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Powerwall for Planned Power Outages

Owner

Active Member
Dec 20, 2012
1,544
356
San Francisco Bay Area
Unless there's an Earthquake... but those never happen in SF... right? :(

Plus we really need to move away from having fools fuel piped into our homes. In an area as temperate as CA that's beyond idiotic. Not sure paying ~$15/mo to have gas available on the rare occasion the grid is out makes any sense...

There are automatic shut off valves for natural gas lines here in CA. Your insurance company gives you discounts for those.

The problem to cut the natural gas is home heating. Even if it is pretty temperate here, we have big swings day to night all year (unlike other parts of the country).

I've looked into electrical heating for radiant floors but did not choose it twice. There were not any standard options yet available to do this when I looked. I didn't want to gerry rig something inadequate.

Ironically I know some folks in town who built a very big house. They put in no heat except for one fireplace in the living room. They wanted to be LEED certified. Okay, so they are LEED certified but are sleeping at probably 50 degrees at night at the warmest half of the year, and then sending a lot of pollutants through the fireplace. Crazy.

Although electric heating is available, it has not been easy to get for substantial homes.
 

Darwin

Member
Jan 12, 2018
75
96
Phoenix, Az
I have a Hubitat hub and currently in the permitting process for installing 2 PWs, in addition to expanding my 7.56kw subscription PV system to 11.34kw. Would love hook it all in to Hubitat.

I put together the following cross-platform app that provides monitoring and control of the Powerwall through both the SmartThings and Hubitat hubs:

Tesla Powerwall Manager app for SmartThings (and Hubitat) Hubs - DarwinsDen.com

The app allows you to automatically command smart devices and Powerwall functions from Hubitat or SmartThings based on the current status of the Powerwall and other smart devices and also provides various mobile status notifications. You can set up schedules for Powerwall mode and state changes (such as Backup-Only/Self Powered/Advanced Time Controls, battery reserve level %, stormwatch, etc) and also select devices that should automatically be turned off in the event that a grid/power outage is detected by the Powerwall.
 

destructure00

Active Member
Mar 2, 2019
1,476
1,672
Scottsdale, AZ
I put together the following cross-platform app that provides monitoring and control of the Powerwall through both the SmartThings and Hubitat hubs:

Tesla Powerwall Manager app for SmartThings (and Hubitat) Hubs - DarwinsDen.com

The app allows you to automatically command smart devices and Powerwall functions from Hubitat or SmartThings based on the current status of the Powerwall and other smart devices and also provides various mobile status notifications. You can set up schedules for Powerwall mode and state changes (such as Backup-Only/Self Powered/Advanced Time Controls, battery reserve level %, stormwatch, etc) and also select devices that should automatically be turned off in the event that a grid/power outage is detected by the Powerwall.


Nice! Bookmarked so I can give it a shot as soon as my PWs are online. Thanks!
 
Unless there's an Earthquake... but those never happen in SF... right? :(

Plus we really need to move away from having fools fuel piped into our homes. In an area as temperate as CA that's beyond idiotic. Not sure paying ~$15/mo to have gas available on the rare occasion the grid is out makes any sense...

Sure that's possible but Owner's goal is to deal short PG&E shutoffs and I am not aware of natural gas shutoff during PG&E shutoffs. In the Bay Area, lots of people already have natural gas for heating including me so there is no additional utility service setup cost to use natural gas.
 

nwdiver

Well-Known Member
Feb 17, 2013
8,477
11,694
United States
There are automatic shut off valves for natural gas lines here in CA. Your insurance company gives you discounts for those.

The problem to cut the natural gas is home heating. Even if it is pretty temperate here, we have big swings day to night all year (unlike other parts of the country).

I've looked into electrical heating for radiant floors but did not choose it twice. There were not any standard options yet available to do this when I looked. I didn't want to gerry rig something inadequate.

Ironically I know some folks in town who built a very big house. They put in no heat except for one fireplace in the living room. They wanted to be LEED certified. Okay, so they are LEED certified but are sleeping at probably 50 degrees at night at the warmest half of the year, and then sending a lot of pollutants through the fireplace. Crazy.

Although electric heating is available, it has not been easy to get for substantial homes.

.... heat pumps.... they work great anywhere that doesn't regularly see temperatures below 0F.

I cut the gas to my house ~7 years ago. Anyone that sees <0F <5x per year should really do the same.
 

Owner

Active Member
Dec 20, 2012
1,544
356
San Francisco Bay Area
.... heat pumps.... they work great anywhere that doesn't regularly see temperatures below 0F.

I cut the gas to my house ~7 years ago. Anyone that sees <0F <5x per year should really do the same.

Okay, so I'm looking into that now. it was not that long ago I replaced my furnace.

Gosh this addition though would completely change the solar equation. How big is your solar system to support a heat pump?
 

nwdiver

Well-Known Member
Feb 17, 2013
8,477
11,694
United States
Okay, so I'm looking into that now. it was not that long ago I replaced my furnace.

Gosh this addition though would completely change the solar equation. How big is your solar system to support a heat pump?

A heat pump is just an Air Conditioner working backwards... so the same size that would support an Air Conditioner. My heat pump is a multi-split so it uses ~1kW per room.
 
  • Informative
Reactions: Darwin

Owner

Active Member
Dec 20, 2012
1,544
356
San Francisco Bay Area
A heat pump is just an Air Conditioner working backwards... so the same size that would support an Air Conditioner. My heat pump is a multi-split so it uses ~1kW per room.

So I got some good numbers on gas usage a year - much easier than solar numbers.
Its almost exactly 1,000 Therms per year
About 1/3 is for the water heater

1,000 therms is basically 30,000 kWh

At a minimum that would be adding on a 15.12kW system for $27,750 without the powerwalls

interesting option.
I put in an email to a local heat pump guy to look at that part.

the offsets would be crazy. Making electricity when its warm, and then using it in the winter.
 

nwdiver

Well-Known Member
Feb 17, 2013
8,477
11,694
United States
So I got some good numbers on gas usage a year - much easier than solar numbers.
Its almost exactly 1,000 Therms per year
About 1/3 is for the water heater

1,000 therms is basically 30,000 kWh

At a minimum that would be adding on a 15.12kW system for $27,750 without the powerwalls

interesting option.
I put in an email to a local heat pump guy to look at that part.

the offsets would be crazy. Making electricity when its warm, and then using it in the winter.

Unless you have a condensing furnace your efficiency is probably ~90% so 30MWh of gas would equal ~27MWh of electricity. Then a heat pump generally as a COP of >3 (>3w of heat per watt of electricity) so to provide the same amount of heat with heat pumps would use <9,000kWh of electricity.

They also make heat pump water heaters.
 
  • Informative
Reactions: Owner

Owner

Active Member
Dec 20, 2012
1,544
356
San Francisco Bay Area
Unless you have a condensing furnace your efficiency is probably ~90% so 30MWh of gas would equal ~27MWh of electricity. Then a heat pump generally as a COP of >3 (>3w of heat per watt of electricity) so to provide the same amount of heat with heat pumps would use <9,000kWh of electricity.

They also make heat pump water heaters.

Okay. So I should replace:

1. The boiler with a heat pump (boiler is very young in its life span)
2. The water heater with an heat pump water heater (this has not been replaced so viable).
3. Add a ton of solar panels
4. Add a couple of power walls

The powerwall situation won't change that much because I have a second heating system with forced air -- kind of an A/C add on. But I'd do 2 powerwalls to ensure some hot water I guess.

Gosh, this is getting complicated!
 

nwdiver

Well-Known Member
Feb 17, 2013
8,477
11,694
United States
Gosh, this is getting complicated!

Not really. 9MWh/yr is ~15 solar panels. Not sure that qualifies as 'a ton'; Depending on the cost of your service removing your gas line could pay for itself in roughly the same amount of time it took for the solar. If we're gonna kick our pathetic addiction to fools fuel it's gotta happen at some point..... sooner better than later.
 
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MorrisonHiker

Well-Known Member
Mar 8, 2015
10,344
10,170
Colorado
Okay. So I should replace:

1. The boiler with a heat pump (boiler is very young in its life span)
2. The water heater with an heat pump water heater (this has not been replaced so viable).
3. Add a ton of solar panels
4. Add a couple of power walls

The powerwall situation won't change that much because I have a second heating system with forced air -- kind of an A/C add on. But I'd do 2 powerwalls to ensure some hot water I guess.

Gosh, this is getting complicated!
We have a boiler that heats the house and also stores water in a separate tank (so no separate hot water heater). A few years back, we researched replacing the boiler with a hybrid hot water heater but it didn't make sense since the hybrid water heater wouldn't have the capacity to replace the boiler. I didn't realize some people had both boilers and hot water heaters.

@nwdiver , do you know if it would be good to replace the hot water tank with a hybrid water heater or just stick with our boiler/hot water tank option?
 

nwdiver

Well-Known Member
Feb 17, 2013
8,477
11,694
United States
We have a boiler that heats the house and also stores water in a separate tank (so no separate hot water heater). A few years back, we researched replacing the boiler with a hybrid hot water heater but it didn't make sense since the hybrid water heater wouldn't have the capacity to replace the boiler. I didn't realize some people had both boilers and hot water heaters.

@nwdiver , do you know if it would be good to replace the hot water tank with a hybrid water heater or just stick with our boiler/hot water tank option?

If you have a boiler that services both your home heating, water heating AND you live in a colder climate something like a Sanden may make the most sense. You could keep your gas heat as backup and allow the Sanden to operate as much as possible.

CO2 heat pumps have a higher COP and can operate at much lower ambient temperatures.
 
  • Helpful
Reactions: MorrisonHiker
Okay. So I should replace:

1. The boiler with a heat pump (boiler is very young in its life span)
2. The water heater with an heat pump water heater (this has not been replaced so viable).
3. Add a ton of solar panels
4. Add a couple of power walls

The powerwall situation won't change that much because I have a second heating system with forced air -- kind of an A/C add on. But I'd do 2 powerwalls to ensure some hot water I guess.

Gosh, this is getting complicated!

Not sure if you still have the original stated primary goal of dealing with PG&E shutoffs. If so, it definitely sounds like a very complicated way to address that goal. On the hand, if your primary goal has changed to minimize fossil fuel usage then the things you listed are actually not so unusual.
 
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Reactions: StealthP3D

zƬesla

Member
Apr 16, 2020
431
166
US-NH
Interesting discussion. I live in a colder climate and have a 30? year old boiler (oil) for heating and hot water. Several years back, I added a cold start to the boiler and a SuperStor tank for storing the hot water and holding it at temp. Then, a few years back, I added mini-splits (two outside units with 5 heads total) for cooling in summer. This winter we started using the mini-splits for heating to save on oil (before prices fell) as they're heat pumps units rated to 5F – doing this however caused our electric bill to skyrocket. So, we're now installing a PV with 2 PowerWalls, something we have been mulling around for a while anyway. The batteries just went live and PV will be turned on as soon as electric company comes out to swap meter. We did a grid out test on the PWs with the mini-splits pumping out heat and didn't even see a light flicker anywhere. If power cuts out for long, we'll manually switch over to oil as a fallback in winter and reduce load on PWs.
 
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Reactions: nwdiver

nwdiver

Well-Known Member
Feb 17, 2013
8,477
11,694
United States
We did a grid out test on the PWs with the mini-splits pumping out heat and didn't even see a light flicker anywhere. If power cuts out for long, we'll manually switch over to oil as a fallback in winter and reduce load on PWs.

Yeah... mini-splits are AWESOME for off-grid use since they're inverter driven so there's no starting surge. My lights flicker more when my fridge cycles than when my HVAC cycles. How old are your mini-splits? The newer ones seem to have better specs for cold weather operation.
 

zƬesla

Member
Apr 16, 2020
431
166
US-NH
Yeah... mini-splits are AWESOME for off-grid use since they're inverter driven so there's no starting surge. My lights flicker more when my fridge cycles than when my HVAC cycles. How old are your mini-splits? The newer ones seem to have better specs for cold weather operation.

If memory serves, one is ~7 years old and the other ~5. These are Mitsubishi Mr. Slim. MSZs. They're rated pretty low but once it starts getting below 20F, I start seeing a bit of drop off in performance.
 

Owner

Active Member
Dec 20, 2012
1,544
356
San Francisco Bay Area
Not sure if you still have the original stated primary goal of dealing with PG&E shutoffs. If so, it definitely sounds like a very complicated way to address that goal. On the hand, if your primary goal has changed to minimize fossil fuel usage then the things you listed are actually not so unusual.

When the house was built the goal was to go as green as possible. But unfortunately at the design time, a lot of this stuff was not mainstream. Even during repairs or replacements I get a lot of funny looks just asking the questions. And I live in Silicon Valley!

Even now I'm having a tough time getting emails or calls back from these HVAC and other folks.

The hard part is trying to figure out timing of all of this. Tesla seems to have the most availability.

The other part is also not wanting to "throw out the existing solar" or the existing boiler etc.... I have had no luck on donating the solar.
 

Owner

Active Member
Dec 20, 2012
1,544
356
San Francisco Bay Area
Why would there be a benefit to thowing out the existing solar?

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."
 

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