What do I need to know? Tesla Solar + Powerwall Install

[Jeremy3292]

Currently building a new house scheduled to be done in June/July timeframe. 2265 sq ft, two stories, rear of house faces almost directly south. South Carolina has a rather impressive 25% state tax credit on top of the 30% federal tax credit, so looking to install 8 kW solar panels + 1 Powerwall. Trying to guesstimate energy usage based on my current house, but I will have all electric heating and cooling at my new house vs natural gas heat at my current house. So I am expecting a hefty increase in the electric bill. I may up to 8.8 or 9.6 kW solar (22 & 24 panels vs 20 panels at 8 kW).

Anyone who has done this already have any tips, tricks, or advice? Are there still long wait times or did Tesla catch up on inventory now?

Is it worth getting 2 Powerwall's or is that overkill? I have read 1 Powerwall really can't support a central HVAC when the grid is down, but solar panels + 1 Powerwall can. You would need 2 Powerwall's to support central HVAC if the grid is down, I think. It's a new house so it'll have a 15 SEER unit which is pretty energy efficient. I have also heard they may move to LFP chemistry for Powerwall soon.

 

[Darmie]

I think that 8 kW is a default size based on their default roof square footage of 913. Click the back arrow above the black 30% fed savings and adjust the roof sq ft size. If you're looking for full solar power, than you may need a 12 to 16 kW size system. From my research 2 power walls are better than 1.
Looking at all this myself for our new home we're building in Santa Fe Texas. I just can't justify the expense of solar over the price of power here. Then I thought I'd do something off grid just to charge the teslas but then I would need a $6,000 + home generator system as power backup. My head hurts. Once we get moved in and get a few power bills under our belt, I'll then get serious at something.

 

[taphil]

Get 2 PW for whole home backup. 1 PW is a lot less useful with selective circuit backup.

 

[Jeremy3292]

Get 2 PW for whole home backup. 1 PW is a lot less useful with selective circuit backup.

We have a pretty reliable grid here in SC with Duke Energy, so my only concern would be the power going out at night and then I don't have whole home backup. During the day if the power goes out solar + 1 powerwall should be able to power the whole house, no? Speaking in generalities of course.

 

[yblaser]

We have a pretty reliable grid here in SC with Duke Energy, so my only concern would be the power going out at night and then I don't have whole home backup. During the day if the power goes out solar + 1 powerwall should be able to power the whole house, no? Speaking in generalities of course.

Not necessarily... It depends on how the system is wired. Generally they would put the loads that are higher than a single powerwall can supply on a non-backed up circuit that would be completely disconnected if the grid goes down. Otherwise if that load kicks in without solar available it would bring the whole system down.

 

[jjrandorin]

During the day if the power goes out solar + 1 powerwall should be able to power the whole house, no? Speaking in generalities of course.

Probably not no, especially since you are talking about an array that is mostly south. You run the risk of one powerwall not being able to take the PV input and the entire system not working during a power outage. Tesla recommends no more than 7kW PV per powerwall.

A system designer can work around it perhaps by having only part of your PV active during a power outage, but tesla itself is likely not designing around that.

 

[taphil]

During the day if the power goes out solar + 1 powerwall should be able to power the whole house, no?

No. Not sure if it's still the case, but in the past, Tesla said 2 PW were required to backup whole home including AC compressor. With just 1 PW, they would only back up selective circuits like your fridge and some rooms, no big applicances or AC. While technically 1 PW + solar can provide enough kW of power to run the AC, 1 PW was not enough to start it or keep it running in addition to the loads for the rest of the house.

 

[Jeremy3292]

Probably not no, especially since you are talking about an array that is mostly south. You run the risk of one powerwall not being able to take the PV input and the entire system not working during a power outage. Tesla recommends no more than 7kW PV per powerwall.

A system designer can work around it perhaps by having only part of your PV active during a power outage, but tesla itself is likely not designing around that.

Isn't an array facing south the most desired direction as the sun moves east to west across the sky? Or I guess what you're saying is that is desirable but it will likely produce too much power for the Powerwall to handle in the event of an outage? When the grid is online, excess solar production will be sent back to the grid via net metering.

 

[jjrandorin]

One more thing, OP. "in general" its best to get as much solar as you can afford and your utility will let you install. Peoples electric use goes up, not down when they get solar. Its not usually as simple as "lets throw a few more panels on there" later, either.

You are planning all electric heating and cooling, you have an EV and its common for people who have one EV to either end up with zero EVs or more than 1 (meaning, you either start transitioning to more EVs or find that you hate it and get rid of it. The former ( buying more EVs) is more common than the latter.

TL ; DR - get those additional panels now, vs later.

 

[jjrandorin]

Isn't an array facing south the most desired direction as the sun moves east to west across the sky? Or I guess what you're saying is that is desirable but it will likely produce too much power for the Powerwall to handle in the event of an outage? When the grid is online, excess solar production will be sent back to the grid via net metering.

Yes, in general a south facing array is desirable from a production standpoint. Yes, what I am saying is that you are likely to produce too much power for one powerwall in any sort of outage situation with a south facing array that is that large.

 

[Jeremy3292]

While technically 1 PW + solar can provide enough kW of power to run the AC, 1 PW was not enough to start it or keep it running in addition to the loads for the rest of the house.

Thanks for the info as I was just thinking in terms of the kW available during the day from the solar array + Powerwall combo, not necessarily start up loads.

 

[Jeremy3292]

One more thing, OP. "in general" its best to get as much solar as you can afford and your utility will let you install. Peoples electric use goes up, not down when they get solar. Its not usually as simple as "lets throw a few more panels on there" later, either.

You are planning all electric heating and cooling, you have an EV and its common for people who have one EV to either end up with zero EVs or more than 1 (meaning, you either start transitioning to more EVs or find that you hate it and get rid of it. The former ( buying more EVs) is more common than the latter.

TL ; DR - get those additional panels now, vs later.

Thanks for the info. My dilemma now based on this thread is how many solar panels do I get vs getting 1 or 2 Powerwalls. I have a new house so it'll be a 200 amp service, but I've read 2 Powerwalls + 60 amp Tesla wall connector may require a panel upgrade even past 200 amps due to load calculations and such.

 

[jjrandorin]

Thanks for the info. My dilemma now based on this thread is how many solar panels do I get vs getting 1 or 2 Powerwalls. I have a new house so it'll be a 200 amp service, but I've read 2 Powerwalls + 60 amp Tesla wall connector may require a panel upgrade even past 200 amps due to load calculations and such.

I dont think you would need a panel upgrade for <10kW solar and 2 powerwalls, with 200 amp service. My own home has 200 amp service, 8.6kW of solar and 2 powerwalls (and 2 wall connectors in a load sharing configuration) for example.

I have the wall connector on the non backed up loads side (its the only thing in my home that isnt backed up, actually). This means that in a power outage I would not be able to charge my car (normally) but I had a 14-50 outlet put on the backup loads side that I would only use during a power outage if I wanted to drain my powerwalls a bit to keep solar generating.

Thats another discussion, but my point is, I dont think you need a panel upgrade, and you can put the wall connectors on the non backed up loads side and have "whole home - tesla wall connector" backup, if you want.

 

[Jeremy3292]

I dont think you would need a panel upgrade for <10kW solar and 2 powerwalls, with 200 amp service. My own home has 200 amp service, 8.6kW of solar and 2 powerwalls (and 2 wall connectors in a load sharing configuration) for example.

I have the wall connector on the non backed up loads side (its the only thing in my home that isnt backed up, actually). This means that in a power outage I would not be able to charge my car (normally) but I had a 14-50 outlet put on the backup loads side that I would only use during a power outage if I wanted to drain my powerwalls a bit to keep solar generating.

Thats another discussion, but my point is, I dont think you need a panel upgrade, and you can put the wall connectors on the non backed up loads side and have "whole home - tesla wall connector" backup, if you want.

So your whole home and central heating/cooling is backed up off 8.6 kW solar array and 2 powerwalls? I think I'll likely have to just place an order and then discuss with Tesla also as the devil is in the details here.

Appreciate the help!

 

[Jeremy3292]

Tesla recommends no more than 7kW PV per powerwall.

Also I don't know if things have changed due to the earlier Powerwall 1 & 2 vs Powerwall+ specs, but Tesla recommends 1 Powerwall battery on their website until you exceed 10 kW solar array, then it says 2 Powerwall's are recommended. Just something I noticed when messing with it online.

Powerwall 2 specs:

Powerwall+ specs:

 

[jjrandorin]

So your whole home and central heating/cooling is backed up off 8.6 kW solar array and 2 powerwalls? I think I'll likely have to just place an order and then discuss with Tesla also as the devil is in the details here.

Appreciate the help!

Yes, my whole home (minus my wall connectors) is backed up on 8.6kW and 2 powerwalls. I wish I had more PV though. I oversized in 2015, and was a net producer (pre EVs) but now I am a net consumer, and my PV is covering roughly 90% of my usage.

Tesla is most likely going to be the cheapest, but they will almost assuredly not be the most flexible. I am not trying to put them down, just pointing out to have the right expectations. You might want to get a couple of other bids as well just to see.

In any case, if I was you, I would be targeting the 9.6 of solar and 2 powerwalls.

 

[BGbreeder]

Also I don't know if things have changed due to the earlier Powerwall 1 & 2 vs Powerwall+ specs, but Tesla recommends 1 Powerwall battery on their website until you exceed 10 kW solar array, then it says 2 Powerwall's are recommended. Just something I noticed when messing with it online.

Powerwall 2 specs:
View attachment 907521

Powerwall+ specs:
View attachment 907520

That's not quite what they are saying. For off grid operation, the important line is 5kW maximum charge rate. If your solar output, less the home consumption, is more than 5kW, the solar may go into protective shutdown due to the inability to ramp down the solar output to a level that the batteries can accept. Non-Tesla systems, e.g. Enphase, are able to gradually reduce output as a function of frequency to better match solar to storage. The most stable way to design this is to have at least one Powerwall for every 5kW of production capacity.

If you believe that your grid energy will be stable and always present, then this isn't an issue.

It is best to maximize the solar at the time of install. It will be much more expensive per watt to add it later.

As far as starting HVAC systems go, modern variable speed inverter design play better with batteries, but again if you don't plan on being off grid, it isn't an issue. (On the subject of HVAC, extra insulation, roof overhangs, better home sealing, and minimizing south facing windows will help.)

All the best,

BG

 

[Jeremy3292]

That's not quite what they are saying. For off grid operation, the important line is 5kW maximum charge rate. If your solar output, less the home consumption, is more than 5kW, the solar may go into protective shutdown due to the inability to ramp down the solar output to a level that the batteries can accept. Non-Tesla systems, e.g. Enphase, are able to gradually reduce output as a function of frequency to better match solar to storage. The most stable way to design this is to have at least one Powerwall for every 5kW of production capacity.

I was pointing out the differences between Powerwall 2 and the newer Powerwall+ in the screenshots I attached.

Please correct me if I'm wrong, but the off-grid specs for Powerwall+ allow for more than 5 kW, no? 9.6 kW max rate in full sun off grid.

 

[charlesj]

Op. Also note that if power is out, day or night, the weather may not cooperate with you to fill up the battery or run your house day in and day out for a week, or longer.
It is also great that you are asking now, not after construction.

I have a small system, 3.8 kW and have 2 powerwalls.

 

[BGbreeder]

I was pointing out the differences between Powerwall 2 and the newer Powerwall+ in the screenshots I attached.

Please correct me if I'm wrong, but the off-grid specs for Powerwall+ allow for more than 5 kW, no? 9.6 kW max rate in full sun off grid.

Yes, you are right the Powerwall+ can sustain 7kW, not 5kW. The Powerwall is a battery, and the Powerwall+ is an inverter and battery combined.

One thing to also bear in mind is that most installations are not optimal, so a 10kW solar installation may max out at 7 or 8kW. Tesla generally has a larger DC/AC ratio to reflect that effect. (Many threads here on that subject.)

Good luck in your plans!

BG