Energy Products

Self-powered mode: What is your percentage and why?

edited November -1 in Energy Products
I have decided to go with 40%.

For my system, 16 kW, even if it is a partly cloudy day the next day, it should recharge to full status.

Only a really overcast rainy day might prevent a full recharge.

I figure if we always have at least 40%, we can likely handle a grid outage no matter when it happens.
If it is middle of the day, fine ... my system is likely at 100%.
If it is middle of the night, fine ... the sun comes up in a few hours.

Florida based, two PW2 units.

What is your Self-powered percentage set at and why?
Hopefully something to be learned from this topic by others sharing their strategy.


  • edited December 2019
    10 kW + 2 PW2 units in NorCal.
    25% reserve in summer and 50% reserve in winter.
    The solar output on a stormy day can be as little as 3 kWHrs for the entire day, so prudent backup protection in winter is different than sunny summer days where I will recharge before noon - even starting from 25%.
  • edited December 2019
    4.8kW + 2 PW2 in SoCal. Smallish home (1500 sqft) and just the two of us retirees living here, and the whole house is on the backup breaker panel. We're also on TOU (time of use) billing from my grid operator with the highest costs between 4 and 9 PM. We have an EV (Chevy Bolt), but don't spend a lot of time driving around (retired!!). We also bought our system outright. No loan, lease or PPA.
    And just as an aside, first true-up last July required I send $8.00 to my grid operator for extra electrons I used from their source.
    So.... I set self-powered at 45% in the summer and am able to recharge by 2pm. I can bank excess and may use some grid with solar on weekends to charge the car. In the winter, it will depend on weather, but I set PWs to 70% and rely on grid during off peak times of day.

    System output can be as high as 30kWh a day in the spring peak and about half that during a sunny day in December and so far it's been trouble free.
  • edited December 2019
    13.2 kWh + 2 PW2's in Edmonds, WA
    We are generally able to operate completely in self powered mode from mid-February through the end of October, exporting about 50+ percent of excess solar back to grid. Our Utility provider actually sent a meter reader out to check our meter this past summer as we had not used any grid energy, and wanted to check to see if something was wrong. It was hilarious..

    We generally keep our self-powered reserve at 25% during summer, and 50% in Winter similar to @Jones. We generally charge up to 100% before 10 a.m. during the summer, but unable to charge up completely during winter due to insufficient solar between November and end of January. Therefore, we need to keep a higher reserve during the Winter when we are more likely to have power outages from wind storms.
  • bpbp
    edited November -1
    Since we've only had the Permission To Operate for a few days, don't have any historical data for planning our reserve % in self-powered mode.

    However, we'll likely go with 20 or 25%.

    We have 4 PowerWalls - so 20-25% would provide us 10-12.5 KWh of power.

    Since our house usually draws 5 KW or less of power, this would provide us at least 2 hours of power for unplanned power outages.

    When a hurricane is approaching, Storm Watch, should be triggered, loading the PowerWalls to 100% - and if we anticipate we could be facing an extended power outage (for days), we'll likely manually turn off nonessential devices to reduce our power draw and ensure we could operate on sun and PowerWall power until they grid power is restored.
  • edited December 2019
    bp: It's funny, because every time I tell folks that my two PWs should see me through a couple of days of grid loss and little sun they proclaim "Hogwash! The average home uses 30kWh per day!" These people obviously don't understand the idea of a "power emergency". Like you, I will unplug all non-essential house loads, and 10kW per day should be way more than enough. The average Energy Star refrigerator use 2-3kWh per day, and being in coastal So. CA, HVAC is of minimal concern, and a sump pump isn't even on my radar. YMMV, depending on location.
  • bpbp
    edited November -1
    We decided to install enough solar panels to provide about 50% of our daily usage (excluding EV charging). That's enough to make a big dent in our monthly electric bills - and allow us to operate for extended periods by reducing the load for non-essential systems.

    Our biggest energy users are the pool pumps, HVAC systems and ovens. We won't run the ovens if we're away from home - so if we have a power outage while the ovens are running, we'll turn them off to conserve power.

    Our pool pumps and HVAC systems have web apps - so if we get an outage while we're away from home, I can remotely reduce or disable those systems until power is restored.

    Especially if we have our PowerWalls fully charged prior to a hurricane, we should be in great shape, unless we get consecutive days without any sun and no grid power - which did happen when Harvey came through and rained - for days...
  • edited December 2019
    Yup. I have an "advantage" in that the most likely event to cause a widespread grid loss here in So. CA is an earthquake. Earthquakes aren't usually accompanied by an all-encompassing cloud cover like a hurricane, so unless my house suffers severe damage, I'll have power indefinitely, and can be a much-needed resource for my suburban neighborhood.
  • edited November -1
    Most hurricanes suck all of the moisture with them. So it is often quite clear and sunny after a hurricane has passed. So if the grid is out for a few days after a hurricane, we can expect reasonably sunny weather after. The key is just making it through the first hours after the grid goes down until the sun comes out.

    Once the sun is out, it is fairly easy to recharge PW2 and make it through the night, then recharge each day.

    StormWatch mode is a different topic. Of course everyone would try to be at 100% prior to a storm, so the self-powered percentage is irrelevant during storm prep.
  • edited January 1
    "Hogwash! The average home uses 30kWh per day!" These people obviously don't understand the idea of a "power emergency"

    27 kwh just doesn't seem like that much to me. The background energy consumption of our house seems to be about 400 watts (0.4 kW) continuously. That is at night with just about everything off. I think the only things running are the refrigerator and the deep freezer in the garage, plus the vampire draw of all the stuff plugged in around the house.

    24 hours X 0.4 kW = 9.6 kWh, so that is almost one full PW2.

    Maybe if we unplug a bunch of stuff (eliminate vampire draw) that might drop to 0.3 kW.
    Maybe if we moved stuff from deep freezer to inside refrigerator and unplug the deep freezer, that might drop a bit more.
    Plus even on a cloudy day a solar system will produce some energy to get through the day. In my experience, even on a cloudy day we get about 20% to 30% of the kWh compared to a good day.

    I would advise everyone to disconnect from the grid for a full two days and see if you can make it through a weekend with just your solar and powerwalls. Walk around the house turning stuff off and on. Get a feel for how much your system can handle. It is a very educational experience.
  • edited January 1
    I simply flip breakers, except the one(s) attached to a refrigerator. Vampires can't suck through an open breaker.
  • edited January 2
    @gregbrew, liked your rant and totally agree. We live in Edmonds, WA with 13.2 kWh solar PV and 2-PW2's and would certainly be able to weather an outage with our 2-PW2's. We are able to operate as a microgrid from February through end of October up here, exporting ~60 percent of our excess solar back to grid. Obviously we would not turn on high usage appliances and unplug our two Tesla's during an outage. We actually had a PUD meter reader come out to check our meter this past summer because we had not drawn any grid energy for the previous 5 months.
  • edited January 2
    9.38 kWh + 2 PW2's in Dallas, TX. I have been using self powered with a reserve of 50%. I chose this number because on average our home uses 17.8kWh in a 24 hour period during the winter (have not hit summer yet with the system.) If the powerall 2 has 13.5 kWh of usable energy is should have 27 kWh with the two. That being said I should be able to make it 1.5 days on battery even if solar is not producing much. I have a question thought, overnight with a low load I am pulling bother PW's down to 50% it seems like I should only be pulling down to 25%. It is acting like I only have one PW. Thoughts?
  • edited January 8
    @easyshot76, what is the kW pull when everyone is asleep? I am assuming all lights are off and the main draw in the house is going to be only refrigerator and vampire draw of stuff plugged in.

    For my house, we also have a deep freezer in the garage, plus a second refrigerator in the garage. It was a full sized refrigerator from a previous house and it didn't fit in our current house. But it was relatively new so we kept it also. We have 4 kids, so we need food storage space. The current kitchen needed a counter depth refrigerator to replace the one that was there when we bought the house.

    TLDR: we have two refrigerators and one deep freezer.

    So late at night when everything else is off in the house, the continuous house consumption is between 0.4 kW and 0.5 kW. So I am guessing continuous draw from PW2 is about 450 watts, because it changes on the app regularly between those two numbers numbers.

    Sunset right now is about 5:45 pm.
    Sunrise right now is about 7:20 am.
    So we have to get through 13.5 hours with our two PW2 units.
    13.5 x 450 watts = 6.1 kWh.
    That is roughly about half of one PW2.

    So if you do anything else during the evening hours from 5:45 pm till everyone goes to bed, that would account for the remaining consumption. It really depends upon what is turned on in your house. In my house we have an electric water heater. So if anyone turns on the shower, the consumption spikes by 4.5 kW for 10-20 minutes. Or the electric stove or electric over can easily spike consumption for 2 kW or so. If my wife does laundry during the evening, that can be 60-90 minutes of 3 to 5 kW consumption.

    It is VERY easy to consume the battery storage of two PW2 units.

    I have placed an order for two additional units to bring our system to four PW2 units.
  • edited November -1
    FYI Papa - if you’re not aware of the new hybrid heat pump hot water heaters you might want to check them out. Crazy efficient - the use a small fraction of the 4-5 kW of power consumed by a traditional electric WH.

    We installed one last year along with a variable speed pool pump. Those two moves alone dropped our consumption enough to fuel our Model 3....
  • bpbp
    edited November -1
    Tesla should add a "dynamic" setting for the reserve power - automatically adjusting the reserve power percentage based on the actual usage. For example:

    When the max power stored in the PowerWalls is less than 90% for several days (or a single day with complete sun), the reserve power percentage could be increased.

    When the max power stored in the PWs goes above 95%, the reserve power % could be decreased.

    Doing something like this would automatically increase the reserve power percentage in the winter, and lower it in the summer.

    This would be similar to what our smart sprinkler system does - automatically increasing and decreasing run times for the sprinklers, based on seasonal needs.
  • edited November -1
    I agree with @Patrick's recommendation regarding Hybrid Heat Pump Water Heaters. We invested in both Heat Pump and Heat Pump Water Heaters 7+ years ago, and have never regretted that decision. They are incredibly efficient and have dramatically reduced our energy demand up in Edmonds, WA. Our total electric use last year from grid was 3,515 kWh, which included charging two Tesla's (2320 kWh) with 13.2 kWh solar PV system and two PW2's.
  • edited January 9
    Great idea bp - suggest submitting to Tesla or tweeting Elon
  • bpbp
    edited January 10
    Submitted via Tesla website support form.

    Anyone else who wants the dynamic reserve feature, please also submit requests to Tesla or Musk...
  • edited November -1
    I’ll submit a feature request via web site as well.

    On a related topic - we just cleared our microgrid inspections yesterday and the system operated overnight for the first time. The 3 PWs started with roughly an 80% charge and still had a 60% charge this morning, but both HVAC units were set to lower temps than usual as no one is living in the home yet.

    During testing this morning I ran both central HVAC units in heat mode for a while. Together they pulled about 7kW of continuous power. The PWs had no problem with the load, but obviously they will discharge much further overnight once the home is occupied and heat thermostats are set to more normal temps.

    Setting our reserve to 20% - we’ll see what happens going forward. Regardless - our first day with a fully self-powered home feels really good! No energy has been pulled from grid since activating the system. Yes!

    Also learned something very interesting today regarding how things work with our configuration using a 400A meter base, two 200A main breaker panels, and a single TEG feeding only one of the 200A main breaker panels. Will post on a new thread as it may help others.
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