System expansion after installation

[tfan2018]

Lol I feel like if someone uses this forum to learn about Tesla Solar, the last company they would pick to install their solar would be Tesla Solar. At least, if they were browsing the site in 2019/2020 when like every third thread was about how Tesla Solar was screwing the pooch.

yeah that's true with all the stories I read , however, I was set on Tesla Solar given the app functionality and how everything including my model 3 all works together in one app, and going with another provider was more expensive so I knew what sort of (poor) Tesla customer service I was getting myself into. even though I hit some major snag after PTO and the installers left a hole in my roof, it is all good (for) now...

 

[holeydonut]

Given my earlier comments about how we don’t plan to stay in this house beyond 5 years this is definitely not going to work

Yeah, the wind won't be strong enough to blow the panels from your current house onto your new house.

With interest rates the way they are... you really think you'll be moving in 5 years?

 

[sunwarriors]

Given my earlier comments about how we don’t plan to stay in this house beyond 5 years this is definitely not going to work

I don't understand why even install solar if one is moving in 5 years. It's not the end of the world to pay for power.

There is a sunk cost and Cost of $$ that can be spent on other investments, even boring T-bills, etc...

Seems like a lot of hassle/waste of time IMO if one is leaving in 5 years. I would personally do something else with my time/$$ if in your shoes and I wouldn't even bother expanding the system.

 

[jjrandorin]

I don't understand why even install solar if one is moving in 5 years. It's not the end of the world to pay for power.

There is a sunk cost and Cost of $$ that can be spent on other investments, even boring T-bills, etc...

Seems like a lot of hassle/waste of time IMO if one is leaving in 5 years. I would personally do something else with my time/$$ if in your shoes and I wouldn't even bother expanding the system.

@lensovet already installed solar, so already had the sunk cost. They were / are trying to find a "cheap" way to install more solar, because their needs have changed.

This is the biggest problem I see with people trying to size their PV systems for "fastest return on investment" because that usually works out to be something less than 100% of current usage, or 100% of current usage at most, while peoples electric usage almost always goes UP, not down.
'

 

[lensovet]

I don't understand why even install solar if one is moving in 5 years. It's not the end of the world to pay for power.

There is a sunk cost and Cost of $$ that can be spent on other investments, even boring T-bills, etc...

Seems like a lot of hassle/waste of time IMO if one is leaving in 5 years. I would personally do something else with my time/$$ if in your shoes and I wouldn't even bother expanding the system.

I mean…this is pretty OT but I’ll bite.

I’m in NJ. Tesla buys out your SRECs in return for an up front discount. The fact that we won’t be here in five years actually means this makes a lot more sense, as I don’t care about the next owners missing out on SREC payments.

I don’t care about paying for electricity, but I do care about where my electricity is coming from, and buying renewable electricity here would have been more expensive than this install.

This system cost us 10k before incentives (not including the cost of the power wall, which I got strictly for storm resiliency and which will never make any sense from an economics standpoint). Tesla gave us 3700 in SREC credits, IRS gave us 1890 in solar credits (more than we expected thanks to the IRA). So that's a net cost of 4400. The average generation we've been getting equates to about $95/mo, so our payback is less than 4 years. The system is financed (3.65%), so the comparison to T-bills is moot as the only "investment" that was made was $1700 paid after inspection for both solar and battery backup. Even if the net cost over 5 years was zero (as opposed to a "gain" of about $1k), it would have been worth it to me to reduce our GHG production, have peace of mind in case of storms, and have another selling point for the house.

Hassle/waste of time? Really? It's not like I was installing the solar myself. Though I might be tempted to do this expansion myself lol.

 

[lensovet]

Sure got a good deal though. Same system today is 12,393 before incentives, the SREC credit isn't any bigger, and interest rates are now 7%.

 

[hmcgregoraz]

Imo the amount of permitting work and headache with warranties and other garbage make a small panel add-on borderline impossible in my experience. The big players have too many installs to take on already, and these small expansions harm their average margins.

Your best bet is to drive around your neighborhood hoping to bump into a crew that is doing a solar install racking/panels. Figure out if you can get a contact information for these folks that seem to be able to lag in mounts/L-feet, know their way with flashing/mastic, cut racking to length, slap in panels, and wire up a new home-run (with ground).

Source a bill of material as if you were going to DIY a solar expansion. But also get a stack of Benjamins in a yellow envelope and label it "not a solar expansion." Include a few 24 packs of beer too.

Something Something Something

Then somehow one day when it's windy a bunch of panels are going to end up on your roof and somehow the wind will also blow your home run to land on some feeder lugs on your inverter or combiner box. Your inverter is still hard-clipped at 3.8 kWp-AC but your production will go up.

Shrug.



PS. I am the dumbest MF-er on this forum, so you may not want to take my advice.

Based on the PowerWall+ specs, the inverter should be 7.6KW.

Should be reasonably safe to go up to about 9-9.5KW of panels depending on the exact panel specs, as long as it stays in the supported DC voltage ranges.

The most relevant specs are:

PV Maximum Input Voltage	600 VDC
PV Operating DC Input Voltage Range	60 – 550 VDC
PV DC MPPT Voltage Range	60 – 480 VDC
MPPTs	4 (1-2-1-2 input connectors per MPPT)
Maximum Current per MPPT	13 A
Maximum Short Circuit Current per MPPT	15 A

I agree that the DIY method may be the only effective method, but it could cause warranty issues with Tesla, and you really need to make sure it is properly permitted, interconnect agreement, etc.

When we expanded our system, we expected we may have to change to the new compensation rate vs the old, We originally installed at a sell back rate of $0.86/kwh, and when we added panels the rate had changed to $0.076/kwh. Supposedly if you changed the system by up to 10% you did not need to move to the new rate. Our Installer stated that this would only apply if we changed our inverters, and since we were already installed and approved at the two 10KW inverters, we would not change rates.

-Harry

 

[holeydonut]

Based on the PowerWall+ specs, the inverter should be 7.6KW.

Should be reasonably safe to go up to about 9-9.5KW of panels depending on the exact panel specs, as long as it stays in the supported DC voltage ranges.

The most relevant specs are:

PV Maximum Input Voltage	600 VDC
PV Operating DC Input Voltage Range	60 – 550 VDC
PV DC MPPT Voltage Range	60 – 480 VDC
MPPTs	4 (1-2-1-2 input connectors per MPPT)
Maximum Current per MPPT	13 A
Maximum Short Circuit Current per MPPT	15 A

I agree that the DIY method may be the only effective method, but it could cause warranty issues with Tesla, and you really need to make sure it is properly permitted, interconnect agreement, etc.

When we expanded our system, we expected we may have to change to the new compensation rate vs the old, We originally installed at a sell back rate of $0.86/kwh, and when we added panels the rate had changed to $0.076/kwh. Supposedly if you changed the system by up to 10% you did not need to move to the new rate. Our Installer stated that this would only apply if we changed our inverters, and since we were already installed and approved at the two 10KW inverters, we would not change rates.

-Harry

Yeah this is the catch-22. Normal installers (especially Tesla) wouldn't waste the time on this expansion since the effort to do it right is high and the profit is low.

But if a gust of un-permitted, un-bonded, un-insured, and un-documented wind does the racking and home run, he wouldn't get it done correctly. I did say I was a dumb-azz-MF-er with bad ideas right?

I also agree the resulting AC/DC ratio is probably too high (it ends up like 1.9 instead of 1.2) and a Tesla inverter will probably melt and catch fire since it'd be running at its max rating basically all sunny-day.

Hey, while it's working he'll be able to charge that BEV with clean energy Powered by solar which was installed by the wind. Infinite money glitch.

 

[lensovet]

Our net metering here is plain dumb net metering with no TOU, so no issues there.

I don’t need to max out the inverter. I only want another 2.4 kW so total would be far below the max.

I can file permits and applications myself, honestly probably do a better job than Tesla, who managed to submit the wrong meter number twice and seemingly didn’t submit anything about the ESS to the utility.

 

[Matt-FL]

Should be reasonably safe to go up to about 9-9.5KW of panels depending on the exact panel specs, as long as it stays in the supported DC voltage ranges.

Actually, no - at least not from my experience. While the Tesla inverters are capable of going above 7.6 in short bursts, they will not sustain for long periods. I have 20.4kW panels with two Tesla 7.6k inverters. On a clear sunny day, I'll get a maximum of 16kW, usually steady at 15.6kW. However, if it is partly cloudy, I'll see short bursts up to 17.5kW, but then drops back down to 15-16kW if the sun stays put for more than a few minutes. From my experience, I wouldn't count on them running 125% for any length of time. Wish I had requested 3 inverters .

 

[sunwarriors]

I mean…this is pretty OT but I’ll bite.

I’m in NJ. Tesla buys out your SRECs in return for an up front discount. The fact that we won’t be here in five years actually means this makes a lot more sense, as I don’t care about the next owners missing out on SREC payments.

I don’t care about paying for electricity, but I do care about where my electricity is coming from, and buying renewable electricity here would have been more expensive than this install.

This system cost us 10k before incentives (not including the cost of the power wall, which I got strictly for storm resiliency and which will never make any sense from an economics standpoint). Tesla gave us 3700 in SREC credits, IRS gave us 1890 in solar credits (more than we expected thanks to the IRA). So that's a net cost of 4400. The average generation we've been getting equates to about $95/mo, so our payback is less than 4 years. The system is financed (3.65%), so the comparison to T-bills is moot as the only "investment" that was made was $1700 paid after inspection for both solar and battery backup. Even if the net cost over 5 years was zero (as opposed to a "gain" of about $1k), it would have been worth it to me to reduce our GHG production, have peace of mind in case of storms, and have another selling point for the house.

Hassle/waste of time? Really? It's not like I was installing the solar myself. Though I might be tempted to do this expansion myself lol.

Your cost was definitely crazy low, but if you're gone anyways from this place in 5 years or less, then just put 2 systems, 3 systems, who really cares? It's not your forever home and from your post, getting green energy is the most important thing so just hire anyone to do it, pay whatever half decent, and get it installed and done.

You can do it yourself and use your time/hassle/$$, but it's still time/$$/hassle which takes away from everything else in life for something very short term IMO.

You said Tesla won't do it, find someone else or self install. As noted, Tesla isn't the most flexible and other installers may not want a small job for obvious reasons. Since your reasons are not for ROI or investment, then like I say regularly, solar/batteries is such an easy decision if ROI is tossed out the window and just do it.

This is of course, all my opinion and in your shoes, I wouldn't have even installed solar a year ago for the SRECs or IRA if I was leaving the house soon. Just seems like work/hassles, but we're all different.

Good luck whatever you plan, and let us know how it plays out.

 

[hmcgregoraz]

Actually, no - at least not from my experience. While the Tesla inverters are capable of going above 7.6 in short bursts, they will not sustain for long periods. I have 20.4kW panels with two Tesla 7.6k inverters. On a clear sunny day, I'll get a maximum of 16kW, usually steady at 15.6kW. However, if it is partly cloudy, I'll see short bursts up to 17.5kW, but then drops back down to 15-16kW if the sun stays put for more than a few minutes. From my experience, I wouldn't count on them running 125% for any length of time. Wish I had requested 3 inverters .

That is normal for over paneling an inverter. What I meant by it being OK is that it won't exceed the DC specs of the inverter, and won't result in inverter failure, not that it would capture all of the extra DC during peak production time and peak production months.

We have 2x 10KW inverters, and max out at about 20.2KW AC.

We have 23.5KW DC of panels.

What you end up doing is clipping the very peak of output, but getting "max" output for far longer. Overall production is still far higher vs lower DC, yes you are throwing away some production during peak output, during peak season, but the rest of the year, rest of the day, etc you get far better output. We tend to only really max out the AC output in April/May range.

-Harry

 

[holeydonut]

That is normal for over paneling an inverter. What I meant by it being OK is that it won't exceed the DC specs of the inverter, and won't result in inverter failure, not that it would capture all of the extra DC during peak production time and peak production months.

We have 2x 10KW inverters, and max out at about 20.2KW AC.

We have 23.5KW DC of panels.

What you end up doing is clipping the very peak of output, but getting "max" output for far longer. Overall production is still far higher vs lower DC, yes you are throwing away some production during peak output, during peak season, but the rest of the year, rest of the day, etc you get far better output. We tend to only really max out the AC output in April/May range.

View attachment 955895

-Harry

Are you sure a Tesla inverter can run at max kW-AC for 4+ hours a day? I feel like it'd catch fire or at least spit out a ton of firmware glitches then start leaking.

 

[hmcgregoraz]

Are you sure a Tesla inverter can run at max kW-AC for 4+ hours a day? I feel like it'd catch fire or at least spit out a ton of firmware glitches then start leaking.

I would be very surprised if any inverter was not rated for at least 4 hours at full output.

Given that the same inverter is used for the powerwall output as well, and that is rated at 5/7KW output, again, I would be very surprised if the Inverter could not handle running at max input for at least 4 hours per day if not more. Virtually everything electrical in solar is based on continuous load, which is why the breakers get de-rated to 80%, etc.

Between 105% and 115% of inverter capacity is relatively normal in the industry. It used to be the panels were by far the most expensive part of the system, and you wanted to make sure you got every electron out of them that you could.

Then the inverters became the most expensive part of the system. Now it really is labor of installation that is the most expensive part of the system.

We had the option of 2x 7.6KW inverters with our original 18.5KW DC of panels, it was $1,000 more to go with 2x 10KW inverters. I had an extra reason for doing that. Our utility requires that solar not be > 70% of the capacity of the transformer you are connected to, across your address, and any neighbors on the same transformer. By going with 2x 10KW, we "claimed" 20KW of capacity on the transformer, if we had gone with 2x 7.6KW, and then added a 3.8KW later, we may not have had room on the transformer to add it.

Since I knew we needed the additional panels, we "reserved" the capacity early.

-Harry

 

[Matt-FL]

That is normal for over paneling an inverter. What I meant by it being OK is that it won't exceed the DC specs of the inverter, and won't result in inverter failure, not that it would capture all of the extra DC during peak production time and peak production months.

We have 2x 10KW inverters, and max out at about 20.2KW AC.

We have 23.5KW DC of panels.

What you end up doing is clipping the very peak of output, but getting "max" output for far longer. Overall production is still far higher vs lower DC, yes you are throwing away some production during peak output, during peak season, but the rest of the year, rest of the day, etc you get far better output. We tend to only really max out the AC output in April/May range.



-Harry

That's a great explanation, and I really appreciate the detail. Makes me feel quite a bit better, and keeping max for longer is the key part I wasn't considering.