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Anyone know if I can combine two solar systems and how the net metering may work?

Well you can always buy out the PPA.

Also if the goal is to charge the car with excess solar, PW+ already supports that without any need to manually downrate the charger. It will do it automatically for you if you’re off-grid.

IMHO my suggestion is buy out the PPA, have everything go through PW+, and get a second PW if your budget allows. Seems strange to me how everyone here is saying to get 2 PW as if they are free.
 
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bhakan

MSLR MSM/Blk/19/FSD, Ord 6/10/21, Del 2/20/22
Jan 2, 2018
643
882
Bethesda, MD
Well you can always buy out the PPA.

Also if the goal is to charge the car with excess solar, PW+ already supports that without any need to manually downrate the charger. It will do it automatically for you if you’re off-grid.

IMHO my suggestion is buy out the PPA, have everything go through PW+, and get a second PW if your budget allows. Seems strange to me how everyone here is saying to get 2 PW as if they are free.
I have fully pre paid for my current system in 2013. What do I buy out? Can you please explain? Thx
 
PPA means you don’t own the panels and instead make a promise to buy a certain amount of power that the panels produce for a fixed cost. The idea is that your up front cost is zero.

Ultimately the panels aren’t yours. You’d need to look at your PPA to see what happens to them. E.g. you terms could be that after 20 years of buying power, you will have paid them off and they become your property. Or after 10 years the agreement is over and the panels are removed from your roof.

When I say buy out I mean that most PPAs will have a table where they will provide the cost of purchasing the solar panels outright based on how many years you are into the PPA. Once you do that, you’re free to do with them whatever you want, such as tie them into the PW+ and new array that you’re adding.
 
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You can't hook up both systems to the single Powerwall because the power produced would likely exceed the Powerwall maximum charging rate, resulting in everything shutting down.
Huh?

PW+ caps out at 9.6 kW. This hypothetical system would be 10.4 kW, but given that OP is in Maryland, it will basically never actually hit that peak rate. And nothing would shut down, PW would just trim excess production for the few hours a year that this actually happens.

No way does the added cost (8k?) make any sense just to save a few kWh per year during the summer months. And it would never be needed in winter.
 
Makes no difference. The gateway controls how many amps the car draws. There is zero interaction with the charger.
The Tesla Gateway that disconnects the house+solar+powerwalls from the grid controls how many amps the car draws? How exactly does it do that?

There is an app setting that will disable EV charging when the Powerwall drops below the selected percentage, but there is no indication that this throttles amps.
 
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Would a Tesla mobile charger be good for using extra power when available with less chance of high drain.
The different adapters will automatically throttle the charging rate without any worry about software control issues:
  • 5-20 - Max 16A @ 120V = 1.92kW
  • 6-15 - Max 12A @ 240V = 2.88kW
  • 6-20 - Max 16A @ 240V = 3.84kW
  • 10-30 - Max 24A @ 240V = 5.76kW
  • 14-30 - Max 24A @ 240V = 5.76kW
  • 14-50 - Max 32A @ 240V = 7.68kW
  • 6-50 - Max 32A @ 240V = 7.68kW
 
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bhakan

MSLR MSM/Blk/19/FSD, Ord 6/10/21, Del 2/20/22
Jan 2, 2018
643
882
Bethesda, MD
Huh?

PW+ caps out at 9.6 kW. This hypothetical system would be 10.4 kW, but given that OP is in Maryland, it will basically never actually hit that peak rate. And nothing would shut down, PW would just trim excess production for the few hours a year that this actually happens.

No way does the added cost (8k?) make any sense just to save a few kWh per year during the summer months. And it would never be needed in winter.
I just did a rough sticky note calculation for the last 4 yrs. Dec and Jan I would not store any on my PW as my production is just around 250kwh. I do not have any electric heater or stove. So it is fine for me. My best months when I could be producing and storing are Feb, Mar, Apr, Oct, and Nov for sure. May, June, July, Aug, Sept (depends) months I may be just producing enough if I have two systems. So it seems like one PW may be ok.
 
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bhakan

MSLR MSM/Blk/19/FSD, Ord 6/10/21, Del 2/20/22
Jan 2, 2018
643
882
Bethesda, MD
PPA means you don’t own the panels and instead make a promise to buy a certain amount of power that the panels produce for a fixed cost. The idea is that your up front cost is zero.

Ultimately the panels aren’t yours. You’d need to look at your PPA to see what happens to them. E.g. you terms could be that after 20 years of buying power, you will have paid them off and they become your property. Or after 10 years the agreement is over and the panels are removed from your roof.

When I say buy out I mean that most PPAs will have a table where they will provide the cost of purchasing the solar panels outright based on how many years you are into the PPA. Once you do that, you’re free to do with them whatever you want, such as tie them into the PW+ and new array that you’re adding.
If I remember correctly after 20 yrs Tesla is supposed to remove them as it is theirs. In those days I did not get any federal or state tax credits for the solar panels in 2013. I noticed in my current design review that there is federal tax credit for the panels and storage tax credit from my state.
 
The Tesla Gateway that disconnects the house+solar+powerwalls from the grid controls how many amps the car draws? How exactly does it do that?

There is an app setting that will disable EV charging when the Powerwall drops below the selected percentage, but there is no indication that this throttles amps.
Yes.

I mean, if you're in off-grid mode, you can't export to the grid. And there's the percentage your battery must be above. So where is the excess power going to go? Into the car.

I don't get what's so difficult about this. The gateway knows your house consumption, it knows your solar production, so it can do some pretty basic math to tell your car how many amps to draw.

This isn't hypothetical, I've done it.
 
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jjrandorin

Moderator, Model 3, Tesla Energy Forums
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Right so if you want to buy them out and have them become your property there's a cost associated with that. It's in your contract based on how many years are left.

They dont have a cost in the contract (mine is a solar city contract as well, but from 2015 not 2013. I am sure its the same). it says something like they will have an appraisal done and charge "fair market value" for it. The issue is there is more than one way to determine value, and the way tesla determines value on it is based on the lost value of not getting the rest of the PPA agreement money / years.

I looked into buying mine out, they sent me the price, and the price they were charging for it was fairly astronomical. My system (for example) is 8.7 kW and they were charging me more for my 6 year old 8.7kW system than tesla would charge for a 12.X sized system brand new on my roof. When I questioned it, they sent me this 1 pager about accounting principles etc.

I asked another member here I know who does accounting stuff in their day job to look at it as a "non professional favor" to me, as I didnt understand what they were saying in the letter other than "here are reasons we feel justified to charge this much for buy out of your system.

End result was, it was due to the type of appraisal they used, etc, and while I could have probably continued to fight, I sort of gave up at that point. I may look at it again in a year or so.

Like most say, PPAs are not the best deal out there. When I got mine, I was making a choice between "no solar" and a PPA, and I have still saved money on it getting it when I did. I would be much better off If I had purchased the system vs getting a PPA, but it has still worked out for me financially (it didnt cost me money, I just am not saving nearly as much as I would be otherwise).


TL; DR -- I doubt the buy out price for the OP will be something they would want to pay, but it is not a contracted buy out price in the contract, its based on an appraisal.
 
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bhakan

MSLR MSM/Blk/19/FSD, Ord 6/10/21, Del 2/20/22
Jan 2, 2018
643
882
Bethesda, MD
They dont have a cost in the contract (mine is a solar city contract as well, but from 2015 not 2013. I am sure its the same). it says something like they will have an appraisal done and charge "fair market value" for it. The issue is there is more than one way to determine value, and the way tesla determines value on it is based on the lost value of not getting the rest of the PPA agreement money / years.

I looked into buying mine out, they sent me the price, and the price they were charging for it was fairly astronomical. My system (for example) is 8.7 kW and they were charging me more for my 6 year old 8.7kW system than tesla would charge for a 12.X sized system brand new on my roof. When I questioned it, they sent me this 1 pager about accounting principles etc.

I asked another member here I know who does accounting stuff in their day job to look at it as a "non professional favor" to me, as I didnt understand what they were saying in the letter other than "here are reasons we feel justified to charge this much for buy out of your system.

End result was, it was due to the type of appraisal they used, etc, and while I could have probably continued to fight, I sort of gave up at that point. I may look at it again in a year or so.

Like most say, PPAs are not the best deal out there. When I got mine, I was making a choice between "no solar" and a PPA, and I have still saved money on it getting it when I did. I would be much better off If I had purchased the system vs getting a PPA, but it has still worked out for me financially (it didnt cost me money, I just am not saving nearly as much as I would be otherwise).


TL; DR -- I doubt the buy out price for the OP will be something they would want to pay, but it is not a contracted buy out price in the contract, its based on an appraisal.
I looked at my contract and the language is the same. See below.
I would not buy at the FMV which may not make economical sense to me. The full prepayment in late 2013 for this 5.4kW system with 7200 kwh annual production guarantee was $9300. it is a 20 yr contract. In those days the full upfront cost was around 25k. There was no way I was going to pay that when there were only two companies that would even put solar panels in our area and I may have been one of the early ones to get solar at that time. There was no federal tax credit for me unless I bought the panels upfront. I easily recovered my money in less than 7 years but now I am at the crossroads and want to consider all the options to help me for at least another 10 yrs.
PXL_20221014_202518237.jpg PXL_20221014_203030072.jpg PXL_20221014_202630482.jpg
 

arnolddeleon

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Jul 21, 2012
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@jjrandorin that’s useful info. The accounting doesn’t surprise me: when the contract was made, they expected to make a certain amount of money. Buying out basically means giving them that money now rather than over X years.

You said you were still able to tie your system into a new PW installation though? How did that work?
My double and then later triple PV system includes a leased system (not quite the same as PPA but similar in that the customer doesn't own the equipment).
I suspect that my situation was helped by the "early days" of Powerwall install and that the "3rd party" happened to be Tesla as well so it was a complete non-issue.

On the technical side, my PV systems were reconnected to a "generation panel" and Tesla put in current sensors on each one so my Powerwall install shows the total of all my PV systems. Today that is 3 PV systems, a roughly 10 kW system I own and was installed around 2002, a 2 kW Solar City leased system installed around 2007 and a 4 kW Tesla one installed in in 2021.

I had lightly researched buyout as well but rapidly came to the conclusion that it made no sense. My lease system has the a renewal option at end (in about a year) or for Solar City (now Tesla) to remove and restore. I have a bet that if I don't renew Tesla will not want to spend the money to remove and restore and I will actually get a good deal.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
17,496
23,439
Riverside Co. CA
@jjrandorin that’s useful info. The accounting doesn’t surprise me: when the contract was made, they expected to make a certain amount of money. Buying out basically means giving them that money now rather than over X years.

You said you were still able to tie your system into a new PW installation though? How did that work?

Yes, I was still able to buy (2) powerwalls and have them installed. My PPA system is Tesla (solar city), and I went through Tesla for the powerwall installs. They never even asked about the PV system, etc.

Tesla was still doing "only powerwall add on" installs (no requirement to purchase PV with them) when I got my powerwalls. They dont currently do that, any longer (at least right now) to my knowledge, so you would have to go through a third party and pay whatever that might cost.
 
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So to answer the OP's question, sounds like all of this is doable. They should be able to install additional panels + PW, you just need to tell them what they have and they should be able to put together a design that combines the two systems and lets you feed them all into a single PW.

I see no issue with installing just one battery, especially if you aren't looking to charge your car during the winter using it and have all-LED lighting in the house.
 
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bhakan

MSLR MSM/Blk/19/FSD, Ord 6/10/21, Del 2/20/22
Jan 2, 2018
643
882
Bethesda, MD
So to answer the OP's question, sounds like all of this is doable. They should be able to install additional panels + PW, you just need to tell them what they have and they should be able to put together a design that combines the two systems and lets you feed them all into a single PW.

I see no issue with installing just one battery, especially if you aren't looking to charge your car during the winter using it and have all-LED lighting in the house.
The proposed design is to have 5.6kW solar panels (14 total) and one PW. I have told them my goal and asked them to combine the two systems. After they give me the plan set I hope they can work with me on that.
 
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