Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

SDG&E - wanting to install a second meter and second solar disconnect

bkp_duke

Well-Known Member
May 15, 2016
6,963
31,631
San Diego, CA
Anyone else run into this with their Powerwall installation?

I have the following configuration:
3 x PW2 in whole-house backup configuration
12 kWh SunPower Solar System

The PW installation was completed 2 months ago, and we have been live with no problems since.

I get a call from Tesla today stating that SDG&E wants a solar disconnect installed and a SECOND meter. This doesn't make any sense to me because:
1) we already have a solar disconnect on the system (what would be the point for a second one)
2) I never agreed to any kind of secondary metering

We are in Step 2 of Large-Scale Storage SGIP, which could be the only reason I could think for this.

Anyone else have any kind of similar experience with the utility requiring an additional disconnect and a second meter?
 
I don’t have the answer to your question, but I wanted to ask you a question about your setup.

You said you have 3 PWs for the whole-house. Was it a requirement to have 3 powerwalls because of the max load of your house? Or did you install them to have more capacity/last longer? Does it work well as a whole-house backup?
 

bkp_duke

Well-Known Member
May 15, 2016
6,963
31,631
San Diego, CA
We needed 3 powerwalls to reach whole-house backup, based upon the number of amps that could be reasonably pulled at the same time (i.e. two ACs come on, wife using the oven, etc.). In theory we could exceed what 3 powerwalls would provide, but then it just pulls the extra from the grid (no damage to the powerwalls).

I have an update since the original post:
1) I will be getting a second "generation meter" to monitor JUST solar production by SDG&E. I managed to get a face to face meeting with the Tesla electrician, SDG&E electrician, and myself. SDG&E said it was a CPUC requirement because we were > 10 kw on the powerwalls (i.e. more than 2). They also admitted that it was purely for their benefit, and that for billing purposes all that anyone cared about was the NET. Tesla is currently working through this process. This soured me to SDG&E so much that I almost gave them the big middle finger and went off-grid. But then I would not get the gigantic SGIP rebate, so I'll deal with it.
2) Cost - the meter + 2 additional boxes will be covered entirely by Tesla under the contract I signed. I don't know what the boxes and labor are by Tesla, but the meter bill was almost $600 by SDG&E.
3) No longer a true "whole house backup" - it's a bit of an aside, but we are building a pool right now. We are only going to be able to put one of the pool pumps on the powerwall setup for backups (fortunately it will be the filter pump, which runs the most). The rest are going to be wired to bypass the powerwalls.

The whole-house backup works GREAT. We had an idiot run into a transformer box here last month on the main street, and had a 12h outage. We were the only house for about a 1/2 mile in each direction that had power (and internet!).
 
I'll share what I did just in case it also helps.

I went with two Powerwalls (no solar), originally with the idea of doing whole home backup, until their Time-Based Control software update come out which it did back in April. I still have two Powerwalls and it works well. I setup my reserve to 25%, however I've ordered a 3rd Powerwalls because my ultimate goal is to use two of the Powerwalls for Time-Based Control, and then set my reserve to 33%, so that one of the Powerwalls is always there as a reserve. I want this setup because I'm in Earthquake zone, so this way I have at a minimum one Powerwall to run as backup. I've calculated that I could use it for about 5 days just for the essentials (fridge, charge the iPhone, and two light bulbs in the house) when there is an earthquake and the grid goes offline.
 
  • Like
Reactions: wesley888

bkp_duke

Well-Known Member
May 15, 2016
6,963
31,631
San Diego, CA
I'll share what I did just in case it also helps.

I went with two Powerwalls (no solar), originally with the idea of doing whole home backup, until their Time-Based Control software update come out which it did back in April. I still have two Powerwalls and it works well. I setup my reserve to 25%, however I've ordered a 3rd Powerwalls because my ultimate goal is to use two of the Powerwalls for Time-Based Control, and then set my reserve to 33%, so that one of the Powerwalls is always there as a reserve. I want this setup because I'm in Earthquake zone, so this way I have at a minimum one Powerwall to run as backup. I've calculated that I could use it for about 5 days just for the essentials (fridge, charge the iPhone, and two light bulbs in the house) when there is an earthquake and the grid goes offline.

Why not get solar instead? Seems that the payback would be FAR quicker, and then if that earthquake hits you have essentially an infinite time-period of power (i.e. PWs charge up every day from the sun).
 
Anyone else run into this with their Powerwall installation?

I have the following configuration:
3 x PW2 in whole-house backup configuration
12 kWh SunPower Solar System

The PW installation was completed 2 months ago, and we have been live with no problems since.

I get a call from Tesla today stating that SDG&E wants a solar disconnect installed and a SECOND meter. This doesn't make any sense to me because:
1) we already have a solar disconnect on the system (what would be the point for a second one)
2) I never agreed to any kind of secondary metering

We are in Step 2 of Large-Scale Storage SGIP, which could be the only reason I could think for this.

Anyone else have any kind of similar experience with the utility requiring an additional disconnect and a second meter?
I'll see but I probably won't have these issues. I'm 10kWh SunPower, and waiting for 2x PW2 in the SCE area. All of SCE is on SmartMeters by now, I believe.

It's good to know 3x PW2 could trigger this ..
 

Tam

Well-Known Member
Nov 25, 2012
11,068
10,068
Visalia, CA
...Why not get solar instead?...

My last year post showing that in theory, arbitrage (taking profits due to price differences in Time of Use electric rate) in PG&E (which covers San Francisco) can recoup your powerwall cost 10 years:

Pacific Gas and Electric Company off-peak rate is $0.12225 while partial peak is $0.24986 and peak rate is $0.45389


rates.png




The price difference between cheapest and most expensive in a day is:

$0.45389-$0.12225=$0.33164

So if you can recharge and discharge during those hours, you earn or save 14kWh x $0.33164 or $4.64296 per day.

$4.64296 x 365 days = $1,694.6804 annually

In 10 years you'll get $16,946.804 which should well cover your cost of investment.

($5,900 powerwall2 + hardwares and installation fees)

If Powerwall Time of Use software works, then you don't use any power from the grid but all from Powerwall during peak hours.

Remember, this is a theory because in real life, who would come home from the middle of work at 2PM (peak rate) to blast the air conditioner and other electrical appliances then go back to work at 8 PM (peak rate's over for each day).
 
Last edited:

miimura

Well-Known Member
Aug 21, 2013
7,335
7,319
Los Altos, CA
There are several problems with this analysis.
1. The rate differential you quoted is only valid in the Summer rate season. 6 months of the year, the Peak rate is ~$0.32 instead of ~$0.45.
2. You can't charge from the grid Off-Peak if you have solar. You have to give up your Part-Peak solar export to fill the batteries M-F.
3. You can't force discharge into the grid during Peak period, you would have to save the money by avoided usage and maximized export during that period. It's pretty hard to use exactly 2kW (14kWh in 7 hours) every day.
4. Weekends. There is only 4 hours of Peak on Sat & Sun. However, the differential between your opportunity cost of solar to fill the battery in the morning and Peak usage supplied by the battery is greater.
 

Tam

Well-Known Member
Nov 25, 2012
11,068
10,068
Visalia, CA
...The rate differential you quoted is only valid in the Summer rate season.

So with decreased peak rate for winter, that lower winter peak rate is still higher than other non-peak rates which still make arbitrage effective but less.

...You can't charge from the grid Off-Peak if you have solar. You have to give up your Part-Peak solar export to fill the batteries M-F...

The simple illustration of Powerwall only is to answer the question above "Why not get solar instead?"

Powerwall only without solar does not qualify for incentives/tax breaks but you don't have strict solar rules above that restrict how Powerwall can be used.

...It's pretty hard to use exactly 2kW (14kWh in 7 hours) every day...

For those cars that don't have unlimited free Supercharging, such as Model 3 LR which is about 75 kWh, 1 powerwall is not enough. Needs to stack up some more for all those who'll be doing Tesla's Ridesharing Network and will only take customers during non-peak rate hours.

...Weekends. There is only 4 hours of Peak on Sat & Sun...

Thanks for reminding about the weekends. Arbitrage may still work but it would just take longer to recoup the investment.

Nevertheless, thanks for pointing out those weaknesses in my illustrations!
 
Last edited:

bkp_duke

Well-Known Member
May 15, 2016
6,963
31,631
San Diego, CA
So let me get this straight . . . you are banking on power rate arbitrage to recoup (you hope) the cost of these.

There are several logical fallacies that I can see with that.
1) power rates fluctuate, and are set by CPUC to benefit the utilities. On average, CPUC allows for major rate changes every 3 years in CA. This places a huge uncertainty on your calculations.
2) as pointed out above, the arbitrage for Winter is very small, and you over-estimated the arbitrage for weekends
3) you are neglecting to calculate a 10% loss in all charge / discharge cycles. The PW2 has a 90% round trip AC to DC to AC efficiency. This will eat into your calculated savings considerably, as I don't see you accounting for this loss.


I would encourage you to do the math on a combined solar+PW2 system to see what the payback is. I would bet it is far lower. In my case, that was the optimal solution (self consumption).
 

Products we're discussing on TMC...

About Us

Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.

Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


SUPPORT TMC
Top