Energy Products

Charge PowerWall from grid?

edited November -1 in Energy Products
Does Tesla have any plans to allow the PW to be charged from the grid? Right now 100% of my solar production goes to offset my energy needs. My PWs will only charge if I select “back up only”.

If I could charge from the grid, I could use off peak energy to supply on peak demand.


  • edited August 2019
    To answer your second question first, some grid operators frown on this as it pulls from their bottom line. If you have TOU (time of use) billing, batteries can come in handy for powering your house during the peak billing hours just after sunset and usually until 9pm.
    In my case, I do just that. I set the powerwalls to Self-Powered mode and the backup % to about 55 in the summer and 35 in the winter. I may set the unit to backup only or adjust the % to 20 above current charge level to force the controller to pull from the grid to charge the car on weekends when the TOU rate is lowest.
    Now, the first question is a tough one as it *depends* on if you have solar or not. A customer with powerwalls only will have a grid tie and will use them for backup only (unless you force an outage by turning off the main breaker), but what's the purpose of that...maybe other than to test backup function.
    And if your powerwalls only charge when in backup mode, I would think something was wrong - unless they were planned to be used in that function only. Good Luck.
  • edited August 2019
    One other thing to mention - STORM WATCH mode. If you have it available in your area and it is activated by a valid NOAA alert, it will fast charge your powerwalls using combination of panel and grid to ensure full charge in the event the storm does actually knock out your power. Pretty cool, eh?
  • edited August 2019
    Smashes - thanks so much for your comments.
    I have a 5kWh system which is not nearly enough to handle the energy needs of the house.

    I like your idea of setting the backup % to 55. My peak usage is typically 7:00 to 8:00 pm.

    I would love to have my 2 PWs offset the grid between 6:30 pm and 9:00 pm. However it seems to me that I have to manually make the change each day. In other words, I need to switch to “back up only” to charge the PW, and then switch to “self powered “ mode at 6:00 pm.

    How are you managing your setting. Do you change them each day ?
  • edited August 2019
    ZD - Here's my setup: 4.8kW array feeding a 4.2kW ABB inverter coupled to two powerwalls to power a fairly modest 1500 sq ft stick and stucco tract home in San Diego about 20 miles from the coast. As I was looking for a system that could nearly zero me out each year with my electric usage, this combo package fit the bill.
    Being retired also helps as I don't put a lot of mileage on the EV we have (Chevy Bolt), so after my first true-up last month, we owed the local grid $8.00 for the year, minus the mandatory monthly meter fee.
    So, that being said, I hardly ever have to switch between modes to charge, as my generation exceeds my consumption most days of the year. Sounds from your comment that you consume all you generate and possibly also pull from the grid during each daily cycle, which would explain the powerwalls charging when in Backup only mode since there's no daily excess from your array.
    The solution? Probably expensive...
  • edited August 2019
    In the US, public electrical utilities generally don't allow charging PWs from the grid, except during Stormwatch emergencies. I remember when it *was* possible, in the late '90s and early '00s, then the utilities woke up to the fact that someone on a TOU and time-shifting their usage was eating their lunch. In those days, it was possible to pay off your battery pack in less than three years using this method.

    If I'm not mistaken, Australian electrical utilities still allow time-shifting with batteries, but for how much longer?
  • edited November -1
    I just spoke w Tesla support today. Apparently Tesla has just changed the algorithm. It appears to be a work in progress.

    I got the PWs last week so it is a bit early to see how the new algorithm works. I’ve got it set to customized/advanced /cost savings. My biggest power usage is 6 to 9 pm and I have the peak period starting at 6 pm (although Peak runs from 10 am to 9 pm). I just want it to offset demand after the sun goes down.

    So far the algorithm has discharged slightly during the day, but has also recharged the PWs so that in they are entering the Peak 6 pm period with +95% capacity.

    I’ll post what happens over next couple of days
  • edited September 2019
    Just following up on my earlier post. So far so good, and very pleased.
    We had a hurricane come thru here 10 days ago, the lights flickered, and the battery backup started -- just as it is supposed to,
    So far the 2 PWs are satisfying 100% of my energy needs between 6:00 pm and 9:00 pm.
  • edited December 2019
    I'm thinking about getting PW to shift the time of use just like what you did. Does PW charge from both solar and grid during off-peak time?
  • edited December 2019
    No. In the USA, the majority of utilities (check with yours) do NOT allow PWs to charge from the grid, except in a an impending power emergency via Stormwatch. They are set up to charge solely from the PV array.
  • edited December 2019
    That really doesn't make sense... I thought folks were able to buy the Powerwall to be used solely as 'backup' power? Even if utility companies 'didn't allow' the PW to charge at the specific times, I'm not sure how it could prevent it. I could relatively easily charge a 200KW battery pack at night using Utilities and then narrow my utility band width.... I can control all that after the 'meter' - Many folks get EV credit from utilities; same concept.
  • bpbp
    edited December 2019
    Also - if you take the 30% US federal tax credit for the PowerWall purchase, they are supposed to be charged only by solar (except for emergencies) during the first 5 years.

    Plus, Tesla's warranty is different if you charge from the grid vs. charging from solar.
  • edited December 2019
    "they are supposed to be charged only by solar (except for emergencies) during the first 5 years"

    What happens at the end of 5 years?
    Will Tesla release more functionality and allow us to specify recharge the PW from the grid?
  • edited December 2019
    Wilkes.r, Yes, you could do it, but you would be doing so without a city building permit. Without utility approval (they won't give it to you), you can't get a building permit. It's part of the process. You'd have to "do it yourself", because any licensed and bonded electrician wouldn't touch such a project, because they could lose their license and insurance, if caught.

    It has nothing to do with safety or infrastructure...the utility simply doesn't want you to reduce their profits by time-shifting with storage. *They* can do it (as with pumped hydro), but you can't. Utilities have strong lobbying divisions...
  • edited June 1
    Here in the UK, the utilities are trying to 'balance the grid' and are encouraging people to use batteries to time shift theuir usage and reduce demand at peak times, shifting some of it to off peak periods, where there is excess generation over demand.

    One of our utility suppliers (Octopus Energy) even occasionally pays us to use grid energy, by charging us less than £0.00 per kWh, a few weeks back the rate was £ -0.10, which earned us over twice what it would cost to buy at off peak rates.

    Charged car to 100% and did the same with my Powerwall by switching it over to 'Back-up Only'.

    I have a Zappi EV Charger that is designed to monitor excess solar and charge your EV from solar (you can adjust the solar/grid percentage to whatever you want) -

    But in addition to its standard features I wanted something that wasn't on offer, so I have 'hacked' my Zappi EV charger so it 'Boost Charges' when the variable tariff I am on drops below the rate I get paid for exporting my excess solar (the rates can change every 30 minutes) -

    The only problem is that when the system activates it takes energy from my Powerwall (that I have filled with solar from my roof), rather than from the grid, where (at that time) it costs less to buy than the rate I get paid for exporting excess solar to the grid.

    I can prevent this by manually switching my Powerwall to 'Back-Up Only' using the app, but I would really like to be able to do this automatically when the rate I am paying per kWh drops below my fixed export rate, as the lower prices often occur early in the morning, while I'm asleep.

    If this could be done, there is a small added bonus in that if the Powerwall isn't fully charged when it switches over to 'Back-Up Only' it will charge to 100% at the cheaper rate.

    Does anyone know how to automate switching over the 'Back-Up Only'? Can it be tied to a variable tariff threshold?

    Being able to export from the Powerwall during peak demand periods would be nice, but in the summer I'm still creating excess solar through the peak periods and my house needs about half of my Powerwalls capacity to run till sun up the next day. In the winter I'm going to need everything that is in the Powerwall to run the house plus some from the grid, so no spare capacity then to sell then. Plus I'm currently on a fixed rate export tariff.

    Maybe an electro-mechanical solution like my Zappi Charger 'hack' could be wired into the gateway to locally do the switching and bypass the app/web based control?
  • bpbp
    edited November -1
    In Texas, they are anticipating high electricity loads during peak summer hours and will likely encourage customers to reduce their daytime energy usage.

    If someone wanted to connect PowerWalls and charge them from the grid overnight so they could run off the PowerWalls during the day as long as the system received the necessary approvals, the utilities should accept installing the PowerWalls.

    PowerWalls charging from the grid wouldn't qualify for the 26% federal tax credit and would have a charge limit on the Tesla warranty.

    Plus, it's unlikely a utility would allow that customer to use a "free nights" plan to charge up the PowerWall overnight for free and power the house (for free) during the day.
  • edited June 2
    In order to qualify for SGIP grants (~$3k each) here in SCE country, Powerwall users must agree to provision the PWs so that the home doesn't pull from the grid during the peak grid load hours of 4-9PM.

    I've set mine up with Custom settings for Peak from 4PM to midnight, with off peak the rest of the time, and a 30% reserve.

    My PWs start most days at 30%, begin recharging at dawn with the TEG directing PV (5kW) to the PWs until they're full. The time-of-day they're full varies with the weather and season. We do our heavy lifting (power-wise) from when they're full, until 4PM. This includes appliances and EV charging. A significant amount of power on the grid during those hours is renewables, and we use our PV directly, lessening our output to a grid already flush with said renewables, and using relatively clean grid power when our PV is inadequate for the tasks at hand. When 4PM rolls around, the TEG directs power from the PWs to the house, and all solar goes out to the grid, supporting it during peak demand times, rather than pulling from it. We pull from the PWs until midnight, or when they're at 30%. We pull off-peak power from the grid from that time, continuing through dawn, and the cycle repeats.

    The SGIP program incentivizes the kinds of behaviors that make the most of residential solar and the renewables available on the grid. I'm still waiting for my $6k check, but am doing "the right thing" anyway. BTW, the PW warranty covers unlimited charge cycles if charging is done exclusively by a PV array, but a limited number of charge cycles if filled from the grid.
  • edited June 6
    @gregbrew That's pretty much what I do (except the EV charging period). By the anticipated $6K SGIP I assume you have 2 Powerwalls. My 1PW starts recharging at first light and mostly finishes around noon. Then, solar feeds the grid until sundown. The PW kicks in at 3:00 (beginning of my shoulder PGE rates) and ends at midnight. When my Model 3 needs charging I start it at midnight when the rates are low.

    How do you manage your EV charging? Do you start it up when the PW has filled up and stop charging at 4:00? If so, that requires daily manual intervention, no? What if the EV needs more charging? Then I assume it would be more manual intervention to start at midnight.

    Like you, I'd rather use up my excess solar and put it into the Model 3 but I can't figure out a way to "automate" that process, so I give more back to PGE and get some offset credits.
  • edited June 7
    The wife and I are both retired, so charging our Bolt is (at most) a weekly endeavor. Right now, it's almost monthly. I just plug it in, and set an alarm for 4PM. It hasn't been still charging at 4PM yet.
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