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Powerwall for Planned Power Outages

nwdiver

Well-Known Member
Feb 17, 2013
8,478
11,697
United States
Can't "add on" ... or can't find someone who will merge two systems.

According to Tesla at least

"Unfortunately Tesla solar panels cannot be added to any third party solar system, you can however add more Tesla solar panels to an already installed Tesla solar system."

I would find someone else or negotiate with Tesla. There's no reason you can't parallel two PV systems... it's no different than if you have PV and so does your neighbor... just less distance. Lots of options out there.
 

Owner

Active Member
Dec 20, 2012
1,544
356
San Francisco Bay Area
I would find someone else or negotiate with Tesla. There's no reason you can't parallel two PV systems... it's no different than if you have PV and so does your neighbor... just less distance. Lots of options out there.

I don't want to find yet another 3rd party, then parallel two systems.
Then later down the road want to add more panels and golly gee have 3 systems in parallel.

The one person who did return my email said that turning hot water into an electric version will cost a lot more monthly. So that seems like a bad option without more panels.
 

nwdiver

Well-Known Member
Feb 17, 2013
8,478
11,697
United States
I don't want to find yet another 3rd party, then parallel two systems.
Then later down the road want to add more panels and golly gee have 3 systems in parallel.

Why would multiple parallel systems matter? Even a small micro inverter based system is >10 'systems' in parallel.

The one person who did return my email said that turning hot water into an electric version will cost a lot more monthly.

They're probably weren't thinking of a heat pump. Heat Pumps use ~70% less electricity.

When I bought my current home it had a gas stove, gas furnace, gas water heater and used ~17MWh/yr in electricity. I replaced the windows, added insulation, replaced the gas stove with electric, replaced the gas furnace with a heat pumps (also a ~2x more efficient A/C), replaced the gas water heater with a heat pump water heater. Now my home uses no fools fuel, I have an electric car AND the house uses ~50% less electricity than it did with gas heat and no electric car. Living responsibly is actually very very easy when you stop wasting effort coming up with excuses as to why it's so hard.......

Just to make things interested recently added 16 panels on a separate off-grid system. Now the grid-tied system exports everything my car doesn't use. My last electric 'bill' was amusing.

Screen Shot 2020-05-09 at 9.04.11 PM.png
 
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Owner

Active Member
Dec 20, 2012
1,544
356
San Francisco Bay Area
Living responsibly is actually very very easy when you stop wasting effort coming up with excuses as to why it's so hard.......

View attachment 543408

Its hard because I can't get calls or emails back from various contractors.
The electric water heater guy will install, but then I need to find a separate electrician. getting an electrician for a small job here is tough.
Heat pumps - no luck yet at all with return contact etc...
that's why its hard, we don't have enough install folks here in the area -- too much demand.
 

Owner

Active Member
Dec 20, 2012
1,544
356
San Francisco Bay Area
Well unfortunately there is no one that can install a heat pump for a radiant floor system. I tried 4 years ago when I replaced the water tank with a boiler (that is supposedly going to last 25 years). Still 4 years later not available. "We get a lot of requests for that but no one in the Bay Area installs them." I don't know if it is because they don't exist for radiant floors or not.

And no non-profit takers for the existing solar.

So the only open question for now until there is an electrical option for radiant flooring (which is more efficient than forced air) and that being 2/3 of the gas bill, makes no sense to do anything else until that option is available. It seems that it likely an efficiency thing.

So perhaps replacing the hot water heater when it breaks with an electrical model and then subsequently upgrading the solar.... The installer said it is a lot more costly to use an electrical vs. gas if you are relying upon piped in energy not solar.

I just don't see spending $10,000 net for one powerwall. Back to the friends house / hotel options.
 

MorrisonHiker

Well-Known Member
Mar 8, 2015
10,347
10,180
Colorado
Well unfortunately there is no one that can install a heat pump for a radiant floor system. I tried 4 years ago when I replaced the water tank with a boiler (that is supposedly going to last 25 years). Still 4 years later not available. "We get a lot of requests for that but no one in the Bay Area installs them." I don't know if it is because they don't exist for radiant floors or not.

And no non-profit takers for the existing solar.

So the only open question for now until there is an electrical option for radiant flooring (which is more efficient than forced air) and that being 2/3 of the gas bill, makes no sense to do anything else until that option is available. It seems that it likely an efficiency thing.

So perhaps replacing the hot water heater when it breaks with an electrical model and then subsequently upgrading the solar.... The installer said it is a lot more costly to use an electrical vs. gas if you are relying upon piped in energy not solar.

I just don't see spending $10,000 net for one powerwall. Back to the friends house / hotel options.
We're installing Schluter's ditra heat system in a master bath. I don't think you'd use it to heat an entire house but it might be a way you could warm up the floors in some rooms. We have hot water heat (from a boiler) everywhere else in the house.
 

jboy210

Well-Known Member
Supporting Member
Dec 2, 2016
5,722
3,709
Northern California
We're installing Schluter's ditra heat system in a master bath. I don't think you'd use it to heat an entire house but it might be a way you could warm up the floors in some rooms. We have hot water heat (from a boiler) everywhere else in the house.

We have a similar system. Nothing so luxurious as a heated bathroom floor.
 
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MorrisonHiker

Well-Known Member
Mar 8, 2015
10,347
10,180
Colorado
@jboy210 @MorrisonHiker – what's the ballpark cost of the full Shluter ditra system and how large of a bath floor does it cover?
Our master bath is less than 90 square feet. Cabinets will cover part of that so we ordered a kit that would cover 60 square feet of tile and 37.5 square feet of that would be heated. Basically, we'll be tiling everything but won't be heating under the cabinets, around the toilet or in the shower, but you can have a heated shower floor as well. We paid less than $500 for the kit, including the wifi thermostat (controllable via mobile device), the heating cable and floor membrane. We also bought a couple extra membrane sheets at $18 each which will allow us to tile the rest of the floor. They have all different sized kits or you can by the items individually. We shopped around and prices vary greatly. There are cheaper systems out there but we went with Schluter since we're totally redoing the tile floor and shower at the same time. We're doing the install ourselves.
 
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jboy210

Well-Known Member
Supporting Member
Dec 2, 2016
5,722
3,709
Northern California
@jboy210 @MorrisonHiker – what's the ballpark cost of the full Shluter ditra system and how large of a bath floor does it cover?

I have no idea, but I don't remember the additional cost to the tiling project giving me pause. It was something we had wanted for a while, so when we remodeled we had them just put it in. There was also some rewiring involved to put it on a separate circuit with a dedicated breaker. And there is also the thermostatic control unit. I believe I bought that for them for $200 or so since I wanted Wifi access.

We have it in the bathroom, toilet room, and closet since they all have the same tile floors. If you don't have the heat on those tile floors are quite cold in the morning when we get up and evenings when we get read for bed. So we have the thermostat programmed to heat them up an hour before we get up and hour before we head to bed.
 

Owner

Active Member
Dec 20, 2012
1,544
356
San Francisco Bay Area
We're installing Schluter's ditra heat system in a master bath. I don't think you'd use it to heat an entire house but it might be a way you could warm up the floors in some rooms. We have hot water heat (from a boiler) everywhere else in the house.

The whole house has radiant heating already installed. It is great. You can really keep the thermostat about 5 degrees lower than with forced air. And also fine tune the heating requirements to each room a lot better than forced air. The only disadvantage I have experienced is that it takes a lot longer to warm up a house after an extended time away with the system off.

Interrupting that system would be quite tricky. I think there are 7 zones in the house with lines coming together in a mechanical room.

Unfortunately retrofitting an electric water heater is pricey. The unit is more but also it needs a dedicated breaker. Right now the unit shares the breaker with the boiler. So even that electrical work would be at least $1,000.
 

jboy210

Well-Known Member
Supporting Member
Dec 2, 2016
5,722
3,709
Northern California
How does that play into the electric floor heating?

It has a schedule in it. So we set the temp to be warmer for times when you be running around barefoot in the bathroom and closet. For us that is getting ready for bed and getting up in the morning. The rest of the day when you are at work or out you can set the temp down so the floor does not pull power.

The floor unit we use is from Nuheat and was pretty cheap, $200 or so. I think they have units that also work with a phone these days. But, not sure how that would play with your system.
 

Freakyguy666

Member
May 14, 2020
60
14
USA
Not sure where else to post this so I thought I’d give this forum a shot....

I’ve got a 400amp main panel with average daily use of 75kW (excluding car charging) with a ~15.2kWp solar system. I’m getting constant outages in my area and am looking to purchase PW for whole home backup only.

I have the budget and space for 8PW’s but from what I understand SCE (my “awesome” utility) needs to “approve” how many PW’s I’m allowed to connect to my home.

Questions:
1) given my average daily use, what would be the ideal # of PW’s?
2) given the size of my solar system, how many PW’s is my utility likely to “allow”?
3) does tesla or the utility require/mandate an emergency load panel or may I simply use the PW’s to backup the entire Main Panel?
 

Mokuzai

Member
Jun 10, 2017
860
5,491
Valencia, CA
1) given my average daily use, what would be the ideal # of PW’s?

Sorta depends on how long of an outage you're planning for. Also would your usage and behavior change during an outage to prolong the backup? The powerwalls just need to last through the night and have enough excess solar during the day to charge back up. On your SCE account go to Data Sharing and Download and download a range of days. On any given hour of any day a negative number will represent excess solar that you can add up to roughly (this won't be exact but will give you an idea) see how much you can pump into a powerwall. Then that needs to last for the positive values through the night.

2) given the size of my solar system, how many PW’s is my utility likely to “allow”?

You can actually just call the NEM department and ask them. PM me if you need the number. It's not exactly based on the system size but some average estimated generation capacity. Our 12.5kw system comes out to 10.xx according to their calculations. I'm being told that we could have up to 3 powerwalls but 4 would exceed their policy. However we're rolling the dice and installing 4 total. When I spoke to SCE they said that they'll evaluate and take into consideration justifications for larger systems. In our case we are trying to backup the AC (whole house, the AC is only item not backed up with our current 2 powerwalls) which we're told requires at least 4 powerwalls to handle the amp load.

3) does tesla or the utility require/mandate an emergency load panel or may I simply use the PW’s to backup the entire Main Panel?

If you're backing up the entire house I'd imagine that they'd skip the 2nd panel but I'm not sure. But this goes back to how many amps do you need to be backed up and how many powerwalls are required to handle that load. When you talk to your solar installer they'll ask for pictures of your AC compressor (if you have one) and main panel to try and calculate the load requirements. If you're using 75kw per day you could probably get permission to expand your solar system which might make it easier to get approval for enough batteries to backup the whole house.
 

Freakyguy666

Member
May 14, 2020
60
14
USA
Sorta depends on how long of an outage you're planning for. Also would your usage and behavior change during an outage to prolong the backup? The powerwalls just need to last through the night and have enough excess solar during the day to charge back up. On your SCE account go to Data Sharing and Download and download a range of days. On any given hour of any day a negative number will represent excess solar that you can add up to roughly (this won't be exact but will give you an idea) see how much you can pump into a powerwall. Then that needs to last for the positive values through the night.

Understood. I am attempting to be prepared for a 24 hour outage that occurs during a period when it is raining (little to no solar production) so therefore the solar production would not have much, if any, bearing. I can infer that your answer in this event would be at least 6 powerwalls given my ave daily use, correct?

You can actually just call the NEM department and ask them. PM me if you need the number. It's not exactly based on the system size but some average estimated generation capacity. Our 12.5kw system comes out to 10.xx according to their calculations. I'm being told that we could have up to 3 powerwalls but 4 would exceed their policy. However we're rolling the dice and installing 4 total. When I spoke to SCE they said that they'll evaluate and take into consideration justifications for larger systems. In our case we are trying to backup the AC (whole house, the AC is only item not backed up with our current 2 powerwalls) which we're told requires at least 4 powerwalls to handle the amp load.

PM sent. Incidentally, have you received any feedback on where you’re allowed to place the PW’s given the recent restrictions on how many may be placed on a Wall?

If you're backing up the entire house I'd imagine that they'd skip the 2nd panel but I'm not sure. But this goes back to how many amps do you need to be backed up and how many powerwalls are required to handle that load. When you talk to your solar installer they'll ask for pictures of your AC compressor (if you have one) and main panel to try and calculate the load requirements. If you're using 75kw per day you could probably get permission to expand your solar system which might make it easier to get approval for enough batteries to backup the whole house.

Solar is maxed out. Only way to increase would be to add inverters & replace panels with 350s in place of 315s. Not sure that’s worth it.

Given the current Gateway is only rated to 200amps, how would they backup my 400amp main without a 2nd panel?
 
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Mokuzai

Member
Jun 10, 2017
860
5,491
Valencia, CA
I can infer that your answer in this event would be at least 6 powerwalls given my ave daily use, correct?

Yes if you're trying to back up 75kw off of powerwalls you would need 6. That would be a tall order getting approved through SCE with your system size.

Incidentally, have you received any feedback on where you’re allowed to place the PW’s given the recent restrictions on how many may be placed on a Wall?

Your solar installer will help finding a location. Ours will be two per wall in different locations so it wouldn't have come up.

Given the current Gateway is only rated to 200amps, how would they backup my 400amp main without a 2nd panel?

That I don't know. Most residential panels are 200 amps max so not sure how they would handle that.

Solar is maxed out. Only way to increase would be to add inverters & replace panels with 350s in place of 315s. Not sure that’s worth it.

Well you could get creative. We turned our patio cover into a solar shade structure.

IMG_5631.JPG IMG_5630.JPG
 
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Not sure where else to post this so I thought I’d give this forum a shot....

I’ve got a 400amp main panel with average daily use of 75kW (excluding car charging) with a ~15.2kWp solar system. I’m getting constant outages in my area and am looking to purchase PW for whole home backup only.

I have the budget and space for 8PW’s but from what I understand SCE (my “awesome” utility) needs to “approve” how many PW’s I’m allowed to connect to my home.

Questions:
1) given my average daily use, what would be the ideal # of PW’s?
2) given the size of my solar system, how many PW’s is my utility likely to “allow”?
3) does tesla or the utility require/mandate an emergency load panel or may I simply use the PW’s to backup the entire Main Panel?

1) At a minimum, I imagine 4 would be required. Six power walls may not be needed if you are able to shed power usage during a power outage. Pool equipment, EV charging, and power for secondary structures could be moved to a non-backup electric panel. Use of an electric cloths dryer can be mitigated by hanging clothes under sun.

Consider average winter use (with an added margin) as your metric for 24 hour backup use. Summer use is higher (with AC loads) and can be mitigated with great summer production.

Note, the extra money spent on two more Powerwalls may be better spent connecting a natural gas backup generator for maximum flexibility. The Powerwall can control the backup generator as needed.

2) Mokuzai has the best answer. As a reminder, the Tesla Powerwall support page states, "To ensure reliable operation during power outages, at least one Powerwall is required for each 7.6 kW AC of solar included in the backup circuit." Three is the minimum for a 15.2 kW-DC system, though four makes better sense.

3) Without knowing how your home is wired, I assume Tesla will install your gateway and Powerwalls based on the below sample layout from the Tesla Powewall Installation guide.

Capture.JPG


Non-critical loads would remain in the 400 A main panel. All your critical loads would be moved to a 200 A "backup-load" panel. A 200-400 A "generation" panel would include your Powerwalls, solar, and generator (if applicable).
 

Freakyguy666

Member
May 14, 2020
60
14
USA
Yes if you're trying to back up 75kw off of powerwalls you would need 6. That would be a tall order getting approved through SCE with your system size.



Your solar installer will help finding a location. Ours will be two per wall in different locations so it wouldn't have come up.



That I don't know. Most residential panels are 200 amps max so not sure how they would handle that.



Well you could get creative. We turned our patio cover into a solar shade structure.

View attachment 544535 View attachment 544536

Interesting idea but, as mentioned, my inverters are at capacity.
 

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