Energy Products

Possible Power Wall Back up Issue

My system which was just installed is 42 Panels, 2 Power Walls in Northern California.

The system has just been turned on.

During the day, I am getting Solar Power approximately 5 kW, (not very much), and the Power Wall Battery on the app showed the batteries charged to 75% during the day.

Around 4 pm the Solar stopped producing Power (no Sun light), and the energy to the house was supplied by the Power Walls (Peak PG&E usage charges).

It only took about 4 hours for the Power Walls to discharge to 24% before the system began using energy from the Grid (PG&E).

This concerns me because in the event of a power outage that is very little energy backup (less than 4 hours).
And there was not much energy being used by the house during this time.

The main reason I wanted the Power Walls to provide energy during PG&E rolling blackouts, 4 hours is not nearly enough.

So are both my Power Walls working?

Is there a problem with the system?

Something does not seem right.

Comments?

Thank you,

Comments

  • It sounds about right for this time of year and we've had a number of cloudy days recently (I'm in the bay area). While in the summer I always had both PWs charged to 100% by midday. Lately, it only gets to 60-70% for the day. For example, yesterday, which had quite a few clouds, it only saved 10.2 kWh to the Powerwalls, not enough to fully charge them to 27 kWh.

    Also, keep in mind solar powers both your house first, and charges the PWs with the excess power. If you're running some major appliances such as an electric dryer, oven, range, etc., these will reduce the amount that goes into the PWs for charging. On a rainy day, you might not get any excess power to charge the PWs.

    You can set the backup threshold. The default is 25%, meaning you have 25% of the PWs, or about 6.75 kWh of backup. You can change this to any value you want, including 100% for backup, rather than powering the house during the evening. The Stormwatch feature will automatically and temporarily set the backup charging to 100% if they think an outage may occur in the next 24 hours, due to fires, storms, etc.
  • How long can you expect the PW's to backup your house during an outage. Some of these PG&E rolling blackouts can last for a few days.

    I installed these in lieu of a generator thinking it was a better solution.

    It appears PW's do not do the same things as generators.
  • I've only started to learn how to use my Powerwalls, but it seems like the first thing I need to learn is how to budget my energy usage during an outage. I've been doing an "energy island" experiment for the past 3 days and have been able to keep my house powered using only the solar panels and Powerwalls so far. But I realize that, given our normal energy needs for November in AZ, the Powerwalls need to be charged to about 75% to 80% when the sun sets (meaning no more solar power) in order to get through the night (meaning solar power production returns). Overnight the Powerwalls discharge about 50% to 60%. So far, the lowest the Powerwalls have gotten is 21% before there is enough solar production to both power the house and begin recharging the Powerwalls. I'll never be able to operate as an "energy island" when summer comes around and I need to use the air conditioning. But I knew that going in. Also, I may have an issue on cloudy days. And it looks like if my peak solar production time during the day is noon, then I'll need to do things like running the washer/dryer/dishwasher from 9am-noon in order to get the Powerwalls charged up enough for the overnight period. Learning when to cook using the electric stove/oven and microwave will be the next challenge.
  • How much energy does your house use per day? After you know that, then you can decide which items to use during the blackouts. Two PW should easily power the whole house for a day with your basic items. We have only 1 PW and it can easily power our house for a day. We use 20 kWh per day, but that is also running the pool. Without the pool pump running we only use about 11 kWh. During a blackout, by only using essential items, we can easily get it down to less than 10 kWh per day.

    We are currently in one of the lowest solar production months and I am still sending more power back to the grid than I am using and my batteries are fully charged by 9:30 am each day, just after 2 hours of sun. Using the batter during the 5 peak hours it goes down to 70% on the average, but that is still watching TV, using the microwave and other appliances, and etc.
  • As written above, it may require some settings tweaks for each season. I find myself adjusting the reserve for my two Powerwalls (27kWh) as the seasons change. I should note that I accepted an SGIF grant, so I'm *required* to operate off the PWs during peak times for a minimum number of hours per year. (I'm willing to put up with these shenanigans for $6k.) Before SGIF, I simply left things in "Backup Only".

    My house uses about 20kWh per day, right now. If the weather is consistent, I look at an average day's production, divide by two, and set the reserve to a level that corresponds to that much energy.

    For example, if my average daily production is 20kWh (it's close, right now), I divide by two for 10kWh. I then set my reserve for 60%. My reasoning is that my PV will need to both provide ~10kWh to run the house (during the day), and ~10kWh to refill the PWs (10kWh is ~40% of the 27kWh in two PWs). My goal is to refill the PWs every day, while leaving a significant reserve capacity for grid loss, while also meeting the requirements of SGIF. Conflicting requirements get tricky.

    This gives a very rough estimate, rather than an accurate ideal, and doesn't properly account for myriad other variables. I'd probably drive myself nuts trying to optimize it any more, and there was a time (in my youth), where I probably would try. (I'm retired, and like to call myself a "recovering engineer". To paraphrase: "You can take the man out of Engineering, but you'll never take Engineering out of the man".)

    This may make sense only to me, but I'm (almost) the only one that has to live with it. (I do keep the spouse apprised of my actions.)

    YMWV (Your Mileage WILL Vary)
  • > @gregbrew_98470014 said:
    > As written above, it may require some settings tweaks for each season. I find myself adjusting the reserve for my two Powerwalls (27kWh) as the seasons change. I should note that I accepted an SGIF grant, so I'm *required* to operate off the PWs during peak times for a minimum number of hours per year. (I'm willing to put up with these shenanigans for $6k.) Before SGIF, I simply left things in "Backup Only".
    >
    > My house uses about 20kWh per day, right now. If the weather is consistent, I look at an average day's production, divide by two, and set the reserve to a level that corresponds to that much energy.
    >
    > For example, if my average daily production is 20kWh (it's close, right now), I divide by two for 10kWh. I then set my reserve for 60%. My reasoning is that my PV will need to both provide ~10kWh to run the house (during the day), and ~10kWh to refill the PWs (10kWh is ~40% of the 27kWh in two PWs). My goal is to refill the PWs every day, while leaving a significant reserve capacity for grid loss, while also meeting the requirements of SGIF. Conflicting requirements get tricky.
    >
    > This gives a very rough estimate, rather than an accurate ideal, and doesn't properly account for myriad other variables. I'd probably drive myself nuts trying to optimize it any more, and there was a time (in my youth), where I probably would try. (I'm retired, and like to call myself a "recovering engineer". To paraphrase: "You can take the man out of Engineering, but you'll never take Engineering out of the man".)
    >
    > This may make sense only to me, but I'm (almost) the only one that has to live with it. (I do keep the spouse apprised of my actions.)
    >
    > YMWV (Your Mileage WILL Vary)

    I have mine set at 60% for the same reason, and use about 20 kWh. I know that will be perfect to back me up until the sun comes up the next day
  • Will the Tesla app show you what your home kWh daily production is?

    It seems to track everything.
  • > @RLSolar said:
    > Will the Tesla app show you what your home kWh daily production is?
    >
    > It seems to track everything.

    Yes. You just click on the the home icon in powerflow.
  • Oops!

    The little house icon will give you the house *consumption* data. Solar *production* can be found by clicking the little solar panel icon.
  • Here are my stats looking at the download usage. Sun down, no solar, 2 Power Walls fully charged turn on at 4:30 pm. At 11:30 pm Power Walls were used up to 25% reserve, and energy was then used from the Grid. My average kW during that time period was 2.21. Based on this the Power Walls as backup would not make it through a night. Am I looking at this correctly?

    Is 2.21 kW a big usage number, and are the Power Walls operating at Spec?

    Thanks
  • What are you using during this period?

    Are any of you appliances natural gas or are they all electric?

    What do you have running that you don’t need to run?

    During the day when nobody is home or during the night, our house averages 300 watts/hr and that’s with a turtle aquarium pump and heater running, I addition to the normal house things.

    During the evening when we’re home watching TV, have some lights on, and using things, we may average about 800 watts/hr.

    When our pool pump is running our house averages 2.3 kWh (the pump alone uses about 1.8 kWH). When we use the microwave, toaster oven, coffee maker, we may peak at over 4 kWh for just a few seconds to a few minutes.

    All of our all appliances are natural gas (water heater, stove/range, dryer, furnace), so all of them use little to no (range and water heater) electricity. So our whole house averages less than 20 kWh per day. In the summer with the AC running and the pool pump running 3 times as long we will get over 50 kWH, but days with little to no AC will be closer to 30 kWh.

    It’s important to see what’s using a lot of power and either shut those things off or reduce their use as much as possible. An electric range by itself will use a lot of electricity. Dishwashers use a lot on their own, and even more if you have an electric water heater.
  • Part of the testing of a PV/PW system's ability to back up a residence is to behave like there's a "Grid Emergency", by turning off all but essential loads. You'd certainly want to do that in a true power emergency.

    Not knowing anything about your house or loads makes it impossible to know if an average load of 2.2kW is reasonable.

    When testing my system, I flipped all breakers off, except for those that powered my two refrigerators, freezer, microwave, one lighting circuit, one circuit for a laptop and cell-phone charging and one circuit that powers my network backbone. Under these conditions, my 1500sf house averages about 500W. My two PWs and 5kW of PV will handle that indefinitely, with ample margin, except for an usually severe weather event. We don't get those very often in So. CA, so I can live with that risk.

    As an aside, I highly recommend the purchase of a "Kill A Watt" meter or something like it. They allow you to measure the energy usage of pretty much anything that plugs into 120V AC. The first step in eliminating energy hogs is to identify them. ~$30 well-spent.

    https://smile.amazon.com/P3-International-P4460-Electricity-Monitor/dp/B000RGF29Q/ref=sr_1_3?dchild=1&keywords=watts+up+meter&qid=1606251216&sr=8-3
  • Or for about $100-$300 you can purchase a home monitoring system such as "Sense" This tells you what are currently being used and how much energy these things are using
  • Night time, when everyone is sleeping, is the perfect time to see how much energy your house uses just on standstill. No appliance and no lights on. If your house is pulling more than 500 watts consistently during this time than there are something things that may be using a lot of power unnecessarily without you realizing it.

    Our house goes from 200 watts and peaks at 500 watts at night. Those peaks are when both refrigerators happen to be running at the same time. But refrigerators only run for a few minutes at a time. The other devices are things like my modem, routers, security cameras, electronics on standby, and all the networked items. My routers alone can pull over 100 watts consistently.

    I average about 300 watt per hour at night. So I know that during an outage that will be more or less what my house will be using during the whole outage time (minus the occasional microwave use, etc.) If I round up to 500 watts, my battery at full charge should run my house for 27 hours without solar recharge. Even now as I am sitting on my computer typing this (a computer with a 1500 watt power supply) at 1:30 PM, my house is currently using 400 watts. My house peaked today at 2.4 kw when the pool pump was running (the pool is not part of my backup load so that won't even factor into use during an outage.)
  • Thanks for the responses. I am scratching my head on this one. At night sleeping, internet router is active, a lot of tech stuff charging, sub zero fridge, another fridge, 2 gas furnaces, nothing else is really on, three ceiling fans, using about 1.4 kW. With the big TV on and a few more lights it does about about 1.7 kW or so. Could something be draining my power that I am not aware of?

    "Part of the testing of a PV/PW system's ability to back up a residence is to behave like there's a "Grid Emergency", by turning off all but essential loads. You'd certainly want to do that in a true power emergency."

    How does the PW do this?
  • Sounds like you have a big place with a lot of things running. Even 2 gas furnace will use quite a bit of power with the blower and condensation pump. So that amount of energy maybe normal. Do you have LED lights? Each incandescent light will use 60-150 watts alone.
  • Sorry, I don't know know about what the PW app shows, but doesn't it show output power?

    Can't the OP just then start turning things off to see where all the power is going?
  • Checking specs on the Professional Plasma Power on 745 Watts.

    That seems like a lot. Kitchen flood lights, 8 lights, 65 Watt bulbs. So between the kitchen lights and TV, we are using 1,265 watts. That has to be where my PW batteries are being used. I got up in the middle of the night and app showed .5 kW.
  • > @RLSolar said:
    > Checking specs on the Professional Plasma Power on 745 Watts.
    >
    > That seems like a lot. Kitchen flood lights, 8 lights, 65 Watt bulbs. So between the kitchen lights and TV, we are using 1,265 watts. That has to be where my PW batteries are being used. I got up in the middle of the night and app showed .5 kW.

    Those things alone use half of that average power. Try to only use the kitchen lights when you need them or replace them with LEDs. And plasma's are only more energy efficient than the old CRTs. Perhaps retire the plasma to a less used room and upgrade your main TV with a more energy efficient LED, LCD, or even OLed TV? New TVs are not only more energy efficient, they are much better than the old plasmas, and they are actually not that expensive.

    What is good to know is that during an outage just keeping the kitchen lights off and reducing your TV time will save a lot of energy and preserve your battery
  • The PW cannot shut off your house loads. It will require that in an emergency, you either go out to the breaker panel and open breakers, or go around the house and unplug stuff. As part of your testing, you might consider identifying which breakers to flip in an emergency, by putting a dot of red nail polish on them.

    Also, about plasma TVs. I'm still running a ten year-old 60" Panasonic top-end 1080P plasma panel for my main viewing area. The good news is that this time of year, it helps keep the room warm. The bad news is that in Spring and Summer, it helps keep the room warm.

    The black levels of plasmas can't be beat, except perhaps by OLEDs, but OLEDs aren't as bright unless you push them too hard, and that can affect longevity. My viewing area is very open to outside ambient lighting.

    I'm holding out for QD-OLED, which is the best of both worlds, but it could be ten more years...
  • I'm a fan of OLED, and they are plenty bright, even during the day and/or at night with lights on in the room. My current panel (4 years old now) has zero burn-in, and it gets used about 6+ hours a day. Newer panels are even brighter. Now if you use it for gaming where part of the screen is bright white for hours on end, you can get burn-in, but I thought even Plasma has that problem. Anyway, worth considering when the Plasma finally gives up or you want that 4K (or 8K) goodness. Agreed some LCDs have even higher brightness, and the black levels have gotten better if you can get a zoned backlight. Still, these LCDs have some halos in some situations you don't get with OLED. Ok, sorry I'm getting off-topic!
  • Yeah, my standard for buying an OLED in the mean time is a mid-to-high feature 65" - 75" model for less than $2k. It's slowly approaching it, but it's looking pretty asymptotic at just above that.

    Now, back to our regularly scheduled programming...
  • How much can you discharge your Power Wall without damaging it. I set my two Batteries for 25%, have no idea why I choose that number. What would happen if I choose 0% and used all the battery to power the house.

    Is it possible that a user could "Brick" his Powerwall?
  • PWs (like EVs) have a built-in margin. What's reported as a 0% SOC, is really something other than zero, like 5%. PWs are designed to be cycled from the reported 100% to 0%, and in fact, if charged exclusively from solar, their warranty allows for unlimited charge-discharge cycles for its duration.

    From what I've seen on these fora, the only way to "brick" a PW is to drain it to zero (really ~5%) and leave it there for several days so internal loads take it down to its actual 0% SOC. Even with that, there's a way to "jump start" a PW, using an external 12V power source.

    My recommendation is to just use the thing to its fullest potential (in your application) and don't worry about it.
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