Tesla Powerwall Calculator

I was wondering if anyone has created a tool to export your Sense usage for a year and find out how many tesla powerwall batteries you would need based on usage?

Easy to export data, but the calculator would depend on what you are trying to do with the PowerWall, which depends on your particulars and utility pricing:

  • Power essential appliances for 24 (or x) hours, when the grid goes out
  • Time shift all your solar, or some % to your highest TOU period
  • Time shift low TOU grid energy to deploy in high TOU periods.

Or some mix of all of those ?

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As I’m looking to use it as backup i would really be looking to compare production vs usage.

Costs of electricity won’t effect it.

OK, two more questions:

  • Do you want to size to run all the devices in your house or a select set (refrigerator, networking, etc.) ?
  • How long a backup do you want or need ?

I’d like to run everything is my goal. Also maybe 2 days, but there is also a max output of 5K per battery, so I wish there was an easy way to see how often I break 5K at once… I know the car does so I need at least two, but am I every breaking 10K load?

Here’s a quick thought / example using Excel.

  • Export hourly Sense data for a year. If you want to look at a longer period, concatenate two CSVs in Excel.
  • Use the filter function plus cut and paste to separately select “Total Usage” and “Solar Production” to create a “wide” spreadsheet with just those two kWh values and DateTime. Add the two to get the Net Usage.

  • Use a PivotTable with the following setup (on right) to aggregate total daily Net Usage as well as computing Max Hourly Usage for each day. Once you have that, you are pretty close to the answers you need. You can see how much net energy you need to survive one day, plus the max you need on an hourly basis.

ps: You can tell the the days that I’m doing car charging :slight_smile:

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Thank you so much! ill try this in the evening :slight_smile: What kinda car? I have a volt so i dont charge nearly as much

We have two - Model S P85 and a Model 3 LR. Both charge above 10kW, with the Model S closer to 20kW. We tend to only charge before or after a long trip. Most day-to-day driving only uses a trickle. Also have a Ford Fusion plug-in, but haven’t been been plugging in recently to make sure 12V battery stays in good shape.

Do you have self driving? thats my goal lol

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I don’t have an electric car, and I will occasionally go past 10kW. Electric dryer runs at around 4-5kW, range/oven at 6+kW, and if you throw AC in the mix, that’s another 2.5kW. Not too hard to break 10, but also easy to stay under 10 if you know that you have to (i.e. don’t run the stove and dryer at the same time).

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Not to be a killjoy, but factoring in needing to charge a (LiPo) battery in your car from a (LiPo) battery, Powerwall, is a questionable goal. I would treat that as an emergencies only process and try an extend the life of your Powerwall.

Load shifting around solar peaks and the weather and minimizing feeding the grid, while covering emergency power (vs getting a gas-powered generator) is where to start.

If a Powerwall’s warranty (10 years) matches it’s realworld lifespan due to “typical” use (car charging etc) then I would target “atypical” use and try and get 20 or 30 years out of it.

The dirty secret of pretty much any battery other than systems like pumped water is that they degenerate and are notoriously difficult to recycle. “Degenerate” in terms of power-providing technology is an ironic term … there is some hard truth there in that it will no doubt take significant energy to recycle the de-generated batteries!

Unless you are in a situation where you know your grid power is rock solid you should assume that in the case of grid loss you’ll want to prioritize keeping things like fridges/freezers powered for as long as possible vs 24/48hrs. i.e. I wouldn’t treat it as a linear equation. And by the way, if you do have “rock solid grid supply” then when something does go wrong you can safely assume it may take longer to restore than you may imagine.

The beauty of having fine-grained Sense data is that you can analyze when exactly to load shift and so minimize solar & battery sizing. Your question is a great one because it opens up the debate about how to best exploit battery power … and as you can tell, I’m coming at it from a skeptical angle.

You don’t have to worry about the car charging off powerwall anymore. The latest Tesla car software fixes this so the car can talk to the powerwall and only provide the required power. Software version 2020.32.3.

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Interesting you bring this up. Good point.

The problem is @evan.h.kent has a Volt.

Is there an EV/battery standard communication/publication protocol emerging? It sucks that Sense (and others) have to attempt magic when all these sophisticated devices know what they are doing or are going to do and could be upfront about it!