Settings for new Powerwall

rosiegirl

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Hi everyone!

We've had Tesla (Solar City) panels for about 8 years here in New York and we recently (finally) got our Powerwall installed by Tesla. Currently we have the Powerwall set to save 30% for possible power outages. If I know we're about to have a storm, I switch to backup only but obviously we don't always have warning for power outages.

Our main need for the Powerwall is to be able to keep our fridge and freezer running since we store our son's medications there (after 2 hurricanes, 1 blizzard and 2 recent wind storms, we were desperate). We really don't *need* to be able to keep anything else running, although the ability to charge a phone would be nice!

My questions are as follows:

1. I have the settings at 30% and the sun sets around 4pm, so by the time we go to bed, the Powerwall is down at the 30%. Does that mean that I only have 30% to run everything overnight and the next day (assuming we're in a storm with no sun)? How do I know how much I need to run the essentials?

2. If what I really want is to run the essentials, do I need to go and turn everything off if there's an outage so that my computers, chargers, lights, etc, aren't draining the Powerwall?

3. Will I know if my power goes out? The installers said there wouldn't be an indication but then how do I know when to start turning things off, especially if it happens at night? I'd hate to have my computer use up my 30% overnight and then not be able to run our fridge with medication.

I hope this makes sense!
 

Ed Woodrick

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You really need to make a decision on what you want to use the Powerwall for, shedding load or providing backup. Yes, you can change, but as you indicated, you may not know the you need to change.

How much 30% is, is dependent on how many panels you have and what your load is. As you mentioned, it seems as if your load may represent over 10% per hour. So it does not sound as if you would make it through the night.

Chargers, lights (as long as they are LED) are big current draws. Computers can be, but if they go into sleep mode, they shouldn't be.

But the one thing that you didn't mention, and may or may not be currently connected is your heating system. Seems to me that someone would much rather have their heating run than anything else in NY. Refrigerators will stay for a period of time. Houses get cold quick. A cold house lets the refrigerator last longer.

So how do you know, notification would be one, but that assumes that you don't sleep through the night. It also assumes that you don't start ignoring after time, as most power outages are relatively short. You soon learn that waking up to turn things off is often a waste of time.

The first answer, and possibly hard for an installed system is to only provide power for those items that you need to provide emergency power to. That may require rewiring the panel, an expensive proposition.

There's not an easy answer, so it comes back to my original point, do you want to load shed or provide backup? It sounds like maybe backup, so 30% may be way too low.
 

Bigriver

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Hi everyone!

We've had Tesla (Solar City) panels for about 8 years here in New York and we recently (finally) got our Powerwall installed by Tesla. Currently we have the Powerwall set to save 30% for possible power outages. If I know we're about to have a storm, I switch to backup only but obviously we don't always have warning for power outages.

Our main need for the Powerwall is to be able to keep our fridge and freezer running since we store our son's medications there (after 2 hurricanes, 1 blizzard and 2 recent wind storms, we were desperate). We really don't *need* to be able to keep anything else running, although the ability to charge a phone would be nice!

My questions are as follows:

1. I have the settings at 30% and the sun sets around 4pm, so by the time we go to bed, the Powerwall is down at the 30%. Does that mean that I only have 30% to run everything overnight and the next day (assuming we're in a storm with no sun)? How do I know how much I need to run the essentials?

2. If what I really want is to run the essentials, do I need to go and turn everything off if there's an outage so that my computers, chargers, lights, etc, aren't draining the Powerwall?

3. Will I know if my power goes out? The installers said there wouldn't be an indication but then how do I know when to start turning things off, especially if it happens at night? I'd hate to have my computer use up my 30% overnight and then not be able to run our fridge with medication.

I hope this makes sense!
Welcome to the forum.

I have powerwalls and solar in PA, which should be pretty similar to New York conditions. I use them very differently in the winter vs the summer. Because solar is so terribly awful in the winter and because there can be days and weeks with extremely low production, I keep the powerwalls totally in backup mode. The basic issue is not just could you get through the night, but when will you again have enough solar to refill them? Days are few and far between in December (and January and February) where we have enough solar to meet our daily needs.

From March to October, I generally let the powerwalls charge and discharge and they generally keep me off the grid as solar production is higher and more consistent. But there are stormy times that I go into backup mode. And if I had a medical necessity for power, I would seriously consider always keeping them in backup mode, or at least keeping the reserve very high. 30% sounds very low to me.

To address your specific questions:
1. If between 4 pm and bedtime you are down to 30%, yes that gives you only 30% if there were a grid outage. You should be able to develop a sense for the load of the essentials by looking at the Tesla app and seeing your daily usage. My base load is between 15-20 kWh per day. In addition major loads are: Blowers for gas heat are about 1 kW, 2-3 kW for a central a/c and 6 kW for electric dryer. Multiply those loads by the hours they are run to get the energy in kWh. Your powerwalls have 13.5 kWh each.

2. Maybe. The powerwalls could have been installed in a way to just power the essentials. For example, we made the choice that the HPWC to charge the cars is not connected; any charging of the cars would have drained the powerwalls too fast. But hopefully your powerwalls are sized to be able to accommodate your basic loads for an extended duration. The backup % you keep for the powerwalls is crucial.

We did have one time when the grid had been down for a couple of hours, and although we had enough energy to make it through the night, the next day solar production looked questionable. In that case we did go around and consciously decide what to keep going, just in case, because you never really know how long the power outage will be. And I would never plan to use my electric dryer when the grid is down.

3. You can know if the grid is down by looking at the Tesla app. It will look like this:
79F1BE01-D9B0-42C0-ADD0-D505557B7FB4.jpeg

There is also a backup history in the app that tells when it has been down. I also sometimes get a notification on my phone when the grid goes and comes back, but not always.
 

garsh

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I didn't think it was possible to install a single powerwall to power an entire home.
I thought Tesla required at least two powerwalls for that use-case.

Have you tried turning off all electricity to your home to see if everything is still powered by the powerwall?
 

rosiegirl

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Thanks all!

We do not have the Powerwall connected to the central air/heating systems. That would have required a second Powerwall and we couldn't do that...it's not a big house so one is fine for everything except heat/air and oven. We're not that worried about heat/air....we've done quite a few days in winter without heat and summer without a/c and, while not pleasant, it was survivable!

We'd love to use solar to power the house as much as possible but not at the risk of not being able to keep the fridge and freezer running during an outage without sun production the next day. So it sounds like I should certainly be above 30% and perhaps even solely on backup for the winter months in New York? What percentage would you leave it?
 

rosiegirl

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To address your specific questions:
1. If between 4 pm and bedtime you are down to 30%, yes that gives you only 30% if there were a grid outage. You should be able to develop a sense for the load of the essentials by looking at the Tesla app and seeing your daily usage. My base load is between 15-20 kWh per day. In addition major loads are: Blowers for gas heat are about 1 kW, 2-3 kW for a central a/c and 6 kW for electric dryer. Multiply those loads by the hours they are run to get the energy in kWh. Your powerwalls have 13.5 kWh each.

How do I know how much my base load is each day, on average? I have been playing with the app but not sure what each number in Power Flow represents!
 

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I think you’re going about this the wrong way. The 30% battery reserve is intended only for prolonging the time you aren’t consuming grid power without destroying that savings by putting too much energy into charging.

So I say re-think your model. Take the energy usage hit once (per “draining event”) and let the battery charge to its maximum level (which may be 90% and not 100%, like in the cars) even if it has to suck power from the grid. With that, you will still be able to reduce grid consumption, but you’ll also have as much backup power as possible.
 

Bigriver

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@rosiegirl, I’m slowly understanding the specifics of your situation. Only one powerwall. Configured so it does not backup some of the major energy hogs such as heater/ac/oven. Good. But running those items will draw from the powerwall if not in the “grid out” mode, thus why you depleted the powerwall all the way to 30% by the time you went to bed. At that point you start using grid power. But let’s say the grid goes down.... you have about 4 kWh in your powerwall (30% of 13.5). You get a bit cold with no heat and the oven isn’t available for a midnight snack 😊. But your refrigerator, freezer and probably most of your basic circuits are on in the house. I’m going to estimate this load is pretty low. Probably no more than 0.5 kW. That would mean your powerwall will last for 8 hours (4/.5). You can check how good my estimate is by making sure none of your major appliances are running, and see if the home usage in the power flow of the Tesla app is near my 0.5 kW guess. If it is higher, you have less than 8 hours, and if lower than 0.5 kW you'll have more than 8 hours. Of course these are just estimates.

So 30% reserve may not be as bad of a setting for your situation as I initially thought. But I don't know the size of your solar setup and what kWh you are generating. Winter is tough, though. I’ve just been through a week of only generating 5 kWh a day from my 12 kW system. My home usage is 20 to 30 kWh per day. Thus, no matter how I slice it, 5 < 20 and most of the energy to power my house has to come from the grid. I pretty much use the solar as it is being generated, and if I had instead sent it to the powerwall, it would be less than 40% of one powerwall. Obviously the powerwall won't make it so you can use only solar if there isn't enough solar being generated. Thus, my conclusion is to just keep the powerwall as a backup in the winter.

The only situation I can think of when someone in the North might want to actively cycle their powerwall in the winter is if they are trying to use it during a high time-of-use energy rate from the grid. That could let them use whatever solar they did produce that day during the most expensive time.

I think I've digressed a bit.... back to your critical need of keeping a refrigerator and freezer going..... I think their energy consumption could vary a bit depending on age and model. It's been awhile since I measured my refrigerator, but I'm remembering it being only about 70 watts. I was surprised by how low it was. Let's double that and round up some, and we're at about 0.2 kW load, and the powerwall (if starting from 100%) could keep that going for over 60 hours if there were an extended outage and you kept everything else off.

Edit: So my conclusion is that 30% reserve should probably give you 8 hours for your critical need, and while that might be enough, it would make me pretty nervous in winter because you might not be able to refill the powerwall easily. I would be more comfortable with a higher reserve, all the way up to 100% which ensures many days of supplying your critical need. I don't have anything as important as you do, but it is the backup capability of the powerwall that is the primary reason we got it.

Hope some of this rambling has helped! Don't hesitate to ask for more clarification.
 
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Bigriver

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@JasonF, I really don't understand anything in your post!
  • "The 30% battery reserve is intended only for prolonging the time you aren’t consuming grid power" - The 30% reserve is about having energy in the powerwall in case there is a grid outage. It can be defined by the user and is the central question of what is the best reserve percentage.
  • "without destroying that savings by putting too much energy into charging." I read this 10 times, and my brain hasn't deciphered it yet.
  • "So I say re-think your model. Take the energy usage hit once (per “draining event”) and let the battery charge to its maximum level" I don't know what you mean by energy usage hit and there is no concern about how full to charge a powerwall; we don't have control over the maximum charge like in a car.
  • "even if it has to suck power from the grid." You can't charge a powerwall from the grid. It can only charge from the solar array.
  • "With that, you will still be able to reduce grid consumption, but you’ll also have as much backup power as possible." Yes, I do understand this statement, and it is what the OP is wanting. Just didn't follow your re-thinking of how to achieve it.
 

JasonF

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@JasonF, I really don't understand anything in your post!

When most solar systems are installed, they are designed to balance cost of the panels vs cost of the electric usage. The most common kinds are either a small set of panels to offset total electric usage, or a set large enough to create a very small surplus that you sell back to the power company for credit toward evening grid usage (net-zero strategy).

Usually if a battery is added, the solar capacity is reduced a little bit, because if you don't need to run everything off of the grid as soon as the sun goes down, you don't need as large a credit built up during the daytime to still reach net-zero. The battery charge level is usually calibrated so that it's not consuming so much solar capacity as to possibly (but not always) force grid draw during the daytime. I would guess that the 30% at night is what's left over after a slow charge all day, and then a light draw as the sun is going down and the solar array is no longer producing sufficient electricity.

From what little I know specifically about the Tesla system, "storm mode" purposely defeats that balance and forces more electric generation and/or grid power to go to charging the battery no matter the cost in order to protect against power outages, and avoids draining it to supplement low solar generation. This is what I'm suggesting, is if you want to use the battery primarily as a battery backup rather than to delay grid usage in the evening, see if it's possible for it to use storm mode all the time, keeping the battery at a much higher level even if it results in some grid usage from time to time. The cost though might be that if your solar array was sized to depend on the battery, it might increase your residual electric bill slightly.
 

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Our main need for the Powerwall is to be able to keep our fridge and freezer running since we store our son's medications there
The other thing to consider is to get a small chest freezer for the purpose. They're more efficient than upright freezers, even when you need to open the door to get stuff out of them. They'll stay cold much longer.

 

rosiegirl

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The other thing to consider is to get a small chest freezer for the purpose. They're more efficient than upright freezers, even when you need to open the door to get stuff out of them. They'll stay cold much longer.

Yup, we have one of those, too. That's where the food we make for the kids (allergies) gets stored. The fridge stores the medications.
 

rosiegirl

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@rosiegirl, Edit: So my conclusion is that 30% reserve should probably give you 8 hours for your critical need, and while that might be enough, it would make me pretty nervous in winter because you might not be able to refill the powerwall easily. I would be more comfortable with a higher reserve, all the way up to 100% which ensures many days of supplying your critical need. I don't have anything as important as you do, but it is the backup capability of the powerwall that is the primary reason we got it.

This is starting to make sense! I think if I keep it at 90% saved for backup in the winter, I'll be okay even with a day of no sun especially if we turn off anything that isn't totally necessary during a blackout that might draw some power. In the summer, I'm sure I can decrease that 90% a bit. How do I know how much I'm using a day? I've been looking at the Power Flow in the app but not quite sure what each of the 4 numbers tells me.
 
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Bigriver

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In the power flow, there are 4 sources or uses of power:
  • Top is solar
  • Left is grid
  • Right is home
  • Bottom is powerwall
The units are kW, which is a rate and is best compared to the speed something is going. It shows what the power is at that moment, so it is dynamically changing as you watch it, showing the direction of what is flowing to where. Solar can go to any of the other 3; the grid can receive from solar and send to the home; the home can receive from any; the powerwall can receive from solar and send to the home.

I like watching the Power Flow, but perhaps of more use is the “Energy Usage” screen that you get to from the 3 vertical lines in the top right hand corner of the “Power Flow” screen. The units here are kWh, and tell the total energy produced or consumed. So if the previous screen was like the speed, this is like the total distance travelled. The energy usage screen again has the same 4 components as in the power flow, and this time you can toggle them on and off by tapping them. It gives you a plot of each component vs time for the day, and if you scroll down it then gives numerical values. Here is what mine looks like right now.
0C574FFA-C17C-4120-A73A-338569773430.jpeg
6CD1B2F4-FFE0-4F54-B7B8-E534FAEC5066.jpeg

Where it says “Today” you could then scroll to the left and see all past days, one by one. Or you can scroll down and see data by the week, month, year or lifetime (since you got the powerwall).
 

rosiegirl

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Where it says “Today” you could then scroll to the left and see all past days, one by one. Or you can scroll down and see data by the week, month, year or lifetime (since you got the powerwall).

Yes I see that! So, is the daily "home usage" what I'm looking for to see my daily usage or do I need to add any of the others in? Sorry for all the novice questions!
 

Bigriver

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Yes I see that! So, is the daily "home usage" what I'm looking for to see my daily usage or do I need to add any of the others in? Sorry for all the novice questions!
Questions are never a problem. Yes, “home usage” is your total. Nothing else to add in. What that won’t tell you, though, is what your home usage would be in a grid outage situation, since you don’t have all your circuits backed up to the powerwall.
 

rosiegirl

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Questions are never a problem. Yes, “home usage” is your total. Nothing else to add in. What that won’t tell you, though, is what your home usage would be in a grid outage situation, since you don’t have all your circuits backed up to the powerwall.

Right, so it would be whatever it says for the day plus whatever the heating/cooling system uses?
 

Bigriver

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Right, so it would be whatever it says for the day plus whatever the heating/cooling system uses?
No, the heating/cooling system electricity is not an extra number. The home usage reported in the app is always the total electricity used by everything in your home.

What may be confusing is that there is a separate normal mode and backup mode. While your heating/ac cannot be powered from the powerwall while it is in backup mode (grid is down), it can be powered by the powerwall while the grid is available.

I am speaking from the basis of assuming that yours is configured like mine, which I think is very typical of how Tesla does it.

You can turn anything on or off in your home and watch the power flow to see the effect it had on the home kW in the Power Flow. I find that fun to play with.
 

rosiegirl

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What may be confusing is that there is a separate normal mode and backup mode. While your heating/ac cannot be powered from the powerwall while it is in backup mode (grid is down), it can be powered by the powerwall while the grid is available.

Ah, that makes sense! So my daily without the central air/heat would actually be a little less than what I'm seeing on the app? Looking back, it seems like we use about 25-30kWh a day. If the Powerwall holds 13.5kWh, wouldn't we not even make it through a day? Or maybe if we turn some things off that would normally be on (and not run the dishwasher, etc) we could preserve it longer for the fridge/freezer. Everyone is working/schooling from home, so there are a lot of things plugged in that didn't used to be!
 

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In normal mode, the powerwall will drain very fast because everything in your house is hooked up to it. One powerwall is not big enough to keep you off the grid at night. I think you mentioned in your original post that it was already down to 30% when you went to bed. That is as I expect. But when the grid is down, it goes into backup mode, and because it is only powering select things in your house, it will last longer. I don’t know how old your kids are, but it might be a great science project for them to systematically turn off different things in your house and see how much the power consumption changes. Some things don’t have much of an effect; some things are big hitters.

Good luck through the snow storm that is hitting tomorrow!
 
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