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Power Outage with Powerwalls

edited November -1 in Energy Products
We have a Tesla Energy PV system and two Powerwall 2's which were commissioned about two months ago. We live in the Phoenix AZ area.

A few days ago, during a thunderstorm, my wife and I were working at our computers in our office when, at 4:30pm, we noticed that the lights flickered off once, and our DSL modem retrained. Our computers were unperturbed. Such a flicker is not all that unusual during thunderstorms, so we went about our internet activities. But about 10 minutes later, I started thinking, "what if there was a power outage, and our home batteries were switched in?" I looked outside, and sure enough, the neighborhood was dark, and we were the only ones with power. I might not have known.

The Tesla application revealed that our battery system was indeed powering the house, and the solar panels were providing no power due to the clouds.

When we realized that we were on backup for a yet undetermined period of time, we increased the thermostats from 80 degrees F to 85 degrees F and turned off unnecessary lights and phantom loads. The main loads resulting in the 0.7kW draw were the refrigerator and a medical device required for recovery from a recent hospital stay. We left a few house lights (LED's) and fans on, but turned off the outside lights to avoid being accused of witchcraft. Our home network, router, and modem were left on. The result was a 0.7kW load.

The backup power source consists to two Tesla Powerwalls 2's in our garage configured via the application to retain a 45% reserve for possible outages throughout all of their activities.

Given the reduced house load, that reserve would last us about 12 hours. After that, we would not open the refrigerator and we would need to use (and possibly order additional, which had me a little worried) mechanical backup for the medical device. The utility company's web page indicated that the outage in our area was projected to last until 8:30am the next day, but they're usually pessimistic. Nevertheless, we had to plan for that.

So, we didn't watch television or listen to the stereo, but we did use the kitchen facilities (blender, seed grinder and lights, while opening and closing the refrigerator numerous times) to make smoothies. And we read and surfed.

I periodically checked the application for status to monitor our reserve capacity, and eventually, round 9:30pm (five hours later), the application indicated that the grid was back up, and the battery reserve was no longer in use.

If we had known that the outage would have been this "short," we may have streamed a movie on our big system or cooked a meal with electric appliances. But, we plan for the worst.

The outage depleted our 45% reserve to 32%. I was concerned that the following day, with extreme AC demand and cloudy weather, there would not be enough excess PV production to recharge the battery to the reserve threshold. However, as soon as the sun came up, all PV production was diverted by the energy gateway to the batteries, and when I got out of bed and checked, the capacity had already been replenished to 45%, and normal operation had resumed. I was impressed with the sophistication of this control algorithm, and overall, my expectations have been exceeded.

One problem that I see is that, whether we were at home or away, we may not have been aware that an outage was in progress and would have gone about running the AC and pool pump and charging the car, thus depleting the battery much more rapidly. We have to keep an eye on that. Since the application runs on a mobile device (not windows, unfortunately ... we had to acquire an android device specifically to run this application), we can monitor the system remotely and get home quickly if we need to.


  • edited November -1
    Great summary of your backup experience, thanks for sharing. We had our 2-PW2’s installed/turned on 24 days ago. We have been thrilled with their performance with our 13.2 kWh solar system, and have not drawn any grid energy since they were turned on. Amazing product. We have our backup set to 50 percent, but have not had any brownouts/blackouts yet.
  • edited July 2018
    Thanks for the story. We recently had a power outage here and it's interesting to contrast the experience. Our power outage was while we were on vacation and was due to "emergency repairs." It appears like my NAS server and router rebooted during the outage, but it appears like power may have bounced up and down a few times before going completely out. Cloudy weather isn't an issue here, and since the outage happened during peak rate hours, ironically my Powerwalls' state of charge went up much higher than usual during the afternoon as they soaked up the excess solar production that would normally have been exported. At sundown, the Powerwalls were at about 95% charged.

    In a way I was sorry we were not home to get the benefit of the Powerwalls, but they did a great job at running the house for the 11 hours power was out.
  • edited July 2018
    Wouldn't it be great if the app could send an alert out to us whenever it triggers from an outage and comes back on, so we would know without being there? Or in fact, when we are there, since the same happened to us and we had no idea the Powerball had taken over. Which is great, but it would be nice to know so we could turn stuff off to extend usage, as you described. Maybe somebody from Tesla Energy reads these boards and can hook that up.
  • edited July 2018
    In addition to writing here, make your suggestion to Tesla via their Powerwall support email address. I made a suggestion that way a few weeks ago and it has been added as a Feature Request.
    I have no idea whether it will be implemented but even if they don't it gives one a warm feeling.
  • edited July 2018
    sashton - Thanks, good idea!
  • edited November -1
    Relative newbe here. My PV and 2 PW system was installed early in June. Since then I've had 2 grid power failures of 6 minutes each and the PWs kicked in perfectly. Except one thing. When I bought my flat screen TV, the sales person said I needed a "power conditioner" to prevent surges (apparently more than just a surge protector, but not a battery UPS). I also have a small battery UPS for my Comcast modem, so that I don't loose phone service when the power goes out. (Prior to the PW system). The power conditioner has a voltage display, which normally shows 123 volts. When the both of the outages occurred, the battery UPS started beeping and the voltage display on the power conditioner showed 115 volts. None of the electric clocks lost their power, so no blinking clocks after the power was restored. I contacted customer service and they did not see anything unusual in the logs. I guess I would not have known anything was odd if the UPS didn't beep and the voltage meter showed the decreased voltage. Has anyone seen anything like this during a power outage? I guess you would have to have a voltage meter to see the change. So I'm not too hopeful of anyone else seeing this, but maybe...
  • edited July 2018
    @mcdonalk, thanks for sharing. How big is your solar system? Are you able to fully charge both batteries
    to 100 pecent each day?

    I have my battery set to 10 percent reserve for backup. So far in about 1 year of use we've loss power 2x.
    But in spring I probably will kick it up to 40 percent (T-storms and Tornado's).
    I have 2 Tesla's and normal household loads. On an average day I usually export +30kw to the grid.
    As many mention, the battery practically keeps me off the grid 24 / 7. Well worth the purchase price.
    My solar system is approx 17kw with 16kw Sonnen battery. I might be adding 2nd battery next spring to
    handle additional loads during normal solar downtime.
  • edited July 2018
    @markbraukman, Welcome and happy to hear you are enjoying your new Powerwall system!
    The Powerwall is similar in a way to the UPS units you are familiar with. A good UPS (all that I know of) is also a "line conditioner" which means it will use the internal battery and a combination of filters to ensure that a steady voltage reaches everything that is connected to it. Normally, grid power is always more "dirty" than what you will produce with a UPS or with the Powerwall, in that there are frequent fluctuations in the voltage. If your UPS has a voltage log you may notice that when you are on grid power, it is not always "123V" but there may be brownouts or spikes (small changes lower or higher than this voltage). The line conditioner function will use the system to keep a steady voltage however, and this is what your TV rep was talking about using for your TV to protect the system.

    When you are on battery voltage from the powerwall it is not unusual to have 115V. The powerwalls are designed to run in a variety of voltage ranges and include filters and conditioners in the unit to ensure a pure and steady voltage/current. The voltage you see is also a function of some resistance drop from the battery source through your gateway and to your wall outlet, but should be very steady (like a UPS) so that there should not be significant fluctuations in voltage during powerwall use. Your UPS is beeping because you likely have it set to alert for certain low or high voltages, but this is not bad.

    If you check the specs for your equipment, tv etc., usually in the manual or on the back of the power supply transformer, you will see specs such as "Input voltage" and "output voltage" etc. Input voltage for most electrical equipment will say something like 100-125V or 100-240V (i.e. international travel chargers). This means that the equipment will function normally with anywhere from 100V to 125V or 100V to 240V depending on what it says, so there will be no adverse effect if the voltage is 115 instead of 123V. I have not seen equipment that would not operate properly on 115V but would on 120V this is too small of a difference to matter, but look at the specs to be sure.

    Enjoy! I myself am on the loooong waiting list for powerwall and I'm hoping to pair it with a solar roof on the new house I'm building (even longer wait). Its always nice to hear people's stories with their Tesla energy products, I can't wait till mine finally gets installed.
  • edited November -1
    Thanks @msparhawk for the informative reply. I know you will really enjoy being "off the grid" with your dual system (PV & PW). There have been several days where my house has been 100% self powered. In the evenings, all power is coming from the PW, and the volt meter shows 123 Volts. But when the grid goes down, the volts drop to 115. Granted that won't cause any problems with the TV or anything else. It just seems strange that when the grid goes down that the PW voltage drops. Maybe that is a built in power conserving factor. The bottom line is that 115 volts is much better than 0.
  • edited July 2018

    Our system is 7.4kW and is projected to provide 50% of our electricity annually if we make no changes, but with our new variable-speed pump, and other possible upgrades, we may do better. Obviously, we are not achieving off-grid-like performance. However, during the non-summer months (as recently as many days last May), we are able to charge the Powerwalls to 100% from PV and avoid using expensive onpeak grid power. During the summer months, with temperatures in PHX very high, the AC units run a lot more, so use of onpeak grid power is necessary, but minimized. In this case, we can maintain our reserve from PV, but cannot charge to 100% in a single day. (This overall performance is achieved using "self-powered" mode, as we do not have the TOU app upgrade yet.)
    The result is that our most recent electric bill was half of what it was for this same period last year.
    Coincidentally, we had another storm last night and lost power for three hours (second > hour outage this month!). My wife noticed the TV flicker and the app revealed that the grid was down. The backup system performed as expected, and we shut down non-essential appliances like in the previous outage but left a few more (LED) lights on.
  • edited November -1
    @mcdonalk, glad yr system is working as designed. Interesting how fast pw’s picked up yr household loads with min disruption.
    Good advice about shutting down non-essential loads.
    When yr pw’s are charged to 100% do they have enough reserve to supply yr off solar needs? I might look into adding another battery.
    I charge both Tesla during peak solar production. 1 at a time. So far, I’m at 100% meeting my electrical needs. I keep a/c at comfortable setting. During a recent blackout I had neighborhood party at my house. Outside air temp’s over 110. My home only one with electricity and a/c. Transformer blew up and burnt the power pole. Outage was 5 hours.
  • edited September 2018
    I called Tesla recently to inquire where they are regarding notifications whenever the Powerwall has disconnected from the grid (it was a feature that they had to stop because of bugs). I was told it is a high priority and should be running again relatively soon.
  • edited December 2018
    Beeping UPS problem solved. When the Powerwalls are fully charged, they adjust the line frequency to 64-65 Hz, which shuts down the grid-tied inverters so the batteries don't overcharge. The high frequency is detected by the UPS as "noisy" power, thus the alarms. The controller on my Lennox air conditioner took a similarly dim view of 64Hz power and refused to operate. The solution turned out to be easy. Deplete the battery to 98% or lower (clothes dryer did the job in a couple of minutes) and the power began to cycle at a normal frequency and every other appliance became happy once again. In the Tesla app, if I set the maximum charge at 98% or below the problem does not recur.
  • edited December 2018
    It's a really great and useful piece of information. Thanks, and please keep up the rewarding work.
  • I have a PW2 and am currently in a blackout. The PW2 kicked in for about 5 minutes to power the house, however it then shut down. I turned the system off and back on and the PW2 resumed providing back up power, however after 5 minutes it again switched itself off. I turned the system off and on again, and the same result 5 minutes of back up power before the PW2 shut itself down. We still have 3% in the battery. Does anyone know why this could be happening?
  • edited January 2019

    My guess is that the demand of your house is exceeding the 5kW that a single powerwall can provide. You may have to do more planning for outages, such as triage the items that you need to power and shut down those that you don't.

    In our case, if the outage occurred when we were charging our car and running the pool pump, the demand would likely exceed what the powerwalls can provide. Therefore, in an outage, I unplug the car and turn off the pool pump.
  • I'm a newbie to Tesla Solar -- we have 50 solar panels on our roof and 3 Powerwall units. I'm not an electrician or engineer, but it occurred to me that there might be what as a layman I'd call "round-trip energy loss" from charging my Powerwalls and then using them in self-powered mode. Is there a typical / expected percentage loss of power generated by solar panels that charge batteries like my Powerwalls? Thanks if any experts can answer this! (I ask because I'm thinking that I may be better to charge my Powerwalls up to a fixed percentage for outages, and have my panels send surplus back to the grid rather than do the self-powered thing.)
  • edited March 2019
    @Thepaulstewart good line of thinking there. There will always be some loss when charging batteries, How much exactly I dont know. there is even more loss in inverting DC to AC. My system is rated at 6.3 KW solar production which is always DC for any solar panel but it's rated at only 5.0 KW AC after the newest HD Wave inverter (optimizers on the back of each panel) but eliminating charging and discharging the powerwalls would increase efficiency. The other thing to consider is if your utility gives you back the power at the same price that you give it to them. A lot of places don't. If they charge you more for electricity then they pay you for electricity then self powering even with the losses will still pay off.

    PS you asked for an expert to respond but I do not fall into that category just so you know. Good luck!
  • edited March 2019
    I believe that the Tesla Powerwall literature specified a round trip efficiency of 89%, with qualifications.
  • I really appreciate the kind of topics you post here. Thanks for sharing us a great information that is actually helpful.
  • edited November -1
  • edited July 2019
    We have 5.8 kW of panels and a Powerwall 2 battery and Tesla Gateway. I have split our switchboard in two. The "backup" board has circuits like fridge, freezers, microwave, lights etc that we want powered when the grid is down. The other circuit has all the rest oven, hot water cylinder, spa, kettle etc. During a power outage the Tesla Gateway only provides power to the backup circuit. This works perfectly, whether or not we are at home. We keep 30% reserved for the backup load. We have had the Poerwall 2 since October 2018. I am pretty satisfied with the system.
  • edited November 2019
    My powerwall is wonderful, especially during the California backouts. I have a question about the Backup History on the app. Our latest power outage lasted 3 or more hours but the Backup History shows and 'event' lasting just16 minutes. Can anyone help me understand this apparent anomaly?
  • edited November 2019
    My powerwall failed after 6 hours during the California blackouts. We were out for 96 hours. Tesla tech support said they would call us back - 3 times - but never did. It is still totally dead. Who do I call now? How do I get it up and running? Are there technicians who can come "on-site" to check the "firmware" the Tesla tech support said failed?
  • edited November 2019
    Did they drain completely while it was backing up the house?
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