+ inverter had an overdrive function that would more than meet the generation of my system and I wouldn't experience clipping. Went ahead with installation in Sept. 2021, and received PTO in January. Now that we reached the longer days/warmer months (in CA) where the overdrive feature either would or would not come to fruition, like several of you, my system caps out at approx. 7.7kw, and I experience clipping for at least 3-4 hours a day. I've got to think that the cost of an extra 3.8kw inverter vs. the lost energy from clipping would pencil out over ten years. I've elevated to tesla, but given my past experience with the company and their managerial responses, I have very little confidence they will seek to resolve this.
I've already requested arbitration on other issues months ago and have yet to receive any formal response. Unfortunately, the solutions at this point may lie in legal remedy.... possibly class action if there are enough of us.
Hope this helps.
But more germane to this issue, I actually called off my installation in Aug. 2021 because nobody could explain to me why I had an inverter rated for 7.6kw but a solar system rated for 10.54. It didn't help that my PA was completely absent during the entire installation period despite reaching out directly for assistance multiple times. I did call the generic support line where a different PA gave me similar advice to several of you.... essentially not to worry, that the PW+ inverter had an overdrive function that would more than meet the generation of my system and I wouldn't experience clipping. Went ahead with installation in Sept. 2021, and received PTO in January. Now that we reached the longer days/warmer months (in CA) where the overdrive feature either would or would not come to fruition, like several of you, my system caps out at approx. 7.7kw, and I experience clipping for at least 3-4 hours a day. I've got to think that the cost of an extra 3.8kw inverter vs. the lost energy from clipping would pencil out over ten years. I've elevated to tesla, but given my past experience with the company and their managerial responses, I have very little confidence they will seek to resolve this.
I've already requested arbitration on other issues months ago and have yet to receive any formal response. Unfortunately, the solutions at this point may lie in legal remedy.... possibly class action if there are enough of us.
Hope this helps.
So what does your PTO paperwork (Interconnection Agreement that you probably docusigned at Tesla's request, I think) show for your inverter size?
Cheers, Wayne
FYI, a 1.2 to 1.3x DC/AC overage (not overdrive) is fairly common when you use other solar company that charge for material use (each inverter add more cost). It is usually cheaper to get to 1.2 to 1.3x DC vs AC to get more generation during the "shoulder" (morning/afternoon before/after clipping) than adding another inverter.
This whole why doesn't my Panel DC match my Inverter AC is a side effect of Tesla's flat rate price structure. Home-owner want to get the most bang for the buck, Tesla want to save $$$ every job.
Circa August 2021 the max overage ratio for the Inverter was a fairly industry common max of 1.4, Tesla have since bumped it up to 1.7, meaning by their spec they can install up to 12.92kw panel for a 7.6 inverter, if those are all south facing panel they would clip like crazy....
For anyone reading, TRY and ask for a 13.2kw ish panel system, so that by their spec they are forced to give you a second inverter even if its only a 3.8
13.2/11.4 is 1.16 ratio which is MUCH more industry average
I had a 12.8Kw system installed a couple months ago, waiting on PTO now They did not provide me with the inverter information during the design phase, but the install was a single 7.8. The panels are a single array, 120° facing in central Texas, PVWatts is estimating ~1000Kw/yr in lost output compared to a 7.8+3.8 inverter set (17,840Kw vs 18,820Kw).
Good for you, we have had a Solar City-Tesla 18 panel system on our home for close to 8 years now. Download the Tesla app. so you can monitor the output on a daily basis. We've only had a couple of issues with our system over the years which Tesla took care of completely. Lucky your are on the other side of the U.S. and far away from San Diego Gas & Electric who have figured out a way to diminish my investment in solar panels.
I am in the same boat (12.75 panels + one 7.6 inverter & 3 PWs), but with one catch. The PO from Tesla clearly states two 7.6 inverters but only one was installed. Been a month since install here in MA just outside of Boston, and I haven’t paid yet. They keep pushing me to but I simply won’t unless they give me a price reduction or come out and install the 2nd inverter. Adding a 3.8 would be the better design choice from what I can see. Getting clipping on sunny days 12-4. Calls and texts with Tesla have gone nowhere. Haven’t tried arbitration route yet. I agree with an earlier poster that a class action is likely brewing here.
jgleigh
Member
That agreement states two. Very odd that they only installed one. Do you currently have one Powerwall+ and two Powerwall 2s, when you should have two Powerwall+ and one Powerwall 2?
Yes, that's correct. They are trying to tell me I need to pay them the same price as what is on that PO despite only installing the one inverter.
It is my belief that a Powerwall+ can support its own PW and one other. So seemingly to support 3 PWs, the installation must include 2 inverters-- the PW+ inverter and another one to operate the third PW. Or, it needs to have at least one inverter coupled to 3 PWs (not PW+s). Perhaps it would help if you posted a picture of your setup. It isn't clear to me what actually has been installed.
Here is the plan I was sent. Not sure how to analyze the two arrays separately in PVWatts, but certainly seems there will be a drop in output with only one 7.6kWh inverter instead of 2 as is stated on the PO. The price sheet doesn't list the quantities, however. Looking for some advice on whether to take this to their resolution team or not, which could result in arbitration presumably. Seems pretty dear to me that the PO has 2 inverters and only one was installed. In my world, the mutually agreed upon PO is the contract. Interested in the expert feedback here though. Thanks in advance!
jgleigh
Member
Can you post the other pages? One of them should list exactly what equipment was installed (or intended to be installed).
And also how the panels are wired into the inverter(s).
And also how the panels are wired into the inverter(s).
jgleigh
Member
The design docs match what you have installed, even though the PO says otherwise. Have you put the system into PVWatts? I'm guessing you're not losing that much generation even though it's clipping all the time. Based on lots of threads on here, Tesla seems to be going for much higher DC/AC ratios than have been used in the past.
I agree it matches this design, but not the PO which is why I want a price reduction. I'm not sure how to model the multiple arrays in PVWatts. Or if I am using all the right factors. Is this something you (or someone here) can help me with? My novice approach showed about 750kwh/year of losses. On a good sunny day the system clips for about 4 hours.
I modeled this using August 5 as a proxy for a clear sunny day, and used 20 panels at 36 tilt, 209 AZ, 6 panels at 36 and 119, and 4 panels at 18 and 299, all at a DC/AC ratio of 1.12 Then I summed the three outputs to obtain the expected shape during the day. Then multiplied the 20 panel data by a factor to get an equivalent single array power, which turned out to be about 12.3kW. The yearly output from the equivalent array was 16,303 kWh, while a AC/DC ratio of 1.68 gave 15,519 kWh. So very close to your estimate--about 800kWh per year, or 5%.
Attachments
If you have 3 differently oriented subarrays on a single inverter (hopefully I got that right, not following the thread super close), then modeling them as 3 separate PVWatts runs, each with a DC/AC ratio of 1.12, is going to underestimate the total production. Because the summing answer will reflect a scenario when clipping occurs whenever a subarray produces more DC power than its proportional share of the AC inverter capacity. While in reality clipping will only occur when the total DC production exceeds the AC capacity.
If PVWatts gives you hourly numbers for each of the 8760 hours of the year, then you could do 3 runs with an AC/DC ratio of 1.0, dump all the numbers, sum them in a spreadsheet, and then cap each hour's production at your AC inverter capacity. That should be close to the correct clipping.
Cheers, Wayne
I agree your method will work-- PVWatts does give production for every hour of the year if you ask for hourly data. But I think my method is also very close. I chose a AC/DC ratio of 1.12 because that's what a possible 3.8kW plus 7.6kW remediation would give. In fact there was no clipping at a 1.12 ratio at any time during the year, according to PVWatts.
