Powerwall for Planned Power Outages

[MorrisonHiker]

May have asked before but could you have continued beyond 8 days or weather just didn't cooperate enough after 8 days?

During the 8 day test, we had one snow storm of about a foot. It was really sunny the next day so we were able to recharge the batteries and continue with the test. A couple days later, we had several more days of heavy snow predicted and we figured it was time to turn the connection to the grid back on.

Now that we are out of "snow" season, we could probably go 5 to 6 months off-grid if we wanted. For the month of May, we've only used 105 kWh from the grid so far but we've powered the house and three Teslas and still sent 991 kWh back to the grid. So while we could've easily lived off grid since late February, we wouldn't have had anywhere to send our excess production after charging the cars and Powerwalls. Our power company lets us send all of that excess production back to the grid and we get 1:1 credit for it...so we get about $0.18/kWh that we send back during peak, ~$0.13/kWh during part-peak and ~$0.09/kWh during off-peak. We chose the "credits" option instead of receiving a check so our excess production credits will roll over month to month until it is used up. It doesn't expire but can't ever be "cashed out". Since March, we've already sent a surplus of 2400 kWh back to the grid. We'll probably have surplus energy production through September/October. Then any credits we've accumulated will be used to help cover any months we don't have a surplus (November- January or so).

Thanks to the Powerwalls, virtually all of our grid usage is only at the $0.09/kWh rate. So while I can send hundreds of kWh back to the grid at the peak and part-peak rates, I never really pay more than the off-peak rate so this helps extend my rolled-over credits even more!

 

[Owner]

What's your budget looks like? The most cost effective option might be swapping your current 3.8kW inverter for a new 3.8kW SMA with SPS (Secure Power Supply). You can probably do that for <$2k.

I looked at this idea, its an interesting one and has its place. I'd end up with a plug in the far corner of the garage and have to snake something into the house to power the fridge. It seems questionable that it would have enough strength for the SubZero anyways.

I'm sure it would be quite a good solution for others.

 

[ra88it]

You can. Solar will continue to charge the Powerwalls even if the grid is down. Only one Powerwall is needed if you only back up certain outlets. If you back up the entire house or need 240V, two Powerwalls are necessary.

We did an endurance test last year and went 8 days (over 200 hours) off the grid, just using solar and Powerwalls.

Wanting to run anything over 30amps worth of draw will require more than 1 powerwall.

 

[Owner]

Wanting to run anything over 30amps worth of draw will require more than 1 powerwall.

The key thing to run is the refrigerator/freezer. I just checked its 15amps.
so that means I would have another 15amps lying around for other minor things - router etc...

 

[Owner]

@Owner, think about donating your solar panels and inverter to something like Habitat for Humanity. .

Well I have contacted Habitat for Humanity, a localish green organization and another building place. So far no takers yet but haven't officially heard back from all of them.

It doesn't seem like a standard thing yet to donate solar systems.

 

[ra88it]

The key thing to run is the refrigerator/freezer. I just checked its 15amps.
so that means I would have another 15amps lying around for other minor things - router etc...

What is your daily consumption & PV production(kWh)?

my bet is that 2 is what you’ll want for even 24hrs off grid outage.

 

[Owner]

What is your daily consumption & PV production(kWh)?

my bet is that 2 is what you’ll want for even 24hrs off grid outage.

That data is upthread. Not a huge amount about 1 powerwall worth.

I think I do want 2 powerwalls but then I need a whole upgraded solar system....

 

[ra88it]

That data is upthread. Not a huge amount about 1 powerwall worth.

I think I do want 2 powerwalls but then I need a whole upgraded solar system....

You should be able to support 2pw with 4kw when we can support 9 with 12kW.

We only have 9 due to not wanting to run a generator, I don’t care if we operate in a 30-85% status on the app for extended periods of time.

 

[charlesj]

The key thing to run is the refrigerator/freezer. I just checked its 15amps.
so that means I would have another 15amps lying around for other minor things - router etc...

Well, it is on that size breaker, yes but unless it is a huge freezer, mine averaged 62 kWh in a 30 day continuous monitoring
with a killAWatt meter, roughly 100 Wh.

 

[SMAlset]

Well I have contacted Habitat for Humanity, a localish green organization and another building place. So far no takers yet but haven't officially heard back from all of them.

It doesn't seem like a standard thing yet to donate solar systems.

I thought I saw the TV news story for recycled solar panels on either KPIX5 or ABC7 within the last few months but haven't located it yet, was hoping to find a lead for you. I do recall it was a story on the homeless and how they were using the panels to help supply power for them to charge phones, run small appliances, etc.

I did find this group, Urban Ore here in the bay area, that has collected used solar panels. Here's an article on them from July of 2019: Is it a good idea to buy used solar panels? . The photos of the used panels in the article is encouraging. If they aren't taking them in any more, maybe they know who is.

Here's their webpage ( https://www.urbanore.com ). Urban Ore is located in Berkeley and they are open during this covid time with reduced hours.

Receiving for Building Materials is limited. Please call extension 315 for more info. Outside Trader Department, which does pick ups and deliveries, is limited. Please call ext. 313 for more info.
​

BTW if people would like to help support Urban Ore and it's workers, here's a link to their GoFundMe site where they are raising money to help with their healthcare plan for their employees. Save Urban Ore's Healthcare #supportbusinessrelief organized by Urban Ore The GoFundMe page was created in March. An aerial photo of Urban Ore's location is posted there along with a video talking about the history of the company and why they need help during this covid19 timeframe. They have negotiated with Kaiser for a payment plan to cover their workers. Sounds like a good company to support, especially if you want to help promote recycling and support many of their long-time workers who have been committed to the recycling effort. (Fun fact: Urban Ore has been in business for 40 years this year and it's founder, Dr. Dan Knapp is now 80).

 

[jboy210]

I thought I saw the TV news story for recycled solar panels on either KPIX5 or ABC7 within the last few months but haven't located it yet, was hoping to find a lead for you. I do recall it was a story on the homeless and how they were using the panels to help supply power for them to charge phones, run small appliances, etc.

I did find this group, Urban Ore here in the bay area, that has collected used solar panels. Here's an article on them from July of 2019: Is it a good idea to buy used solar panels? . The photos of the used panels in the article is encouraging. If they aren't taking them in any more, maybe they know who is.

Here's their webpage ( https://www.urbanore.com ). Urban Ore is located in Berkeley and they are open during this covid time with reduced hours.

Receiving for Building Materials is limited. Please call extension 315 for more info. Outside Trader Department, which does pick ups and deliveries, is limited. Please call ext. 313 for more info.
​

BTW if people would like to help support Urban Ore and it's workers, here's a link to their GoFundMe site where they are raising money to help with their healthcare plan for their employees. Save Urban Ore's Healthcare #supportbusinessrelief organized by Urban Ore The GoFundMe page was created in March. An aerial photo of Urban Ore's location is posted there along with a video talking about the history of the company and why they need help during this covid19 timeframe. They have negotiated with Kaiser for a payment plan to cover their workers. Sounds like a good company to support, especially if you want to help promote recycling and support many of their long-time workers who have been committed to the recycling effort. (Fun fact: Urban Ore has been in business for 40 years this year and it's founder, Dr. Dan Knapp is now 80).

Thanks for the info. Big fan of urban ore from my days working down the street in Emeryville. Nice people. Glad to see there is fund and will make a donation.

 

[gpez]

Wanting to run anything over 30amps worth of draw will require more than 1 powerwall.

While this is absolutely correct it's a bit misleading

The Powerwall provides split-phase power. This means it has two 120v legs, just like most typical US households, which can be combined in to a 240v leg. Each leg is limited to 30amps and the total wattage (amps x volts) is limited to constant 5,000 watts (or 7,000 watts for 10 seconds). The Powerwall can provide 100% imbalanced power so it doesn't matter if one 120v leg is at 30 amps the other is at 10 or if they're perfectly split 20 amps / 20 amps.

Details are on the Powerwall datasheet.

The key thing to run is the refrigerator/freezer. I just checked its 15amps.
so that means I would have another 15amps lying around for other minor things - router etc...

And this is why it's misleading!

@Owner since your fridge and freezer are most likely 120v you still actually have much more power available even with 1 Powerwall. Note too that 15amps is the maximum at startup (aka surge). LRA rating is important here.

What you'll need to do is enumerate all of the appliances that could be running at the same time and determine the startup wattage and operating wattage, then calculate how many Powerwalls you need. A typical modern kitchen fridge, for example, will run and draw 300 watts but require 900 watts to start up. At 120v, that's only 2.5 amps and 7.5 amps - still lots left of the 30 amps max the Powerwall can provide on that one leg. The more important number is the 300 watts while running still leaves 4,700 watts. Plenty for all sorts of stuff! Remember too that the Powerwall can provide an additional 2,000 watts for up to 10s so even if your near the maximum a fridge starting up won't cause it to overload. Also remember your fridge doesn't run 24/7, it starts and stops throughout the day.

 

[jfabula]

I live in California in an area that PG&E can sometimes decide to turn off the power.
I live on the peninsula on the west side of the San Francisco Bay. We are not very windy and don't have those dreadful winds that other areas of California get. But PG&E can decide what they will. Where I immediately live they did not turn the power off in 2019.

But now with the coronavirus, the former backup plan was to just pack up a few things and find a hotel with the power on. Seems like a less viable solution now. And food in the refrigerator and freezer seems more valuable than in 2020. The former argument was say even a $300 a night hotel for say 3 nights would be only $1000 a year if it is required.

So looking for a powerwall or another brand equivalent. Elon's recent behavior makes me much more open to a non-Tesla alternative. I have briefly looked at a generator option but these do not seem any cheaper and the greenie in me rebels against the thought.

I have a 13 year old solar system that I think is producing 3.8kW - but I for the life of me can't find the documentation. It is a little less than I could use as I pay up a couple hundred dollars a year to PG&E, but it is likely too old to expand.

What I have not been able to find anywhere is succinct information on why I can't keep charging the powerwall during an outage if the solar is active. If this capability were there, I think 1 powerwall would be enough. But the Tesla person said that feature is not available. Technically why not?

I'm perfectly okay with just running the fridge, the internet, and a few small devices such as laptop, microwave, phones etc... during an outage. If this low usage model will work with 13.5kWh, 1 powerwall should be sufficient. No need to run things like dishwasher, laundry, A/C (its not that hot here) or charge the car (go to a supercharger). Am I missing something?

Any Grid tie solar or battery system will not stay ON if the grid is down, it is a safety issues mandated by the utilities..... unless you do have an ATS (automatic transfer switch) or ABT with a generator.

 

[ra88it]

Any Grid tie solar or battery system will not stay ON if the grid is down, it is a safety issues mandated by the utilities..... unless you do have an ATS (automatic transfer switch) or ABT with a generator.

The TEG handles this beautifully and without issue.

 

[Owner]

The TEG handles this beautifully and without issue.

What is a TEG?

 

[jboy210]

What is a TEG?

Tesla Energy Gateway, the "brains" of the system. It routes power from the various sources (inverters, PowerWalls, utility grid) to the correct places in real-time. It also detect detects grid failures and isolates your PWs and solar from the grid, so you can continue to charge your PWs and draw from solar and PW without the grid. And it detects when the grid comes back and seamlessly restores normal operations (such as sending excess power to the grid for resale). And all of this happens fast enough that you might never notice a change.

And being cool, it has a interfaces (via wifi, Ethernet, cellular) that can be used to monitor all of this via the Tesla App, or with an application you write ( I believe via local wifi & Ethernet only).

 

[cali8484]

You should be able to support 2pw with 4kw when we can support 9 with 12kW.

We only have 9 due to not wanting to run a generator, I don’t care if we operate in a 30-85% status on the app for extended periods of time.

That's interesting that you choose to undercharge your PW's on purpose. How long of an outage based on your consumption do you expect the undercharged PW's to be able to support?

 

[gpez]

That's interesting that you choose to undercharge your PW's on purpose. How long of an outage based on your consumption do you expect the undercharged PW's to be able to support?

What do you mean by "undercharge"?

The energy production of your PV system is a rate, measured in kilowatts (rate)
The energy storage of your Powerwall is capacity, measured in kilowatt-hours (rate and time)
These are related, but different, concepts.

You could have a 4kw PV system and 10 Powerwalls or a 10kw PV system and 1 Powerwall - they're completely independent. Inverter limitations and efficiency discussions aside the only thing you're changing is your storage/production ratio you have which in turn changes how much time it takes your PV system to charge the Powerwall(s) to full.

If you're trying to loosely correlate a PV system to consumption I guess that's ok but there are lots of other factors that come in to play as neither of those are static over a year (especially in climates that have large temperature and sun variations through the seasons).

I guess you could also mean ra88it's statement on 30-85% status being "undercharged" but I interpreted that to mean that during an extended outage the relatively small PV system wouldn't be able to completely keep up with the house demand so the Powerwalls will drain over time to accommodate. That doesn't mean ra88it is keeping them at 30-85% all the time, though, so I'm again confused by "undercharge".

@Owner I do not believe you need to change your PV system if you want to go for 2 Powerwalls instead of 1.

 

[Owner]

Okay, here's my current thinking the three options.

1. Buy one powerwall $7,600
2. Buy two powerwalls $14,100
3. Upgrade to a new system 7.56kW $24,790 after tax credit

I think but am not sure that I have eliminated just one Powerwall. I would like to be able to be relaxed if and when a power outage occurs. Just one Powerwall might be enough. But two ready to go during wildfire season would be quite comfortable with charging the Tesla at the superchargers nearby.

The new solar system would be double of what I have, which is fine. I don't really mind giving away electricity for free as it helps the environment.

I got one response on donating the panels, but no follow back email yet. Sounds like it is not an easy or standard process. I may end up trying to find a friend who can use it instead or selling them for a marginal amount of money if I don't hear back in a few days. I looked through craigslist and there doesn't seem to be much selling of old solar systems - just a panel here and there for $30.

Very much on the fence still but appreciate everyone's help. You are all much more knowledgeable than the folks at Tesla. One person did give me a specialist that I could call but haven't done so yet.

Is it worth the effort to look at other solar companies? I am not a nickel and dime person.

Any strong opinions on the three options? My electrical bill annually will only be $500 max with the existing panels.

 

[jboy210]

Okay, here's my current thinking the three options.

1. Buy one powerwall $7,600
2. Buy two powerwalls $14,100
3. Upgrade to a new system 7.56kW $24,790 after tax credit

I think but am not sure that I have eliminated just one Powerwall. I would like to be able to be relaxed if and when a power outage occurs. Just one Powerwall might be enough. But two ready to go during wildfire season would be quite comfortable with charging the Tesla at the superchargers nearby.

The new solar system would be double of what I have, which is fine. I don't really mind giving away electricity for free as it helps the environment.

I got one response on donating the panels, but no follow back email yet. Sounds like it is not an easy or standard process. I may end up trying to find a friend who can use it instead or selling them for a marginal amount of money if I don't hear back in a few days.

Very much on the fence still but appreciate everyone's help. You are all much more knowledgeable than the folks at Tesla. One person did give me a specialist that I could call but haven't done so yet.

Is it worth the effort to look at other solar companies? I am not a nickel and dime person.

Any strong opinions on the three options? My electrical bill annually will only be $500 max with the existing panels.

I can never hurt to talk to other solar companies.

The downside may be price. Tesla seems to sells the PowerWalls cheaper than anyone else. A friend wanted to buy 3 PWs for his existing solar. The bid he got from Tesla was up to 40% less than any of the 3rd party vendors. The other vendors will willing to do some paperwork that might get him some money back on additional credits, but he was not sure he qualifies.

My leaning on your options is 2 and 3.