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

[bhakan]

I have a 5.4 kW solar panel system installed by Solar City (now Tesla) in late 2013 with Aurora inverter. It was a full PPA with a performance guarantee. It was activated in the first week of Jan 2014. My utility is Pepco in MD and I have net metering. However, I don't think I ever got the full amount I produced and there was always about 40% of the cookie bite. Now I am planning to add another system and working with Tesla to get some estimates and it seems like another 4.8kW system may work for me. I am thinking about getting one Powerwall with the new system. I have a Tesla wall charger on a 60amp circuit and would like to add it to the Powerwall to be able to charge my car if and when power goes out. In addition, I also have a 17kW Generac back-up generator ( connected to natural gas supply) that accomodates most of my electric needs except the second AC and few other things.

Does anyone have experience in combining two systems and how are they added to my net metering so that my utility will look at the total production from both the systems? Currently my production from one system ranges about 6100kWh-6200kWh and I was guaranteed 7200kWh when I signed the contract in late 2013.

If I add a Powerwall will the production from both systems be stored in the Powerwall so that I can pretty much use all the energy I produce and not depend on my utility? What am I supposed to tell Tesla during their planning phase and will Tesla be able to do that?

TIA

 

[h2ofun]

I have a 5.4 kW solar panel system installed by Solar City (now Tesla) in late 2013 with Aurora inverter. It was a full PPA with a performance guarantee. It was activated in the first week of Jan 2014. My utility is Pepco in MD and I have net metering. However, I don't think I ever got the full amount I produced and there was always about 40% of the cookie bite. Now I am planning to add another system and working with Tesla to get some estimates and it seems like another 4.8kW system may work for me. I am thinking about getting one Powerwall with the new system. I have a Tesla wall charger on a 60amp circuit and would like to add it to the Powerwall to be able to charge my car if and when power goes out. In addition, I also have a 17kW Generac back-up generator ( connected to natural gas supply) that accomodates most of my electric needs except the second AC and few other things.

Does anyone have experience in combining two systems and how are they added to my net metering so that my utility will look at the total production from both the systems? Currently my production from one system ranges about 6100kWh-6200kWh and I was guaranteed 7200kWh when I signed the contract in late 2013.

If I add a Powerwall will the production from both systems be stored in the Powerwall so that I can pretty much use all the energy I produce and not depend on my utility? What am I supposed to tell Tesla during their planning phase and will Tesla be able to do that?

TIA

One PW to not depend on utility? What is your heat? I have 5 PW's and I still have to pull from the grid in winter with my 99% electric house when the solar panels produce next to nothing.

 

[jjrandorin]

I have a Tesla wall charger on a 60amp circuit and would like to add it to the Powerwall to be able to charge my car if and when power goes out.

while you can do that, planning on using a powerwall in that fashion is like using a triple A battery to charge 3-4 D batteries. Having a powerwall would allow you to keep the solar system running / producing during a power outage, but "to charge my car" is not a really good use of powerwall power imo.

If I add a Powerwall will the production from both systems be stored in the Powerwall so that I can pretty much use all the energy I produce and not depend on my utility?

There is virtually zero chance that 1 powerwall (which stores 13.5kWh of energy) would store all of the energy produced by 2 PV systems that add up to about 10kW of power. If the goal is "use all the energy I produce" then you will need more than one powerwall, for sure.

Both systems would be combined for any net metering, but your utility may make you get PTO all over again with whatever they have in place as far as plans / net metering right now. You wouldnt be grandfathered in under your old plan.

I also dont understand what you mean bu "they kept 40% of the cookie bite" as if they kept 40% of your production without crediting you for it in some manner, but unfortunately it can be very difficult to follow what utilities do for net metering etc (unless you are @Redhill_qik , who we are still waiting for the TED talk on utility net metering from, lol).

 

[bhakan]

One PW to not depend on utility? What is your heat? I have 5 PW's and I still have to pull from the grid in winter with my 99% electric house when the solar panels produce next to nothing.

I have natural gas heat to heat my house, a gas dryer, gas water heater, and gas for cooking. So, my electric dependency is not like what you quoted for you. Energy efficient home being a connected home and just one person household (the last 2 yrs after kids went to college etc) with about 2800-3000 sqft home with two zones ( upstairs and downstairs) for HVAC. My utility bills were surprisingly only around $300-$400 for the whole year. Even tho i charged my Tesla these years I also had free supercharging and used that to me advantage. Now I don't have that for my refresh MSLR.

 

[h2ofun]

I have natural gas heat to heat my house, a gas dryer, gas water heater, and gas for cooking. So, my electric dependency is not like what you quoted for you. Energy efficient home being a connected home and just one person household (the last 2 yrs after kids went to college etc) with about 2800-3000 sqft home with two zones ( upstairs and downstairs) for HVAC. My utility bills were surprisingly only around $300-$400 for the whole year. Even tho i charged my Tesla these years I also had free supercharging and used that to me advantage. Now I don't have that for my refresh MSLR.

Okay, non issue for winter, but since solar does not product much, one can easily use up on PW with a microwave, oven, etc.
In the summer, assuming you use AC, guess it depends on use..

Everyone I know if they get like one PW, its to use only for lights and refrig if power goes out. NO way charging an EV.
I am trying to add 2 more PW's to have 7, and still would drain 4 of them in the winter running my electric heaters and limited solar if raining.

 

[gaswalla]

lots of opinions here about doing things the 'right way'
for net metering, it is based on your electrical meter -you can have multiple inputs and outputs and your utility will just see what's going to the meter and whats coming from the meter. (note that they may not approve or want you to have multiple sources, but that's another matter)

 

[bhakan]

while you can do that, planning on using a powerwall in that fashion is like using a triple A battery to charge 3-4 D batteries. Having a powerwall would allow you to keep the solar system running / producing during a power outage, but "to charge my car" is not a really good use of powerwall power imo.



There is virtually zero chance that 1 powerwall (which stores 13.5kWh of energy) would store all of the energy produced by 2 PV systems that add up to about 10kW of power. If the goal is "use all the energy I produce" then you will need more than one powerwall, for sure.

Both systems would be combined for any net metering, but your utility may make you get PTO all over again with whatever they have in place as far as plans / net metering right now. You wouldnt be grandfathered in under your old plan.

I also dont understand what you mean bu "they kept 40% of the cookie bite" as if they kept 40% of your production without crediting you for it in some manner, but unfortunately it can be very difficult to follow what utilities do for net metering etc (unless you are @Redhill_qik , who we are still waiting for the TED talk on utility net metering from, lol).

The reason I mentioned using Powerwall to charge my car is when I was considering Powerwalls little more than 4 yrs ago I was informed by Tesla that with my 5.4kW system I cannot charge my car as they cannot add that circuit to the Powerwall. Hence that question.

Thanks for the storage capacity of one PW, 13.5kWh. With my current system on decent days even in Sept I produce around 21kWh in a day. So it is more. However, my thinking was that if I can charge my car (as that seems to be a good chunk if I charge before my electricity rate goes up at 12 noon) with the combined production that I can tap into I won't send much back to the grid as my utility does not give full credit to my production. this addresses your last comment. What I see in my Tesla app as what I am producing in a day and what my utility company provides in my daily chart for net metering are two worlds away. So that was the reason I mentioned that i get credit for roughly 40% of what I produced in a month in my monthly net metering amount. The more I think about it since I have a backup generator also I can skip the PW and just eat all the cookies myself .

Yes. Tesla's plan includes an inspection and a PTO after they install.

 

[jjrandorin]

What I see in my Tesla app as what I am producing in a day and what my utility company provides in my daily chart for net metering are two worlds away

Im certainly not looking at what you are looking at, but many times when people make this statement, they are not remembering that net metering is only for what is sent to the utility, and your production during the day is also partially consumed by your home (so the utility never sees what you are producing in a day).

Unless your home charger is on less than a 30 amp breaker, one powerwall wont be able to charge it at all during a power outage. I dont see a reason for you to have only one powerwall, unless the desire is "I want to use my solar during a power outage" (not "I want to charge my car during a power outage).

You are better off either considering 2 powerwalls, or none.

 

[bhakan]

Okay, non issue for winter, but since solar does not product much, one can easily use up on PW with a microwave, oven, etc.
In the summer, assuming you use AC, guess it depends on use..

Everyone I know if they get like one PW, its to use only for lights and refrig if power goes out. NO way charging an EV.
I am trying to add 2 more PW's to have 7, and still would drain 4 of them in the winter running my electric heaters and limited solar if raining.

Yes. I have two separate Carrier 5T systems for AC for two zones that keep my entire house nice and cool.

My Generac backup will take care of most of my systems. So the PW will be only for the initial backup.

 

[bhakan]

lots of opinions here about doing things the 'right way'
for net metering, it is based on your electrical meter -you can have multiple inputs and outputs and your utility will just see what's going to the meter and whats coming from the meter. (note that they may not approve or want you to have multiple sources, but that's another matter)

I am afraid about your comment in the parenthesis. That is where I need to know how Tesla will manage the two inverter outputs. I have an inverter output for interconnection for my current PV system in my electric Main panel and when Tesla installs a separate one for the new system I need to know how that feeds into my net metering.

 

[bhakan]

Im certainly not looking at what you are looking at, but many times when people make this statement, they are not remembering that net metering is only for what is sent to the utility, and your production during the day is also partially consumed by your home (so the utility never sees what you are producing in a day).

Unless your home charger is on less than a 30 amp breaker, one powerwall wont be able to charge it at all during a power outage. I dont see a reason for you to have only one powerwall, unless the desire is "I want to use my solar during a power outage" (not "I want to charge my car during a power outage).

You are better off either considering 2 powerwalls, or none.

My home charger is on a 60amp breaker. So it won't work unless i charge my car from my dryer outlet which is not being used as I have a gas dryer that goes on a regular 120v outlet. May have to rethink the PW.

 

[jjrandorin]

I am afraid about your comment in the parenthesis. That is where I need to know how Tesla will manage the two inverter outputs. I have an inverter output for interconnection for my current PV system in my electric Main panel and when Tesla installs a separate one for the new system I need to know how that feeds into my net metering.

Everything is behind your meter. You will need to get new PTO since the size of your "system" will change, but we have people here that have 2 and even 3 separate systems on one house.

 

[jjrandorin]

My home charger is on a 60amp breaker. So it won't work unless i charge my car from my dryer outlet which is not being used as I have a gas dryer that goes on a regular 120v outlet. May have to rethink the PW.

Even if 1 powerwall could support that size (it cant), a 60amp circuit is 48amp continuous, at 240 volts its 11.5kW. Even if it could support it, charging your car for 1 hour would take the powerwall from full to virtually empty on that size circuit.

1 powerwall is not capable of powering that circuit though, so as I mentioned, it would be 2, or none.

 

[lensovet]

Doesn't the Tesla wall charger let you downrate how many amps it pulls? Who said the charging needs to happen at full speed?

PW+ will support 9 kW with full solar output if you're charging during the day and 7 kW in off-grid mode. the 5.4 limitation is only when you're grid-connected, which is irrelevant during an outage.

 

[Redhill_qik]

Even if 1 powerwall could support that size (it cant), a 60amp circuit is 48amp continuous, at 240 volts its 11.5kW. Even if it could support it, charging your car for 1 hour would take the powerwall from full to virtually empty on that size circuit.

1 powerwall is not capable of powering that circuit though, so as I mentioned, it would be 2, or none.

Just because the wall charger is on a 60A breaker and can charge at 48A doesn't mean that it has to. You can drop the charge rate down to something that works with the extra solar that isn't needed by the house and Powerwall. If you have an extra 4kW being generated then set the charge rate at 16A.

 

[jjrandorin]

Just because the wall charger is on a 60A breaker and can charge at 48A doesn't mean that it has to. You can drop the charge rate down to something that works with the extra solar that isn't needed by the house and Powerwall. If you have an extra 4kW being generated then set the charge rate at 16A.

Sure, it doesnt have to, but the OP didnt mention that they were interested in slowing it down. One should never depend on the car to turn down the charging rate (even though it can, there are times when for "reasons" that fails) so the wall connector itself would need to be configured to provide slower charge.

That can absolutely be done, but most people who install a wall connector and get it setup for the "fastest available" are not interested in "having" to turn it down.

In this OPs case (already has backup generator, not interested in the use of a powerwall for backup power) perhaps I am missing something, but there is very little benefit to a powerwall for them, and that benefit isnt "I can charge my car from my powerwall".

 

[DrSmile]

Although you could hook up just one of the systems to your Powerwall, if the power goes out your other system would be off line because there is nowhere for the power to go. 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.

I have two Powerwalls and I can vouch for the Powerwall inverters being underrated as I can charge my Teslas at 48 amps and run my house for hours off grid without issue (usually 11-12 KW continuous). The 2 Powerwalls can also handle the 11.4 KW inverter solar production without issue. You should get 2 Powerwalls with the amount of solar you're considering.

 

[bhakan]

Sure, it doesnt have to, but the OP didnt mention that they were interested in slowing it down. One should never depend on the car to turn down the charging rate (even though it can, there are times when for "reasons" that fails) so the wall connector itself would need to be configured to provide slower charge.

That can absolutely be done, but most people who install a wall connector and get it setup for the "fastest available" are not interested in "having" to turn it down.

In this OPs case (already has backup generator, not interested in the use of a powerwall for backup power) perhaps I am missing something, but there is very little benefit to a powerwall for them, and that benefit isnt "I can charge my car from my powerwall".

If there is extra power that my panels have generated, it will be useful for me to tap into that. I had not known that. That is useful for me to do even when I did not lose power when I can use the stored power from the PW. In reading Tesla's website about Powewalls when a client has a backup generator I noticed that the system will use the PW storage first and then only move to the backup generator.

 

[CrazyRabbit]

You said your existing system is on a PPA. You can not add that system to your Tesla powerwall…

 

[bhakan]

You said your existing system is on a PPA. You can not add that system to your Tesla powerwall…

Thx. Wish Tesla would have notified me that. I sent my questions asking for clarification.