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Can Powerwall be configured to reduce demand charges?

edited November -1 in Energy Products
Can powerwall be configured to lower demand charges? For example, when load exceeds 10kW can powerwall kick in to keep the utility load to 10kW?


  • edited November 2017
    Currently there is no way to setup triggers like that in the app.

    However the energy for your loads should be supplied by the solar panels, whatever the panels cannot cover is supplied by the Powerwall, and whatever the Powerwall cannot covered is supplied by the utility. So that 10kW load could largely or entirely be supplied by a combination of Solar + Powerwall(s).

    A single Powerwall supplies 5kW of continuous power. So you may need two powerwalls for a 10 kW load.
  • My understanding is that what @tkaiser describes is exactly what will happen and it should keep the load under 10 kW for as long as you have charge in the battery. Remember that each PW holds 13 kWh so two full, new PWs will only be able to deliver 10 kW for 2.6 hours.
  • edited November -1
    Are there any plans to update the programming? I can see where the current programming is designed for places where there is no net metering.

    But in places where there is net metering, demand charges, and/or TOU plans, there are much better algorithms to optimize ROI.

    Related question - when grid goes down, does the standard installation have the PW power a subset of circuits, or is that something the installer would have to do external to the PW?
  • edited November 2017
    Software development is ongoing to provide richer and more flexible features. For example, ToU is scheduled for the end of this year (2017) or early next year.

    By default, the PW-2 is installed either as a whole home or partial (critical circuits) backup. Essentially, the PW-2 connects to grid, solar and the home, solar powers the home, charges the battery and exports to the grid if the battery is full and there is excess. During lower light on solar, power is provided from battery and/or solar. Obviously at night, power is from battery and/or grid.

    If the grid fails, the PW-2 acts as a UPS and is limited to 5 kW continuous power so this aspect should be considered as part of a whole home backup or just critical circuits. PW's can be combined in parallel to increase this limit.

    There are more detailed descriptions of function elsewhere in the forums.


    Harry E.
  • edited November 2017
    Demand meters are typically on commercial users with 3 phase 480vac. Demand meters measure the highest average kw draw over any 15 minute period. We pay $20/kW ; and use 5000 kWhrs per month. So if the draw could be entirely leveled out it would be a 7kW continuous draw. We typically see 30 kW Demand charge; so it would save us $460/month. Our utility is shifting their revenue stream from kWhrs to Demand charge.
  • edited February 2018
    I'm with you s.grot --- looking for ideas for my building to cut demand charge. I don't qualify for Tesla Solar on the building as I don't have enough usage but maybe a grid connected powerwall would take care of those peak demand charges. I am about in the same situation as you.
  • edited November -1
    I am also with s.grot. Don't know why rather then bringing the peak to the average of 7kw, how about bringing the peak to 0 kw? If the facility ran off of the battery and the batteries only drew power 13 out of every 15 minutes, then wouldn't the peak charges be $0? Saving $600 per month.
  • edited August 2018
    If the meter measures the kWh every 15 minutes and then multiplies by 4 to get the kW number, drawing for 13 of every 15 minutes does not drop the usage to 0.
  • being able to do demand charge shaving w/ a powerwall would be amazing! I would strongly consider installing one at my inn if it were possible
  • edited May 2019
    Any updates on this thread? Has this functionality been introduced yet?
  • edited May 2019
    The PW still does not currently support demand leveling or shaving to some user defined demand goal.

    With advanced time-based controls added last year however, from my experience, the PowerWall can work well to manage demand if you have an appropriately sized system (PV kW + # of batteries) so that you can configure the entire system for zero net usage for your entire peak period.

    After two months of PowerWall operation with solar, my maximum demand during peak periods (that include several hours past sunset and an hour or so before sunrise) has been 200W even with a 4kW air conditioner running periodically (day and night). I'm in the Phoenix area and my utility is SRP.
  • edited June 2019
    Darwin.e. Thanks for the information.
    How many PW do you have and what Kw solar panels you got.?
    I’m in the process of getting the panels. They’re suggesting a 4kw and my srp 1 year without solar is 13000kw. I’m worried about that srp on demand periods, will a PW help or do I need 2.
  • edited June 2019
    We have 2-PW2's (27 kWh) integrated with our 13.2 kWh solar system operating in self-powered mode, and the batteries keep our grid draws at zero for 9 months of the year supporting all our electricity needs after the sun goes down for our all electric home, including two Tesla's (MS and M3). They work incredibly well. I live in Edmonds, WA and do have to rely on our grid based energy between November-January to supplement our solar, when there is insufficient solar to fully charge the PW2's.
  • edited June 2019
    Sumanth, I am getting a 4kw system and 1PW. This will be plenty for managing SRP's demand charges. If you want to email/ text me I can go over my system details and why it should be enough for most people. [email protected] or 480-297-8855.
  • edited June 2019
    You can configure the Powerwall setup to compensate for demand peak charges in several ways. Note that you do have to have a setup of backing up the whole house/establishment with at least 2 Powerwall 2's. The way I do it is to adjust the Powerwall Reserve setting. Right now in Summer I have it set at 70%. I could go even lower but at this setting I'm powered by solar and battery up to about 9 PM when BGE power becomes cheaper right at 9 PM . I do have enough reserve to go completely self powered but I'm concerned that there's a critical number of full discharges that wears the battery down. I researched this online trying to figure out whether my reasoning is correct that fewer full or near full discharges are likely to lead to longer battery life but I couldn't find anything. Considering what happens to Tesla car batteries conjecture has it that I'm probably right.
  • irir
    edited June 2019
    With lithium ion batteries, 1 full charge / discharge cycle wears the battery as much as 2 half charge / discharge cycles (excluding over charging & over discharging and extreme battery temperatures which accelerates wear).

    With Tesla’s active battery management system, you should measure the life of your batteries like a car’s odometer: “total kWh charged over lifetime of batteries”.

    Home battery usage is far gentler than in a car, where the batteries regularly have to output full power during acceleration and than rapidly recharged during regenerative braking. Causing sudden temperature changes. Powerwalls should last far longer than Tesla car batteries.
  • edited July 2019
    I loose power from the grid usually in the winter during ice storms, and sometimes during blizzards. Depending upon the amount of damage to power lines determines how long I am without grid power. Obviously there usually is. dry little solar power during these time periods. So is it possible me to use power wall battery setup and still use a generator for any long power outages? I work from home and need power to connect to the office via vpn.
  • edited July 2019
    you should configure the powerwall #2 to charge during the day with solar and stay charged till night time when solar is no longer charging before taking back from the powerwall unit , I like the storm watch function it keeps the powerwall charged at 97-99 percent till storm watch is over, then it goes back to normal use,
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